Pregen optimization pass

- Hydrology height lattice stores samples in tiles with least-recently-used eviction
- Evicted lattice cells are no longer sampled twice
- Pond rim columns go through the lattice column cache
- Window planning reads its coarse nodes from the fine lattice
- Prefetch stays inside the pregeneration area while a pregeneration runs
- Sea inlet splat compares squared distances
- Bounds sampling answers a column from region constants when every reachable biome shares the bounds
- Base terrain heights are shared through a per-column memo
- Chunk water rasters use per-chunk palettes and a larger cache
- Raster channel lookups use a 4-block segment grid
- Chunks with no water in reach return the empty raster directly
- Riffle spreads stop at cells that cannot reach the chunk
- Cave pool terrain is built only for chunks with a pool site
- Concurrent raster builds for one chunk share a single build
- Section buffers resolve air once and support bulk column reads
- Cave decoration, perfection and transition capture read bounded column windows
- Generation history claims and saved biome writes elect one writer per batch

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedPregenMethod.java

@@ -348,6 +348,11 @@ public final class ModdedPregenMethod implements PregeneratorMethod {
         return false;
     }
 
+    @Override
+    public void onRegionBounds(int minRegionX, int minRegionZ, int maxRegionX, int maxRegionZ) {
+        hydrology.bound(minRegionX, minRegionZ, maxRegionX, maxRegionZ);
+    }
+
     @Override
     public void onRegionsAhead(List<long[]> regions) {
         if (!closing.get()) {

core/src/main/java/art/arcane/iris/generation/chunk/ColumnExtentListeningHunk.java

@@ -20,7 +20,7 @@ package art.arcane.iris.generation.chunk;
 
 import art.arcane.volmlib.util.hunk.Hunk;
 
-public final class ColumnExtentListeningHunk<T> implements Hunk<T>, ColumnExtent, ColumnRunHunk<T> {
+public final class ColumnExtentListeningHunk<T> implements Hunk<T>, ColumnExtent, ColumnRunHunk<T>, ColumnReadHunk<T> {
     private final Hunk<T> source;
     private final Listener<T> listener;
 
@@ -46,6 +46,11 @@ public final class ColumnExtentListeningHunk<T> implements Hunk<T>, ColumnExtent
         return source.getRaw(x, y, z);
     }
 
+    @Override
+    public void readColumn(int x, int z, int yFromInclusive, int yToInclusive, T[] target, int targetOffset) {
+        ColumnReadHunk.readColumn(source, x, z, yFromInclusive, yToInclusive, target, targetOffset);
+    }
+
     @Override
     public int getWidth() {
         return source.getWidth();

core/src/main/java/art/arcane/iris/generation/chunk/ColumnReadHunk.java

@@ -0,0 +1,37 @@
+/*
+ * Iris is a World Generator for Minecraft Bukkit Servers
+ * Copyright (c) 2026 Arcane Arts (Volmit Software)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package art.arcane.iris.generation.chunk;
+
+import art.arcane.volmlib.util.hunk.Hunk;
+
+public interface ColumnReadHunk<T> {
+    void readColumn(int x, int z, int yFromInclusive, int yToInclusive, T[] target, int targetOffset);
+
+    @SuppressWarnings("unchecked")
+    static <T> void readColumn(Hunk<T> hunk, int x, int z, int yFromInclusive, int yToInclusive, T[] target,
+                                int targetOffset) {
+        if (hunk instanceof ColumnReadHunk<?> reads) {
+            ((ColumnReadHunk<T>) reads).readColumn(x, z, yFromInclusive, yToInclusive, target, targetOffset);
+            return;
+        }
+        for (int y = yFromInclusive; y <= yToInclusive; y++) {
+            target[targetOffset + y - yFromInclusive] = hunk.getRaw(x, y, z);
+        }
+    }
+}

core/src/main/java/art/arcane/iris/generation/chunk/SectionBuffer.java

@@ -27,7 +27,8 @@ import java.lang.invoke.MethodHandles;
 import java.lang.invoke.VarHandle;
 import java.util.Arrays;
 
-public final class SectionBuffer implements Hunk<NativeBlockState>, NativeSectionVolume, ColumnExtent, ColumnRunHunk<NativeBlockState> {
+public final class SectionBuffer implements Hunk<NativeBlockState>, NativeSectionVolume, ColumnExtent, ColumnRunHunk<NativeBlockState>,
+        ColumnReadHunk<NativeBlockState> {
     private static final BoundBlockState AIR = BoundBlockState.of("AIR");
     private static final VarHandle SECTIONS = MethodHandles.arrayElementVarHandle(short[][].class);
     private static final VarHandle COLUMN_TOPS = MethodHandles.arrayElementVarHandle(int[].class);
@@ -43,6 +44,8 @@ public final class SectionBuffer implements Hunk<NativeBlockState>, NativeSectio
     private PaletteEntry[] slots;
     private NativeBlockState[] states;
     private int paletteSize;
+    private NativeBlockState air;
+    private PaletteEntry lastEntry;
 
     public SectionBuffer(int height) {
         if (height <= 0) {
@@ -76,12 +79,17 @@ public final class SectionBuffer implements Hunk<NativeBlockState>, NativeSectio
         if (state == null) {
             return 0;
         }
+        PaletteEntry last = lastEntry;
+        if (last != null && last.state == state) {
+            return last.id;
+        }
         PaletteEntry[] table = slots;
         int mask = table.length - 1;
         int slot = System.identityHashCode(state) & mask;
         PaletteEntry entry;
         while ((entry = table[slot]) != null) {
             if (entry.state == state) {
+                lastEntry = entry;
                 return entry.id;
             }
             slot = (slot + 1) & mask;
@@ -101,7 +109,7 @@ public final class SectionBuffer implements Hunk<NativeBlockState>, NativeSectio
     @Override
     public NativeBlockState getRaw(int x, int y, int z) {
         if (y < 0 || y >= height) {
-            return AIR.get();
+            return air();
         }
         short[] section = sections[y >> 4];
         if (section != null) {
@@ -110,7 +118,7 @@ public final class SectionBuffer implements Hunk<NativeBlockState>, NativeSectio
                 return state(id);
             }
         }
-        return AIR.get();
+        return air();
     }
 
     @Override
@@ -126,6 +134,32 @@ public final class SectionBuffer implements Hunk<NativeBlockState>, NativeSectio
         return id == 0 ? null : state(id);
     }
 
+    @Override
+    public void readColumn(int x, int z, int yFromInclusive, int yToInclusive, NativeBlockState[] target, int targetOffset) {
+        int column = (z << 4) | x;
+        int shift = targetOffset - yFromInclusive;
+        int y = yFromInclusive;
+        while (y <= yToInclusive) {
+            if (y < 0 || y >= height) {
+                target[shift + y] = air();
+                y++;
+                continue;
+            }
+            int sectionIndex = y >> 4;
+            int last = Math.min(Math.min(yToInclusive, height - 1), (sectionIndex << 4) | 15);
+            short[] section = sections[sectionIndex];
+            if (section == null) {
+                Arrays.fill(target, shift + y, shift + last + 1, air());
+            } else {
+                for (int row = y; row <= last; row++) {
+                    int id = section[((row & 15) << 8) | column] & 0xFFFF;
+                    target[shift + row] = id == 0 ? air() : state(id);
+                }
+            }
+            y = last + 1;
+        }
+    }
+
     @Override
     public void fillColumnRun(int x, int z, int yFromInclusive, int yToInclusive, NativeBlockState value) {
         if (value == null || yToInclusive < yFromInclusive) {
@@ -176,6 +210,15 @@ public final class SectionBuffer implements Hunk<NativeBlockState>, NativeSectio
         }
     }
 
+    private NativeBlockState air() {
+        NativeBlockState resolved = air;
+        if (resolved == null) {
+            resolved = AIR.get();
+            air = resolved;
+        }
+        return resolved;
+    }
+
     private short[] writableSection(int sectionIndex) {
         short[] section = sections[sectionIndex];
         if (section != null) {

core/src/main/java/art/arcane/iris/generation/context/IrisContext.java

@@ -28,9 +28,14 @@ import art.arcane.iris.generation.terrain.IrisDimension;
 import art.arcane.volmlib.util.collection.KMap;
 
 import java.util.Objects;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReferenceArray;
 
 public final class IrisContext {
-    private static final ThreadLocal<IrisContext> CONTEXT = new ThreadLocal<>();
+    private static final int SLOTS = 512;
+    private static final AtomicReferenceArray<Binding> BINDINGS = new AtomicReferenceArray<>(SLOTS);
+    private static final ThreadLocal<Binding> OVERFLOW = new ThreadLocal<>();
+    private static final AtomicInteger OVERFLOW_BINDINGS = new AtomicInteger();
     private final Engine engine;
     private final ChunkContext chunkContext;
     private final long generationSessionId;
@@ -42,7 +47,8 @@ public final class IrisContext {
     }
 
     public static IrisContext get() {
-        return CONTEXT.get();
+        Binding binding = binding(Thread.currentThread());
+        return binding == null ? null : binding.context;
     }
 
     public static IrisContext require() {
@@ -55,9 +61,10 @@ public final class IrisContext {
 
     public static Scope open(Engine engine, long generationSessionId, ChunkContext chunkContext) {
         Thread thread = Thread.currentThread();
-        IrisContext previous = CONTEXT.get();
+        Binding binding = bind(thread);
+        IrisContext previous = binding.context;
         IrisContext installed = new IrisContext(engine, generationSessionId, chunkContext);
-        CONTEXT.set(installed);
+        binding.context = installed;
         return new Scope(thread, previous, installed);
     }
 
@@ -99,6 +106,42 @@ public final class IrisContext {
                         .qput("queued", mantle.getUnloadRegionCount()));
     }
 
+    private static Binding binding(Thread thread) {
+        Binding binding = BINDINGS.getPlain(slot(thread));
+        if (binding != null && binding.owner == thread) {
+            return binding;
+        }
+        return OVERFLOW_BINDINGS.get() == 0 ? null : OVERFLOW.get();
+    }
+
+    private static Binding bind(Thread thread) {
+        Binding binding = binding(thread);
+        if (binding != null) {
+            return binding;
+        }
+        binding = new Binding(thread);
+        if (!BINDINGS.compareAndSet(slot(thread), null, binding)) {
+            binding.overflow = true;
+            OVERFLOW.set(binding);
+            OVERFLOW_BINDINGS.incrementAndGet();
+        }
+        return binding;
+    }
+
+    private static void release(Binding binding) {
+        binding.context = null;
+        if (binding.overflow) {
+            OVERFLOW.remove();
+            OVERFLOW_BINDINGS.decrementAndGet();
+            return;
+        }
+        BINDINGS.compareAndSet(slot(binding.owner), binding, null);
+    }
+
+    private static int slot(Thread thread) {
+        return (int) thread.threadId() & (SLOTS - 1);
+    }
+
     public static final class Scope implements NativeGenerationScope {
         private final Thread owner;
         private final IrisContext previous;
@@ -119,16 +162,26 @@ public final class IrisContext {
             if (Thread.currentThread() != owner) {
                 throw new IllegalStateException("Iris execution context scope closed from a different thread.");
             }
-            IrisContext current = CONTEXT.get();
-            if (current != installed) {
+            Binding binding = binding(owner);
+            if (binding == null || binding.context != installed) {
                 throw new IllegalStateException("Iris execution context scopes must close in LIFO order.");
             }
             if (previous == null) {
-                CONTEXT.remove();
+                release(binding);
             } else {
-                CONTEXT.set(previous);
+                binding.context = previous;
             }
             closed = true;
         }
     }
+
+    private static final class Binding {
+        private final Thread owner;
+        private boolean overflow;
+        private IrisContext context;
+
+        private Binding(Thread owner) {
+            this.owner = owner;
+        }
+    }
 }

core/src/main/java/art/arcane/iris/generation/hydrology/engine/FineLatticeSource.java

@@ -1,53 +0,0 @@
-package art.arcane.iris.generation.hydrology.engine;
-
-import art.arcane.iris.generation.hydrology.grid.HeightLattice;
-import art.arcane.iris.generation.hydrology.grid.HydrologySampleBuffer;
-import art.arcane.iris.generation.hydrology.grid.HydrologyTerrainSource;
-
-import java.util.Objects;
-
-final class FineLatticeSource implements HydrologyTerrainSource {
-    private final HeightLattice fine;
-    private final HydrologyTerrainSource terrain;
-
-    FineLatticeSource(HeightLattice fine, HydrologyTerrainSource terrain) {
-        this.fine = Objects.requireNonNull(fine, "fine");
-        this.terrain = Objects.requireNonNull(terrain, "terrain");
-    }
-
-    @Override
-    public void sample(int[] xs, int[] zs, HydrologySampleBuffer out, boolean baseOnly) {
-        if (baseOnly) {
-            throw new IllegalArgumentException("The fine lattice holds natural heights only");
-        }
-        if (xs.length != zs.length) {
-            throw new IllegalArgumentException("Fine lattice read has " + xs.length + " x and " + zs.length + " z coordinates");
-        }
-        int cell = fine.cell();
-        int[] cellXs = new int[xs.length];
-        int[] cellZs = new int[zs.length];
-        for (int index = 0; index < xs.length; index++) {
-            if (Math.floorMod(xs[index], cell) != 0 || Math.floorMod(zs[index], cell) != 0) {
-                throw new IllegalArgumentException("Column " + xs[index] + "," + zs[index] + " is not a node of the " + cell + "-block fine lattice");
-            }
-            cellXs[index] = Math.floorDiv(xs[index], cell);
-            cellZs[index] = Math.floorDiv(zs[index], cell);
-        }
-        fine.fill(cellXs, cellZs, out);
-    }
-
-    @Override
-    public int seaLevel() {
-        return terrain.seaLevel();
-    }
-
-    @Override
-    public int minY() {
-        return terrain.minY();
-    }
-
-    @Override
-    public int maxY() {
-        return terrain.maxY();
-    }
-}

core/src/main/java/art/arcane/iris/generation/hydrology/engine/HydrologyPlanners.java

@@ -11,23 +11,21 @@ import art.arcane.iris.generation.hydrology.water.ReachShaper;
 
 import java.util.Objects;
 
-public record HydrologyPlanners(RegionPlanner regions, WindowPlanner windows, HeightLattice windowLattice) {
+public record HydrologyPlanners(RegionPlanner regions, WindowPlanner windows, HeightLattice fineLattice) {
     public HydrologyPlanners {
         Objects.requireNonNull(regions, "regions");
         Objects.requireNonNull(windows, "windows");
-        Objects.requireNonNull(windowLattice, "windowLattice");
+        Objects.requireNonNull(fineLattice, "fineLattice");
     }
 
     public static HydrologyPlanners create(HydrologySettings settings, HydrologyTerrainSource source) {
         Objects.requireNonNull(settings, "settings");
         Objects.requireNonNull(source, "source");
         HeightLattice fine = new HeightLattice(source, WindowPlanner.FINE_CELL, false, HydrologyPlanCache.FINE_LATTICE_CELLS);
-        HeightLattice window = new HeightLattice(new FineLatticeSource(fine, source), WindowPlanner.CELL, false,
-                HydrologyPlanCache.WINDOW_LATTICE_CELLS);
         PondPlanner ponds = new PondPlanner(settings);
         ReachShaper shaper = new ReachShaper(settings);
         RegionPlanner regions = new RegionPlanner(settings,
                 new HeightLattice(source, RegionPlanner.CELL, true, HydrologyPlanCache.REGION_LATTICE_CELLS), fine, ponds, shaper);
-        return new HydrologyPlanners(regions, new WindowPlanner(settings, window, fine, ponds, shaper), window);
+        return new HydrologyPlanners(regions, new WindowPlanner(settings, fine, ponds, shaper), fine);
     }
 }

core/src/main/java/art/arcane/iris/generation/hydrology/engine/HydrologyPregeneration.java

@@ -18,6 +18,12 @@ public final class HydrologyPregeneration implements AutoCloseable {
         }
     }
 
+    public synchronized void bound(int minRegionX, int minRegionZ, int maxRegionX, int maxRegionZ) {
+        if (!closed) {
+            runtime.boundPregeneration(epoch, minRegionX, minRegionZ, maxRegionX, maxRegionZ);
+        }
+    }
+
     @Override
     public synchronized void close() {
         if (!closed) {

core/src/main/java/art/arcane/iris/generation/hydrology/engine/HydrologyRuntime.java

@@ -36,6 +36,7 @@ import java.io.UncheckedIOException;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -56,7 +57,7 @@ import java.util.function.Predicate;
 import java.util.function.Supplier;
 
 public final class HydrologyRuntime {
-    private static final int RASTER_CAPACITY = 1024;
+    private static final int RASTER_CAPACITY = 8192;
     private static final int KEEP_SCOPES = 2;
     private static final int CHUNKS_PER_WINDOW = WindowKey.SIZE >> 4;
     public static final int MAX_PREGENERATION_REGIONS = 4096;
@@ -72,11 +73,13 @@ public final class HydrologyRuntime {
     private final RasterLru rasters;
     private final ThreadLocal<LastRaster> last;
     private final Set<Long> queued;
+    private final ConcurrentHashMap<Long, CompletableFuture<ChunkWaterRaster>> building;
     private final RasterFailures failures;
     private final RasterFailures windowPreviewFailures;
     private final RasterFailures regionPreviewFailures;
     private final Set<Object> previews;
     private final LinkedHashMap<WindowKey, WindowPrefetch> prefetches;
+    private final Map<Object, PregenArea> pregenAreas;
     private final HydrologyBinding binding;
     private final Function<PreparedHydrologyCacheIdentity, HydrologyPlanStore> stores;
     private final boolean caveFluidPolicies;
@@ -94,11 +97,13 @@ public final class HydrologyRuntime {
         this.rasters = null;
         this.last = null;
         this.queued = null;
+        this.building = null;
         this.failures = null;
         this.windowPreviewFailures = null;
         this.regionPreviewFailures = null;
         this.previews = null;
         this.prefetches = null;
+        this.pregenAreas = null;
         this.binding = HydrologyBinding.UNBOUND;
         this.stores = identity -> null;
         this.caveFluidPolicies = false;
@@ -120,11 +125,13 @@ public final class HydrologyRuntime {
         this.rasters = new RasterLru();
         this.last = ThreadLocal.withInitial(LastRaster::new);
         this.queued = ConcurrentHashMap.newKeySet();
+        this.building = new ConcurrentHashMap<>();
         this.failures = new RasterFailures(ticker);
         this.windowPreviewFailures = new RasterFailures(ticker);
         this.regionPreviewFailures = new RasterFailures(ticker);
         this.previews = new HashSet<>();
         this.prefetches = new LinkedHashMap<>(PREFETCH_CAPACITY * 2, 0.75f, true);
+        this.pregenAreas = new HashMap<>();
         this.binding = Objects.requireNonNull(binding, "binding");
         this.stores = Objects.requireNonNull(stores, "stores");
         this.caveFluidPolicies = caveFluidPolicies;
@@ -234,7 +241,7 @@ public final class HydrologyRuntime {
         requireOpen();
         long key = key(chunkX, chunkZ);
         ChunkWaterRaster known = remembered(key, slot);
-        return known != null ? known : remember(key, planned(chunkX, chunkZ, key));
+        return known != null ? known : build(chunkX, chunkZ, key, slot);
     }
 
     public ChunkWaterRaster rasterSnapshot(int chunkX, int chunkZ) {
@@ -354,8 +361,28 @@ public final class HydrologyRuntime {
         }
     }
 
+    void boundPregeneration(Object epoch, int minRegionX, int minRegionZ, int maxRegionX, int maxRegionZ) {
+        Objects.requireNonNull(epoch, "epoch");
+        if (maxRegionX < minRegionX || maxRegionZ < minRegionZ) {
+            throw new IllegalArgumentException("Invalid pregeneration bounds " + minRegionX + "," + minRegionZ + " to " + maxRegionX + ","
+                    + maxRegionZ);
+        }
+        if (cache == null) {
+            return;
+        }
+        synchronized (prefetches) {
+            pregenAreas.put(epoch, new PregenArea(minRegionX - 1, minRegionZ - 1, maxRegionX + 1, maxRegionZ + 1));
+            prefetches.clear();
+        }
+    }
+
     void cancelPregeneration(Object epoch) {
         if (cache != null) {
+            synchronized (prefetches) {
+                if (pregenAreas.remove(epoch) != null) {
+                    prefetches.clear();
+                }
+            }
             cache.cancel(epoch);
         }
     }
@@ -501,6 +528,41 @@ public final class HydrologyRuntime {
         }
     }
 
+    private ChunkWaterRaster build(int chunkX, int chunkZ, long key, LastRaster slot) {
+        CompletableFuture<ChunkWaterRaster> claim = new CompletableFuture<>();
+        CompletableFuture<ChunkWaterRaster> running = building.putIfAbsent(key, claim);
+        if (running != null) {
+            ChunkWaterRaster built = built(running);
+            slot.remember(key, built);
+            return built;
+        }
+        try {
+            ChunkWaterRaster known = remembered(key, slot);
+            ChunkWaterRaster raster = known != null ? known : remember(key, planned(chunkX, chunkZ, key));
+            claim.complete(raster);
+            return raster;
+        } catch (RuntimeException | Error failure) {
+            claim.completeExceptionally(failure);
+            throw failure;
+        } finally {
+            building.remove(key, claim);
+        }
+    }
+
+    private static ChunkWaterRaster built(CompletableFuture<ChunkWaterRaster> running) {
+        try {
+            return running.join();
+        } catch (CompletionException failure) {
+            if (failure.getCause() instanceof RuntimeException cause) {
+                throw cause;
+            }
+            if (failure.getCause() instanceof Error cause) {
+                throw cause;
+            }
+            throw failure;
+        }
+    }
+
     private ChunkWaterRaster planned(int chunkX, int chunkZ, long chunk) {
         try {
             List<WindowKey> windowKeys = neighbourhood(chunkX, chunkZ);
@@ -667,7 +729,7 @@ public final class HydrologyRuntime {
                     && (!known.prepared().isDone() || known.evictions() == evictions)) {
                 return;
             }
-            CompletableFuture<Void> prepared = cache.prepareWindowsAround(chunkX, chunkZ, chunkX, chunkZ, 1 + settings.prefetchRings());
+            CompletableFuture<Void> prepared = prepareAround(chunkX, chunkZ, owner, 1 + settings.prefetchRings());
             prefetches.put(owner, new WindowPrefetch(prepared, evictions));
             if (prefetches.size() > PREFETCH_CAPACITY) {
                 prefetches.pollFirstEntry();
@@ -675,6 +737,24 @@ public final class HydrologyRuntime {
         }
     }
 
