Share cave density lattice

- Adaptive plane lattice samples cached per carver across neighbour chunks
- Grid cleared with carvers on hotload

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

@@ -0,0 +1,84 @@
+package art.arcane.iris.generation.mantle;
+
+import art.arcane.iris.generation.cache.ConcurrentClockCache;
+
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
+import java.util.Arrays;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReferenceArray;
+
+/**
+ * Shares the adaptive cave planes' 8-block density lattice between neighbouring chunks. Every lattice column on a
+ * chunk edge is sampled by two chunks and every corner by four, with identical coordinates and carver noise, so a
+ * value computed once is reused bit for bit. Racing writers store the same value.
+ */
+final class CaveDensityGrid {
+    static final int LATTICE_SHIFT = 3;
+    private static final int SEGMENT_SHIFT = 5;
+    private static final int SEGMENT_SIZE = 1 << SEGMENT_SHIFT;
+    private static final long COORDINATE_MASK = 0xFFFFFFL;
+    private static final VarHandle VALUES = MethodHandles.arrayElementVarHandle(double[].class);
+    private static final AtomicInteger OWNERS = new AtomicInteger();
+
+    private final ConcurrentClockCache<Column> columns;
+
+    CaveDensityGrid(int capacity) {
+        columns = new ConcurrentClockCache<>(capacity);
+    }
+
+    static int nextOwner() {
+        return OWNERS.getAndIncrement();
+    }
+
+    Column column(Object owner, int ownerId, int height, int latticeX, int latticeZ) {
+        long key = (long) (ownerId & 0xFFFF) << 48 | (latticeX & COORDINATE_MASK) << 24 | (latticeZ & COORDINATE_MASK);
+        Column cached = columns.get(key);
+        if (cached == null) {
+            cached = columns.putIfAbsent(key, new Column(owner, latticeX, latticeZ, height));
+        }
+        return cached.owner == owner && cached.latticeX == latticeX && cached.latticeZ == latticeZ ? cached : null;
+    }
+
+    void clear() {
+        columns.clear();
+    }
+
+    static final class Column {
+        private final Object owner;
+        private final int latticeX;
+        private final int latticeZ;
+        private final AtomicReferenceArray<double[]> segments;
+
+        private Column(Object owner, int latticeX, int latticeZ, int height) {
+            this.owner = owner;
+            this.latticeX = latticeX;
+            this.latticeZ = latticeZ;
+            segments = new AtomicReferenceArray<>(Math.ceilDiv(Math.max(1, height), SEGMENT_SIZE));
+        }
+
+        double get(int y) {
+            int segment = y >> SEGMENT_SHIFT;
+            if (segment >= segments.length()) {
+                return Double.NaN;
+            }
+            double[] values = segments.getAcquire(segment);
+            return values == null ? Double.NaN : (double) VALUES.getOpaque(values, y & (SEGMENT_SIZE - 1));
+        }
+
+        void set(int y, double value) {
+            int segment = y >> SEGMENT_SHIFT;
+            if (segment >= segments.length()) {
+                return;
+            }
+            double[] values = segments.getAcquire(segment);
+            if (values == null) {
+                double[] created = new double[SEGMENT_SIZE];
+                Arrays.fill(created, Double.NaN);
+                double[] published = segments.compareAndExchange(segment, null, created);
+                values = published == null ? created : published;
+            }
+            VALUES.setOpaque(values, y & (SEGMENT_SIZE - 1), value);
+        }
+    }
+}

core/src/main/java/art/arcane/iris/generation/mantle/IrisCaveCarver3D.java

@@ -61,6 +61,7 @@ public class IrisCaveCarver3D {
     private static final int MINIMUM_PARALLEL_DENSITY_CELLS = 16_384;
     private static final int MAXIMUM_DENSITY_WORKERS = 4;
     private static final int[] LATTICE_TILE_OFFSETS = {0, 1, 16, 17};
+    private static final int STANDALONE_DENSITY_GRID_COLUMNS = 1024;
 
     private final Engine engine;
     private final IrisData data;
@@ -96,9 +97,16 @@ public class IrisCaveCarver3D {
     private final int densityMaximumY;
     private final ThreadLocal<Boolean> carving = ThreadLocal.withInitial(() -> false);
     private final ThreadLocal<CaveCarveScratch> scratchCache = ThreadLocal.withInitial(CaveCarveScratch::new);
+    private final CaveDensityGrid densityGrid;
+    private final int densityGridOwner = CaveDensityGrid.nextOwner();
 
