Deposit clump fast paths

- Clump randoms use a plain-field LCG with the RNG sequence and a step jump
- Single-block palettes build footprints from row masks and jump the pick draws
- Ellipsoid nodes, row offsets and node sines reuse thread scratch and size tables
- Terrain-scoped footprint plans that cannot reach the chunk surface are skipped
- Above-terrain plans are skipped when no solid host sits above the surface
- Preparation runs as at most four balanced slices with one join per chunk
- Placement caches target, bedrock and replaceable checks per block state

core/src/main/java/art/arcane/iris/generation/decoration/DepositRandom.java

@@ -0,0 +1,82 @@
+/*
+ * 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.decoration;
+
+import art.arcane.volmlib.util.math.RNG;
+
+public final class DepositRandom extends RNG {
+    private static final long MULTIPLIER = 0x5DEECE66DL;
+    private static final long ADDEND = 0xBL;
+    private static final long MASK = (1L << 48) - 1L;
+    private static final int JUMP_TABLE_SIZE = 48;
+    private static final long[] JUMP_MULTIPLIERS = new long[JUMP_TABLE_SIZE];
+    private static final long[] JUMP_ADDENDS = new long[JUMP_TABLE_SIZE];
+
+    static {
+        long multiplier = MULTIPLIER;
+        long addend = ADDEND;
+        for (int bit = 0; bit < JUMP_TABLE_SIZE; bit++) {
+            JUMP_MULTIPLIERS[bit] = multiplier;
+            JUMP_ADDENDS[bit] = addend;
+            addend = (addend * multiplier + addend) & MASK;
+            multiplier = (multiplier * multiplier) & MASK;
+        }
+    }
+
+    private long state;
+
+    public DepositRandom() {
+        super(0L);
+    }
+
+    public DepositRandom(long seed) {
+        super(seed);
+    }
+
+    @Override
+    public void setSeed(long seed) {
+        state = (seed ^ MULTIPLIER) & MASK;
+    }
+
+    @Override
+    protected int next(int bits) {
+        long advanced = (state * MULTIPLIER + ADDEND) & MASK;
+        state = advanced;
+        return (int) (advanced >>> (48 - bits));
+    }
+
+    public long state() {
+        return state;
+    }
+
+    public void restore(long state) {
+        this.state = state & MASK;
+    }
+
+    public void skip(long steps) {
+        long remaining = steps;
+        long advanced = state;
+        for (int bit = 0; remaining != 0L && bit < JUMP_TABLE_SIZE; bit++, remaining >>>= 1) {
+            if ((remaining & 1L) != 0L) {
+                advanced = (advanced * JUMP_MULTIPLIERS[bit] + JUMP_ADDENDS[bit]) & MASK;
+            }
+        }
+        state = advanced;
+    }
+}

core/src/main/java/art/arcane/iris/generation/decoration/IrisDepositGenerator.java

@@ -58,6 +58,7 @@ import lombok.experimental.Accessors;
 public class IrisDepositGenerator {
     private static final int FOOTPRINT_MAXIMUM_SIZE = 64;
     private static final ThreadLocal<FootprintCells> FOOTPRINT_CELLS = ThreadLocal.withInitial(FootprintCells::new);
+    private static final double[][] NODE_SINES = nodeSines();
     private static final long FNV_OFFSET_BASIS = 0xcbf29ce484222325L;
     private static final long FNV_PRIME = 0x100000001b3L;
 
@@ -283,28 +284,52 @@ public class IrisDepositGenerator {
      * only for clumps it keeps. Returns null without drawing when the shape has no footprint path.
      */
     public ClumpFootprint sampleClumpFootprint(RNG rng, IrisData rdata) {
-        if (shape != IrisDepositShape.VANILLA_ELLIPSOID || minSize > FOOTPRINT_MAXIMUM_SIZE
+        if (!usesClumpFootprints(rdata)) {
-                || maxSize > FOOTPRINT_MAXIMUM_SIZE) {
-            return null;
-        }
-        int paletteSize = getBlockData(rdata).size();
-        if (paletteSize == 0) {
             return null;
         }
+        KList<NativeBlockState> resolvedPalette = getBlockData(rdata);
+        int paletteSize = resolvedPalette.size();
         int size = rng.i(minSize, maxSize + 1);
         if (size <= 0) {
             return ClumpFootprint.EMPTY;
         }
         FootprintCells cells = FOOTPRINT_CELLS.get();
         cells.reset();
-        vanillaEllipsoidCells(rng, size, cells);
+        if (paletteSize == 1) {
-        if (cells.count == 0) {
+            emitEllipsoidRows(rng, size, cells);
-            return ClumpFootprint.EMPTY;
+            if (cells.count == 0) {
+                return ClumpFootprint.EMPTY;
+            }
+            skipUniformPicks(rng, cells.count);
+        } else {
+            emitEllipsoidCells(rng, size, cells, cells.scratch);
+            if (cells.count == 0) {
+                return ClumpFootprint.EMPTY;
+            }
+            for (int cell = 0; cell < cells.count; cell++) {
+                cells.picks[cell] = rng.i(0, paletteSize);
+            }
         }
-        for (int cell = 0; cell < cells.count; cell++) {
+        return new ClumpFootprint(cells.extentX * 2 + 1, cells.minY, cells, cells.stamp, resolvedPalette);
-            cells.picks[cell] = rng.i(0, paletteSize);
+    }
+
+    public boolean usesClumpFootprints(IrisData rdata) {
+        return shape == IrisDepositShape.VANILLA_ELLIPSOID && minSize <= FOOTPRINT_MAXIMUM_SIZE
+                && maxSize <= FOOTPRINT_MAXIMUM_SIZE && !getBlockData(rdata).isEmpty();
+    }
+
+    public static int lowestFootprintOffset(int size) {
+        return -4 - (Math.max(0, size) + 15) / 16;
+    }
+
+    private static void skipUniformPicks(RNG rng, int count) {
+        if (rng instanceof DepositRandom random) {
+            random.skip(2L * count);
+            return;
+        }
+        for (int cell = 0; cell < count; cell++) {
+            rng.nextDouble();
         }
-        return new ClumpFootprint(cells.extentX * 2 + 1, cells.minY, cells, cells.stamp, getBlockData(rdata));
     }
 