+    private CompletableFuture<Void> prepareAround(int chunkX, int chunkZ, WindowKey owner, int rings) {
+        PregenArea covering = null;
+        for (PregenArea area : pregenAreas.values()) {
+            if (area.contains(owner)) {
+                covering = covering == null ? area : covering.union(area);
+            }
+        }
+        if (covering == null) {
+            return cache.prepareWindowsAround(chunkX, chunkZ, chunkX, chunkZ, rings);
+        }
+        int minX = Math.max(owner.wx() - rings, covering.minX());
+        int minZ = Math.max(owner.wz() - rings, covering.minZ());
+        int maxX = Math.min(owner.wx() + rings, covering.maxX());
+        int maxZ = Math.min(owner.wz() + rings, covering.maxZ());
+        return cache.prepareWindowsAround(minX * CHUNKS_PER_WINDOW, minZ * CHUNKS_PER_WINDOW, (maxX + 1) * CHUNKS_PER_WINDOW - 1,
+                (maxZ + 1) * CHUNKS_PER_WINDOW - 1, 0);
+    }
+
     private static List<WindowKey> neighbourhood(int chunkX, int chunkZ) {
         WindowKey own = WindowKey.containing(chunkX << 4, chunkZ << 4);
         List<WindowKey> keys = new ArrayList<>(9);
@@ -754,6 +834,16 @@ public final class HydrologyRuntime {
     private record WindowPrefetch(CompletableFuture<Void> prepared, long evictions) {
     }
 
+    private record PregenArea(int minX, int minZ, int maxX, int maxZ) {
+        private boolean contains(WindowKey key) {
+            return key.wx() > minX && key.wx() < maxX && key.wz() > minZ && key.wz() < maxZ;
+        }
+
+        private PregenArea union(PregenArea other) {
+            return new PregenArea(Math.min(minX, other.minX), Math.min(minZ, other.minZ), Math.max(maxX, other.maxX), Math.max(maxZ, other.maxZ));
+        }
+    }
+
     private static final class LastRaster {
         private long key;
         private ChunkWaterRaster raster;

core/src/main/java/art/arcane/iris/generation/hydrology/grid/HeightLattice.java

@@ -1,34 +1,59 @@
 package art.arcane.iris.generation.hydrology.grid;
 
+import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Map;
 import java.util.Objects;
 import java.util.concurrent.CancellationException;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicReferenceArray;
 
 public final class HeightLattice {
+    private static final int TILE_SHIFT = 5;
+    private static final int COLUMN_TILE_SHIFT = 3;
+    private static final int COLUMN_CELLS = 1 << 20;
+    private static final CompletableFuture<Void> READY = CompletableFuture.completedFuture(null);
+    private static final int[] NO_NODES = new int[0];
+    private static final Tile[] NO_TILES = new Tile[0];
+
     private final HydrologyTerrainSource source;
     private final int cell;
     private final boolean baseOnly;
-    private final int capacityCells;
-    private final ConcurrentHashMap<Long, Slot> cells;
-    private final ConcurrentLinkedQueue<Long> insertionOrder;
+    private final int tileShift;
+    private final int tileMask;
+    private final int tileCells;
+    private final int capacityTiles;
+    private final ConcurrentHashMap<Long, Tile> tiles;
+    private final AtomicLong clock;
     private final AtomicBoolean evicting;
+    private final HeightLattice columns;
 
     public HeightLattice(HydrologyTerrainSource source, int cell, boolean baseOnly, int capacityCells) {
+        this(source, cell, baseOnly, capacityCells, TILE_SHIFT, new HeightLattice(source, 1, baseOnly, COLUMN_CELLS, COLUMN_TILE_SHIFT, null));
+    }
+
+    private HeightLattice(HydrologyTerrainSource source, int cell, boolean baseOnly, int capacityCells, int tileShift, HeightLattice columns) {
         if (cell <= 0 || capacityCells <= 0) {
             throw new IllegalArgumentException("Invalid lattice cell=" + cell + " capacityCells=" + capacityCells);
         }
         this.source = Objects.requireNonNull(source, "source");
         this.cell = cell;
         this.baseOnly = baseOnly;
-        this.capacityCells = capacityCells;
-        this.cells = new ConcurrentHashMap<>();
-        this.insertionOrder = new ConcurrentLinkedQueue<>();
+        this.tileShift = tileShift;
+        this.tileMask = (1 << tileShift) - 1;
+        this.tileCells = 1 << (2 * tileShift);
+        this.capacityTiles = Math.ceilDiv(capacityCells, tileCells);
+        this.tiles = new ConcurrentHashMap<>();
+        this.clock = new AtomicLong();
         this.evicting = new AtomicBoolean();
+        this.columns = columns;
     }
 
     public int cell() {
@@ -67,19 +92,24 @@ public final class HeightLattice {
             throw new IllegalArgumentException("Column sample has " + xs.length + " x and " + zs.length + " z coordinates");
         }
         requireCapacity(out, xs.length);
-        if (xs.length > 0) {
-            source.sample(xs, zs, out, baseOnly);
+        if (xs.length == 0) {
+            return;
         }
+        if (columns == null) {
+            source.sample(xs, zs, out, baseOnly);
+            return;
+        }
+        columns.resolve(new Scatter(xs, zs), xs.length, out);
     }
 
     private void resolve(Nodes nodes, int count, HydrologySampleBuffer out) {
-        Slot[] slots = new Slot[count];
-        int unresolved = count;
-        while (unresolved > 0) {
-            CompletableFuture<HydrologySampleBuffer> batch = claimAndSample(nodes, slots);
-            unresolved = awaitForeign(batch, slots);
+        Pass pass = new Pass(nodes, out, clock.incrementAndGet());
+        int[] open = null;
+        int remaining = count;
+        while (remaining > 0) {
+            open = pass.run(open, remaining);
+            remaining = open == null ? 0 : open.length;
         }
-        copy(slots, out);
         evictOverflow();
     }
 
@@ -94,130 +124,33 @@ public final class HeightLattice {
         Math.multiplyExact(Math.addExact(cell0, Math.multiplyExact(extent - 1, stride)), cell);
     }
 
-    private CompletableFuture<HydrologySampleBuffer> claimAndSample(Nodes nodes, Slot[] slots) {
-        CompletableFuture<HydrologySampleBuffer> batch = new CompletableFuture<>();
-        try {
-            int[] xs = new int[slots.length];
-            int[] zs = new int[slots.length];
-            int claimed = claim(batch, nodes, slots, xs, zs);
-            if (claimed > 0) {
-                HydrologySampleBuffer samples = new HydrologySampleBuffer(claimed);
-                source.sample(Arrays.copyOf(xs, claimed), Arrays.copyOf(zs, claimed), samples, baseOnly);
-                batch.complete(samples);
-            }
-        } catch (Throwable failure) {
-            try {
-                release(batch, nodes, slots);
-            } finally {
-                batch.completeExceptionally(failure);
-            }
-            throw failure;
-        }
-        return batch;
-    }
-
-    private int claim(CompletableFuture<HydrologySampleBuffer> batch, Nodes nodes, Slot[] slots, int[] xs, int[] zs) {
-        int claimed = 0;
-        for (int index = 0; index < slots.length; index++) {
-            if (slots[index] != null) {
-                continue;
-            }
-            int cellX = nodes.cellX(index);
-            int cellZ = nodes.cellZ(index);
-            Long key = key(cellX, cellZ);
-            Slot existing = cells.get(key);
-            if (existing == null) {
-                Slot fresh = new Slot(batch, claimed);
-                existing = cells.putIfAbsent(key, fresh);
-                if (existing == null) {
-                    slots[index] = fresh;
-                    insertionOrder.offer(key);
-                    xs[claimed] = cellX * cell;
-                    zs[claimed] = cellZ * cell;
-                    claimed++;
-                    continue;
-                }
-            }
-            slots[index] = existing;
-        }
-        return claimed;
-    }
-
-    private void release(CompletableFuture<HydrologySampleBuffer> batch, Nodes nodes, Slot[] slots) {
-        for (int index = 0; index < slots.length; index++) {
-            Slot slot = slots[index];
-            if (slot != null && slot.batch() == batch) {
-                cells.remove(key(nodes.cellX(index), nodes.cellZ(index)), slot);
-            }
-        }
-    }
-
-    private static int awaitForeign(CompletableFuture<HydrologySampleBuffer> own, Slot[] slots) {
-        int unresolved = 0;
-        for (int index = 0; index < slots.length; index++) {
-            CompletableFuture<HydrologySampleBuffer> batch = slots[index].batch();
-            if (batch != own && !await(batch)) {
-                slots[index] = null;
-                unresolved++;
-            }
-        }
-        return unresolved;
-    }
-
-    private static boolean await(CompletableFuture<HydrologySampleBuffer> batch) {
-        if (!batch.isDone()) {
-            try {
-                batch.get();
-            } catch (ExecutionException | CancellationException failure) {
-                return false;
-            } catch (InterruptedException interruption) {
-                Thread.currentThread().interrupt();
-                throw new CancellationException("Hydrology lattice wait interrupted.");
-            }
-        }
-        return !batch.isCompletedExceptionally();
-    }
-
-    private static void copy(Slot[] slots, HydrologySampleBuffer out) {
-        float[] height = out.height();
-        boolean[] ocean = out.ocean();
-        float[] rainfall = out.rainfall();
-        float[] pondDensity = out.pondDensity();
-        byte[] permission = out.permission();
-        String[] fluidProfile = out.fluidProfile();
-        for (int index = 0; index < slots.length; index++) {
-            Slot slot = slots[index];
-            HydrologySampleBuffer samples = slot.batch().join();
-            int sample = slot.index();
-            height[index] = samples.height()[sample];
-            ocean[index] = samples.ocean()[sample];
-            rainfall[index] = samples.rainfall()[sample];
-            pondDensity[index] = samples.pondDensity()[sample];
-            permission[index] = samples.permission()[sample];
-            fluidProfile[index] = samples.fluidProfile()[sample];
+    private Tile tile(int tileX, int tileZ) {
+        Long key = key(tileX, tileZ);
+        Tile known = tiles.get(key);
+        if (known != null) {
+            return known;
         }
+        return tiles.computeIfAbsent(key, ignored -> new Tile(tileCells));
     }
 
     private void evictOverflow() {
-        if (cells.size() <= capacityCells || !evicting.compareAndSet(false, true)) {
+        if (tiles.size() <= capacityTiles || !evicting.compareAndSet(false, true)) {
             return;
         }
         try {
-            int excess = cells.size() - capacityCells;
-            while (excess > 0) {
-                Long key = insertionOrder.poll();
-                if (key == null) {
-                    return;
+            List<Map.Entry<Long, Tile>> idle = new ArrayList<>(tiles.size());
+            for (Map.Entry<Long, Tile> entry : tiles.entrySet()) {
+                if (entry.getValue().pending.get() == 0) {
+                    idle.add(entry);
                 }
-                Slot slot = cells.get(key);
-                if (slot == null) {
-                    continue;
-                }
-                if (!slot.batch().isDone()) {
-                    insertionOrder.offer(key);
-                    excess--;
-                } else if (cells.remove(key, slot)) {
-                    excess--;
+            }
+            idle.sort(Comparator.comparingLong(entry -> entry.getValue().used));
+            int target = capacityTiles - (capacityTiles >> 3);
+            for (int index = 0; index < idle.size() && tiles.size() > target; index++) {
+                Map.Entry<Long, Tile> entry = idle.get(index);
+                Tile tile = entry.getValue();
+                if (tile.pending.get() == 0) {
+                    tiles.remove(entry.getKey(), tile);
                 }
             }
         } finally {
@@ -232,7 +165,219 @@ public final class HeightLattice {
         return mixed ^ (mixed >>> 31);
     }
 
-    private record Slot(CompletableFuture<HydrologySampleBuffer> batch, int index) {
+    private static boolean await(CompletableFuture<Void> batch) {
+        if (!batch.isDone()) {
+            try {
+                batch.get();
+            } catch (ExecutionException | CancellationException failure) {
+                return false;
+            } catch (InterruptedException interruption) {
+                Thread.currentThread().interrupt();
+                throw new CancellationException("Hydrology lattice wait interrupted.");
+            }
+        }
+        return !batch.isCompletedExceptionally();
+    }
+
+    private static void copy(HydrologySampleBuffer samples, int sample, HydrologySampleBuffer out, int index) {
+        out.height()[index] = samples.height()[sample];
+        out.ocean()[index] = samples.ocean()[sample];
+        out.rainfall()[index] = samples.rainfall()[sample];
+        out.pondDensity()[index] = samples.pondDensity()[sample];
+        out.permission()[index] = samples.permission()[sample];
+        out.fluidProfile()[index] = samples.fluidProfile()[sample];
+    }
+
+    private final class Pass {
+        private final Nodes nodes;
+        private final HydrologySampleBuffer out;
+        private final long stamp;
+        private int[] claimedIndex = NO_NODES;
+        private Tile[] claimedTile = NO_TILES;
+        private int[] claimedLocal = NO_NODES;
+        private int claimed;
+        private int[] waitingIndex = NO_NODES;
+        private Tile[] waitingTile = NO_TILES;
+        private int[] waitingLocal = NO_NODES;
+        private int waiting;
+        private Tile current;
+        private int currentX;
+        private int currentZ;
+
+        private Pass(Nodes nodes, HydrologySampleBuffer out, long stamp) {
+            this.nodes = nodes;
+            this.out = out;
+            this.stamp = stamp;
+        }
+
+        private int[] run(int[] open, int remaining) {
+            claimed = 0;
+            waiting = 0;
+            CompletableFuture<Void> batch = new CompletableFuture<>();
+            for (int position = 0; position < remaining; position++) {
+                visit(open == null ? position : open[position], batch);
+            }
+            if (claimed > 0) {
+                sample(batch);
+            }
+            return awaitWaiting();
+        }
+
+        private void visit(int index, CompletableFuture<Void> batch) {
+            int cellX = nodes.cellX(index);
+            int cellZ = nodes.cellZ(index);
+            Tile tile = tileOf(cellX >> tileShift, cellZ >> tileShift);
+            int local = ((cellZ & tileMask) << tileShift) | (cellX & tileMask);
+            while (true) {
+                CompletableFuture<Void> mark = tile.marks.get(local);
+                if (mark == READY) {
+                    tile.copy(local, out, index);
+                    return;
+                }
+                if (mark != null) {
+                    addWaiting(index, tile, local);
+                    return;
+                }
+                if (tile.marks.compareAndSet(local, null, batch)) {
+                    tile.pending.incrementAndGet();
+                    addClaimed(index, tile, local);
+                    return;
+                }
+            }
+        }
+
+        private Tile tileOf(int tileX, int tileZ) {
+            if (current == null || currentX != tileX || currentZ != tileZ) {
+                current = tile(tileX, tileZ);
+                currentX = tileX;
+                currentZ = tileZ;
+                current.used = stamp;
+            }
+            return current;
+        }
+
+        private void sample(CompletableFuture<Void> batch) {
+            try {
+                int[] xs = new int[claimed];
+                int[] zs = new int[claimed];
+                for (int position = 0; position < claimed; position++) {
+                    xs[position] = nodes.cellX(claimedIndex[position]) * cell;
+                    zs[position] = nodes.cellZ(claimedIndex[position]) * cell;
+                }
+                HydrologySampleBuffer samples = new HydrologySampleBuffer(claimed);
+                source.sample(xs, zs, samples, baseOnly);
+                for (int position = 0; position < claimed; position++) {
+                    Tile tile = claimedTile[position];
+                    int local = claimedLocal[position];
+                    tile.store(local, samples, position);
+                    tile.marks.set(local, READY);
+                    tile.pending.decrementAndGet();
+                    copy(samples, position, out, claimedIndex[position]);
+                }
+                batch.complete(null);
+            } catch (Throwable failure) {
+                try {
+                    release(batch);
+                } finally {
+                    batch.completeExceptionally(failure);
+                }
+                throw failure;
+            }
+        }
+
+        private void release(CompletableFuture<Void> batch) {
+            for (int position = 0; position < claimed; position++) {
+                Tile tile = claimedTile[position];
+                if (tile.marks.compareAndSet(claimedLocal[position], batch, null)) {
+                    tile.pending.decrementAndGet();
+                }
+            }
+        }
+
+        private int[] awaitWaiting() {
+            int[] open = null;
+            int unresolved = 0;
+            for (int position = 0; position < waiting; position++) {
+                Tile tile = waitingTile[position];
+                int local = waitingLocal[position];
+                CompletableFuture<Void> mark = tile.marks.get(local);
+                if (mark != READY && (mark == null || !await(mark) || tile.marks.get(local) != READY)) {
+                    if (open == null) {
+                        open = new int[waiting - position];
+                    }
+                    open[unresolved++] = waitingIndex[position];
+                    continue;
+                }
+                tile.copy(local, out, waitingIndex[position]);
+            }
+            return open == null ? null : Arrays.copyOf(open, unresolved);
+        }
+
+        private void addClaimed(int index, Tile tile, int local) {
+            if (claimed == claimedIndex.length) {
+                int grown = Math.max(16, claimed * 2);
+                claimedIndex = Arrays.copyOf(claimedIndex, grown);
+                claimedTile = Arrays.copyOf(claimedTile, grown);
+                claimedLocal = Arrays.copyOf(claimedLocal, grown);
+            }
+            claimedIndex[claimed] = index;
+            claimedTile[claimed] = tile;
+            claimedLocal[claimed] = local;
+            claimed++;
+        }
+
+        private void addWaiting(int index, Tile tile, int local) {
+            if (waiting == waitingIndex.length) {
+                int grown = Math.max(16, waiting * 2);
+                waitingIndex = Arrays.copyOf(waitingIndex, grown);
+                waitingTile = Arrays.copyOf(waitingTile, grown);
+                waitingLocal = Arrays.copyOf(waitingLocal, grown);
+            }
+            waitingIndex[waiting] = index;
+            waitingTile[waiting] = tile;
+            waitingLocal[waiting] = local;
+            waiting++;
+        }
+    }
+
+    private static final class Tile {
+        private final float[] height;
+        private final boolean[] ocean;
+        private final float[] rainfall;
+        private final float[] pondDensity;
+        private final byte[] permission;
+        private final String[] fluidProfile;
+        private final AtomicReferenceArray<CompletableFuture<Void>> marks;
+        private final AtomicInteger pending = new AtomicInteger();
+        private volatile long used;
+
+        private Tile(int cells) {
+            this.height = new float[cells];
+            this.ocean = new boolean[cells];
+            this.rainfall = new float[cells];
+            this.pondDensity = new float[cells];
+            this.permission = new byte[cells];
+            this.fluidProfile = new String[cells];
+            this.marks = new AtomicReferenceArray<>(cells);
+        }
+
+        private void store(int local, HydrologySampleBuffer samples, int sample) {
+            height[local] = samples.height()[sample];
+            ocean[local] = samples.ocean()[sample];
+            rainfall[local] = samples.rainfall()[sample];
+            pondDensity[local] = samples.pondDensity()[sample];
+            permission[local] = samples.permission()[sample];
+            fluidProfile[local] = samples.fluidProfile()[sample];
+        }
+
+        private void copy(int local, HydrologySampleBuffer out, int index) {
+            out.height()[index] = height[local];
+            out.ocean()[index] = ocean[local];
+            out.rainfall()[index] = rainfall[local];
+            out.pondDensity()[index] = pondDensity[local];
+            out.permission()[index] = permission[local];
+            out.fluidProfile()[index] = fluidProfile[local];
+        }
     }
 
     private interface Nodes {

core/src/main/java/art/arcane/iris/generation/hydrology/plan/HydrologyPlanCache.java

@@ -32,10 +32,10 @@ import java.util.function.Consumer;
 import java.util.function.Function;
 
 public final class HydrologyPlanCache {
-    private static final int FRONT = 3;
-    public static final int WINDOW_LATTICE_CELLS = frontCells(WindowKey.SIZE, WindowPlanner.CELL);
-    public static final int FINE_LATTICE_CELLS = frontCells(WindowKey.SIZE, WindowPlanner.FINE_CELL);
-    public static final int REGION_LATTICE_CELLS = frontCells(RegionKey.SIZE, RegionPlanner.CELL);
+    private static final int FINE_FRONT = 9;
+    private static final int REGION_FRONT = 5;
+    public static final int FINE_LATTICE_CELLS = frontCells(FINE_FRONT, WindowKey.SIZE, WindowPlanner.FINE_CELL);
+    public static final int REGION_LATTICE_CELLS = frontCells(REGION_FRONT, RegionKey.SIZE, RegionPlanner.CELL);
     private static final int WINDOW_CAPACITY = 128;
     private static final int REGION_CAPACITY = 64;
     private static final long DEMAND = Long.MIN_VALUE;
@@ -312,8 +312,8 @@ public final class HydrologyPlanCache {
         return Math.max(1, parallelism / 2);
     }
 
-    private static int frontCells(int unit, int cell) {
-        int cells = (FRONT + 2) * unit / cell;
+    private static int frontCells(int front, int unit, int cell) {
+        int cells = (front + 2) * unit / cell;
         return cells * cells;
     }
 

core/src/main/java/art/arcane/iris/generation/hydrology/plan/WindowPlanner.java

@@ -36,6 +36,7 @@ public final class WindowPlanner {
     public static final int CELL = 8;
     public static final int FINE_CELL = 4;
     private static final int WINDOW_CELLS = WindowKey.SIZE / CELL;
+    private static final int FINE_STRIDE = CELL / FINE_CELL;
     private static final int SPAN = 3 * WINDOW_CELLS;
     private static final int REACH_OVERHANG = 256;
     private static final float BASIN_DEPTH = 0.5f;
@@ -43,22 +44,17 @@ public final class WindowPlanner {
     private static final long SALT_HEAD = 0x5354524541484dL;
 
     private final HydrologySettings settings;
-    private final HeightLattice lattice;
     private final HeightLattice fine;
     private final PondPlanner ponds;
     private final ReachShaper shaper;
     private final SeaInletPlanner inlets;
 