     public IrisCaveCarver3D(Engine engine, IrisCaveProfile profile) {
+        this(engine, profile, new CaveDensityGrid(STANDALONE_DENSITY_GRID_COLUMNS));
+    }
+
+    IrisCaveCarver3D(Engine engine, IrisCaveProfile profile, CaveDensityGrid densityGrid) {
         this.engine = engine;
+        this.densityGrid = densityGrid;
         this.data = engine.getData();
         this.profile = profile;
         this.carveAir = new MatterCavern(true, "", LIQUID_AIR);
@@ -1542,7 +1550,7 @@ public class IrisCaveCarver3D {
             int rowOffset = sampleXIndex * axisSamples;
             for (int sampleZIndex = adaptivePlaneSampleBounds[2]; sampleZIndex <= adaptivePlaneSampleBounds[3]; sampleZIndex++) {
                 int sampleLocalZ = Math.min(sampleZIndex * adaptiveSampleStep, 16);
-                adaptivePlaneDensity[rowOffset + sampleZIndex] = sampleDensityNoWarpNoModules(x, y, z0 + sampleLocalZ);
+                adaptivePlaneDensity[rowOffset + sampleZIndex] = latticeDensity(scratch, x, y, z0 + sampleLocalZ);
             }
         }
 
@@ -1595,7 +1603,7 @@ public class IrisCaveCarver3D {
             int rowOffset = sampleXIndex * axisSamples;
             for (int sampleZIndex = adaptivePlaneSampleBounds[2]; sampleZIndex <= adaptivePlaneSampleBounds[3]; sampleZIndex++) {
                 int sampleLocalZ = Math.min(sampleZIndex * adaptiveSampleStep, 16);
-                adaptivePlaneDensity[rowOffset + sampleZIndex] = sampleDensityNoWarpNoModules(x, y, z0 + sampleLocalZ);
+                adaptivePlaneDensity[rowOffset + sampleZIndex] = latticeDensity(scratch, x, y, z0 + sampleLocalZ);
             }
         }
 
@@ -1643,7 +1651,7 @@ public class IrisCaveCarver3D {
             int rowOffset = sampleXIndex * axisSamples;
             for (int sampleZIndex = adaptivePlaneSampleBounds[2]; sampleZIndex <= adaptivePlaneSampleBounds[3]; sampleZIndex++) {
                 int sampleLocalZ = Math.min(sampleZIndex * adaptiveSampleStep, 16);
-                adaptivePlaneDensity[rowOffset + sampleZIndex] = sampleDensityWarpOnly(scratch, x, y, z0 + sampleLocalZ);
+                adaptivePlaneDensity[rowOffset + sampleZIndex] = latticeDensity(scratch, x, y, z0 + sampleLocalZ);
             }
         }
 
@@ -1696,14 +1704,7 @@ public class IrisCaveCarver3D {
             int rowOffset = sampleXIndex * axisSamples;
             for (int sampleZIndex = adaptivePlaneSampleBounds[2]; sampleZIndex <= adaptivePlaneSampleBounds[3]; sampleZIndex++) {
                 int sampleLocalZ = Math.min(sampleZIndex * adaptiveSampleStep, 16);
-                adaptivePlaneDensity[rowOffset + sampleZIndex] = sampleDensityWarpModules(
+                adaptivePlaneDensity[rowOffset + sampleZIndex] = latticeDensity(scratch, x, y, z0 + sampleLocalZ);
-                        scratch,
-                        x,
-                        y,
-                        z0 + sampleLocalZ,
-                        localModules,
-                        activeModuleCount
-                );
             }
         }
 
@@ -2463,6 +2464,33 @@ public class IrisCaveCarver3D {
         scratch.adaptiveGeometryAxisCells = axisCells;
     }
 
+    private double latticeDensity(CaveCarveScratch scratch, int x, int y, int z) {
+        int latticeMask = (1 << CaveDensityGrid.LATTICE_SHIFT) - 1;
+        CaveDensityGrid.Column column = ((x | z) & latticeMask) != 0 ? null : densityGrid.column(this, densityGridOwner,
+                densityMaximumY + 1, x >> CaveDensityGrid.LATTICE_SHIFT, z >> CaveDensityGrid.LATTICE_SHIFT);
+        if (column == null) {
+            return samplePlaneDensity(scratch, x, y, z);
+        }
+        double cached = column.get(y);
+        if (!Double.isNaN(cached)) {
+            return cached;
+        }
+        double density = samplePlaneDensity(scratch, x, y, z);
+        column.set(y, density);
+        return density;
+    }
+
+    private double samplePlaneDensity(CaveCarveScratch scratch, int x, int y, int z) {
+        if (!hasWarp) {
+            return sampleDensityNoWarpNoModules(x, y, z);
+        }
+        int activeModuleCount = hasModules ? prepareActiveModules(scratch, y) : 0;
+        if (activeModuleCount == 0) {
+            return sampleDensityWarpOnly(scratch, x, y, z);
+        }
+        return sampleDensityWarpModules(scratch, x, y, z, scratch.activeModules, activeModuleCount);
+    }
+
     private double sampleDensityNoWarpNoModules(int x, int y, int z) {
         double density = baseDensity.noiseFastSigned3D(x, y, z) * baseWeight;
         density += detailDensity.noiseFastSigned3D(x, y, z) * detailWeight;