     /**
@@ -313,15 +338,87 @@ public class IrisDepositGenerator {
      * test is bit-identical to evaluating {@code nx * nx + ny * ny + nz * nz} in place.
      */
     static void vanillaEllipsoidCells(RNG rng, int size, CellSink sink) {
+        emitEllipsoidCells(rng, size, sink, new EllipsoidScratch());
+    }
+
+    private static void emitEllipsoidCells(RNG rng, int size, CellSink sink, EllipsoidScratch scratch) {
+        double[] nodes = ellipsoidNodes(rng, size, scratch);
+        for (int node = 0; node < size; node++) {
+            if (!scratch.sphere(nodes, node)) {
+                continue;
+            }
+            double[] squaredY = scratch.squaredY;
+            double[] squaredZ = scratch.squaredZ;
+            for (int x = scratch.minX; x <= scratch.maxX; x++) {
+                double nx = (x + 0.5D - scratch.centerX) / scratch.radius;
+                double squaredX = nx * nx;
+                if (squaredX >= 1D) {
+                    continue;
+                }
+                for (int y = 0; y < scratch.spanY; y++) {
+                    double squaredXY = squaredX + squaredY[y];
+                    if (squaredXY >= 1D) {
+                        continue;
+                    }
+                    for (int z = 0; z < scratch.spanZ; z++) {
+                        if (squaredXY + squaredZ[z] < 1D) {
+                            sink.add(x, scratch.minY + y, scratch.minZ + z);
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    private static void emitEllipsoidRows(RNG rng, int size, FootprintCells cells) {
+        EllipsoidScratch scratch = cells.scratch;
+        double[] nodes = ellipsoidNodes(rng, size, scratch);
+        for (int node = 0; node < size; node++) {
+            if (!scratch.sphere(nodes, node)) {
+                continue;
+            }
+            double[] squaredY = scratch.squaredY;
+            double[] squaredZ = scratch.squaredZ;
+            int zShift = scratch.minZ + FootprintCells.OFFSET;
+            for (int x = scratch.minX; x <= scratch.maxX; x++) {
+                double nx = (x + 0.5D - scratch.centerX) / scratch.radius;
+                double squaredX = nx * nx;
+                if (squaredX >= 1D) {
+                    continue;
+                }
+                for (int y = 0; y < scratch.spanY; y++) {
+                    double squaredXY = squaredX + squaredY[y];
+                    if (squaredXY >= 1D) {
+                        continue;
+                    }
+                    long row = 0L;
+                    for (int z = 0; z < scratch.spanZ; z++) {
+                        if (squaredXY + squaredZ[z] < 1D) {
+                            row |= 1L << (zShift + z);
+                        }
+                    }
+                    if (row != 0L) {
+                        cells.addRow(x, scratch.minY + y, row);
+                    }
+                }
+            }
+        }
+        cells.finishRows();
+    }
+
+    private static double[] ellipsoidNodes(RNG rng, int size, EllipsoidScratch scratch) {
         float angle = rng.nextFloat() * (float) Math.PI;
         float reach = size / 8F;
-        double startX = Math.sin(angle) * reach;
+        double sine = Math.sin(angle);
-        double endX = -Math.sin(angle) * reach;
+        double cosine = Math.cos(angle);
-        double startZ = Math.cos(angle) * reach;
+        double startX = sine * reach;
-        double endZ = -Math.cos(angle) * reach;
+        double endX = -sine * reach;
+        double startZ = cosine * reach;
+        double endZ = -cosine * reach;
         double startY = rng.nextInt(3) - 2;
         double endY = rng.nextInt(3) - 2;
-        double[] nodes = new double[size * 4];
+        double[] nodes = scratch.nodes(size * 4);
+        double[] sines = size < NODE_SINES.length ? NODE_SINES[size] : null;
 
         for (int i = 0; i < size; i++) {
             float progress = (float) i / size;
@@ -329,7 +426,8 @@ public class IrisDepositGenerator {
             nodes[i * 4] = startX + (endX - startX) * progress;
             nodes[i * 4 + 1] = startY + (endY - startY) * progress;
             nodes[i * 4 + 2] = startZ + (endZ - startZ) * progress;
-            nodes[i * 4 + 3] = ((Math.sin(Math.PI * progress) + 1D) * radiusNoise + 1D) / 2D;
+            double arc = sines == null ? Math.sin(Math.PI * progress) : sines[i];
+            nodes[i * 4 + 3] = ((arc + 1D) * radiusNoise + 1D) / 2D;
         }
 
         for (int i = 0; i < size - 1; i++) {
@@ -354,59 +452,20 @@ public class IrisDepositGenerator {
                 }
             }
         }
+        return nodes;
+    }
 