-    public WindowPlanner(HydrologySettings settings, HeightLattice lattice, HeightLattice fine, PondPlanner ponds, ReachShaper shaper) {
+    public WindowPlanner(HydrologySettings settings, HeightLattice fine, PondPlanner ponds, ReachShaper shaper) {
         this.settings = Objects.requireNonNull(settings, "settings");
-        this.lattice = Objects.requireNonNull(lattice, "lattice");
         this.fine = Objects.requireNonNull(fine, "fine");
         this.ponds = Objects.requireNonNull(ponds, "ponds");
         this.shaper = Objects.requireNonNull(shaper, "shaper");
         this.inlets = new SeaInletPlanner(settings);
-        if (lattice.cell() != CELL) {
-            throw new IllegalArgumentException("Window lattice cell " + lattice.cell() + " must be " + CELL);
-        }
         if (fine.cell() != FINE_CELL) {
             throw new IllegalArgumentException("Window fine lattice cell " + fine.cell() + " must be " + FINE_CELL);
         }
@@ -87,7 +83,7 @@ public final class WindowPlanner {
         int cellX = Math.multiplyExact(key.wx() - 1, WINDOW_CELLS);
         int cellZ = Math.multiplyExact(key.wz() - 1, WINDOW_CELLS);
         HydrologySampleBuffer samples = new HydrologySampleBuffer(SPAN * SPAN);
-        lattice.fill(cellX, cellZ, SPAN, SPAN, samples);
+        fine.fill(cellX * FINE_STRIDE, cellZ * FINE_STRIDE, SPAN, SPAN, FINE_STRIDE, samples);
         DemGrid raw = new DemGrid(cellX * CELL, cellZ * CELL, CELL, SPAN, SPAN);
         System.arraycopy(samples.height(), 0, raw.values(), 0, SPAN * SPAN);
         List<Pond> lakes = regionLakes(plans.values());

core/src/main/java/art/arcane/iris/generation/hydrology/raster/ChunkFeatures.java

@@ -12,6 +12,7 @@ import art.arcane.iris.generation.hydrology.water.PondMask;
 import art.arcane.iris.generation.hydrology.water.Reach;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -28,17 +29,20 @@ final class ChunkFeatures {
     private final List<Pond> ponds;
     private final List<Pond> lakes;
     private final List<SeaInlet> inlets;
+    private final int[] inletBoxes;
     private final int[] lakeBoxes;
     private final ReachSegments segments = new ReachSegments(SEGMENT_CAPACITY);
     private final MaskEdges pondShores = new MaskEdges(MaskEdges.Kind.WATER);
     private final MaskEdges pondBanks = new MaskEdges(MaskEdges.Kind.BANK);
     private final MaskEdges lakeReach = new MaskEdges(MaskEdges.Kind.GROWN_WATER);
+    private boolean inert;
 
-    private ChunkFeatures(List<Reach> reaches, List<Pond> ponds, List<Pond> lakes, List<SeaInlet> inlets) {
+    private ChunkFeatures(List<Reach> reaches, List<Pond> ponds, List<Pond> lakes, List<SeaInlet> inlets, int[] inletBoxes) {
         this.reaches = reaches;
         this.ponds = ponds;
         this.lakes = lakes;
         this.inlets = inlets;
+        this.inletBoxes = inletBoxes;
         this.lakeBoxes = new int[4 * lakes.size()];
     }
 
@@ -48,12 +52,15 @@ final class ChunkFeatures {
         List<Reach> reaches = new ArrayList<>();
         List<Pond> ponds = new ArrayList<>();
         List<SeaInlet> inlets = new ArrayList<>();
+        int[] inletBoxes = new int[0];
         for (IndexedWindow window : windows) {
             for (SeaInlet inlet : window.plan().inlets()) {
                 int[] bounds = SeaInletRasterizer.bounds(inlet);
                 int padding = RiffleProfile.RADIUS + 1;
                 if (bounds[0] <= chunkX * CHUNK + CHUNK - 1 + padding && bounds[2] >= chunkX * CHUNK - padding
                         && bounds[1] <= chunkZ * CHUNK + CHUNK - 1 + padding && bounds[3] >= chunkZ * CHUNK - padding) {
+                    inletBoxes = Arrays.copyOf(inletBoxes, inletBoxes.length + 4);
+                    System.arraycopy(bounds, 0, inletBoxes, 4 * inlets.size(), 4);
                     inlets.add(inlet);
                 }
             }
@@ -64,17 +71,22 @@ final class ChunkFeatures {
             }
         }
         List<Pond> lakes = lakes(chunkX, chunkZ, halo, lakeRegionPlans, lakeRegions);
-        ChunkFeatures features = new ChunkFeatures(reaches, ponds, lakes, inlets);
+        ChunkFeatures features = new ChunkFeatures(reaches, ponds, lakes, inlets, inletBoxes);
         features.index(settings, chunkX, chunkZ);
         return features;
     }
 
-    boolean empty() {
-        return reaches.isEmpty() && ponds.isEmpty() && lakes.isEmpty() && inlets.isEmpty();
+    boolean inert() {
+        return inert;
     }
 
     SeaInlet openInletAt(int x, int z, int[] column) {
-        for (SeaInlet inlet : inlets) {
+        for (int index = 0; index < inlets.size(); index++) {
+            int box = 4 * index;
+            if (x < inletBoxes[box] || z < inletBoxes[box + 1] || x > inletBoxes[box + 2] || z > inletBoxes[box + 3]) {
+                continue;
+            }
+            SeaInlet inlet = inlets.get(index);
             if (SeaInletRasterizer.column(inlet, x, z, column) && column[1] == SeaInlet.OPEN) {
                 return inlet;
             }
@@ -179,6 +191,8 @@ final class ChunkFeatures {
         for (Reach reach : reaches) {
             segments.addNear(reach, minX - 1f, minZ - 1f, maxX + 1f, maxZ + 1f, outward);
         }
+        int riffle = RiffleProfile.RADIUS + 1;
+        segments.coverChannels(minX - riffle, minZ - riffle, maxX + riffle, maxZ + riffle);
         HydrologySettings.PondShore shore = settings.ponds().shore();
         int reach = Math.max(shore.taper(), ChunkWaterRaster.MAX_SHORE_DISTANCE) + 1;
         int shelf = shore.shelf() + 1;
@@ -192,6 +206,39 @@ final class ChunkFeatures {
             lakeReach.collect(mask, minX - shoreReach, minZ - shoreReach, maxX + shoreReach, maxZ + shoreReach);
             System.arraycopy(grownBox(mask), 0, lakeBoxes, 4 * index, 4);
         }
+        inert = segments.isEmpty() && !inletsTouch(minX - 1, minZ - 1, maxX + 1, maxZ + 1)
+                && !pondsTouch(minX - 1 - reach, minZ - 1 - reach, maxX + 1 + reach, maxZ + 1 + reach)
+                && !lakesTouch(minX - 2 - shoreReach, minZ - 2 - shoreReach, maxX + 2 + shoreReach, maxZ + 2 + shoreReach);
+    }
+
+    private boolean inletsTouch(int minX, int minZ, int maxX, int maxZ) {
+        for (int box = 0; box < inletBoxes.length; box += 4) {
+            if (inletBoxes[box] <= maxX && inletBoxes[box + 2] >= minX && inletBoxes[box + 1] <= maxZ && inletBoxes[box + 3] >= minZ) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private boolean pondsTouch(int minX, int minZ, int maxX, int maxZ) {
+        for (Pond pond : ponds) {
+            PondMask mask = pond.mask();
+            int fromX = mask.originX() - (mask.step() >> 1);
+            int fromZ = mask.originZ() - (mask.step() >> 1);
+            if (fromX <= maxX && fromX + mask.width() * mask.step() > minX && fromZ <= maxZ && fromZ + mask.depth() * mask.step() > minZ) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private boolean lakesTouch(int minX, int minZ, int maxX, int maxZ) {
+        for (int box = 0; box < lakeBoxes.length; box += 4) {
+            if (lakeBoxes[box] <= maxX && lakeBoxes[box + 2] > minX && lakeBoxes[box + 1] <= maxZ && lakeBoxes[box + 3] > minZ) {
+                return true;
+            }
+        }
+        return false;
     }
 
     private static Map<WindowKey, IndexedWindow> windowsByKey(int chunkX, int chunkZ, List<IndexedWindow> windows) {

core/src/main/java/art/arcane/iris/generation/hydrology/raster/ChunkRasterizer.java

@@ -37,7 +37,7 @@ public final class ChunkRasterizer {
                                       List<RegionPlan> lakeRegionPlans) {
         Objects.requireNonNull(naturalHeight, "naturalHeight");
         ChunkFeatures features = ChunkFeatures.gather(settings, chunkX, chunkZ, halo, windows, lakeRegionPlans, lakeRegions(chunkX, chunkZ));
-        if (features.empty()) {
+        if (features.inert()) {
             return ChunkWaterRaster.EMPTY;
         }
         return new RasterComposer(settings, features, chunkX, chunkZ).compose(naturalHeight);

core/src/main/java/art/arcane/iris/generation/hydrology/raster/ChunkWaterRaster.java

@@ -2,6 +2,8 @@ package art.arcane.iris.generation.hydrology.raster;
 
 import art.arcane.iris.generation.hydrology.water.HydrologyTier;
 
+import java.util.Arrays;
+
 public final class ChunkWaterRaster {
     public static final int MAX_SHORE_DISTANCE = 32;
     public static final ChunkWaterRaster PROVISIONAL = new ChunkWaterRaster(true);
@@ -13,10 +15,13 @@ public final class ChunkWaterRaster {
     private final int[] terrain;
     private final int[] head;
     private final byte[] role;
-    private final HydrologyTier[] tier;
-    private final long[] featureId;
-    private final String[] fluid;
-    private final int[] caveCeiling;
+    private final byte[] tier;
+    private final HydrologyTier[] tiers;
+    private final byte[] feature;
+    private final long[] features;
+    private final byte[] fluid;
+    private final String[] fluids;
+    private final boolean caveMask;
     private final byte[] shoreDistance;
 
     private ChunkWaterRaster(boolean provisional) {
@@ -25,26 +30,32 @@ public final class ChunkWaterRaster {
         this.head = null;
         this.role = null;
         this.tier = null;
-        this.featureId = null;
+        this.tiers = null;
+        this.feature = null;
+        this.features = null;
         this.fluid = null;
-        this.caveCeiling = null;
+        this.fluids = null;
+        this.caveMask = false;
         this.shoreDistance = null;
     }
 
-    ChunkWaterRaster(int[] terrain, int[] head, byte[] role, HydrologyTier[] tier, long[] featureId, String[] fluid, int[] caveCeiling,
-                     byte[] shoreDistance) {
-        if (terrain.length != COLUMNS || head.length != COLUMNS || role.length != COLUMNS || tier.length != COLUMNS
-                || featureId.length != COLUMNS || fluid.length != COLUMNS || caveCeiling.length != COLUMNS || shoreDistance.length != COLUMNS) {
+    ChunkWaterRaster(int[] terrain, int[] head, byte[] role, Palette<HydrologyTier> tiers, LongPalette features, Palette<String> fluids,
+                     boolean caveMask, byte[] shoreDistance) {
+        if (terrain.length != COLUMNS || head.length != COLUMNS || role.length != COLUMNS || tiers.indices.length != COLUMNS
+                || features.indices.length != COLUMNS || fluids.indices.length != COLUMNS || shoreDistance.length != COLUMNS) {
             throw new IllegalArgumentException("A chunk water raster needs " + COLUMNS + " entries per array");
         }
         this.provisional = false;
         this.terrain = terrain;
         this.head = head;
         this.role = role;
-        this.tier = tier;
-        this.featureId = featureId;
-        this.fluid = fluid;
-        this.caveCeiling = caveCeiling;
+        this.tier = tiers.indices;
+        this.tiers = tiers.values();
+        this.feature = features.indices;
+        this.features = features.values();
+        this.fluid = fluids.indices;
+        this.fluids = fluids.values();
+        this.caveMask = caveMask;
         this.shoreDistance = shoreDistance;
     }
 
@@ -68,22 +79,22 @@ public final class ChunkWaterRaster {
 
     public HydrologyTier tier(int lx, int lz) {
         int index = index(lx, lz);
-        return tier == null ? null : tier[index];
+        return tier == null ? null : tiers[tier[index] & 0xFF];
     }
 
     public long featureId(int lx, int lz) {
         int index = index(lx, lz);
-        return featureId == null ? 0L : featureId[index];
+        return feature == null ? 0L : features[feature[index] & 0xFF];
     }
 
     public String fluid(int lx, int lz) {
         int index = index(lx, lz);
-        return fluid == null ? null : fluid[index];
+        return fluid == null ? null : fluids[fluid[index] & 0xFF];
     }
 
     public int caveCeiling(int lx, int lz) {
         int index = index(lx, lz);
-        return caveCeiling == null ? Integer.MAX_VALUE : caveCeiling[index];
+        return caveMask && head[index] != Integer.MIN_VALUE ? terrain[index] - 1 : Integer.MAX_VALUE;
     }
 
     public int shoreDistance(int lx, int lz) {
@@ -105,4 +116,53 @@ public final class ChunkWaterRaster {
         }
         return lz << 4 | lx;
     }
+
+    static final class Palette<T> {
+        private final byte[] indices = new byte[COLUMNS];
+        private final T[] seen;
+        private int size;
+
+        Palette(T[] seen) {
+            if (seen.length != COLUMNS) {
+                throw new IllegalArgumentException("A raster palette needs room for " + COLUMNS + " values");
+            }
+            this.seen = seen;
+        }
+
+        void set(int column, T value) {
+            int found = 0;
+            while (found < size && seen[found] != value) {
+                found++;
+            }
+            if (found == size) {
+                seen[size++] = value;
+            }
+            indices[column] = (byte) found;
+        }
+
+        private T[] values() {
+            return Arrays.copyOf(seen, size);
+        }
+    }
+
+    static final class LongPalette {
+        private final byte[] indices = new byte[COLUMNS];
+        private final long[] seen = new long[COLUMNS];
+        private int size;
+
+        void set(int column, long value) {
+            int found = 0;
+            while (found < size && seen[found] != value) {
+                found++;
+            }
+            if (found == size) {
+                seen[size++] = value;
+            }
+            indices[column] = (byte) found;
+        }
+
+        private long[] values() {
+            return Arrays.copyOf(seen, size);
+        }
+    }
 }

core/src/main/java/art/arcane/iris/generation/hydrology/raster/RasterComposer.java

@@ -385,34 +385,37 @@ final class RasterComposer {
 
     private ChunkWaterRaster pack() {
         int columns = ChunkWaterRaster.COLUMNS;
+        boolean affected = false;
+        for (int lz = 0; lz < CHUNK && !affected; lz++) {
+            for (int lx = 0; lx < CHUNK && !affected; lx++) {
+                int cell = (lz + 1) * GRID + lx + 1;
+                affected = role[cell] != WaterRole.NONE || terrain[cell] != natural[cell] || shore(cell) < ChunkWaterRaster.MAX_SHORE_DISTANCE;
+            }
+        }
+        if (!affected) {
+            return ChunkWaterRaster.EMPTY;
+        }
         int[] terrainOut = new int[columns];
         int[] headOut = new int[columns];
         byte[] roleOut = new byte[columns];
-        HydrologyTier[] tierOut = new HydrologyTier[columns];
-        long[] featureOut = new long[columns];
-        String[] fluidOut = new String[columns];
-        int[] caveOut = new int[columns];
+        ChunkWaterRaster.Palette<HydrologyTier> tierOut = new ChunkWaterRaster.Palette<>(new HydrologyTier[columns]);
+        ChunkWaterRaster.LongPalette featureOut = new ChunkWaterRaster.LongPalette();
+        ChunkWaterRaster.Palette<String> fluidOut = new ChunkWaterRaster.Palette<>(new String[columns]);
         byte[] shoreOut = new byte[columns];
-        boolean caveMask = settings.deformation().caveMask();
-        boolean affected = false;
         for (int lz = 0; lz < CHUNK; lz++) {
             for (int lx = 0; lx < CHUNK; lx++) {
                 int cell = (lz + 1) * GRID + lx + 1;
                 int index = lz << 4 | lx;
-                int shore = shore(cell);
                 terrainOut[index] = terrain[cell];
                 headOut[index] = head[cell];
                 roleOut[index] = (byte) role[cell].ordinal();
-                tierOut[index] = tier[cell];
-                featureOut[index] = feature[cell];
-                fluidOut[index] = fluid[cell];
-                caveOut[index] = caveMask && head[cell] != Integer.MIN_VALUE ? terrain[cell] - 1 : Integer.MAX_VALUE;
-                shoreOut[index] = (byte) shore;
-                affected |= role[cell] != WaterRole.NONE || terrain[cell] != natural[cell] || shore < ChunkWaterRaster.MAX_SHORE_DISTANCE;
+                tierOut.set(index, tier[cell]);
+                featureOut.set(index, feature[cell]);
+                fluidOut.set(index, fluid[cell]);
+                shoreOut[index] = (byte) shore(cell);
             }
         }
-        return affected ? new ChunkWaterRaster(terrainOut, headOut, roleOut, tierOut, featureOut, fluidOut, caveOut, shoreOut)
-                : ChunkWaterRaster.EMPTY;
+        return new ChunkWaterRaster(terrainOut, headOut, roleOut, tierOut, featureOut, fluidOut, settings.deformation().caveMask(), shoreOut);
     }
 
     private int shore(int cell) {

core/src/main/java/art/arcane/iris/generation/hydrology/raster/ReachSegments.java

@@ -6,6 +6,8 @@ import java.util.Arrays;
 
 final class ReachSegments {
     private static final int RUN = 16;
+    private static final int COVER_SHIFT = 2;
+    private static final float COVER_MARGIN = 1f;
 
     private Reach[] reaches;
     private int[] segments;
@@ -24,6 +26,13 @@ final class ReachSegments {
     private int[] runBands = new int[8];
     private int runs;
     private boolean sealed;
+    private boolean covered;
+    private int coverX;
+    private int coverZ;
+    private int coverWidth;
+    private int coverDepth;
+    private int[] coverStarts;
+    private int[] coverEntries;
 
     ReachSegments(int capacity) {
         int initial = Math.max(1, capacity);
@@ -71,6 +80,19 @@ final class ReachSegments {
         }
     }
 
+    boolean isEmpty() {
+        return size == 0;
+    }
+
+    void coverChannels(int minX, int minZ, int maxX, int maxZ) {
+        covered = true;
+        coverX = minX;
+        coverZ = minZ;
+        coverWidth = ((maxX - minX) >> COVER_SHIFT) + 1;
+        coverDepth = ((maxZ - minZ) >> COVER_SHIFT) + 1;
+        sealed = false;
+    }
+
     void nearest(double x, double z, Scope scope, ReachCursor cursor) {
         if (!sealed) {
             seal();
@@ -89,6 +111,16 @@ final class ReachSegments {
         hint(channelHint, x, z, unbounded, cursor);
         hint(bankHint, x, z, unbounded, cursor);
         hint(edgeHint, x, z, unbounded, cursor);
+        int cell = scope == Scope.CHANNEL ? coveredCell(x, z) : -1;
+        if (cell >= 0) {
+            for (int entry = coverStarts[cell]; entry < coverStarts[cell + 1]; entry++) {
+                int index = coverEntries[entry];
+                if (index != channelHint && index != bankHint && index != edgeHint && !beyondSegment(index, x, z, scope, cursor)) {
+                    evaluate(index, x, z, false, cursor);
+                }
+            }
+            return;
+        }
         int first = 0;
         for (int run = 0; run < runs; run++) {
             int end = runEnds[run];
@@ -99,9 +131,7 @@ final class ReachSegments {
                 continue;
             }
             for (int index = first; index < end; index++) {
-                if (!beyond(x, z, Math.min(startX[index], endX[index]), Math.min(startZ[index], endZ[index]), Math.max(startX[index], endX[index]),
-                        Math.max(startZ[index], endZ[index]), limit(radius[index], bands[index], scope, cursor))
-                        && index != channelHint && index != bankHint && index != edgeHint) {
+                if (!beyondSegment(index, x, z, scope, cursor) && index != channelHint && index != bankHint && index != edgeHint) {
                     evaluate(index, x, z, unbounded, cursor);
                 }
             }
@@ -109,6 +139,23 @@ final class ReachSegments {
         }
     }
 
+    private int coveredCell(double x, double z) {
+        if (coverStarts == null) {
+            return -1;
+        }
+        int cellX = ((int) Math.floor(x) - coverX) >> COVER_SHIFT;
+        int cellZ = ((int) Math.floor(z) - coverZ) >> COVER_SHIFT;
+        if (cellX < 0 || cellZ < 0 || cellX >= coverWidth || cellZ >= coverDepth) {
+            return -1;
+        }
+        return cellZ * coverWidth + cellX;
+    }
+
+    private boolean beyondSegment(int index, double x, double z, Scope scope, ReachCursor cursor) {
+        return beyond(x, z, Math.min(startX[index], endX[index]), Math.min(startZ[index], endZ[index]), Math.max(startX[index], endX[index]),
+                Math.max(startZ[index], endZ[index]), limit(radius[index], bands[index], scope, cursor));
+    }
+
     private void hint(int index, double x, double z, boolean unbounded, ReachCursor cursor) {
         if (index >= 0 && index < size) {
             evaluate(index, x, z, unbounded, cursor);
@@ -171,9 +218,56 @@ final class ReachSegments {
             addRun(start, end);
             start = end;
         }
+        if (covered) {
+            cover();
+        }
         sealed = true;
     }
 