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

@@ -54,6 +54,8 @@ public class MantleCarvingComponent extends IrisMantleComponent {
     private static final double THRESHOLD_PENALTY = 0.24D;
     private static final int MAX_BLENDED_PROFILE_PASSES = 2;
     private static final int MAX_POOLED_WEIGHT_BUFFERS = 64;
+    /** Lattice columns kept for neighbouring chunks: about 3 KB each on land, roughly 50 MB when full. */
+    private static final int DENSITY_GRID_COLUMNS = 16_384;
     private static final int KERNEL_WIDTH = (BLEND_RADIUS * 2) + 1;
     private static final int KERNEL_SIZE = KERNEL_WIDTH * KERNEL_WIDTH;
     private static final int[] KERNEL_DX = new int[KERNEL_SIZE];
@@ -62,6 +64,7 @@ public class MantleCarvingComponent extends IrisMantleComponent {
     private static final ThreadLocal<BlendScratch> BLEND_SCRATCH = ThreadLocal.withInitial(BlendScratch::new);
 
     private final Object profileCarverLock = new Object();
+    private final CaveDensityGrid densityGrid = new CaveDensityGrid(DENSITY_GRID_COLUMNS);
     private volatile Map<IrisCaveProfile, IrisCaveCarver3D> profileCarvers = new IdentityHashMap<>();
 
     static {
@@ -94,6 +97,7 @@ public class MantleCarvingComponent extends IrisMantleComponent {
         // Carvers rebuild deterministically from the carve seed, so output is unchanged.
         synchronized (profileCarverLock) {
             profileCarvers = new IdentityHashMap<>();
+            densityGrid.clear();
         }
     }
 
@@ -524,7 +528,7 @@ public class MantleCarvingComponent extends IrisMantleComponent {
             return carver;
         }
 
-        IrisCaveCarver3D createdCarver = new IrisCaveCarver3D(getEngineMantle().getEngine(), profile);
+        IrisCaveCarver3D createdCarver = new IrisCaveCarver3D(getEngineMantle().getEngine(), profile, densityGrid);
         synchronized (profileCarverLock) {
             IrisCaveCarver3D published = profileCarvers.get(profile);
             if (published != null) {

core/src/test/java/art/arcane/iris/generation/mantle/IrisCaveCarver3DNearParityTest.java

@@ -1038,6 +1038,40 @@ public class IrisCaveCarver3DNearParityTest {
                 largestPlane < 192);
     }
 
+    @Test
+    public void sharedDensityLatticeReproducesIsolatedCarvesAcrossNeighbourChunks() throws Exception {
+        Engine engine = createEngine(96, 90);
+        for (boolean warp : new boolean[]{false, true}) {
+            for (boolean modules : new boolean[]{false, true}) {
+                AtomicLong sharedSamples = new AtomicLong();
+                AtomicLong isolatedSamples = new AtomicLong();
+                IrisCaveCarver3D shared = new IrisCaveCarver3D(engine,
+                        createProfile(warp, modules).setAdaptiveSampling(true), new CaveDensityGrid(4096));
+                baseDensityField.set(shared, new CountingCNG((CNG) baseDensityField.get(shared), sharedSamples));
+                for (int chunkX = -1; chunkX <= 1; chunkX++) {
+                    for (int chunkZ = -1; chunkZ <= 1; chunkZ++) {
+                        WriterCapture sharedCapture = createWriterCapture(96);
+                        int sharedCarved = shared.carve(sharedCapture.writer, chunkX, chunkZ, fullWeights(), 0D, 0D,
+                                null, filledHeights(90));
+                        IrisCaveCarver3D isolated = new IrisCaveCarver3D(engine,
+                                createProfile(warp, modules).setAdaptiveSampling(true));
+                        baseDensityField.set(isolated, new CountingCNG((CNG) baseDensityField.get(isolated), isolatedSamples));
+                        WriterCapture isolatedCapture = createWriterCapture(96);
+                        int isolatedCarved = isolated.carve(isolatedCapture.writer, chunkX, chunkZ, fullWeights(), 0D, 0D,
+                                null, filledHeights(90));
+                        assertTrue(isolatedCarved > 0);
+                        assertEquals(isolatedCarved, sharedCarved);
+                        assertEquals(isolatedCapture.carvedCells, sharedCapture.carvedCells);
+                        assertEquals(isolatedCapture.carvedLiquids, sharedCapture.carvedLiquids);
+                    }
+                }
+                assertTrue("warp=" + warp + " modules=" + modules + " shared=" + sharedSamples.get()
+                                + " isolated=" + isolatedSamples.get(),
+                        sharedSamples.get() < isolatedSamples.get() * 3 / 4);
+            }
+        }
+    }
+
     private void assertExactParity(boolean warp, boolean modules, boolean adaptiveSampling) throws Exception {
         Engine engine = createEngine(96, 90);
         double[] columnWeights = fullWeights();