-        double[] squaredY = new double[16];
+    private static double[][] nodeSines() {
-        double[] squaredZ = new double[16];
+        double[][] sines = new double[FOOTPRINT_MAXIMUM_SIZE + 1][];
-        for (int i = 0; i < size; i++) {
+        for (int size = 1; size <= FOOTPRINT_MAXIMUM_SIZE; size++) {
-            double radius = nodes[i * 4 + 3];
+            double[] values = new double[size];
-            if (radius < 0D) {
+            for (int i = 0; i < size; i++) {
-                continue;
+                float progress = (float) i / size;
-            }
+                values[i] = Math.sin(Math.PI * progress);
-            double centerX = nodes[i * 4];
-            double centerY = nodes[i * 4 + 1];
-            double centerZ = nodes[i * 4 + 2];
-            int minX = (int) Math.floor(centerX - radius);
-            int maxX = Math.max((int) Math.floor(centerX + radius), minX);
-            int minY = (int) Math.floor(centerY - radius);
-            int maxY = Math.max((int) Math.floor(centerY + radius), minY);
-            int minZ = (int) Math.floor(centerZ - radius);
-            int maxZ = Math.max((int) Math.floor(centerZ + radius), minZ);
-            int spanY = maxY - minY + 1;
-            int spanZ = maxZ - minZ + 1;
-            if (spanY > squaredY.length) {
-                squaredY = new double[spanY];
-            }
-            if (spanZ > squaredZ.length) {
-                squaredZ = new double[spanZ];
-            }
-            for (int y = 0; y < spanY; y++) {
-                double ny = (minY + y + 0.5D - centerY) / radius;
-                squaredY[y] = ny * ny;
-            }
-            for (int z = 0; z < spanZ; z++) {
-                double nz = (minZ + z + 0.5D - centerZ) / radius;
-                squaredZ[z] = nz * nz;
-            }
-
-            for (int x = minX; x <= maxX; x++) {
-                double nx = (x + 0.5D - centerX) / radius;
-                double squaredX = nx * nx;
-                if (squaredX >= 1D) {
-                    continue;
-                }
-                for (int y = 0; y < spanY; y++) {
-                    double squaredXY = squaredX + squaredY[y];
-                    if (squaredXY >= 1D) {
-                        continue;
-                    }
-                    for (int z = 0; z < spanZ; z++) {
-                        if (squaredXY + squaredZ[z] < 1D) {
-                            sink.add(x, minY + y, minZ + z);
-                        }
-                    }
-                }
             }
+            sines[size] = values;
         }
+        return sines;
     }
 
     IrisObject generateVanillaScattered(RNG rng, IrisData rdata, int size) {
@@ -672,14 +731,16 @@ public class IrisDepositGenerator {
     }
 
     public static final class ClumpCells {
-        static final ClumpCells EMPTY = new ClumpCells(new int[0], new NativeBlockState[0]);
+        static final ClumpCells EMPTY = new ClumpCells(new int[0], new NativeBlockState[0], null);
 
         private final int[] positions;
         private final NativeBlockState[] blocks;
+        private final NativeBlockState uniform;
 
-        private ClumpCells(int[] positions, NativeBlockState[] blocks) {
+        private ClumpCells(int[] positions, NativeBlockState[] blocks, NativeBlockState uniform) {
             this.positions = positions;
             this.blocks = blocks;
+            this.uniform = uniform;
         }
 
         public int size() {
@@ -699,7 +760,63 @@ public class IrisDepositGenerator {
         }
 
         public NativeBlockState block(int cell) {
-            return blocks[cell];
+            return blocks == null ? uniform : blocks[cell];
+        }
+    }
+
+    private static final class EllipsoidScratch {
+        private double[] nodes = new double[256];
+        private double[] squaredY = new double[16];
+        private double[] squaredZ = new double[16];
+        private double centerX;
+        private double radius;
+        private int minX;
+        private int maxX;
+        private int minY;
+        private int spanY;
+        private int minZ;
+        private int spanZ;
+
+        private double[] nodes(int length) {
+            if (nodes.length < length) {
+                nodes = new double[length];
+            }
+            return nodes;
+        }
+
+        private boolean sphere(double[] values, int node) {
+            double sphereRadius = values[node * 4 + 3];
+            if (sphereRadius < 0D) {
+                return false;
+            }
+            double sphereX = values[node * 4];
+            double sphereY = values[node * 4 + 1];
+            double sphereZ = values[node * 4 + 2];
+            minX = (int) Math.floor(sphereX - sphereRadius);
+            maxX = Math.max((int) Math.floor(sphereX + sphereRadius), minX);
+            minY = (int) Math.floor(sphereY - sphereRadius);
+            int maxY = Math.max((int) Math.floor(sphereY + sphereRadius), minY);
+            minZ = (int) Math.floor(sphereZ - sphereRadius);
+            int maxZ = Math.max((int) Math.floor(sphereZ + sphereRadius), minZ);
+            spanY = maxY - minY + 1;
+            spanZ = maxZ - minZ + 1;
+            if (spanY > squaredY.length) {
+                squaredY = new double[spanY];
+            }
+            if (spanZ > squaredZ.length) {
+                squaredZ = new double[spanZ];
+            }
+            for (int y = 0; y < spanY; y++) {
+                double ny = (minY + y + 0.5D - sphereY) / sphereRadius;
+                squaredY[y] = ny * ny;
+            }
+            for (int z = 0; z < spanZ; z++) {
+                double nz = (minZ + z + 0.5D - sphereZ) / sphereRadius;
+                squaredZ[z] = nz * nz;
+            }
+            centerX = sphereX;
+            radius = sphereRadius;
+            return true;
         }
     }
 