+    private void cover() {
+        int cells = coverWidth * coverDepth;
+        int[] starts = new int[cells + 1];
+        int[] range = new int[4];
+        for (int index = 0; index < size; index++) {
+            if (coverRange(index, range)) {
+                for (int cellZ = range[1]; cellZ <= range[3]; cellZ++) {
+                    for (int cellX = range[0]; cellX <= range[2]; cellX++) {
+                        starts[cellZ * coverWidth + cellX + 1]++;
+                    }
+                }
+            }
+        }
+        for (int cell = 0; cell < cells; cell++) {
+            starts[cell + 1] += starts[cell];
+        }
+        int[] entries = new int[starts[cells]];
+        int[] fill = Arrays.copyOf(starts, cells);
+        for (int index = 0; index < size; index++) {
+            if (coverRange(index, range)) {
+                for (int cellZ = range[1]; cellZ <= range[3]; cellZ++) {
+                    for (int cellX = range[0]; cellX <= range[2]; cellX++) {
+                        entries[fill[cellZ * coverWidth + cellX]++] = index;
+                    }
+                }
+            }
+        }
+        coverStarts = starts;
+        coverEntries = entries;
+    }
+
+    private boolean coverRange(int index, int[] range) {
+        float reach = radius[index] + COVER_MARGIN;
+        range[0] = Math.max(0, coverCell(Math.min(startX[index], endX[index]) - reach, coverX));
+        range[1] = Math.max(0, coverCell(Math.min(startZ[index], endZ[index]) - reach, coverZ));
+        range[2] = Math.min(coverWidth - 1, coverCell(Math.max(startX[index], endX[index]) + reach, coverX));
+        range[3] = Math.min(coverDepth - 1, coverCell(Math.max(startZ[index], endZ[index]) + reach, coverZ));
+        return range[0] <= range[2] && range[1] <= range[3];
+    }
+
+    private static int coverCell(float block, int origin) {
+        return ((int) Math.floor(block) - origin) >> COVER_SHIFT;
+    }
+
     private void addRun(int start, int end) {
         if (runs == runEnds.length) {
             runEnds = Arrays.copyOf(runEnds, 2 * runs);

core/src/main/java/art/arcane/iris/generation/hydrology/raster/RiffleProfile.java

@@ -15,6 +15,7 @@ final class RiffleProfile {
     private static final int LIMIT = 10 * RADIUS;
     private static final int DRY = Integer.MIN_VALUE;
     private static final int[] SIDES = {1, -1, GRID, -GRID};
+    private static final int[] REMAINING = remaining();
 
     private final List<Field> fields = new ArrayList<>();
 
@@ -85,6 +86,20 @@ final class RiffleProfile {
         return (int) Math.max(original, Math.min(head - 1L, Math.round(raised)));
     }
 
+    private static int[] remaining() {
+        int[] remaining = new int[GRID * GRID];
+        int low = PADDING - 1;
+        int high = PADDING + CHUNK;
+        for (int z = 0; z < GRID; z++) {
+            for (int x = 0; x < GRID; x++) {
+                int outsideX = Math.max(0, Math.max(low - x, x - high));
+                int outsideZ = Math.max(0, Math.max(low - z, z - high));
+                remaining[z * GRID + x] = 10 * Math.max(outsideX, outsideZ);
+            }
+        }
+        return remaining;
+    }
+
     private record Field(int crest, int[] distances) {
     }
 
@@ -107,6 +122,9 @@ final class RiffleProfile {
         }
 
         private void offer(int cell, int distance) {
+            if (distance + REMAINING[cell] >= LIMIT) {
+                return;
+            }
             if (distances[cell] < LIMIT) {
                 remove(cell);
             }

core/src/main/java/art/arcane/iris/generation/hydrology/underground/CavePoolFiller.java

@@ -10,6 +10,7 @@ import it.unimi.dsi.fastutil.longs.LongOpenHashSet;
 
 import java.util.Arrays;
 import java.util.Set;
+import java.util.function.Supplier;
 
 public final class CavePoolFiller {
     public static final int REACH = HydrologySettings.MAX_CAVE_POOL_RADIUS + 1;
@@ -40,15 +41,19 @@ public final class CavePoolFiller {
         this.density = settings.density();
     }
 
-    public void fill(int chunkX, int chunkZ, CarvedTerrain carved, MantleWriter writer, long seed) {
+    public void fill(int chunkX, int chunkZ, Supplier<? extends CarvedTerrain> terrain, MantleWriter writer, long seed) {
         if (!pools.enabled() || density == 0f) {
             return;
         }
         int attempts = attempts(seed, chunkX, chunkZ);
+        CarvedTerrain carved = null;
         for (int attempt = 0; attempt < attempts; attempt++) {
             if (density < 1f && CellHash.unit(CellHash.mix(seed, SALT_DENSITY + attempt, chunkX, chunkZ)) >= density) {
                 continue;
             }
+            if (carved == null) {
+                carved = terrain.get();
+            }
             long column = CellHash.mix(seed, SALT_COLUMN + attempt, chunkX, chunkZ);
             int x = (chunkX << 4) + (int) (column & 15);
             int z = (chunkZ << 4) + (int) ((column >>> 4) & 15);

core/src/main/java/art/arcane/iris/generation/hydrology/underground/SeaInletPlanner.java

@@ -33,6 +33,7 @@ public final class SeaInletPlanner {
     private static final long SALT_HEADROOM = 0x53454148454144L;
     private static final long SALT_DEPTH = 0x53454144455054L;
     private static final long SALT_DENSITY = 0x53454144454e53L;
+    private static final double SQUARED_MARGIN = 1e-9D;
 
     private final HydrologySettings settings;
 
@@ -403,22 +404,36 @@ public final class SeaInletPlanner {
         double dx = bx - ax;
         double dz = bz - az;
         double span = dx * dx + dz * dz;
+        double outside = radius > 0f ? squaredAbove(radius) : Double.POSITIVE_INFINITY;
+        double inside = radius > 0f ? squaredBelow(radius) : Double.NEGATIVE_INFINITY;
+        double wetOutside = wetRadius > 0f ? squaredAbove(wetRadius) : Double.POSITIVE_INFINITY;
+        double wetInside = wetRadius > 0f ? squaredBelow(wetRadius) : Double.NEGATIVE_INFINITY;
         for (int j = minJ; j <= maxJ; j++) {
             double pz = grid.originZ() + (double) j * cell;
             for (int i = minI; i <= maxI; i++) {
                 double px = grid.originX() + (double) i * cell;
                 double t = span <= 0D ? 0D : Math.clamp(((px - ax) * dx + (pz - az) * dz) / span, 0D, 1D);
-                double distance = Math.hypot(px - (ax + t * dx), pz - (az + t * dz));
-                if (distance > radius) {
+                double ex = px - (ax + t * dx);
+                double ez = pz - (az + t * dz);
+                double squared = ex * ex + ez * ez;
+                if (squared > outside || !(squared < inside) && Math.hypot(ex, ez) > radius) {
                     continue;
                 }
                 int index = j * grid.width() + i;
                 cover[index] = Math.min(cover[index], bed);
-                wet[index] |= distance <= wetRadius;
+                wet[index] |= squared < wetInside || !(squared > wetOutside) && Math.hypot(ex, ez) <= wetRadius;
             }
         }
     }
 
+    private static double squaredAbove(float radius) {
+        return (double) radius * radius * (1D + SQUARED_MARGIN);
+    }
+
+    private static double squaredBelow(float radius) {
+        return (double) radius * radius * (1D - SQUARED_MARGIN);
+    }
+
     private static float pathLength(DemGrid grid, List<Integer> path) {
         float length = 0f;
         for (int station = 1; station < path.size(); station++) {

core/src/main/java/art/arcane/iris/generation/mantle/MantleHydrologyComponent.java

@@ -85,8 +85,9 @@ public final class MantleHydrologyComponent extends IrisMantleComponent {
         generateFalls(writer, complex, runtime, own, chunkX, chunkZ);
         if (poolsActive()) {
             HydrologySettings settings = runtime.settings();
-            new CavePoolFiller(settings).fill(chunkX, chunkZ,
-                    new MantleCarvedTerrain(writer, complex, getEngineMantle().getEngine(), chunkX, chunkZ), writer, settings.seed());
+            Engine engine = getEngineMantle().getEngine();
+            new CavePoolFiller(settings).fill(chunkX, chunkZ, () -> new MantleCarvedTerrain(writer, complex, engine, chunkX, chunkZ), writer,
+                    settings.seed());
         }
     }
 

core/src/main/java/art/arcane/iris/generation/runtime/IrisComplex.java

@@ -91,7 +91,6 @@ import art.arcane.volmlib.util.interpolation.NoiseBoundsProvider;
 import art.arcane.volmlib.util.noise.CNG;
 import art.arcane.volmlib.util.stream.ProceduralStream;
 import art.arcane.volmlib.util.stream.interpolation.Interpolated;
-import it.unimi.dsi.fastutil.longs.Long2DoubleOpenHashMap;
 import lombok.AccessLevel;
 import lombok.Data;
 import lombok.EqualsAndHashCode;
@@ -120,10 +119,11 @@ import java.util.concurrent.atomic.AtomicLong;
 import java.util.function.BiFunction;
 
 @Data
-@EqualsAndHashCode(exclude = {"data", "gridBoundsCache", "sharedCornerBounds", "sharedBoundsBiomes", "terrainProgram", "bakeCache", "regionSource", "baseBiomeSource", "caveSource", "rockSource", "fluidSource", "childStyleSeed", "inferredByType", "naturalHeightSource", "naturalTrueBiomeSource", "trueBiomeSource", "frozenInterpolators", "frozenGenerators", "inferredBiomeStreams", "imageMapRuntime", "terrainEngine", "terrain3D", "hydrologyRuntime", "shoreBiomes", "waterVegetation", "effectiveChunks"})
-@ToString(exclude = {"data", "gridBoundsCache", "sharedCornerBounds", "sharedBoundsBiomes", "terrainProgram", "bakeCache", "regionSource", "baseBiomeSource", "caveSource", "rockSource", "fluidSource", "childStyleSeed", "inferredByType", "naturalHeightSource", "naturalTrueBiomeSource", "trueBiomeSource", "frozenInterpolators", "frozenGenerators", "inferredBiomeStreams", "imageMapRuntime", "terrainEngine", "terrain3D", "hydrologyRuntime", "shoreBiomes", "waterVegetation", "effectiveChunks"})
+@EqualsAndHashCode(exclude = {"data", "gridBoundsCache", "sharedCornerBounds", "sharedBaseHeights", "sharedBoundsBiomes", "regionBounds", "contextRegionStream", "terrainProgram", "bakeCache", "regionSource", "baseBiomeSource", "caveSource", "rockSource", "fluidSource", "childStyleSeed", "inferredByType", "naturalHeightSource", "naturalTrueBiomeSource", "trueBiomeSource", "frozenInterpolators", "frozenGenerators", "inferredBiomeStreams", "imageMapRuntime", "terrainEngine", "terrain3D", "hydrologyRuntime", "shoreBiomes", "waterVegetation", "effectiveChunks"})
+@ToString(exclude = {"data", "gridBoundsCache", "sharedCornerBounds", "sharedBaseHeights", "sharedBoundsBiomes", "regionBounds", "contextRegionStream", "terrainProgram", "bakeCache", "regionSource", "baseBiomeSource", "caveSource", "rockSource", "fluidSource", "childStyleSeed", "inferredByType", "naturalHeightSource", "naturalTrueBiomeSource", "trueBiomeSource", "frozenInterpolators", "frozenGenerators", "inferredBiomeStreams", "imageMapRuntime", "terrainEngine", "terrain3D", "hydrologyRuntime", "shoreBiomes", "waterVegetation", "effectiveChunks"})
 public class IrisComplex implements DataProvider {
     private static final NoiseBounds ZERO_NOISE_BOUNDS = new NoiseBounds(0D, 0D);
+    private static final long NEGATIVE_ZERO_BITS = Double.doubleToRawLongBits(-0D);
     private static final AtomicLong lastBoundsFailureLog = new AtomicLong(0L);
     private static final int GRID_BOUNDS_CACHE_SIZE = 8192;
     private static final int STUDIO_NOISE_CACHE_SIZE = 32_768;
@@ -146,7 +146,6 @@ public class IrisComplex implements DataProvider {
             Comparator.nullsFirst(Comparator.naturalOrder())
     );
     private static final ThreadLocal<TerrainBatchScratch> BATCH_SCRATCH = ThreadLocal.withInitial(TerrainBatchScratch::new);
-    private static final ThreadLocal<HydrologyBaseHeights> HYDROLOGY_BASE_HEIGHTS = new ThreadLocal<>();
     private static final InferredType[] INFERRED_BIOME_PREPARATION_ORDER = {
             InferredType.LAND,
             InferredType.CAVE,
@@ -160,6 +159,7 @@ public class IrisComplex implements DataProvider {
     @Getter(AccessLevel.NONE)
     private final int biomeBoundsSamplingStep;
     private transient volatile SharedCornerBounds sharedCornerBounds;
+    private transient volatile SharedBaseHeights sharedBaseHeights;
     private transient volatile SharedBoundsBiomes sharedBoundsBiomes;
     @Getter(AccessLevel.NONE)
     @Setter(AccessLevel.NONE)
@@ -259,6 +259,10 @@ public class IrisComplex implements DataProvider {
     private IrisBiome focusBiome;
     private IrisRegion focusRegion;
     private Map<IrisInterpolator, IdentityHashMap<IrisBiome, GeneratorBounds>> generatorBounds;
+    @Getter(AccessLevel.NONE)
+    private final transient RegionBounds regionBounds;
+    @Getter(AccessLevel.NONE)
+    private final transient ProceduralStream<IrisRegion> contextRegionStream;
     private Set<IrisBiome> generatorBiomes;
     @Setter(AccessLevel.NONE)
     private final transient HydrologyRuntime hydrologyRuntime;
@@ -386,6 +390,9 @@ public class IrisComplex implements DataProvider {
             frozenGenerators[frozenIndex] = generatorGroups[frozenIndex].generators();
         }
         generatorBounds = buildGeneratorBounds(engine);
+        regionBounds = focusedBiomes == null && !imageMapRuntime.has(IrisImageMapApplication.BIOME)
+                ? RegionBounds.compile(preparedRegions, frozenInterpolators.length, new BoundsReach(), this::groupBounds)
+                : null;
         biomeBuffetGenerators = compileBuffetGeneratorGroups();
         chunkHeightBatch = engine.getDimension().getTerrainSamplingStep() == 1 && biomeBuffetGenerators.isEmpty()
                 && (biomeBuffet == null || biomeBuffet.cells().isEmpty());
@@ -417,20 +424,21 @@ public class IrisComplex implements DataProvider {
                 : RegionSelection.select(new RegionSelection.Options(
                         engine.getDimension(), data, regionStyleStream, imageMapRuntime, null));
         regionStream = focusedRegions != null ? focusedRegions : new BakedStream<>(bakeCache, BakePlane.REGION, regionSource);
-        caveSource = GenerationStreams.contextInjecting(regionStream, engine, (c, x, z) -> c.getRegion().get(x, z))
+        contextRegionStream = GenerationStreams.contextInjecting(regionStream, engine, (c, x, z) -> c.getRegion().get(x, z));
+        caveSource = contextRegionStream
                 .convert((r) -> createInferredBiomeStream(r, InferredType.CAVE))
                 .convertAware2D(ProceduralStream::get);
         caveBiomeStream = new BakedStream<>(bakeCache, BakePlane.CAVE_BIOME, caveSource);
         inferredStreams.put(InferredType.CAVE, caveBiomeStream);
-        landBiomeStream = GenerationStreams.contextInjecting(regionStream, engine, (c, x, z) -> c.getRegion().get(x, z))
+        landBiomeStream = contextRegionStream
                 .convert((r) -> createInferredBiomeStream(r, InferredType.LAND))
                 .convertAware2D(ProceduralStream::get);
         inferredStreams.put(InferredType.LAND, landBiomeStream);
-        seaBiomeStream = GenerationStreams.contextInjecting(regionStream, engine, (c, x, z) -> c.getRegion().get(x, z))
+        seaBiomeStream = contextRegionStream
                 .convert((r) -> createInferredBiomeStream(r, InferredType.SEA))
                 .convertAware2D(ProceduralStream::get);
         inferredStreams.put(InferredType.SEA, seaBiomeStream);
-        shoreBiomeStream = GenerationStreams.contextInjecting(regionStream, engine, (c, x, z) -> c.getRegion().get(x, z))
+        shoreBiomeStream = contextRegionStream
                 .convert((r) -> createInferredBiomeStream(r, InferredType.SHORE))
                 .convertAware2D(ProceduralStream::get);
         inferredStreams.put(InferredType.SHORE, shoreBiomeStream);
@@ -812,17 +820,35 @@ public class IrisComplex implements DataProvider {
             }
             return;
         }
+        SharedBaseHeights memo = sharedBaseHeights();
         TerrainBatchScratch scratch = BATCH_SCRATCH.get();
         int mark = scratch.mark();
         int indexMark = scratch.indexMark();
         try {
             double[] batchXs = scratch.buffer(count);
             double[] batchZs = scratch.buffer(count);
+            double[] computed = scratch.buffer(count);
+            int[] slots = scratch.indices(count);
+            int missing = 0;
             for (int index = 0; index < count; index++) {
-                batchXs[index] = xs[from + index];
-                batchZs[index] = zs[from + index];
+                int x = xs[from + index];
+                int z = zs[from + index];
+                double known = memo.get(x, z);
+                if (Double.isNaN(known)) {
+                    batchXs[missing] = x;
+                    batchZs[missing] = z;
+                    slots[missing++] = index;
+                } else {
+                    heights[index] = known;
+                }
+            }
+            if (missing > 0) {
+                batchBaseHeights(scratch, batchXs, batchZs, missing, computed);
+                for (int index = 0; index < missing; index++) {
+                    heights[slots[index]] = computed[index];
+                    memo.put((int) batchXs[index], (int) batchZs[index], computed[index]);
+                }
             }
-            batchBaseHeights(scratch, batchXs, batchZs, count, heights);
         } finally {
             scratch.reset(mark);
             scratch.resetIndices(indexMark);
@@ -830,23 +856,9 @@ public class IrisComplex implements DataProvider {
         if (baseOnly || terrain3D == null && transitionDisplacement == null) {
             return;
         }
-        Long2DoubleOpenHashMap known = new Long2DoubleOpenHashMap(count);
-        known.defaultReturnValue(Double.NaN);
         for (int index = 0; index < count; index++) {
-            known.put(hydrologyColumnKey(xs[from + index], zs[from + index]), heights[index]);
+            heights[index] = naturalHeightStream.getDouble(xs[from + index], zs[from + index]);
         }
-        HYDROLOGY_BASE_HEIGHTS.set(new HydrologyBaseHeights(this, known));
-        try {
-            for (int index = 0; index < count; index++) {
-                heights[index] = naturalHeightStream.getDouble(xs[from + index], zs[from + index]);
-            }
-        } finally {
-            HYDROLOGY_BASE_HEIGHTS.remove();
-        }
-    }
-
-    private static long hydrologyColumnKey(int x, int z) {
-        return ((long) x << 32) | (z & 0xFFFFFFFFL);
     }
 
     private void bakeBaseHeights(int chunkX, int chunkZ, long[] missing, double[] values) {
@@ -1082,15 +1094,21 @@ public class IrisComplex implements DataProvider {
     }
 
     private double sampleUnblendedNaturalTerrainHeight(double x, double z) {
-        HydrologyBaseHeights batched = HYDROLOGY_BASE_HEIGHTS.get();
-        if (batched != null && batched.owner() == this && (int) x == x && (int) z == z) {
-            double known = batched.heights().get(hydrologyColumnKey((int) x, (int) z));
-            if (!Double.isNaN(known)) {
-                return known;
-            }
+        if (!memoColumn(x) || !memoColumn(z)) {
+            return imageMapRuntime.sampleTerrainHeight(x, z, proceduralTerrainHeight.sample(x, z));
         }
-        double proceduralHeight = proceduralTerrainHeight.sample(x, z);
-        return imageMapRuntime.sampleTerrainHeight(x, z, proceduralHeight);
+        SharedBaseHeights memo = sharedBaseHeights();
+        double known = memo.get((int) x, (int) z);
+        if (!Double.isNaN(known)) {
+            return known;
+        }
+        double height = imageMapRuntime.sampleTerrainHeight(x, z, proceduralTerrainHeight.sample(x, z));
+        memo.put((int) x, (int) z, height);
+        return height;
+    }
+
+    private static boolean memoColumn(double coordinate) {
+        return (int) coordinate == coordinate && Double.doubleToRawLongBits(coordinate) != NEGATIVE_ZERO_BITS;
     }
 
     static double calculateNaturalSlope(double naturalHeight, double easternHeight, double southernHeight) {
@@ -1885,7 +1903,7 @@ public class IrisComplex implements DataProvider {
         int grid = biomeBoundsSamplingStep;
         GridBoundsCache cache = gridBoundsCache.get();
         if (grid <= 1) {
-            return sampleBoundsRaw(cache, engine, interpolator, generators, x, z);
+            return sampleBoundsRaw(cache, engine, interpolator, interpolatorIndex, generators, x, z);
         }
 
         int xi = (int) Math.floor(x);
@@ -1941,7 +1959,7 @@ public class IrisComplex implements DataProvider {
             if (GenerationCounter.ENABLED) {
                 GenerationCounter.CORNER_STARCASTS.increment();
             }
-            packed = computePackedBounds(cache, engine, interpolator, generators, gx, gz);
+            packed = computePackedBounds(cache, engine, interpolator, interpolatorIndex, generators, gx, gz);
             if (!Double.isFinite(boundsLow(packed)) || !Double.isFinite(boundsHigh(packed))) {
                 // A non-finite corner is a transient sampling fault, not a fact about the terrain:
                 // hand it back uncached so the next sample recomputes it instead of pinning it.
@@ -1972,6 +1990,20 @@ public class IrisComplex implements DataProvider {
         return shared;
     }
 
+    private SharedBaseHeights sharedBaseHeights() {
+        SharedBaseHeights shared = sharedBaseHeights;
+        if (shared == null) {
+            synchronized (this) {
+                shared = sharedBaseHeights;
+                if (shared == null) {
+                    shared = new SharedBaseHeights(SharedBaseHeights.capacityFor(Runtime.getRuntime().maxMemory()));
+                    sharedBaseHeights = shared;
+                }
+            }
+        }
+        return shared;
+    }
+
     private SharedBoundsBiomes sharedBoundsBiomes(ProceduralStream<IrisBiome> source) {
         SharedBoundsBiomes shared = sharedBoundsBiomes;
         if (shared != null && shared.source() == source) {
@@ -1987,8 +2019,9 @@ public class IrisComplex implements DataProvider {
         }
     }
 
-    private long computePackedBounds(GridBoundsCache cache, Engine engine, IrisInterpolator interpolator, IrisGenerator[] generators, int gx, int gz) {
-        NoiseBounds bounds = sampleBoundsRaw(cache, engine, interpolator, generators, gx, gz);
+    private long computePackedBounds(GridBoundsCache cache, Engine engine, IrisInterpolator interpolator, int interpolatorIndex,
+                                     IrisGenerator[] generators, int gx, int gz) {
+        NoiseBounds bounds = sampleBoundsRaw(cache, engine, interpolator, interpolatorIndex, generators, gx, gz);
         return (((long) Float.floatToRawIntBits((float) bounds.min())) << 32) | (Float.floatToRawIntBits((float) bounds.max()) & 0xFFFFFFFFL);
     }
 
@@ -2006,10 +2039,11 @@ public class IrisComplex implements DataProvider {
         return a + ((b - a) * fz);
     }
 
-    private NoiseBounds sampleBoundsRaw(GridBoundsCache cache, Engine engine, IrisInterpolator interpolator, IrisGenerator[] generators, double x, double z) {
+    private NoiseBounds sampleBoundsRaw(GridBoundsCache cache, Engine engine, IrisInterpolator interpolator, int interpolatorIndex,
+                                        IrisGenerator[] generators, double x, double z) {
         IdentityHashMap<IrisBiome, GeneratorBounds> cachedBounds = generatorBounds.get(interpolator);
         BoundsSampler sampler = cache.sampler.isInUse() ? new BoundsSampler() : cache.sampler;
-        sampler.bind(this, engine, generators, cachedBounds);
+        sampler.bind(this, engine, interpolatorIndex, generators, cachedBounds);
 
         try {
             return interpolator.interpolateBounds(x, z, sampler);
@@ -2297,6 +2331,11 @@ public class IrisComplex implements DataProvider {
         return reached;
     }
 
+    private NoiseBounds groupBounds(int group, IrisBiome biome) {
+        GeneratorBounds cached = generatorBounds.get(frozenInterpolators[group]).get(biome);
+        return (cached == null ? computeGeneratorBounds(frozenGenerators[group], biome) : cached).noiseBounds;
+    }
+
     static double averageGeneratorHeights(
             IrisGenerator[] generators,
             double low,
@@ -2604,6 +2643,32 @@ public class IrisComplex implements DataProvider {
         }
     }
 
+    private final class BoundsReach implements RegionBounds.Reach {
+        @Override
+        public List<IrisBiome> picks(IrisRegion region, InferredType type) {
+            return loadInferredBiomes(biomeKeys(region, type), type);
+        }
+
+        @Override
+        public Collection<IrisBiome> descendants(IrisBiome biome) {
+            Set<IrisBiome> reached = Collections.newSetFromMap(new IdentityHashMap<>());
+            ArrayDeque<IrisBiome> pending = new ArrayDeque<>();
+            pending.add(biome);
+            while (!pending.isEmpty()) {
+                IrisBiome next = pending.poll();
+                if (!reached.add(next)) {
+                    continue;
+                }
+                for (IrisBiome child : next.getRealChildren(IrisComplex.this)) {
+                    if (child != null) {
+                        pending.add(child);
+                    }
+                }
+            }
+            return reached;
+        }
+    }
+
     /**
      * Reusable per-thread bounds provider. Holds the biome memo and the lazily computed generator
      * bounds for one sampleBoundsRaw pass so the pass allocates nothing; {@link #bind}
@@ -2619,9 +2684,12 @@ public class IrisComplex implements DataProvider {
         private final IdentityHashMap<IrisBiome, GeneratorBounds> localBounds = new IdentityHashMap<>(8);
         private IrisComplex complex;
         private Engine engine;
+        private int group;
         private IrisGenerator[] generators;
         private IdentityHashMap<IrisBiome, GeneratorBounds> cachedBounds;
         private SharedBoundsBiomes sharedBiomes;
+        private BakedStream<IrisBiome> bakedBiomes;
+        private RegionBounds regional;
         private boolean integerCoordinates;
         private boolean inUse;
 
@@ -2629,14 +2697,19 @@ public class IrisComplex implements DataProvider {
             return inUse;
         }
 
-        private void bind(IrisComplex complex, Engine engine, IrisGenerator[] generators, IdentityHashMap<IrisBiome, GeneratorBounds> cachedBounds) {
+        private void bind(IrisComplex complex, Engine engine, int group, IrisGenerator[] generators,
+                          IdentityHashMap<IrisBiome, GeneratorBounds> cachedBounds) {
             this.complex = complex;
             this.engine = engine;
+            this.group = group;
             this.generators = generators;
             this.cachedBounds = cachedBounds;
             this.integerCoordinates = complex.baseBiomeStream instanceof BakedStream<?>
                     || complex.baseBiomeStream instanceof CachedStream2D<?>;
             this.sharedBiomes = integerCoordinates ? complex.sharedBoundsBiomes(complex.baseBiomeStream) : null;
+            this.bakedBiomes = complex.regionBounds != null && complex.baseBiomeStream instanceof BakedStream<IrisBiome> baked
+                    ? baked : null;
+            this.regional = bakedBiomes == null ? null : complex.regionBounds;
             this.inUse = true;
             if (sampleSource.get() != complex.baseBiomeStream) {
                 sampleCache.clear();
@@ -2654,6 +2727,8 @@ public class IrisComplex implements DataProvider {
             generators = null;
             cachedBounds = null;
             sharedBiomes = null;
+            bakedBiomes = null;
+            regional = null;
             inUse = false;
         }
 
@@ -2662,25 +2737,23 @@ public class IrisComplex implements DataProvider {
             try {
                 double sampleX = integerCoordinates ? (int) xx : xx;
                 double sampleZ = integerCoordinates ? (int) zz : zz;
-                IrisBiome bx = sampleCache.get(sampleX, sampleZ);
-                if (bx == null) {
-                    bx = sharedBiomes == null ? null : sharedBiomes.get((int) sampleX, (int) sampleZ);
-                    if (bx == null) {
-                        ChunkBakeCache.enterSparse();
-                        try {
-                            bx = complex.baseBiomeStream.get(xx, zz);
-                        } finally {
-                            ChunkBakeCache.exitSparse();
-                        }
-                        if (sharedBiomes != null) {
-                            sharedBiomes.put((int) sampleX, (int) sampleZ, bx);
-                        }
+                Object known = sampleCache.get(sampleX, sampleZ);
+                if (known == null && sharedBiomes != null) {
+                    known = sharedBiomes.get((int) sampleX, (int) sampleZ);
+                    if (known != null) {
+                        sampleCache.put(sampleX, sampleZ, known);
                     }
-                    sampleCache.put(sampleX, sampleZ, bx);
                 }
-
-                GeneratorBounds bounds = complex.resolveGeneratorBounds(engine, generators, bx, cachedBounds, localBounds);
-                return bounds.noiseBounds;
+                if (known instanceof IrisBiome biome) {
+                    return bounds(biome);
+                }
+                ChunkBakeCache.enterSparse();
+                try {
+                    return regional == null ? bounds(remember(sampleX, sampleZ, complex.baseBiomeStream.get(xx, zz)))
+                            : regionalBounds(known, sampleX, sampleZ);
+                } finally {
+                    ChunkBakeCache.exitSparse();
+                }
             } catch (Throwable e) {
                 GenerationFailures.rethrowEngineFailure(e);
                 long now = System.currentTimeMillis();
@@ -2696,6 +2769,49 @@ public class IrisComplex implements DataProvider {
 
             return ZERO_NOISE_BOUNDS;
         }
+
+        private NoiseBounds regionalBounds(Object known, double x, double z) {
+            RegionBounds.Pick pick = known instanceof RegionBounds.Pick picked ? picked : null;
+            IrisRegion region = pick != null ? pick.region() : known instanceof IrisRegion cached ? cached : null;
+            if (region == null) {
+                IrisBiome baked = bakedBiomes.baked((int) x, (int) z);
+                if (baked != null) {
+                    return bounds(remember(x, z, baked));
+                }
+                region = remember(x, z, complex.contextRegionStream.get(x, z));
+            }
+            RegionBounds.Constants constants = regional.of(region);
+            NoiseBounds constant = constants == null ? null : constants.any(group);
+            if (constant != null) {
+                return constant;
+            }
+            InferredType type = pick != null ? pick.type() : complex.bridgeStream.get(x, z);
+            constant = constants == null ? null : constants.typed(type, group);
+            if (constant != null) {
+                return constant;
+            }
+            IrisBiome picked = pick != null ? pick.biome() : complex.createInferredBiomeStream(region, type).get(x, z);
+            constant = regional.pick(picked, group);
+            if (constant != null) {
+                if (pick == null) {
+                    remember(x, z, new RegionBounds.Pick(region, type, picked));
+                }
+                return constant;
+            }
+            return bounds(remember(x, z, complex.implode(picked, x, z)));
+        }
+
+        private NoiseBounds bounds(IrisBiome biome) {
+            return complex.resolveGeneratorBounds(engine, generators, biome, cachedBounds, localBounds).noiseBounds;
+        }
+
+        private <T> T remember(double x, double z, T sample) {
+            if (sharedBiomes != null) {
+                sharedBiomes.put((int) x, (int) z, sample);
+            }
+            sampleCache.put(x, z, sample);
+            return sample;
+        }
     }
 
     /**
@@ -2705,13 +2821,13 @@ public class IrisComplex implements DataProvider {
     private static final class CoordinateBiomeCache {
         private final long[] xBits;
         private final long[] zBits;
-        private final IrisBiome[] values;
+        private final Object[] values;
         private final int mask;
 
         private CoordinateBiomeCache(int capacity) {
             xBits = new long[capacity];
             zBits = new long[capacity];
-            values = new IrisBiome[capacity];
+            values = new Object[capacity];
             mask = capacity - 1;
         }
 
@@ -2719,20 +2835,20 @@ public class IrisComplex implements DataProvider {
             Arrays.fill(values, null);
         }
 
-        private IrisBiome get(double x, double z) {
+        private Object get(double x, double z) {
             long xb = Double.doubleToLongBits(x);
             long zb = Double.doubleToLongBits(z);
             int slot = mix(xb, zb) & mask;
             return xBits[slot] == xb && zBits[slot] == zb ? values[slot] : null;
         }
 
-        private void put(double x, double z, IrisBiome biome) {
+        private void put(double x, double z, Object sample) {
             long xb = Double.doubleToLongBits(x);
             long zb = Double.doubleToLongBits(z);
             int slot = mix(xb, zb) & mask;
             xBits[slot] = xb;
             zBits[slot] = zb;
-            values[slot] = biome;
+            values[slot] = sample;
         }
 
         private int mix(long xb, long zb) {
@@ -2784,7 +2900,4 @@ public class IrisComplex implements DataProvider {
             transitionDisplacement.clear();
         }
     }
-
-    private record HydrologyBaseHeights(IrisComplex owner, Long2DoubleOpenHashMap heights) {
-    }
 }

core/src/main/java/art/arcane/iris/generation/runtime/RegionBounds.java

@@ -0,0 +1,120 @@
+package art.arcane.iris.generation.runtime;
+
+import art.arcane.iris.generation.biome.IrisBiome;
+import art.arcane.iris.generation.terrain.InferredType;
+import art.arcane.iris.generation.terrain.IrisRegion;
+import art.arcane.volmlib.util.interpolation.NoiseBounds;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.IdentityHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+final class RegionBounds {
+    private final Map<IrisRegion, Constants> regions;
+    private final Map<IrisBiome, NoiseBounds[]> picks;
+
+    private RegionBounds(Map<IrisRegion, Constants> regions, Map<IrisBiome, NoiseBounds[]> picks) {
+        this.regions = regions;
+        this.picks = picks;
+    }
+
+    static RegionBounds compile(Collection<IrisRegion> regions, int groups, Reach reach, GroupBounds bounds) {
+        IdentityHashMap<IrisRegion, Constants> compiled = new IdentityHashMap<>(Math.max(16, regions.size() * 2));
+        IdentityHashMap<IrisBiome, NoiseBounds[]> picks = new IdentityHashMap<>();
+        for (IrisRegion region : regions) {
+            if (compiled.containsKey(region)) {
+                continue;
+            }
+            NoiseBounds[] land = typeConstants(reach.picks(region, InferredType.LAND), groups, reach, bounds, picks);
+            NoiseBounds[] sea = typeConstants(reach.picks(region, InferredType.SEA), groups, reach, bounds, picks);
+            NoiseBounds[] any = new NoiseBounds[groups];
+            for (int group = 0; group < groups; group++) {
+                any[group] = land[group] != null && sea[group] != null && sameBits(land[group], sea[group]) ? land[group] : null;
+            }
+            compiled.put(region, new Constants(any, land, sea));
+        }
+        return new RegionBounds(compiled, picks);
+    }
+
+    Constants of(IrisRegion region) {
+        return regions.get(region);
+    }
+
+    NoiseBounds pick(IrisBiome picked, int group) {
+        NoiseBounds[] constants = picks.get(picked);
+        return constants == null ? null : constants[group];
+    }
+
+    private static NoiseBounds[] typeConstants(List<IrisBiome> picked, int groups, Reach reach, GroupBounds bounds,
+                                               Map<IrisBiome, NoiseBounds[]> picks) {
+        if (picked.isEmpty()) {
+            return new NoiseBounds[groups];
+        }
+        Set<IrisBiome> reached = Collections.newSetFromMap(new IdentityHashMap<>());
+        for (IrisBiome biome : picked) {
+            Collection<IrisBiome> descendants = reach.descendants(biome);
+            reached.addAll(descendants);
+            if (!picks.containsKey(biome)) {
+                picks.put(biome, constants(descendants, groups, bounds));
+            }
+        }
+        return constants(reached, groups, bounds);
+    }
+
+    private static NoiseBounds[] constants(Collection<IrisBiome> biomes, int groups, GroupBounds bounds) {
+        NoiseBounds[] constants = new NoiseBounds[groups];
+        for (int group = 0; group < groups; group++) {
+            constants[group] = constant(biomes, group, bounds);
+        }
+        return constants;
+    }
+
+    private static NoiseBounds constant(Collection<IrisBiome> biomes, int group, GroupBounds bounds) {
+        NoiseBounds first = null;
+        for (IrisBiome biome : biomes) {
+            NoiseBounds next = bounds.of(group, biome);
+            if (first == null) {
+                first = next;
+            } else if (!sameBits(first, next)) {
+                return null;
+            }
+        }
+        return first;
+    }
+
+    private static boolean sameBits(NoiseBounds first, NoiseBounds second) {
+        return Double.doubleToRawLongBits(first.min()) == Double.doubleToRawLongBits(second.min())
+                && Double.doubleToRawLongBits(first.max()) == Double.doubleToRawLongBits(second.max());
+    }
+
+    record Constants(NoiseBounds[] any, NoiseBounds[] land, NoiseBounds[] sea) {
+        NoiseBounds any(int group) {
+            return any[group];
+        }
+
+        NoiseBounds typed(InferredType type, int group) {
+            return switch (type) {
+                case LAND -> land[group];
+                case SEA -> sea[group];
+                case SHORE, CAVE -> null;
+            };
+        }
+    }
+
+    record Pick(IrisRegion region, InferredType type, IrisBiome biome) {
+    }
+
+    interface Reach {
+        List<IrisBiome> picks(IrisRegion region, InferredType type);
+
+        Collection<IrisBiome> descendants(IrisBiome biome);
+    }
+
+    @FunctionalInterface
+    interface GroupBounds {
+        NoiseBounds of(int group, IrisBiome biome);
+    }
+}

core/src/main/java/art/arcane/iris/generation/runtime/SharedBaseHeights.java

@@ -0,0 +1,76 @@
+package art.arcane.iris.generation.runtime;
+
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
+
+final class SharedBaseHeights {
+    static final int MINIMUM_CAPACITY = 1 << 16;
+    static final int MAXIMUM_CAPACITY = 1 << 21;
+    static final long BYTES_PER_ENTRY = 20L;
+    static final long HEAP_SHARE = 256L;
+    private static final VarHandle INTS = MethodHandles.arrayElementVarHandle(int[].class);
+    private static final VarHandle LONGS = MethodHandles.arrayElementVarHandle(long[].class);
+
+    private final long[] keys;
+    private final long[] values;
+    private final int[] stamps;
+    private final int mask;
+
+    SharedBaseHeights(int capacity) {
+        if (capacity < 2 || Integer.bitCount(capacity) != 1) {
+            throw new IllegalArgumentException("capacity must be a power of two of at least 2");
+        }
+        this.keys = new long[capacity];
+        this.values = new long[capacity];
+        this.stamps = new int[capacity];
+        this.mask = capacity - 1;
+    }
+
+    static int capacityFor(long maxMemory) {
+        long entries = Math.max(0L, maxMemory) / HEAP_SHARE / BYTES_PER_ENTRY;
+        long bounded = Math.max(MINIMUM_CAPACITY, Math.min(MAXIMUM_CAPACITY, entries));
+        return Integer.highestOneBit((int) bounded);
+    }
+
+    double get(int x, int z) {
+        long key = key(x, z);
+        int slot = slot(key);
+        int before = (int) INTS.getAcquire(stamps, slot);
+        if (before == 0 || (before & 1) != 0) {
+            return Double.NaN;
+        }
+        long storedKey = (long) LONGS.getAcquire(keys, slot);
+        long value = (long) LONGS.getAcquire(values, slot);
+        VarHandle.loadLoadFence();
+        int after = (int) INTS.getAcquire(stamps, slot);
+        if (before != after || storedKey != key) {
+            return Double.NaN;
+        }
+        return Double.longBitsToDouble(value);
+    }
+
+    void put(int x, int z, double height) {
+        if (!Double.isFinite(height)) {
+            return;
+        }
+        long key = key(x, z);
+        int slot = slot(key);
+        int stamp = (int) INTS.getAcquire(stamps, slot);
+        if ((stamp & 1) != 0 || !INTS.compareAndSet(stamps, slot, stamp, stamp + 1)) {
+            return;
+        }
+        LONGS.setRelease(keys, slot, key);
+        LONGS.setRelease(values, slot, Double.doubleToRawLongBits(height));
+        INTS.setRelease(stamps, slot, stamp + 2);
+    }
+
+    private int slot(long key) {
+        long mixed = (key ^ (key >>> 30)) * 0xBF58476D1CE4E5B9L;
+        mixed = (mixed ^ (mixed >>> 27)) * 0x94D049BB133111EBL;
+        return (int) ((mixed ^ (mixed >>> 31)) & mask);
+    }
+
+    private static long key(int x, int z) {
+        return ((long) x << 32) | (z & 0xFFFFFFFFL);
+    }
+}

core/src/main/java/art/arcane/iris/generation/runtime/SharedBoundsBiomes.java

@@ -1,7 +1,5 @@
 package art.arcane.iris.generation.runtime;
 
-import art.arcane.iris.generation.biome.IrisBiome;
-
 import java.lang.invoke.MethodHandles;
 import java.lang.invoke.VarHandle;
 import java.util.Objects;
@@ -49,7 +47,7 @@ final class SharedBoundsBiomes {
         return (int) ((mixed ^ (mixed >>> 31)) & mask);
     }
 
-    IrisBiome get(int x, int z) {
+    Object get(int x, int z) {
         long key = key(x, z);
         int slot = slot(x, z);
         int before = (int) INTS.getAcquire(stamps, slot);
@@ -63,11 +61,11 @@ final class SharedBoundsBiomes {
         if (before != after || storedKey != key) {
             return null;
         }
-        return (IrisBiome) value;
+        return value;
     }
 
-    void put(int x, int z, IrisBiome biome) {
-        if (biome == null) {
+    void put(int x, int z, Object sample) {
+        if (sample == null) {
             return;
         }
         int slot = slot(x, z);
@@ -76,7 +74,7 @@ final class SharedBoundsBiomes {
             return;
         }
         LONGS.setRelease(keys, slot, key(x, z));
-        OBJECTS.setRelease(values, slot, biome);
+        OBJECTS.setRelease(values, slot, sample);
         INTS.setRelease(stamps, slot, stamp + 2);
     }
 

core/src/main/java/art/arcane/iris/generation/stage/IrisCarveModifier.java

@@ -49,6 +49,7 @@ import art.arcane.iris.generation.hydrology.cave.HydrologyCaveCell;
 import art.arcane.iris.generation.hydrology.cave.HydrologyCaveStorage;
 import art.arcane.iris.generation.hydrology.raster.ChunkWaterRaster;
 import art.arcane.iris.generation.chunk.ColumnExtent;
+import art.arcane.iris.generation.chunk.ColumnReadHunk;
 import art.arcane.iris.generation.context.ChunkContext;
 import art.arcane.iris.generation.context.IrisContext;
 import art.arcane.iris.generation.block.B;
@@ -1086,19 +1087,21 @@ public class IrisCarveModifier extends EngineAssignedModifier<NativeBlockState>
         int height = output.getHeight();
         ColumnExtent extent = output instanceof ColumnExtent columnExtent ? columnExtent : null;
         SolidMemo solids = new SolidMemo();
+        ColumnWindow column = new ColumnWindow(output, height);
         for (int localX = 0; localX < width; localX++) {
             for (int localZ = 0; localZ < depth; localZ++) {
                 int worldX = blockX + localX;
                 int worldZ = blockZ + localZ;
                 int floor = -1;
                 int top = extent == null ? height - 1 : extent.highestStoredY(localX, localZ);
+                column.begin(localX, localZ, top);
                 boolean previousKnown = false;
                 boolean previousSolid = false;
                 for (int y = 1; y < height; y++) {
                     if (y > top) {
                         break;
                     }
-                    boolean solid = solids.test(output.getRaw(localX, y, localZ));
+                    boolean solid = solids.test(column.get(y));
                     boolean decorated = false;
                     if (solid) {
                         if (floor >= 0) {
@@ -1122,11 +1125,12 @@ public class IrisCarveModifier extends EngineAssignedModifier<NativeBlockState>
                                 if (extent != null) {
                                     top = extent.highestStoredY(localX, localZ);
                                 }
+                                column.begin(localX, localZ, top);
                             }
                             floor = -1;
                         }
                     } else if (floor < 0 && (previousKnown ? previousSolid
-                            : solids.test(output.getRaw(localX, y - 1, localZ)))) {
+                            : solids.test(column.get(y - 1)))) {
                         floor = y;
                     }
                     previousSolid = solid;
@@ -1472,6 +1476,43 @@ public class IrisCarveModifier extends EngineAssignedModifier<NativeBlockState>
     private record CaveColumn(long key, IrisBiome surface, IrisBiome cave, int surfaceY, int minimumDepth) {
     }
 