@@ -708,6 +825,7 @@ public class IrisDepositGenerator {
         private static final int AXIS = 64;
         private final long[] occupied = new long[AXIS * AXIS * AXIS / 64];
         private final int[] touched = new int[AXIS * AXIS * AXIS / 64];
+        private final EllipsoidScratch scratch = new EllipsoidScratch();
         private int[] order = new int[256];
         private int[] picks = new int[256];
         private long[] sortKeys = new long[256];
@@ -715,6 +833,7 @@ public class IrisDepositGenerator {
         private int count;
         private int extentX;
         private int minY;
+        private boolean uniform;
         private long stamp;
 
         private void reset() {
@@ -725,6 +844,7 @@ public class IrisDepositGenerator {
             count = 0;
             extentX = 0;
             minY = Integer.MAX_VALUE;
+            uniform = false;
             stamp++;
         }
 
@@ -751,7 +871,35 @@ public class IrisDepositGenerator {
             minY = Math.min(minY, y);
         }
 
+        private void addRow(int x, int y, long row) {
+            int word = (x + OFFSET) * AXIS + (y + OFFSET);
+            long current = occupied[word];
+            if (current == 0L) {
+                touched[touchedCount++] = word;
+            }
+            occupied[word] = current | row;
+        }
+
+        private void finishRows() {
+            int cells = 0;
+            int extent = 0;
+            int lowest = Integer.MAX_VALUE;
+            for (int index = 0; index < touchedCount; index++) {
+                int word = touched[index];
+                cells += Long.bitCount(occupied[word]);
+                extent = Math.max(extent, Math.abs(word / AXIS - OFFSET));
+                lowest = Math.min(lowest, word % AXIS - OFFSET);
+            }
+            count = cells;
+            extentX = extent;
+            minY = lowest;
+            uniform = true;
+        }
+
         private ClumpCells toCells(KList<NativeBlockState> palette) {
+            if (uniform) {
+                return toUniformCells(palette.get(0));
+            }
             for (int cell = 0; cell < count; cell++) {
                 sortKeys[cell] = ((long) order[cell] << 32) | picks[cell];
             }
@@ -763,7 +911,22 @@ public class IrisDepositGenerator {
                 positions[cell] = (int) (key >>> 32);
                 blocks[cell] = palette.get((int) key);
             }
-            return new ClumpCells(positions, blocks);
+            return new ClumpCells(positions, blocks, null);
+        }
+
+        private ClumpCells toUniformCells(NativeBlockState block) {
+            Arrays.sort(touched, 0, touchedCount);
+            int[] positions = new int[count];
+            int cell = 0;
+            for (int index = 0; index < touchedCount; index++) {
+                int word = touched[index];
+                long row = occupied[word];
+                while (row != 0L) {
+                    positions[cell++] = (word << 6) | Long.numberOfTrailingZeros(row);
+                    row &= row - 1L;
+                }
+            }
+            return new ClumpCells(positions, null, block);
         }
     }
 }

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

@@ -23,6 +23,8 @@ import art.arcane.iris.generation.runtime.IrisEngine;
 import art.arcane.iris.generation.runtime.EngineAssignedModifier;
 import art.arcane.iris.generation.runtime.DimensionStackLayout;
 import art.arcane.iris.generation.biome.IrisBiome;
+import art.arcane.iris.generation.chunk.ColumnExtent;
+import art.arcane.iris.generation.decoration.DepositRandom;
 import art.arcane.iris.generation.decoration.IrisDepositBiomeScope;
 import art.arcane.iris.generation.decoration.IrisDepositGenerator;
 import art.arcane.iris.generation.decoration.IrisDepositHeightDistribution;
@@ -55,8 +57,8 @@ import java.util.List;
 import java.util.function.Predicate;
 
 public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState> {
-    private static final int CLUMPS_PER_BATCH = 8;
+    private static final int PREPARATION_TASKS = 4;
-    private static final int PREPARATION_BATCH_COUNT = 4;
+    private static final int MINIMUM_TASK_ATTEMPTS = 96;
 