+    private static final class ColumnWindow {
+        private static final int ROWS = 16;
+
+        private final Hunk<NativeBlockState> output;
+        private final NativeBlockState[] states;
+        private int x;
+        private int z;
+        private int limit;
+        private int from;
+        private int to;
+
+        private ColumnWindow(Hunk<NativeBlockState> output, int height) {
+            this.output = output;
+            this.states = new NativeBlockState[height];
+        }
+
+        private void begin(int localX, int localZ, int top) {
+            x = localX;
+            z = localZ;
+            limit = Math.min(top, states.length - 1);
+            from = 0;
+            to = -1;
+        }
+
+        private NativeBlockState get(int y) {
+            if (y < from || y > to) {
+                if (y > limit) {
+                    return output.getRaw(x, y, z);
+                }
+                from = y;
+                to = Math.min(limit, y + ROWS - 1);
+                ColumnReadHunk.readColumn(output, x, z, from, to, states, from);
+            }
+            return states[y];
+        }
+    }
+
     private static final class SolidMemo {
         private NativeBlockState state;
         private boolean solid;

core/src/main/java/art/arcane/iris/generation/stage/IrisPerfectionModifier.java

@@ -19,6 +19,7 @@
 package art.arcane.iris.generation.stage;
 
 import art.arcane.iris.generation.chunk.ColumnExtent;
+import art.arcane.iris.generation.chunk.ColumnReadHunk;
 import art.arcane.iris.generation.decoration.IrisSpeleothems;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.generation.runtime.EngineAssignedModifier;
@@ -105,24 +106,29 @@ public class IrisPerfectionModifier extends EngineAssignedModifier<NativeBlockSt
         StateFlags states = new StateFlags();
         NativeBlockState air = AIR.get();
         NativeBlockState water = WATER.get();
+        NativeBlockState[] column = new NativeBlockState[output.getHeight()];
         for (int x = firstSlice; x < lastSlice; x++) {
             for (int z = 0; z < 16; z++) {
-                perfectColumn(output, x, z, surfaces, states, air, water);
+                perfectColumn(output, x, z, surfaces, states, air, water, column);
             }
         }
     }
 
     private static void perfectColumn(Hunk<NativeBlockState> output, int x, int z, IntArrayList surfaces,
-                                      StateFlags states, NativeBlockState air, NativeBlockState water) {
+                                      StateFlags states, NativeBlockState air, NativeBlockState water,
+                                      NativeBlockState[] column) {
         do {
             surfaces.clear();
-            int top = getHeight(output, x, z, states);
+            int highest = Math.min(output.getHeight() - 1, ColumnExtent.highestStoredY(output, x, z));
+            ColumnReadHunk.readColumn(output, x, z, 0, Math.max(0, highest), column, 0);
+            int top = getHeight(column, highest, states);
             boolean inside = true;
             surfaces.add(top);
             NativeBlockState classified = null;
             int classifiedFlags = 0;
+            boolean columnRead = true;
             for (int y = top; y >= 0; y--) {
-                NativeBlockState block = output.get(x, y, z);
+                NativeBlockState block = columnRead ? column[y] : output.get(x, y, z);
                 int flags = 0;
                 if (block != null) {
                     if (block != classified) {
@@ -133,6 +139,7 @@ public class IrisPerfectionModifier extends EngineAssignedModifier<NativeBlockSt
                     if ((flags & SPIKE) != 0) {
                         block = normalizeSpike(block, output, x, z, y, air, water);
                         flags = block == null ? 0 : states.of(block);
+                        columnRead = false;
                     }
                 }
                 boolean now = (flags & SOLID) != 0;
@@ -233,11 +240,11 @@ public class IrisPerfectionModifier extends EngineAssignedModifier<NativeBlockSt
         burst.complete();
     }
 
-    private static int getHeight(Hunk<NativeBlockState> output, int x, int z, StateFlags states) {
+    private static int getHeight(NativeBlockState[] column, int highest, StateFlags states) {
         NativeBlockState classified = null;
         int classifiedFlags = 0;
-        for (int i = Math.min(output.getHeight() - 1, ColumnExtent.highestStoredY(output, x, z)); i >= 0; i--) {
-            NativeBlockState state = output.get(x, i, z);
+        for (int i = highest; i >= 0; i--) {
+            NativeBlockState state = column[i];
             if (state == null) {
                 continue;
             }

core/src/main/java/art/arcane/iris/generation/stage/IrisTransitionGeometryActuator.java

@@ -1,5 +1,6 @@
 package art.arcane.iris.generation.stage;
 
+import art.arcane.iris.generation.chunk.ColumnReadHunk;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.generation.runtime.EngineAssignedComponent;
 import art.arcane.iris.generation.runtime.EngineStage;
@@ -111,6 +112,7 @@ public final class IrisTransitionGeometryActuator extends EngineAssignedComponen
         private final ChunkContext context;
         private final Map<NativeBlockState, BoundaryColumnGeometry.Voxel> voxels = new IdentityHashMap<>();
         private NativeBlockState air;
+        private NativeBlockState[] column = new NativeBlockState[0];
         private NativeBlockState lastState;
         private BoundaryColumnGeometry.Voxel lastVoxel;
 
@@ -132,10 +134,14 @@ public final class IrisTransitionGeometryActuator extends EngineAssignedComponen
                 return;
             }
             int base = minimumY - this.minimumY;
-            NativeBlockState runState = stateAt(localX, base, localZ);
+            if (column.length < height) {
+                column = new NativeBlockState[height];
+            }
+            ColumnReadHunk.readColumn(blocks, localX, localZ, base, base + height - 1, column, 0);
+            NativeBlockState runState = orAir(column[0]);
             int start = 0;
             for (int offset = 1; offset < height; offset++) {
-                NativeBlockState state = stateAt(localX, base + offset, localZ);
+                NativeBlockState state = orAir(column[offset]);
                 if (state != runState) {
                     runs.add(start, offset, voxelOf(runState));
                     start = offset;
@@ -146,7 +152,10 @@ public final class IrisTransitionGeometryActuator extends EngineAssignedComponen
         }
 
         private NativeBlockState stateAt(int localX, int offset, int localZ) {
-            NativeBlockState state = blocks.getRaw(localX, offset, localZ);
+            return orAir(blocks.getRaw(localX, offset, localZ));
+        }
+
+        private NativeBlockState orAir(NativeBlockState state) {
             if (state != null) {
                 return state;
             }

core/src/main/java/art/arcane/iris/generation/stream/BakedStream.java

@@ -39,6 +39,13 @@ public final class BakedStream<T> extends BasicStream<T> implements ChunkFillabl
         return value;
     }
 
+    @SuppressWarnings("unchecked")
+    public T baked(int blockX, int blockZ) {
+        int index = ((blockZ & 15) << 4) | (blockX & 15);
+        ChunkPlanes.Plane values = cache.planeIfPresent(plane, blockX >> 4, blockZ >> 4);
+        return values != null && values.ready(index) ? (T) values.objectAt(index) : null;
+    }
+
     @Override
     public T get(double x, double y, double z) {
         return scalar.get(x, y, z);

core/src/main/java/art/arcane/iris/world/history/GenerationHistory.java

@@ -26,6 +26,8 @@ import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.locks.LockSupport;
 import java.util.function.Predicate;
 
 public final class GenerationHistory {
@@ -34,6 +36,7 @@ public final class GenerationHistory {
     private static final int MAXIMUM_CACHED_TRANSITION_PLANS = 4;
     private static final int MAXIMUM_SEMANTIC_BATCH = 32;
     private static final int MAXIMUM_PENDING_SEMANTIC_CLAIMS = 128;
+    private static final long SEMANTIC_CLAIM_PARK_NANOS = 10_000_000L;
 
     private final GenerationHistoryPaths paths;
     private final GenerationPackRepository packs;
@@ -50,6 +53,7 @@ public final class GenerationHistory {
     private final Map<Long, TransitionGenerationPlan> transitionPlanCache;
     private final ArrayBlockingQueue<PendingSemanticClaim> pendingSemanticClaims =
             new ArrayBlockingQueue<>(MAXIMUM_PENDING_SEMANTIC_CLAIMS);
+    private final AtomicBoolean semanticWriter = new AtomicBoolean();
 
     private GenerationHistory(
             GenerationHistoryPaths paths,
@@ -776,12 +780,26 @@ public final class GenerationHistory {
                 persistPendingSemanticClaims();
             }
         }
-        synchronized (this) {
-            while (!pending.claim.completed) {
-                persistPendingSemanticClaims();
+        while (!pending.settled) {
+            if (!semanticWriter.compareAndSet(false, true)) {
+                LockSupport.parkNanos(pending, SEMANTIC_CLAIM_PARK_NANOS);
+                continue;
+            }
+            try {
+                synchronized (this) {
+                    while (!pending.claim.completed) {
+                        persistPendingSemanticClaims();
+                    }
+                }
+            } finally {
+                semanticWriter.set(false);
+                PendingSemanticClaim next = pendingSemanticClaims.peek();
+                if (next != null) {
+                    LockSupport.unpark(next.owner);
+                }
             }
-            return pending.claim.result();
         }
+        return pending.claim.result();
     }
 
     private void persistPendingSemanticClaims() {
@@ -814,10 +832,15 @@ public final class GenerationHistory {
             }
             while ((current = pendingSemanticClaims.poll()) != null) {
                 reported |= current.claim.fail(failure);
+                current.settle();
             }
             if (!reported) {
                 throw failure;
             }
+        } finally {
+            for (PendingSemanticClaim pending : batch) {
+                pending.settle();
+            }
         }
     }
 
@@ -1354,11 +1377,21 @@ public final class GenerationHistory {
     private static final class PendingSemanticClaim {
         private final GenerationStage stage;
         private final GenerationSemanticIndex.Claim claim;
+        private final Thread owner = Thread.currentThread();
+        private volatile boolean settled;
 
         private PendingSemanticClaim(GenerationStage stage, ChunkGenerationSemantics update) {
             this.stage = stage;
             this.claim = new GenerationSemanticIndex.Claim(update);
         }
+
+        private void settle() {
+            if (!claim.completed || settled) {
+                return;
+            }
+            settled = true;
+            LockSupport.unpark(owner);
+        }
     }
 
     public static final class GenerationStage implements AutoCloseable {

core/src/main/java/art/arcane/iris/world/history/GenerationSemanticCapture.java

@@ -35,7 +35,7 @@ import art.arcane.volmlib.util.matter.MatterCavern;
 import art.arcane.volmlib.util.matter.MatterStructurePOI;
 
 import java.util.ArrayDeque;
-import java.util.BitSet;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -238,7 +238,7 @@ public final class GenerationSemanticCapture {
         Mantle<Matter> mantle = engine.getMantle().getMantle();
         int minimumX = Math.multiplyExact(chunkX, CHUNK_SIZE);
         int minimumZ = Math.multiplyExact(chunkZ, CHUNK_SIZE);
-        BitSet resolvedCaves = new BitSet();
+        CavePositions resolvedCaves = new CavePositions();
         CaveBiomes caveBiomes = new CaveBiomes(engine, scoped);
         mantle.iterateChunk(chunkX, chunkZ, MatterCavern.class, (localX, y, localZ, cavern) -> {
             if (!caveSpace.test(localX, y, localZ)) {
@@ -370,17 +370,15 @@ public final class GenerationSemanticCapture {
     private static void captureCave(
             CaveBiomes caveBiomes,
             ChunkGenerationSemantics.Builder semantics,
-            BitSet resolvedCaves,
+            CavePositions resolvedCaves,
             int blockX,
             int y,
             int blockZ,
             String explicitBiomeKey
     ) {
-        int position = (y << 8) | ((blockX & 15) << 4) | (blockZ & 15);
-        if (resolvedCaves.get(position)) {
+        if (!resolvedCaves.add((y << 8) | ((blockX & 15) << 4) | (blockZ & 15))) {
             return;
         }
-        resolvedCaves.set(position);
         if (explicitBiomeKey != null && !explicitBiomeKey.isBlank()) {
             caveBiomes.add(semantics, explicitBiomeKey);
             return;
@@ -493,6 +491,25 @@ public final class GenerationSemanticCapture {
         }
     }
 
+    private static final class CavePositions {
+        private static final int INITIAL_WORDS = 1536;
+
+        private long[] words = new long[INITIAL_WORDS];
+
+        private boolean add(int position) {
+            int word = position >>> 6;
+            if (word >= words.length) {
+                words = Arrays.copyOf(words, Math.max(word + 1, words.length << 1));
+            }
+            long bit = 1L << position;
+            if ((words[word] & bit) != 0L) {
+                return false;
+            }
+            words[word] |= bit;
+            return true;
+        }
+    }
+
     private static final class CaveBiomes {
         private final Engine engine;
         private final boolean scoped;

core/src/main/java/art/arcane/iris/world/history/SavedBiomeStore.java

@@ -29,6 +29,8 @@ import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.locks.LockSupport;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.zip.CRC32;
@@ -49,6 +51,7 @@ public final class SavedBiomeStore {
     private static final int MAXIMUM_CACHED_CHUNKS = 128;
     private static final long MAXIMUM_CACHED_BYTES = 64L * 1024L * 1024L;
     private static final int MAXIMUM_WRITE_BATCH = 64;
+    private static final long WRITE_PARK_NANOS = 10_000_000L;
     private static final ThreadLocal<Deflater> DEFLATERS = ThreadLocal.withInitial(() -> new Deflater(Deflater.BEST_SPEED));
 
     private final Path dimensionRoot;
@@ -132,19 +135,34 @@ public final class SavedBiomeStore {
                 .putInt(body.length).put(body).putInt(checksum(body)).array();
         PendingWrite pending = new PendingWrite(required, record);
         lock.pending.add(pending);
-        synchronized (lock) {
-            while (!pending.completed) {
-                persistPending(lock);
+        while (!pending.settled) {
+            if (!lock.writer.compareAndSet(false, true)) {
+                LockSupport.parkNanos(pending, WRITE_PARK_NANOS);
+                continue;
             }
-            if (pending.failure != null) {
-                throw pending.failure;
+            try {
+                synchronized (lock) {
+                    while (!pending.completed) {
+                        persistPending(lock);
+                    }
+                }
+            } finally {
+                lock.writer.set(false);
+                PendingWrite next = lock.pending.peek();
+                if (next != null) {
+                    LockSupport.unpark(next.owner);
+                }
             }
-            return pending.persisted;
         }
+        if (pending.failure != null) {
+            throw pending.failure;
+        }
+        return pending.persisted;
     }
 
     private void persistPending(WriteStripe stripe) {
         Map<Long, List<PendingWrite>> batches = new LinkedHashMap<>();
+        List<PendingWrite> polled = new ArrayList<>(MAXIMUM_WRITE_BATCH);
         PendingWrite grouping = null;
         try {
             for (int count = 0; count < MAXIMUM_WRITE_BATCH; count++) {
@@ -152,6 +170,7 @@ public final class SavedBiomeStore {
                 if (grouping == null) {
                     break;
                 }
+                polled.add(grouping);
                 long regionKey = key(grouping.chunk.chunkX() >> 5, grouping.chunk.chunkZ() >> 5);
                 batches.computeIfAbsent(regionKey, ignored -> new ArrayList<>()).add(grouping);
                 grouping = null;
@@ -175,6 +194,10 @@ public final class SavedBiomeStore {
                 }
             }
             throw failure;
+        } finally {
+            for (PendingWrite pending : polled) {
+                pending.settle();
+            }
         }
     }
 
@@ -822,19 +845,30 @@ public final class SavedBiomeStore {
 
     private static final class WriteStripe {
         private final ConcurrentLinkedQueue<PendingWrite> pending = new ConcurrentLinkedQueue<>();
+        private final AtomicBoolean writer = new AtomicBoolean();
     }
 
     private static final class PendingWrite {
         private final SavedBiomeChunk chunk;
         private final byte[] record;
+        private final Thread owner = Thread.currentThread();
         private boolean completed;
         private boolean persisted;
         private IOException failure;
+        private volatile boolean settled;
 
         private PendingWrite(SavedBiomeChunk chunk, byte[] record) {
             this.chunk = chunk;
             this.record = record;
         }
+
+        private void settle() {
+            if (!completed || settled) {
+                return;
+            }
+            settled = true;
+            LockSupport.unpark(owner);
+        }
     }
 
     private static final class DecodeBudget {

core/src/main/java/art/arcane/iris/world/pregen/AsyncPregenMethod.java

@@ -268,6 +268,7 @@ public class AsyncPregenMethod implements PregeneratorMethod {
     @Override
     public void onRegionBounds(int minRegionX, int minRegionZ, int maxRegionX, int maxRegionZ) {
         retention = createRetention(minRegionX, minRegionZ, maxRegionX, maxRegionZ);
+        hydrology.bound(minRegionX, minRegionZ, maxRegionX, maxRegionZ);
     }
 
     private PregenChunkRetention createRetention(int minRegionX, int minRegionZ, int maxRegionX, int maxRegionZ) {

core/src/main/java/art/arcane/iris/world/pregen/MedievalPregenMethod.java

@@ -219,6 +219,11 @@ public class MedievalPregenMethod implements PregeneratorMethod {
         return false;
     }
 
+    @Override
+    public void onRegionBounds(int minRegionX, int minRegionZ, int maxRegionX, int maxRegionZ) {
+        hydrology.bound(minRegionX, minRegionZ, maxRegionX, maxRegionZ);
+    }
+
     @Override
     public void onRegionsAhead(List<long[]> regions) {
         if (!closing.get()) {

core/src/main/java/art/arcane/iris/world/pregen/PregenHydrology.java

@@ -13,6 +13,7 @@ public final class PregenHydrology implements AutoCloseable {
     private final Supplier<Engine> engine;
     private HydrologyRuntime owner;
     private HydrologyPregeneration epoch;
+    private int[] bounds;
     private boolean closed;
 
     public PregenHydrology(Supplier<Engine> engine) {
@@ -28,12 +29,21 @@ public final class PregenHydrology implements AutoCloseable {
             withdraw();
             owner = runtime;
             epoch = runtime == null ? null : runtime.openPregeneration();
+            applyBounds();
         }
         if (epoch != null) {
             epoch.prepare(regions);
         }
     }
 
+    public synchronized void bound(int minRegionX, int minRegionZ, int maxRegionX, int maxRegionZ) {
+        if (closed) {
+            return;
+        }
+        bounds = new int[]{minRegionX, minRegionZ, maxRegionX, maxRegionZ};
+        applyBounds();
+    }
+
     @Override
     public synchronized void close() {
         closed = true;
@@ -41,6 +51,12 @@ public final class PregenHydrology implements AutoCloseable {
         owner = null;
     }
 
+    private void applyBounds() {
+        if (epoch != null && bounds != null) {
+            epoch.bound(bounds[0], bounds[1], bounds[2], bounds[3]);
+        }
+    }
+
     private void withdraw() {
         if (epoch != null) {
             epoch.close();

core/src/test/java/art/arcane/iris/generation/block/PlatformStateRebindTest.java

@@ -44,7 +44,7 @@ public class PlatformStateRebindTest {
     }
 
     @Test
-    public void chunkDataAirIsResolvedAgainstTheCurrentlyBoundPlatform() {
+    public void chunkDataAirIsResolvedAgainstThePlatformBoundWhenTheBufferFirstReadsIt() {
         NativeBlockState first = bindPlatform("first");
         SectionBuffer holder = new SectionBuffer(384);
 
@@ -53,7 +53,8 @@ public class PlatformStateRebindTest {
         IrisPlatforms.unbind();
         NativeBlockState second = bindPlatform("second");
 
-        assertSame(second, holder.getRaw(0, -1, 0));
+        assertSame(first, holder.getRaw(0, -1, 0));
+        assertSame(second, new SectionBuffer(384).getRaw(0, -1, 0));
     }
 
     @Test

core/src/test/java/art/arcane/iris/generation/chunk/SectionBufferTest.java

@@ -264,6 +264,42 @@ public class SectionBufferTest {
         assertEquals(List.of(9, 8, 7), order);
     }
 
+    @Test
+    public void columnReadsMatchSingleReadsAcrossEmptySectionsAndBufferEdges() {
+        SectionBuffer buffer = new SectionBuffer(40);
+        NativeBlockState stone = mock(NativeBlockState.class);
+        NativeBlockState dirt = mock(NativeBlockState.class);
+        buffer.setRaw(3, 2, 9, stone);
+        buffer.setRaw(3, 33, 9, dirt);
+        buffer.setRaw(3, 39, 9, stone);
+        ColumnExtentListeningHunk<NativeBlockState> listening = new ColumnExtentListeningHunk<>(buffer, (x, y, z, state) -> {
+        });
+        NativeBlockState[] column = new NativeBlockState[52];
+
+        ColumnReadHunk.readColumn(listening, 3, 9, -3, 44, column, 4);
+
+        for (int y = -3; y <= 44; y++) {
+            assertSame("y=" + y, buffer.getRaw(3, y, 9), column[4 + y + 3]);
+        }
+        assertNull(column[0]);
+        assertSame(dirt, column[4 + 33 + 3]);
+    }
+
+    @Test
+    public void plainHunksAnswerColumnReadsWithSingleReads() {
+        Hunk<NativeBlockState> array = Hunk.newArrayHunk(16, 32, 16);
+        NativeBlockState stone = mock(NativeBlockState.class);
+        array.setRaw(5, 7, 1, stone);
+        NativeBlockState[] column = new NativeBlockState[10];
+
+        ColumnReadHunk.readColumn(array, 5, 1, 6, 8, column, 2);
+
+        assertNull(column[2]);
+        assertSame(stone, column[3]);
+        assertNull(column[4]);
+        assertNull(column[5]);
+    }
+
     private static void assertSameContents(SectionBuffer expected, SectionBuffer actual) {
         assertEquals(expected.sectionCount(), actual.sectionCount());
         NativeBlockState[] expectedPalette = expected.palette();

core/src/test/java/art/arcane/iris/generation/context/IrisContextIsolationTest.java

@@ -3,6 +3,8 @@ package art.arcane.iris.generation.context;
 import art.arcane.iris.generation.runtime.Engine;
 import org.junit.Test;
 
+import java.util.ArrayList;
+import java.util.List;
 import java.util.concurrent.BrokenBarrierException;
 import java.util.concurrent.CyclicBarrier;
 import java.util.concurrent.TimeUnit;
@@ -50,6 +52,42 @@ public class IrisContextIsolationTest {
         assertNull(rightAfterClose.get());
     }
 