     private final RNG rng;
     private volatile PackScan packScan;
@@ -88,31 +90,67 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
         BurstExecutor burst = burst().burst(multicore);
         long seed = x * 341873128712L + z * 132897987541L;
         int highestSurface = highestTerrainSurface(x, z, null, context);
-        PreparedDeposit[] prepared = new PreparedDeposit[PREPARATION_BATCH_COUNT];
-        int pending = 0;
         IrisEngine generationEngine = getEngine() instanceof IrisEngine irisEngine
                 && irisEngine.hasGenerationRuntimeScope() ? irisEngine : null;
-        PreparationContext preparation = new PreparationContext(context, generationEngine,
-                generationEngine == null ? null : generationEngine.captureGenerationRuntimeBinding(), new Throwable[PREPARATION_BATCH_COUNT]);
         MantleChunk chunk = getEngine().getMantle().getMantle().useChunk(x, z);
+        PreparationContext preparation = null;
         Throwable callerFailure = null;
         try {
+            List<DepositPlan> plans = new ArrayList<>(generators.size());
+            AboveTerrainHosts aboveTerrainHosts = new AboveTerrainHosts(terrain, context);
+            int attempts = 0;
             for (int i = 0; i < generators.size(); i++) {
                 DepositPlan plan = plan(generators.get(i), rng.nextParallelRNG(seed * (i + 1L)), context);
-                for (int first = 0; first < plan.attempts(); first += CLUMPS_PER_BATCH) {
+                if (plan.attempts() == 0 || footprintsMissTerrain(plan, highestSurface)
-                    int firstAttempt = first;
+                        || plan.generator().getPlacementScope() == IrisDepositPlacementScope.ABOVE_TERRAIN
-                    int limit = Math.min(plan.attempts(), first + CLUMPS_PER_BATCH);
+                        && !aboveTerrainHosts.present(plan.generator().getSurfaceClearance())) {
-                    int index = pending++;
+                    continue;
-                    burst.queue(scopedDepositTask(
+                }
-                            () -> prepared[index] = prepare(plan, firstAttempt, limit, x, z, null, context, highestSurface),
+                plans.add(plan);
-                            preparation, index));
+                attempts += plan.attempts();
-                    if (pending == prepared.length) {
+            }
-                        completeBatches(burst, prepared, chunk, terrain, x, z, preparation);
+            if (attempts == 0) {
-                        pending = 0;
+                return;
+            }
+            int tasks = multicore
+                    ? Math.max(1, Math.min(PREPARATION_TASKS, Math.ceilDiv(attempts, MINIMUM_TASK_ATTEMPTS)))
+                    : 1;
+            int attemptsPerTask = Math.ceilDiv(attempts, tasks);
+            preparation = new PreparationContext(context, generationEngine,
+                    generationEngine == null ? null : generationEngine.captureGenerationRuntimeBinding(), new Throwable[tasks]);
+            PreparedDeposit[][] prepared = new PreparedDeposit[tasks][];
+            for (int task = 0; task < tasks; task++) {
+                int first = task * attemptsPerTask;
+                int last = Math.min(attempts, first + attemptsPerTask);
+                if (first >= last) {
+                    break;
+                }
+                int index = task;
+                burst.queue(scopedDepositTask(
+                        () -> prepared[index] = prepareSlice(plans, first, last, x, z, context, highestSurface),
+                        preparation, index));
+            }
+            burst.complete();
+            Throwable failure = preparation.takeFailure(null);
+            if (failure instanceof Error error) {
+                throw error;
+            }
+            if (failure instanceof RuntimeException exception) {
+                throw exception;
+            }
+            if (failure != null) {
+                throw new IllegalStateException("Deposit preparation failed", failure);
+            }
+            try (IrisContext.Scope chunkScope = IrisContext.open(getEngine(), context.getGenerationSessionId(), context)) {
+                for (PreparedDeposit[] slice : prepared) {
+                    if (slice == null) {
+                        continue;
+                    }
+                    for (PreparedDeposit deposit : slice) {
+                        place(deposit, chunk, terrain, x, z, null, context);
                     }
                 }
             }
-            completeBatches(burst, prepared, chunk, terrain, x, z, preparation);
         } catch (Throwable failure) {
             callerFailure = failure;
             throw failure;
@@ -121,7 +159,7 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
             // submitted burst tasks must never write into a released chunk.
             try {
                 burst.complete();
-                if (callerFailure != null) {
+                if (callerFailure != null && preparation != null) {
                     preparation.takeFailure(callerFailure);
                 }
             } finally {
@@ -130,28 +168,22 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
         }
     }
 
-    private void completeBatches(BurstExecutor burst, PreparedDeposit[] prepared, MantleChunk chunk,
+    private PreparedDeposit[] prepareSlice(List<DepositPlan> plans, int first, int last, int cx, int cz,
-                                 Hunk<NativeBlockState> terrain, int x, int z, PreparationContext preparation) {
+                                           ChunkContext context, int highestSurface) {
-        burst.complete();
+        List<PreparedDeposit> deposits = new ArrayList<>();
-        Throwable failure = preparation.takeFailure(null);
+        int offset = 0;
-        if (failure instanceof Error error) {
+        for (DepositPlan plan : plans) {
-            throw error;
+            int start = Math.max(first, offset);
-        }
+            int end = Math.min(last, offset + plan.attempts());
-        if (failure instanceof RuntimeException exception) {
+            if (start < end) {
-            throw exception;
+                deposits.add(prepare(plan, start - offset, end - offset, cx, cz, null, context, highestSurface));
-        }
+            }
-        if (failure != null) {
+            offset += plan.attempts();
-            throw new IllegalStateException("Deposit preparation failed", failure);
+            if (offset >= last) {
-        }
+                break;
-        try (IrisContext.Scope chunkScope = IrisContext.open(getEngine(), preparation.chunk().getGenerationSessionId(), preparation.chunk())) {
-            for (int i = 0; i < prepared.length; i++) {
-                PreparedDeposit deposit = prepared[i];
-                prepared[i] = null;
-                if (deposit != null) {
-                    place(deposit, chunk, terrain, x, z, null, preparation.chunk());
-                }
             }
         }
+        return deposits.toArray(new PreparedDeposit[0]);
     }
 