+    @Test
+    public void contextsStayIsolatedWhenThreadsOutnumberTheBindingSlots() throws Exception {
+        Engine engine = mock(Engine.class);
+        int threads = 640;
+        CyclicBarrier allBound = new CyclicBarrier(threads);
+        AtomicReference<Throwable> failure = new AtomicReference<>();
+        List<Thread> workers = new ArrayList<>(threads);
+        for (int index = 0; index < threads; index++) {
+            long session = index + 1L;
+            Thread worker = new Thread(() -> {
+                try (IrisContext.Scope ignored = IrisContext.open(engine, session, null)) {
+                    allBound.await(30L, TimeUnit.SECONDS);
+                    if (IrisContext.get().getGenerationSessionId() != session) {
+                        failure.compareAndSet(null, new AssertionError("Thread observed session "
+                                + IrisContext.get().getGenerationSessionId() + " instead of " + session));
+                    }
+                    allBound.await(30L, TimeUnit.SECONDS);
+                } catch (Throwable thrown) {
+                    failure.compareAndSet(null, thrown);
+                }
+                if (IrisContext.get() != null) {
+                    failure.compareAndSet(null, new AssertionError("Context survived its scope"));
+                }
+            }, "iris-context-crowd-" + index);
+            workers.add(worker);
+            worker.start();
+        }
+        for (Thread worker : workers) {
+            worker.join(60000L);
+            assertFalse("Context worker did not finish.", worker.isAlive());
+        }
+
+        assertNull(failure.get());
+        assertNull(IrisContext.get());
+    }
+
     @Test
     public void scopeRebindsWorkerWhenEngineChanges() throws Exception {
         Engine firstEngine = mock(Engine.class);

core/src/test/java/art/arcane/iris/generation/hydrology/engine/FineLatticeSourceTest.java

@@ -1,80 +0,0 @@
-package art.arcane.iris.generation.hydrology.engine;
-
-import art.arcane.iris.generation.hydrology.grid.HeightLattice;
-import art.arcane.iris.generation.hydrology.grid.HydrologySampleBuffer;
-import art.arcane.iris.generation.hydrology.grid.HydrologyTerrainSource;
-import org.junit.Test;
-
-import java.util.concurrent.atomic.AtomicLong;
-
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertThrows;
-
-public class FineLatticeSourceTest {
-    @Test
-    public void windowLatticeReadsItsNodesFromTheFineLattice() {
-        CountingTerrain terrain = new CountingTerrain();
-        HeightLattice fine = new HeightLattice(terrain, 4, false, 1 << 16);
-        HeightLattice window = new HeightLattice(new FineLatticeSource(fine, terrain), 8, false, 1 << 16);
-
-        fine.fill(0, 0, 64, 64, new HydrologySampleBuffer(64 * 64));
-        assertEquals(4096L, terrain.samples.get());
-        HydrologySampleBuffer held = new HydrologySampleBuffer(32 * 32);
-        window.fill(0, 0, 32, 32, held);
-        assertEquals(4096L, terrain.samples.get());
-        assertHeights(held, 0, 0, 32);
-
-        HydrologySampleBuffer fresh = new HydrologySampleBuffer(16 * 16);
-        window.fill(32, 0, 16, 16, fresh);
-        assertEquals(4096L + 256L, terrain.samples.get());
-        assertHeights(fresh, 32, 0, 16);
-        fine.fill(64, 0, 32, 32, new HydrologySampleBuffer(32 * 32));
-        assertEquals(4096L + 1024L, terrain.samples.get());
-
-        FineLatticeSource source = new FineLatticeSource(fine, terrain);
-        assertThrows(IllegalArgumentException.class, () -> source.sample(new int[]{8}, new int[]{8}, new HydrologySampleBuffer(1), true));
-        assertThrows(IllegalArgumentException.class, () -> source.sample(new int[]{6}, new int[]{8}, new HydrologySampleBuffer(1), false));
-    }
-
-    private static void assertHeights(HydrologySampleBuffer samples, int cellX0, int cellZ0, int side) {
-        for (int index = 0; index < side * side; index++) {
-            int x = (cellX0 + index % side) * 8;
-            int z = (cellZ0 + index / side) * 8;
-            assertEquals(x + "," + z, Float.floatToRawIntBits(CountingTerrain.height(x, z)), Float.floatToRawIntBits(samples.height()[index]));
-        }
-    }
-
-    private static final class CountingTerrain implements HydrologyTerrainSource {
-        private final AtomicLong samples = new AtomicLong();
-
-        private static float height(int x, int z) {
-            return 64f + (float) Math.sin(x * 0.013D) * 9f + (float) Math.cos(z * 0.021D) * 7f;
-        }
-
-        @Override
-        public void sample(int[] xs, int[] zs, HydrologySampleBuffer out, boolean baseOnly) {
-            samples.addAndGet(xs.length);
-            for (int index = 0; index < xs.length; index++) {
-                out.height()[index] = height(xs[index], zs[index]);
-                out.permission()[index] = HydrologySampleBuffer.ALLOW_STREAMS | HydrologySampleBuffer.ALLOW_PONDS;
-                out.rainfall()[index] = 1f;
-                out.pondDensity()[index] = 1f;
-            }
-        }
-
-        @Override
-        public int seaLevel() {
-            return 40;
-        }
-
-        @Override
-        public int minY() {
-            return 0;
-        }
-
-        @Override
-        public int maxY() {
-            return 384;
-        }
-    }
-}

core/src/test/java/art/arcane/iris/generation/hydrology/engine/HydrologyRuntimeTest.java

@@ -67,6 +67,7 @@ import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.BooleanSupplier;
 import java.util.stream.Stream;
 
+import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
@@ -215,6 +216,34 @@ public class HydrologyRuntimeTest {
         assertEquals(planned + 1L, runtime.previewRevision());
     }
 
+    @Test(timeout = 180_000L)
+    public void concurrentDemandsShareOneRasterBuild() throws Exception {
+        FakePlanners planners = new FakePlanners(settings(0, false));
+        HydrologyRuntime runtime = runtime(planners, () -> false);
+        runtime.prepareWindowsAround(0, 0, 0, 0, 1).get(TIMEOUT_SECONDS, TimeUnit.SECONDS);
+        CountDownLatch gate = new CountDownLatch(1);
+        planners.naturalGate = gate;
+        AtomicReference<ChunkWaterRaster> first = new AtomicReference<>();
+        AtomicReference<ChunkWaterRaster> second = new AtomicReference<>();
+        Thread leader = new Thread(() -> first.set(runtime.raster(0, 0)));
+        Thread follower = new Thread(() -> second.set(runtime.raster(0, 0)));
+        try {
+            leader.start();
+            await(() -> planners.naturalSamples.get() > 0, "the first demand starts sampling");
+            follower.start();
+            await(() -> follower.getState() == Thread.State.WAITING || follower.getState() == Thread.State.TIMED_WAITING,
+                    "the second demand waits");
+            assertEquals(0, planners.naturalSamplesOn(follower));
+        } finally {
+            gate.countDown();
+            leader.join(TimeUnit.SECONDS.toMillis(TIMEOUT_SECONDS));
+            follower.join(TimeUnit.SECONDS.toMillis(TIMEOUT_SECONDS));
+        }
+        assertFalse(first.get().provisional());
+        assertSame(first.get(), second.get());
+        assertEquals(0, planners.naturalSamplesOn(follower));
+    }
+
     @Test(timeout = 180_000L)
     public void failedRasterDoesNotAdvancePreviewRevision() throws Exception {
         FakePlanners planners = new FakePlanners(settings(0, false));
@@ -414,6 +443,35 @@ public class HydrologyRuntimeTest {
         assertEquals(3, prefetches.get());
     }
 
+    @Test(timeout = 180_000L)
+    public void boundedPregenerationPrefetchesOnlyWindowsItsChunksNeed() {
+        FakePlanners planners = new FakePlanners(settings());
+        HydrologyPlanCache cache = spy(new HydrologyPlanCache(planners.settings, planners::region, planners::window,
+                pool(planners, 2), () -> false));
+        List<int[]> prepared = Collections.synchronizedList(new ArrayList<>());
+        doAnswer(invocation -> {
+            prepared.add(new int[]{invocation.getArgument(0), invocation.getArgument(1), invocation.getArgument(2), invocation.getArgument(3),
+                    invocation.getArgument(4)});
+            return CompletableFuture.completedFuture(null);
+        }).when(cache).prepareWindowsAround(anyInt(), anyInt(), anyInt(), anyInt(), anyInt());
+        HydrologyRuntime runtime = new HydrologyRuntime(planners.settings, cache, planners::natural, () -> false, planners.ticker::get);
+        runtimes.add(runtime);
+        int chunks = WindowKey.SIZE >> 4;
+        HydrologyPregeneration pregeneration = runtime.openPregeneration();
+        pregeneration.bound(0, 0, 1, 1);
+
+        runtime.raster(0, 0);
+        assertArrayEquals(new int[]{-chunks, -chunks, 3 * chunks - 1, 3 * chunks - 1, 0}, prepared.getLast());
+        runtime.raster(chunks + 5, chunks + 5);
+        assertArrayEquals(new int[]{-chunks, -chunks, 3 * chunks - 1, 3 * chunks - 1, 0}, prepared.getLast());
+        runtime.raster(-3 * chunks, 0);
+        assertArrayEquals(new int[]{-3 * chunks, 0, -3 * chunks, 0, 2}, prepared.getLast());
+
+        pregeneration.close();
+        runtime.raster(1, 1);
+        assertArrayEquals(new int[]{1, 1, 1, 1, 2}, prepared.getLast());
+    }
+
     @Test(timeout = 180_000L)
     public void preparePregenerationPlansRegionsInOrder() throws Exception {
         FakePlanners planners = new FakePlanners(settings());

core/src/test/java/art/arcane/iris/generation/hydrology/engine/IrisHydrologyTerrainSourceTest.java

@@ -154,10 +154,9 @@ public class IrisHydrologyTerrainSourceTest {
         HydrologySampleBuffer rect = new HydrologySampleBuffer(32 * 32);
         fine.fill(-600, 400, 32, 32, rect);
         assertMatchesScalar(reference, "fine rect", rect, nodes(-600, 400, 32, 1, 4), false);
-        HeightLattice window = new HeightLattice(new FineLatticeSource(fine, source), 8, false, 1 << 16);
         HydrologySampleBuffer strided = new HydrologySampleBuffer(16 * 16);
-        window.fill(-150, 300, 16, 16, 3, strided);
-        assertMatchesScalar(reference, "window strided", strided, nodes(-150, 300, 16, 3, 8), false);
+        fine.fill(-300, 600, 16, 16, 6, strided);
+        assertMatchesScalar(reference, "fine strided", strided, nodes(-300, 600, 16, 6, 4), false);
         HeightLattice coarse = new HeightLattice(source, 64, true, 1 << 12);
         HydrologySampleBuffer coarseBase = new HydrologySampleBuffer(16 * 16);
         coarse.fill(-8, -8, 16, 16, coarseBase);

core/src/test/java/art/arcane/iris/generation/hydrology/grid/HeightLatticeTest.java

@@ -287,6 +287,31 @@ public class HeightLatticeTest {
         assertThrows(IllegalArgumentException.class, () -> lattice.fill(cellXs, cellZs, new HydrologySampleBuffer(5)));
     }
 
+    @Test
+    public void sampledColumnsAreReadOnceAndMatchTheSource() {
+        CountingSource source = new CountingSource();
+        HeightLattice lattice = new HeightLattice(source, 4, false, 1 << 16);
+        int[] xs = {5, -13, 5, 1027, -13, 6};
+        int[] zs = {-2, 77, -2, 3, 77, -2};
+        HydrologySampleBuffer first = new HydrologySampleBuffer(xs.length);
+        lattice.sampleColumns(xs, zs, first);
+        assertEquals(4, source.samples());
+        HydrologySampleBuffer second = new HydrologySampleBuffer(xs.length);
+        lattice.sampleColumns(xs, zs, second);
+        assertEquals(4, source.samples());
+        HydrologySampleBuffer expected = new HydrologySampleBuffer(xs.length);
+        new CountingSource().sample(xs, zs, expected, false);
+        for (int index = 0; index < xs.length; index++) {
+            assertEquals(Float.floatToIntBits(expected.height()[index]), Float.floatToIntBits(first.height()[index]));
+            assertEquals(Float.floatToIntBits(expected.height()[index]), Float.floatToIntBits(second.height()[index]));
+            assertEquals(expected.ocean()[index], second.ocean()[index]);
+            assertEquals(expected.permission()[index], second.permission()[index]);
+            assertEquals(expected.fluidProfile()[index], second.fluidProfile()[index]);
+        }
+        lattice.sampleColumns(new int[0], new int[0], new HydrologySampleBuffer(0));
+        assertEquals(1, source.calls());
+    }
+
     private static void fillWindow(HeightLattice lattice, int wx, int wz, int cell, boolean baseOnly) {
         assertFill(lattice, cell, baseOnly, (wx - 1) * WINDOW, (wz - 1) * WINDOW, AREA, AREA);
     }

core/src/test/java/art/arcane/iris/generation/hydrology/plan/HydrologyPlanCacheTest.java

@@ -1045,7 +1045,7 @@ public class HydrologyPlanCacheTest {
     }
 
     private static WindowPlanner windowPlanner(HydrologySettings settings, SyntheticTerrain terrain) {
-        return new WindowPlanner(settings, new HeightLattice(terrain, WindowPlanner.CELL, false, HydrologyPlanCache.WINDOW_LATTICE_CELLS),
+        return new WindowPlanner(settings,
                 new HeightLattice(terrain, WindowPlanner.FINE_CELL, false, HydrologyPlanCache.FINE_LATTICE_CELLS), new PondPlanner(settings),
                 new ReachShaper(settings));
     }

core/src/test/java/art/arcane/iris/generation/hydrology/plan/HydrologyPlanCodecTest.java

@@ -81,7 +81,7 @@ public class HydrologyPlanCodecTest {
             assertEquals(planned, HydrologyPlanCodec.decodeRegion(settings, HydrologyPlanCodec.encode(settings, planned)).orElseThrow());
             regions.add(planned);
         }
-        WindowPlan planned = new WindowPlanner(settings, new HeightLattice(terrain, WindowPlanner.CELL, false, 1 << 18),
+        WindowPlan planned = new WindowPlanner(settings,
                 new HeightLattice(terrain, WindowPlanner.FINE_CELL, false, 1 << 21), new PondPlanner(settings), new ReachShaper(settings))
                 .plan(LAND, regions);
         assertFalse(planned.reaches().isEmpty());

core/src/test/java/art/arcane/iris/generation/hydrology/plan/WindowPlannerTest.java

@@ -83,7 +83,7 @@ public class WindowPlannerTest {
                     new int[]{head, head}, new float[]{2f, 2f}, new float[]{2f, 2f}, new ReachStyle[]{ReachStyle.RUN, ReachStyle.RUN}, 1000f);
             return new ShapedNetwork(List.of(outlet), List.of(pond.withOutletReachId(outlet.id())));
         }).when(shaper).shape(any(), any(), any(), any(), any(), any(), anyLong());
-        WindowPlanner planner = new WindowPlanner(settings, new HeightLattice(terrain, WindowPlanner.CELL, false, 1 << 18),
+        WindowPlanner planner = new WindowPlanner(settings,
                 new HeightLattice(terrain, WindowPlanner.FINE_CELL, false, 1 << 18), ponds, shaper);
 
         WindowComputation settled = planner.compute(ORIGIN, noRegions(ORIGIN));
@@ -587,7 +587,7 @@ public class WindowPlannerTest {
             }
             return network;
         }).when(shaper).shape(any(), any(), any(), any(), any(), any(), anyLong());
-        return new WindowPlanner(settings, new HeightLattice(terrain, WindowPlanner.CELL, false, 1 << 18),
+        return new WindowPlanner(settings,
                 new HeightLattice(terrain, WindowPlanner.FINE_CELL, false, 1 << 21), new PondPlanner(settings), shaper);
     }
 
@@ -715,7 +715,7 @@ public class WindowPlannerTest {
     }
 
     private static WindowPlanner planner(HydrologySettings settings, SyntheticTerrain terrain) {
-        return new WindowPlanner(settings, new HeightLattice(terrain, WindowPlanner.CELL, false, 1 << 18),
+        return new WindowPlanner(settings,
                 new HeightLattice(terrain, WindowPlanner.FINE_CELL, false, 1 << 21), new PondPlanner(settings), new ReachShaper(settings));
     }
 

core/src/test/java/art/arcane/iris/generation/hydrology/raster/ReachSegmentsTest.java

@@ -0,0 +1,95 @@
+package art.arcane.iris.generation.hydrology.raster;
+
+import art.arcane.iris.generation.hydrology.config.IrisBankStyle;
+import art.arcane.iris.generation.hydrology.config.IrisHydrologyMaterials;
+import art.arcane.iris.generation.hydrology.water.HydrologyTier;
+import art.arcane.iris.generation.hydrology.water.Reach;
+import art.arcane.iris.generation.hydrology.water.ReachStyle;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.SplittableRandom;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+
+public class ReachSegmentsTest {
+    private static final HydrologyTier TIER = new HydrologyTier("test", 0f, 1f, 4f, 1f, 0.4f, 1, true, 6, 4, IrisBankStyle.SMOOTH,
+            false, new IrisHydrologyMaterials(), "water", List.of());
+
+    @Test
+    public void coveredChannelLookupsMatchTheFullScan() {
+        SplittableRandom random = new SplittableRandom(1337L);
+        int hits = 0;
+        for (int trial = 0; trial < 40; trial++) {
+            int originX = random.nextInt(-2000, 2000) << 4;
+            int originZ = random.nextInt(-2000, 2000) << 4;
+            List<Reach> reaches = new ArrayList<>();
+            int count = 1 + random.nextInt(12);
+            for (int walk = 0; walk < count; walk++) {
+                reaches.add(randomWalk(trial * 100L + walk, originX + 8, originZ + 8, random));
+            }
+            ReachSegments scanned = segments(reaches, originX, originZ);
+            ReachSegments covered = segments(reaches, originX, originZ);
+            covered.coverChannels(originX - 17, originZ - 17, originX + 32, originZ + 32);
+            ReachCursor scan = new ReachCursor();
+            ReachCursor cover = new ReachCursor();
+            for (int z = originZ - 20; z <= originZ + 35; z++) {
+                for (int x = originX - 20; x <= originX + 35; x++) {
+                    ReachSegments.Scope scope = random.nextInt(4) == 0 ? ReachSegments.Scope.SHORE : ReachSegments.Scope.CHANNEL;
+                    scanned.nearest(x, z, scope, scan);
+                    covered.nearest(x, z, scope, cover);
+                    String at = scope + " at " + x + "," + z;
+                    assertSameChoice(at + " channel", scan.channel, cover.channel);
+                    assertSameChoice(at + " bank", scan.bank, cover.bank);
+                    assertSameChoice(at + " edge", scan.edge, cover.edge);
+                    if (scan.channel.reach != null) {
+                        hits++;
+                    }
+                }
+            }
+        }
+        assertTrue("random walks cross the covered area, hits=" + hits, hits > 1000);
+    }
+
+    private static void assertSameChoice(String what, ReachCursor.Choice expected, ReachCursor.Choice actual) {
+        assertSame(what, expected.reach, actual.reach);
+        assertEquals(what, expected.segment, actual.segment);
+        assertEquals(what, expected.index, actual.index);
+        assertEquals(what, Double.doubleToLongBits(expected.t), Double.doubleToLongBits(actual.t));
+        assertEquals(what, Double.doubleToLongBits(expected.distance), Double.doubleToLongBits(actual.distance));
+    }
+
+    private static ReachSegments segments(List<Reach> reaches, int originX, int originZ) {
+        ReachSegments segments = new ReachSegments(16);
+        for (Reach reach : reaches) {
+            segments.addNear(reach, originX - 1f, originZ - 1f, originX + 16f, originZ + 16f, ChunkWaterRaster.MAX_SHORE_DISTANCE + 1f);
+        }
+        return segments;
+    }
+
+    private static Reach randomWalk(long id, int centerX, int centerZ, SplittableRandom random) {
+        int points = 2 + random.nextInt(30);
+        float[] xs = new float[points];
+        float[] zs = new float[points];
+        float[] halfWidth = new float[points];
+        xs[0] = centerX + (float) random.nextDouble(-60D, 60D);
+        zs[0] = centerZ + (float) random.nextDouble(-60D, 60D);
+        halfWidth[0] = (float) random.nextDouble(0.5D, 9D);
+        for (int point = 1; point < points; point++) {
+            xs[point] = xs[point - 1] + (float) random.nextDouble(-12D, 12D);
+            zs[point] = zs[point - 1] + (float) random.nextDouble(-12D, 12D);
+            halfWidth[point] = random.nextInt(8) == 0 ? halfWidth[point - 1] : (float) random.nextDouble(0.5D, 9D);
+        }
+        int[] grade = new int[points];
+        float[] depth = new float[points];
+        ReachStyle[] style = new ReachStyle[points];
+        Arrays.fill(grade, 64);
+        Arrays.fill(depth, 1f);
+        Arrays.fill(style, ReachStyle.RUN);
+        return new Reach(id, TIER, -1L, xs, zs, grade, halfWidth, depth, style, 100f);
+    }
+}

core/src/test/java/art/arcane/iris/generation/hydrology/underground/CavePoolFillerTest.java

@@ -15,6 +15,7 @@ import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Consumer;
 import java.util.function.IntFunction;
 
@@ -50,18 +51,37 @@ public class CavePoolFillerTest {
             return 0;
         });
         for (int chunkX = 0; chunkX < 1024; chunkX++) {
-            filler.fill(chunkX, 0, carved, writer, SEED);
+            filler.fill(chunkX, 0, () -> carved, writer, SEED);
         }
         assertTrue("half density samples approximately half the candidate columns", columns.size() > 3600 && columns.size() < 4500);
         Set<Long> repeated = new HashSet<>(columns);
         columns.clear();
         for (int chunkX = 1023; chunkX >= 0; chunkX--) {
-            filler.fill(chunkX, 0, carved, writer, SEED);
+            filler.fill(chunkX, 0, () -> carved, writer, SEED);
         }
         assertEquals(repeated, columns);
         verifyNoInteractions(writer);
     }
 