     private Runnable scopedDepositTask(Runnable task, PreparationContext preparation, int index) {
@@ -172,10 +204,25 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
 
     public void generate(IrisDepositGenerator k, MantleChunk chunk, Hunk<NativeBlockState> data, RNG rng, int cx, int cz, boolean safe, HeightMap he, ChunkContext context) {
         DepositPlan plan = plan(k, rng, context);
-        for (int first = 0; first < plan.attempts(); first += CLUMPS_PER_BATCH) {
+        if (plan.attempts() == 0) {
-            int limit = Math.min(plan.attempts(), first + CLUMPS_PER_BATCH);
+            return;
-            place(prepare(plan, first, limit, cx, cz, he, context, Integer.MIN_VALUE), chunk, data, cx, cz, he, context);
         }
+        place(prepare(plan, 0, plan.attempts(), cx, cz, he, context, Integer.MIN_VALUE), chunk, data, cx, cz, he, context);
+    }
+
+    private boolean footprintsMissTerrain(DepositPlan plan, int highestSurface) {
+        IrisDepositGenerator generator = plan.generator();
+        if (highestSurface == Integer.MIN_VALUE
+                || generator.getPlacementScope() != IrisDepositPlacementScope.TERRAIN
+                || !generator.usesClumpFootprints(getData())
+                || plan.ore() && packScan().oreScaling()) {
+            return false;
+        }
+        int minimum = generator.getHeightDistribution() == IrisDepositHeightDistribution.CLIPPED_UNIFORM
+                ? Math.max(0, generator.getMinHeight())
+                : generator.getMinHeight();
+        long lowest = (long) minimum + IrisDepositGenerator.lowestFootprintOffset(generator.getMaxSize());
+        return lowest > (long) highestSurface - Math.max(0, generator.getSurfaceClearance());
     }
 
     private DepositPlan plan(IrisDepositGenerator generator, RNG rng, ChunkContext context) {
@@ -227,7 +274,7 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
         int engineHeight = getEngine().getHeight();
         List<PreparedClump> clumps = new ArrayList<>(limit - first);
         for (int l = first; l < limit; l++) {
-            RNG clumpRng = new RNG(clumpSeed(plan.seed(), l));
+            DepositRandom clumpRng = new DepositRandom(clumpSeed(plan.seed(), l));
             if (k.getPerClumpSpawnChance() < clumpRng.d()) {
                 continue;
             }
@@ -628,6 +675,102 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
     private record DepositPlan(IrisDepositGenerator generator, long seed, boolean ore, int attempts) {
     }
 
+    private static final class HostStates {
+        private static final int SLOTS = 32;
+        private static final byte BEDROCK_KNOWN = 1;
+        private static final byte BEDROCK = 2;
+        private static final byte REPLACEABLE_KNOWN = 4;
+        private static final byte REPLACEABLE = 8;
+        private static final byte TARGET_KNOWN = 16;
+        private static final byte TARGET = 32;
+
+        private final IrisDepositGenerator generator;
+        private final NativeBlockState[] states = new NativeBlockState[SLOTS];
+        private final byte[] flags = new byte[SLOTS];
+
+        private HostStates(IrisDepositGenerator generator) {
+            this.generator = generator;
+        }
+
+        private boolean target(NativeBlockState state) {
+            int slot = slot(state);
+            byte known = flags[slot];
+            if ((known & TARGET_KNOWN) == 0) {
+                boolean target = canReplaceDepositTarget(state);
+                known = (byte) (known | TARGET_KNOWN | (target ? TARGET : 0));
+                flags[slot] = known;
+            }
+            return (known & TARGET) != 0;
+        }
+
+        private boolean bedrock(NativeBlockState state) {
+            int slot = slot(state);
+            byte known = flags[slot];
+            if ((known & BEDROCK_KNOWN) == 0) {
+                boolean bedrock = IrisProceduralBlocks.materialKey(state).equals("minecraft:bedrock");
+                known = (byte) (known | BEDROCK_KNOWN | (bedrock ? BEDROCK : 0));
+                flags[slot] = known;
+            }
+            return (known & BEDROCK) != 0;
+        }
+
+        private boolean replaceable(NativeBlockState state) {
+            int slot = slot(state);
+            byte known = flags[slot];
+            if ((known & REPLACEABLE_KNOWN) == 0) {
+                boolean replaceable = generator.canReplace(state);
+                known = (byte) (known | REPLACEABLE_KNOWN | (replaceable ? REPLACEABLE : 0));
+                flags[slot] = known;
+            }
+            return (known & REPLACEABLE) != 0;
+        }
+
+        private int slot(NativeBlockState state) {
+            int slot = System.identityHashCode(state) & (SLOTS - 1);
+            if (states[slot] != state) {
+                states[slot] = state;
+                flags[slot] = 0;
+            }
+            return slot;
+        }
+    }
+
+    private static final class AboveTerrainHosts {
+        private final Hunk<NativeBlockState> terrain;
+        private final ChunkContext context;
+        private int scannedClearance = -1;
+        private boolean present;
+
+        private AboveTerrainHosts(Hunk<NativeBlockState> terrain, ChunkContext context) {
+            this.terrain = terrain;
+            this.context = context;
+        }
+
+        private boolean present(int surfaceClearance) {
+            int clearance = Math.max(0, surfaceClearance);
+            if (clearance != scannedClearance) {
+                present = scan(clearance);
+                scannedClearance = clearance;
+            }
+            return present;
+        }
+
+        private boolean scan(int clearance) {
+            int height = terrain.getHeight();
+            for (int z = 0; z < terrain.getDepth(); z++) {
+                for (int x = 0; x < terrain.getWidth(); x++) {
+                    long floor = Math.max(-1L, (long) context.getRoundedHeight(x, z) + clearance);
+                    for (int y = Math.min(height - 1, ColumnExtent.highestStoredY(terrain, x, z)); y > floor; y--) {
+                        if (canReplaceDepositTarget(terrain.get(x, y, z))) {
+                            return true;
+                        }
+                    }
+                }
+            }
+            return false;
+        }
+    }
+
     private record PackScan(IrisData data, boolean variants, boolean oreScaling) {
     }
 
@@ -648,11 +791,13 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
         private final ChunkContext context;
         private final boolean variants;
         private final IrisDimension dimension;
-        private final IrisDimensionCarvingResolver.State carvingState = new IrisDimensionCarvingResolver.State();
+        private IrisDimensionCarvingResolver.State carvingState;
         private final IrisDepositPlacementScope scope;
         private final int surfaceClearance;
         private final double discardChance;
         private final int height;
+        private final boolean replaceBedrock;
+        private final HostStates hosts;
 
         private ClumpPlacement(IrisDepositGenerator generator, boolean ore, MantleChunk chunk,
                                Hunk<NativeBlockState> data, int chunkX, int chunkZ, HeightMap heightMap,
@@ -671,6 +816,17 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
             this.surfaceClearance = generator.getSurfaceClearance();
             this.discardChance = generator.getDiscardChanceOnAirExposure();
             this.height = getEngine().getHeight();
+            this.replaceBedrock = generator.isReplaceBedrock();
+            this.hosts = new HostStates(generator);
+        }
+
+        private IrisDimensionCarvingResolver.State carvingState() {
+            IrisDimensionCarvingResolver.State state = carvingState;
+            if (state == null) {
+                state = new IrisDimensionCarvingResolver.State();
+                carvingState = state;
+            }
+            return state;
         }
 
         private void place(int nx, int ny, int nz, NativeBlockState block, RNG rng) {
@@ -688,10 +844,10 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
             }
 
             NativeBlockState current = data.get(nx, ny, nz);
-            if (!canReplaceDepositTarget(current)) {
+            if (current == null || !hosts.target(current)) {
                 return;
             }
-            if (!generator.isReplaceBedrock() && IrisProceduralBlocks.materialKey(current).equals("minecraft:bedrock")) {
+            if (!replaceBedrock && hosts.bedrock(current)) {
                 return;
             }
 
@@ -702,7 +858,9 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
                 exteriorSurface = generator.hasSurfaceReplaceableBlocks(candidateSurfaceBiome)
                         && isTerrainSurface(data, nx, ny, nz, columnSurface);
             }
-            if (!canReplaceDepositHost(generator, current, candidateSurfaceBiome, exteriorSurface)) {
+            if (exteriorSurface
+                    ? !canReplaceDepositHost(generator, current, candidateSurfaceBiome, true)
+                    : !hosts.replaceable(current)) {
                 return;
             }
             if (discardChance > 0D) {
@@ -714,7 +872,7 @@ public class IrisDepositModifier extends EngineAssignedModifier<NativeBlockState
 
             if (chunk.get(nx, ny, nz, MatterCavern.class) == null) {
                 NativeBlockState remapped = variants ? resolveDepositVariant(
-                        chunkX, chunkZ, nx, ny, nz, block, dimension, context, carvingState) : null;
+                        chunkX, chunkZ, nx, ny, nz, block, dimension, context, carvingState()) : null;
                 data.set(nx, ny, nz, remapped != null ? remapped : B.toDeepSlateOre(current, block));
             }
         }