+    @Test
+    public void chunksWithoutAPoolSiteNeverOpenTheirCaves() {
+        IrisHydrology config = new IrisHydrology().setDensity(0.5D);
+        config.getUnderground().getCavePools().setDensity(0.05D);
+        CavePoolFiller filler = new CavePoolFiller(HydrologySettings.compile(config, SEED, 63, 0, 384));
+        CarvedTerrain carved = mock(CarvedTerrain.class);
+        MantleWriter writer = mock(MantleWriter.class);
+        AtomicInteger opened = new AtomicInteger();
+        int chunks = 1024;
+        for (int chunkX = 0; chunkX < chunks; chunkX++) {
+            filler.fill(chunkX, 0, () -> {
+                opened.incrementAndGet();
+                return carved;
+            }, writer, SEED);
+        }
+        assertTrue("only chunks drawing a pool site open their caves, opened " + opened.get(), opened.get() > 0 && opened.get() < chunks / 8);
+        verifyNoInteractions(writer);
+    }
+
     @Test
     public void zeroGlobalDensityDoesNotReadCaves() {
         IrisHydrology config = new IrisHydrology().setDensity(0D);
@@ -69,7 +89,7 @@ public class CavePoolFillerTest {
         CavePoolFiller filler = new CavePoolFiller(HydrologySettings.compile(config, SEED, 63, 0, 384));
         CarvedTerrain carved = mock(CarvedTerrain.class);
         MantleWriter writer = mock(MantleWriter.class);
-        filler.fill(0, 0, carved, writer, SEED);
+        filler.fill(0, 0, () -> carved, writer, SEED);
         verifyNoInteractions(carved, writer);
     }
 
@@ -143,10 +163,10 @@ public class CavePoolFillerTest {
         MantleWriter forwardWriter = writer(forward);
         MantleWriter reverseWriter = writer(reverse);
         for (int index = 0; index < 9; index++) {
-            new CavePoolFiller(settings).fill(index % 3 - 1, index / 3 - 1, world, forwardWriter, SEED);
+            new CavePoolFiller(settings).fill(index % 3 - 1, index / 3 - 1, () -> world, forwardWriter, SEED);
         }
         for (int index = 8; index >= 0; index--) {
-            new CavePoolFiller(settings).fill(index % 3 - 1, index / 3 - 1, world, reverseWriter, SEED);
+            new CavePoolFiller(settings).fill(index % 3 - 1, index / 3 - 1, () -> world, reverseWriter, SEED);
         }
 
         assertFalse(forward.isEmpty());
@@ -284,7 +304,7 @@ public class CavePoolFillerTest {
 
     private static Map<Long, HydrologyCaveCell> fill(HydrologySettings settings, VoxelWorld world, int chunkX, int chunkZ) {
         Map<Long, HydrologyCaveCell> written = new HashMap<>();
-        new CavePoolFiller(settings).fill(chunkX, chunkZ, world, writer(written), SEED);
+        new CavePoolFiller(settings).fill(chunkX, chunkZ, () -> world, writer(written), SEED);
         return written;
     }
 

core/src/test/java/art/arcane/iris/generation/mantle/MantleCarvedTerrainTest.java

@@ -324,7 +324,7 @@ public class MantleCarvedTerrainTest {
                 for (SeaInlet inlet : complex.getHydrologyRuntime().inlets(0, chunkZ)) {
                     rasterizer.write(inlet, 0, chunkZ, writer, HydrologyCaveCell.SEA_FLUID, "", SeaInletRasterizer.SubterrainFluid.NOWHERE);
                 }
-                new CavePoolFiller(settings).fill(0, chunkZ, new MantleCarvedTerrain(writer, complex, engine, 0, chunkZ), writer, SEED);
+                new CavePoolFiller(settings).fill(0, chunkZ, () -> new MantleCarvedTerrain(writer, complex, engine, 0, chunkZ), writer, SEED);
             }
             return cells;
         }

core/src/test/java/art/arcane/iris/generation/runtime/IrisComplexBakeParityTest.java

@@ -22,11 +22,13 @@ import org.junit.rules.TemporaryFolder;
 import org.mockito.MockedStatic;
 import org.mockito.Mockito;
 
+import java.lang.reflect.Field;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.SplittableRandom;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.Answers.CALLS_REAL_METHODS;
 import static org.mockito.ArgumentMatchers.any;
@@ -81,6 +83,24 @@ public class IrisComplexBakeParityTest {
         }
     }
 
+    @Test
+    public void regionConstantBoundsEqualFullBiomeBoundsBitForBit() throws Exception {
+        try (Statics ignored = new Statics(); Fixture shortcut = new Fixture(pack()); Fixture full = new Fixture(pack())) {
+            Field regionBounds = IrisComplex.class.getDeclaredField("regionBounds");
+            regionBounds.setAccessible(true);
+            assertNotNull(regionBounds.get(shortcut.complex));
+            regionBounds.set(full.complex, null);
+            SplittableRandom random = new SplittableRandom(0x5EEDL);
+            for (int column = 0; column < 2048; column++) {
+                int x = random.nextInt(-6400, 6400);
+                int z = random.nextInt(-6400, 6400);
+                assertEquals("column " + x + "," + z,
+                        Double.doubleToRawLongBits(full.complex.getBaseTerrainHeightStream().getDouble(x, z)),
+                        Double.doubleToRawLongBits(shortcut.complex.getBaseTerrainHeightStream().getDouble(x, z)));
+            }
+        }
+    }
+
     @Test
     public void batchedChunksEvaluateExactlyTheScalarGeneratorSet() throws Exception {
         try (Statics ignored = new Statics(); Fixture batched = new Fixture(pack()); Fixture scalar = new Fixture(pack())) {

core/src/test/java/art/arcane/iris/generation/runtime/IrisComplexBoundsBiomeCacheTest.java

@@ -243,7 +243,7 @@ public class IrisComplexBoundsBiomeCacheTest {
         constructor.setAccessible(true);
         Object cache = constructor.newInstance(4096);
         Method get = type.getDeclaredMethod("get", double.class, double.class);
-        Method put = type.getDeclaredMethod("put", double.class, double.class, IrisBiome.class);
+        Method put = type.getDeclaredMethod("put", double.class, double.class, Object.class);
         get.setAccessible(true);
         put.setAccessible(true);
         IrisBiome first = new IrisBiome();
@@ -266,7 +266,7 @@ public class IrisComplexBoundsBiomeCacheTest {
         }
         Field values = type.getDeclaredField("values");
         values.setAccessible(true);
-        assertEquals(4096, ((IrisBiome[]) values.get(cache)).length);
+        assertEquals(4096, ((Object[]) values.get(cache)).length);
     }
 
     private static ProceduralStream<IrisBiome> constant(IrisBiome biome) {
@@ -295,7 +295,7 @@ public class IrisComplexBoundsBiomeCacheTest {
             constructor.setAccessible(true);
             cache = constructor.newInstance();
             sample = IrisComplex.class.getDeclaredMethod("sampleBoundsRaw", cacheClass, Engine.class,
-                    IrisInterpolator.class, IrisGenerator[].class, double.class, double.class);
+                    IrisInterpolator.class, int.class, IrisGenerator[].class, double.class, double.class);
             sample.setAccessible(true);
             boundsConstructor = Class.forName("art.arcane.iris.generation.runtime.IrisComplex$GeneratorBounds")
                     .getDeclaredConstructor(double.class, double.class);
@@ -313,7 +313,7 @@ public class IrisComplexBoundsBiomeCacheTest {
 
         private NoiseBounds sample(Object gridCache, IrisInterpolator interpolator, double x, double z)
                 throws ReflectiveOperationException {
-            return (NoiseBounds) sample.invoke(complex, gridCache, null, interpolator, new IrisGenerator[0], x, z);
+            return (NoiseBounds) sample.invoke(complex, gridCache, null, interpolator, 0, new IrisGenerator[0], x, z);
         }
 
         private Object newGridCache() throws ReflectiveOperationException {

core/src/test/java/art/arcane/iris/generation/runtime/RegionBoundsTest.java

@@ -0,0 +1,136 @@
+package art.arcane.iris.generation.runtime;
+
+import art.arcane.iris.generation.biome.IrisBiome;
+import art.arcane.iris.generation.terrain.InferredType;
+import art.arcane.iris.generation.terrain.IrisRegion;
+import art.arcane.volmlib.util.interpolation.NoiseBounds;
+import org.junit.Test;
+
+import java.util.Collection;
+import java.util.IdentityHashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+
+public class RegionBoundsTest {
+    private static final NoiseBounds FLAT = new NoiseBounds(0D, 0D);
+    private static final NoiseBounds HILLS = new NoiseBounds(4D, 30D);
+
+    @Test
+    public void groupsEveryReachableBiomeAgreesOnAreConstantForTheRegion() {
+        IrisBiome plains = new IrisBiome();
+        IrisBiome forest = new IrisBiome();
+        IrisBiome ocean = new IrisBiome();
+        IrisRegion region = new IrisRegion();
+        Map<IrisBiome, NoiseBounds[]> bounds = new IdentityHashMap<>();
+        bounds.put(plains, new NoiseBounds[]{FLAT, HILLS});
+        bounds.put(forest, new NoiseBounds[]{new NoiseBounds(0D, 0D), new NoiseBounds(2D, 30D)});
+        bounds.put(ocean, new NoiseBounds[]{FLAT, HILLS});
+
+        RegionBounds compiled = RegionBounds.compile(List.of(region), 2,
+                new Fixed(Map.of(InferredType.LAND, List.of(plains, forest), InferredType.SEA, List.of(ocean)), Map.of()),
+                (group, biome) -> bounds.get(biome)[group]);
+        RegionBounds.Constants constants = compiled.of(region);
+
+        assertBits(FLAT, constants.any(0));
+        assertBits(FLAT, constants.typed(InferredType.LAND, 0));
+        assertBits(FLAT, constants.typed(InferredType.SEA, 0));
+        assertNull(constants.any(1));
+        assertNull(constants.typed(InferredType.LAND, 1));
+        assertSame(HILLS, constants.typed(InferredType.SEA, 1));
+        assertSame(HILLS, compiled.pick(plains, 1));
+        assertBits(new NoiseBounds(2D, 30D), compiled.pick(forest, 1));
+    }
+
+    @Test
+    public void picksAreConstantOnlyWhenEveryDescendantAgrees() {
+        IrisBiome steppe = new IrisBiome();
+        IrisBiome meadow = new IrisBiome();
+        IrisBiome mesa = new IrisBiome();
+        IrisBiome canyon = new IrisBiome();
+        IrisRegion region = new IrisRegion();
+        Map<IrisBiome, NoiseBounds> bounds = new IdentityHashMap<>();
+        bounds.put(steppe, FLAT);
+        bounds.put(meadow, new NoiseBounds(0D, 0D));
+        bounds.put(mesa, FLAT);
+        bounds.put(canyon, HILLS);
+
+        RegionBounds compiled = RegionBounds.compile(List.of(region), 1,
+                new Fixed(Map.of(InferredType.LAND, List.of(steppe, mesa), InferredType.SEA, List.of()),
+                        descendants(steppe, List.of(steppe, meadow), mesa, List.of(mesa, canyon))),
+                (group, biome) -> bounds.get(biome));
+
+        assertNull(compiled.of(region).typed(InferredType.LAND, 0));
+        assertSame(FLAT, compiled.pick(steppe, 0));
+        assertNull(compiled.pick(mesa, 0));
+        assertNull(compiled.pick(canyon, 0));
+    }
+
+    @Test
+    public void landAndSeaConstantsOnlyMergeWhenTheirBitsMatch() {
+        IrisBiome beach = new IrisBiome();
+        IrisBiome reef = new IrisBiome();
+        IrisRegion region = new IrisRegion();
+        Map<IrisBiome, NoiseBounds> bounds = new IdentityHashMap<>();
+        bounds.put(beach, new NoiseBounds(0D, 0D));
+        bounds.put(reef, new NoiseBounds(-0D, 0D));
+
+        RegionBounds.Constants constants = RegionBounds.compile(List.of(region), 1,
+                new Fixed(Map.of(InferredType.LAND, List.of(beach), InferredType.SEA, List.of(reef)), Map.of()),
+                (group, biome) -> bounds.get(biome)).of(region);
+
+        assertNull(constants.any(0));
+        assertSame(bounds.get(beach), constants.typed(InferredType.LAND, 0));
+        assertSame(bounds.get(reef), constants.typed(InferredType.SEA, 0));
+    }
+
+    @Test
+    public void emptyBiomeListsAndUnknownRegionsHaveNoConstant() {
+        IrisRegion region = new IrisRegion();
+        IrisBiome only = new IrisBiome();
+        RegionBounds compiled = RegionBounds.compile(List.of(region), 1,
+                new Fixed(Map.of(InferredType.LAND, List.of(only), InferredType.SEA, List.of()), Map.of()),
+                (group, biome) -> FLAT);
+        RegionBounds.Constants constants = compiled.of(region);
+
+        assertSame(FLAT, constants.typed(InferredType.LAND, 0));
+        assertNull(constants.typed(InferredType.SEA, 0));
+        assertNull(constants.any(0));
+        assertNull(constants.typed(InferredType.SHORE, 0));
+        assertNull(constants.typed(InferredType.CAVE, 0));
+        assertNull(compiled.of(new IrisRegion()));
+        assertNull(compiled.of(null));
+        assertNull(compiled.pick(new IrisBiome(), 0));
+        assertNull(compiled.pick(null, 0));
+    }
+
+    private static Map<IrisBiome, List<IrisBiome>> descendants(IrisBiome first, List<IrisBiome> firstDescendants,
+                                                               IrisBiome second, List<IrisBiome> secondDescendants) {
+        Map<IrisBiome, List<IrisBiome>> descendants = new IdentityHashMap<>();
+        descendants.put(first, firstDescendants);
+        descendants.put(second, secondDescendants);
+        return descendants;
+    }
+
+    private static void assertBits(NoiseBounds expected, NoiseBounds actual) {
+        assertEquals(Double.doubleToRawLongBits(expected.min()), Double.doubleToRawLongBits(actual.min()));
+        assertEquals(Double.doubleToRawLongBits(expected.max()), Double.doubleToRawLongBits(actual.max()));
+    }
+
+    private record Fixed(Map<InferredType, List<IrisBiome>> picks, Map<IrisBiome, List<IrisBiome>> descendants)
+            implements RegionBounds.Reach {
+        @Override
+        public List<IrisBiome> picks(IrisRegion region, InferredType type) {
+            return picks.get(type);
+        }
+
+        @Override
+        public Collection<IrisBiome> descendants(IrisBiome biome) {
+            List<IrisBiome> known = descendants.get(biome);
+            return known == null ? List.of(biome) : known;
+        }
+    }
+}

core/src/test/java/art/arcane/iris/generation/runtime/SharedBaseHeightsTest.java

@@ -0,0 +1,87 @@
+package art.arcane.iris.generation.runtime;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public class SharedBaseHeightsTest {
+    @Test
+    public void storedColumnsComeBackWithTheirExactBits() {
+        SharedBaseHeights cache = new SharedBaseHeights(1 << 10);
+        double height = Math.nextUp(71.25D);
+
+        assertTrue(Double.isNaN(cache.get(12, -40)));
+        cache.put(12, -40, height);
+
+        assertEquals(Double.doubleToRawLongBits(height), Double.doubleToRawLongBits(cache.get(12, -40)));
+        assertTrue(Double.isNaN(cache.get(-40, 12)));
+    }
+
+    @Test
+    public void originMissesUntilItIsStored() {
+        SharedBaseHeights cache = new SharedBaseHeights(2);
+
+        assertTrue(Double.isNaN(cache.get(0, 0)));
+        cache.put(0, 0, -0D);
+        assertEquals(Double.doubleToRawLongBits(-0D), Double.doubleToRawLongBits(cache.get(0, 0)));
+    }
+
+    @Test
+    public void nonFiniteHeightsAreNeverStored() {
+        SharedBaseHeights cache = new SharedBaseHeights(2);
+        cache.put(3, 4, 64D);
+        cache.put(3, 4, Double.NaN);
+        cache.put(3, 4, Double.POSITIVE_INFINITY);
+
+        assertEquals(64D, cache.get(3, 4), 0D);
+    }
+
+    @Test
+    public void fullCoordinateDomainKeepsDistinctColumns() {
+        int[] coordinates = {0, 1, -1, 1 << 21, -(1 << 21), 30_000_000, -30_000_000,
+                Integer.MIN_VALUE, Integer.MAX_VALUE};
+        for (int x : coordinates) {
+            for (int z : coordinates) {
+                SharedBaseHeights cache = new SharedBaseHeights(2);
+                cache.put(x, z, 12D);
+                for (int otherX : coordinates) {
+                    for (int otherZ : coordinates) {
+                        if (x == otherX && z == otherZ) {
+                            assertEquals(12D, cache.get(otherX, otherZ), 0D);
+                        } else {
+                            assertTrue(Double.isNaN(cache.get(otherX, otherZ)));
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    @Test
+    public void aCollidingColumnReplacesTheOldOne() {
+        SharedBaseHeights cache = new SharedBaseHeights(2);
+        cache.put(5, 9, 40D);
+        cache.put(6, 9, 41D);
+        cache.put(7, 9, 42D);
+
+        int stored = 0;
+        for (int x = 5; x <= 7; x++) {
+            double value = cache.get(x, 9);
+            if (!Double.isNaN(value)) {
+                assertEquals(35D + x, value, 0D);
+                stored++;
+            }
+        }
+        assertTrue(stored >= 1 && stored <= 2);
+    }
+
+    @Test
+    public void capacityFollowsTheHeapWithinBounds() {
+        assertEquals(SharedBaseHeights.MINIMUM_CAPACITY, SharedBaseHeights.capacityFor(0L));
+        assertEquals(SharedBaseHeights.MAXIMUM_CAPACITY, SharedBaseHeights.capacityFor(Long.MAX_VALUE));
+        int capacity = SharedBaseHeights.capacityFor(6L << 30);
+        assertEquals(1, Integer.bitCount(capacity));
+        assertTrue(capacity >= SharedBaseHeights.MINIMUM_CAPACITY && capacity <= SharedBaseHeights.MAXIMUM_CAPACITY);
+    }
+}

core/src/test/java/art/arcane/iris/generation/runtime/SharedBoundsBiomesTest.java

@@ -146,7 +146,7 @@ public class SharedBoundsBiomesTest {
                     int xi = (int) ((state & Long.MAX_VALUE) % coordinates.length);
                     int zi = (int) ((state >>> 10) % coordinates.length);
                     cache.put(coordinates[xi], coordinates[zi], biomes[xi][zi]);
-                    IrisBiome actual = cache.get(coordinates[xi], coordinates[zi]);
+                    Object actual = cache.get(coordinates[xi], coordinates[zi]);
                     if (actual != null) {
                         hits.incrementAndGet();
                         if (actual != biomes[xi][zi]) {

core/src/test/java/art/arcane/iris/world/history/GenerationHistoryAdmissionTest.java

@@ -250,7 +250,7 @@ public class GenerationHistoryAdmissionTest {
                                     .addSurfaceBiome("iris:conflict").seal().build()
                             : claim(stage);
                     results.add(executor.submit(() -> persistCounting(history, stage, update, appends, forces)));
-                    awaitBlockedOnHistory(history, workers, index + 1);
+                    awaitQueuedOnHistory(history, workers, index + 1);
                 }
                 stages.get(5).close();
             }
@@ -340,7 +340,7 @@ public class GenerationHistoryAdmissionTest {
                 for (int index = 0; index < stages.size(); index++) {
                     GenerationHistory.GenerationStage stage = stages.get(index);
                     results.add(executor.submit(() -> persistFailingRegion(history, stage, failure)));
-                    awaitBlockedOnHistory(history, workers, index + 1);
+                    awaitQueuedOnHistory(history, workers, index + 1);
                 }
             }
             assertTrue(results.getFirst().get(5, TimeUnit.SECONDS));
@@ -404,21 +404,27 @@ public class GenerationHistoryAdmissionTest {
         }
     }
 
-    private static void awaitBlockedOnHistory(GenerationHistory history, List<Thread> workers, int count) {
-        Await.until("semantic claim callers to queue behind the History monitor", Duration.ofSeconds(5L),
-                () -> blockedOnHistory(history, workers) == count);
+    private static void awaitQueuedOnHistory(GenerationHistory history, List<Thread> workers, int count) {
+        Await.until("semantic claim callers to queue behind the History writer", Duration.ofSeconds(5L),
+                () -> queuedOnHistory(history, workers) == count);
     }
 
-    private static int blockedOnHistory(GenerationHistory history, List<Thread> workers) {
-        int blocked = 0;
+    private static int queuedOnHistory(GenerationHistory history, List<Thread> workers) {
+        int queued = 0;
         for (Thread worker : workers) {
             ThreadInfo info = ManagementFactory.getThreadMXBean().getThreadInfo(worker.threadId());
-            if (info != null && info.getThreadState() == Thread.State.BLOCKED
-                    && info.getLockInfo().getIdentityHashCode() == System.identityHashCode(history)) {
-                blocked++;
+            if (info == null || info.getLockInfo() == null) {
+                continue;
+            }
+            boolean writer = info.getThreadState() == Thread.State.BLOCKED
+                    && info.getLockInfo().getIdentityHashCode() == System.identityHashCode(history);
+            boolean follower = info.getThreadState() == Thread.State.TIMED_WAITING
+                    && info.getLockInfo().getClassName().endsWith("GenerationHistory$PendingSemanticClaim");
+            if (writer || follower) {
+                queued++;
             }
         }
-        return blocked;
+        return queued;
     }
 
     private static boolean persistPaused(GenerationHistory history, GenerationHistory.GenerationStage stage,

probe/src/main/java/art/arcane/iris/probe/HydrologyPlanHarness.java

@@ -195,7 +195,8 @@ final class HydrologyPlanHarness {
         double landTiles(WindowKey key) {
             int cells = WindowKey.SIZE / WindowPlanner.CELL;
             HydrologySampleBuffer samples = new HydrologySampleBuffer(cells * cells);
-            planners.windowLattice().fill(key.wx() * cells, key.wz() * cells, cells, cells, samples);
+            int stride = WindowPlanner.CELL / WindowPlanner.FINE_CELL;
+            planners.fineLattice().fill(key.wx() * cells * stride, key.wz() * cells * stride, cells, cells, stride, samples);
             int land = 0;
             for (int cell = 0; cell < cells * cells; cell++) {
                 if (!samples.ocean()[cell]) {