core/src/test/java/art/arcane/iris/generation/decoration/DepositRandomTest.java

@@ -0,0 +1,65 @@
+package art.arcane.iris.generation.decoration;
+
+import art.arcane.volmlib.util.math.RNG;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class DepositRandomTest {
+    @Test
+    public void everyDrawMatchesTheRngSequence() {
+        int[] bounds = {1, 2, 3, 5, 7, 16, 100, 1 << 20, Integer.MAX_VALUE};
+        for (long seed : new long[]{0L, 1L, -1L, 42L, 0x9E3779B97F4A7C15L, Long.MIN_VALUE}) {
+            RNG reference = new RNG(seed);
+            DepositRandom random = new DepositRandom(seed);
+            assertEquals(reference.getSeed(), random.getSeed());
+            for (int draw = 0; draw < 4000; draw++) {
+                int bound = bounds[draw % bounds.length];
+                switch (draw % 9) {
+                    case 0 -> assertEquals(reference.nextInt(), random.nextInt());
+                    case 1 -> assertEquals(reference.nextInt(bound), random.nextInt(bound));
+                    case 2 -> assertEquals(reference.nextLong(), random.nextLong());
+                    case 3 -> assertEquals(Double.doubleToRawLongBits(reference.nextDouble()),
+                            Double.doubleToRawLongBits(random.nextDouble()));
+                    case 4 -> assertEquals(Float.floatToRawIntBits(reference.nextFloat()),
+                            Float.floatToRawIntBits(random.nextFloat()));
+                    case 5 -> assertEquals(reference.nextBoolean(), random.nextBoolean());
+                    case 6 -> assertEquals(Double.doubleToRawLongBits(reference.d()),
+                            Double.doubleToRawLongBits(random.d()));
+                    case 7 -> assertEquals(reference.i(-bound / 2, bound), random.i(-bound / 2, bound));
+                    default -> assertEquals(reference.i(0, 1), random.i(0, 1));
+                }
+            }
+        }
+    }
+
+    @Test
+    public void skipAdvancesExactlyLikeRepeatedSteps() {
+        for (long seed : new long[]{3L, -11L, 0x5DEECE66DL}) {
+            for (long steps : new long[]{0L, 1L, 2L, 3L, 7L, 64L, 65L, 1000L, 123457L}) {
+                DepositRandom stepped = new DepositRandom(seed);
+                DepositRandom jumped = new DepositRandom(seed);
+                for (long step = 0L; step < steps; step++) {
+                    stepped.nextInt();
+                }
+                jumped.skip(steps);
+                assertEquals("seed " + seed + " steps " + steps, stepped.state(), jumped.state());
+                assertEquals(stepped.nextLong(), jumped.nextLong());
+            }
+        }
+    }
+
+    @Test
+    public void reseedingAndRestoringReproduceTheSequence() {
+        DepositRandom random = new DepositRandom();
+        for (long seed : new long[]{5L, 77L, -9001L}) {
+            random.setSeed(seed);
+            RNG reference = new RNG(seed);
+            long saved = random.state();
+            long first = random.nextLong();
+            assertEquals(reference.nextLong(), first);
+            random.restore(saved);
+            assertEquals(first, random.nextLong());
+        }
+    }
+}

core/src/test/java/art/arcane/iris/generation/decoration/IrisDepositTuningTest.java

@@ -260,6 +260,56 @@ public class IrisDepositTuningTest {
         assertNull(generator.sampleClumpFootprint(new RNG(1L), data));
     }
 
+    @Test
+    public void uniformEllipsoidFootprintCellsMatchTheBuiltClumpForEitherRandom() {
+        IrisData data = mock(IrisData.class);
+        IrisDepositGenerator generator = generatorWithState(data, true);
+        generator.setShape(IrisDepositShape.VANILLA_ELLIPSOID);
+        for (int size : new int[]{0, 1, 2, 3, 4, 9, 17, 20, 25, 48, 64}) {
+            generator.setMinSize(size).setMaxSize(size);
+            for (long seed = 0; seed < 300; seed++) {
+                RNG built = new RNG(seed);
+                IrisObject clump = generator.getClump(null, built, data);
+                long expectedNext = built.nextLong();
+                List<String> expected = new ArrayList<>();
+                VectorMap<NativeBlockState>.Cursor cursor = clump.getBlocks().cursor();
+                while (cursor.next()) {
+                    expected.add(cursor.key().getBlockX() + "," + cursor.key().getBlockY() + ","
+                            + cursor.key().getBlockZ() + "=" + cursor.value().key());
+                }
+                for (RNG sampled : new RNG[]{new RNG(seed), new DepositRandom(seed)}) {
+                    IrisDepositGenerator.ClumpFootprint footprint = generator.sampleClumpFootprint(sampled, data);
+                    assertEquals(clump.getW(), footprint.width());
+                    IrisDepositGenerator.ClumpCells cells = footprint.cells();
+                    List<String> actual = new ArrayList<>();
+                    for (int cell = 0; cell < cells.size(); cell++) {
+                        actual.add(cells.x(cell) + "," + cells.y(cell) + "," + cells.z(cell) + "="
+                                + cells.block(cell).key());
+                    }
+                    assertEquals("size " + size + " seed " + seed, expected, actual);
+                    assertEquals("size " + size + " seed " + seed, expectedNext, sampled.nextLong());
+                }
+            }
+        }
+    }
+
+    @Test
+    public void footprintOffsetBoundNeverExceedsTheLowestEllipsoidCell() {
+        IrisData data = mock(IrisData.class);
+        IrisDepositGenerator generator = generatorWithState(data, true);
+        generator.setShape(IrisDepositShape.VANILLA_ELLIPSOID);
+        for (int size = 1; size <= 64; size++) {
+            generator.setMinSize(size).setMaxSize(size);
+            int bound = IrisDepositGenerator.lowestFootprintOffset(size);
+            for (long seed = 0; seed < 400; seed++) {
+                IrisDepositGenerator.ClumpFootprint footprint = generator.sampleClumpFootprint(new DepositRandom(seed), data);
+                if (!footprint.empty()) {
+                    assertTrue("size " + size + " seed " + seed, footprint.minY() >= bound);
+                }
+            }
+        }
+    }
+
     @Test
     public void ellipsoidFootprintCellsMatchTheBuiltClumpInPlacementOrder() {
         IrisData data = mock(IrisData.class);

core/src/test/java/art/arcane/iris/generation/stage/IrisDepositModifierContextTest.java

@@ -54,8 +54,8 @@ public class IrisDepositModifierContextTest {
         try (Fixture fixture = new Fixture(engine, true)) {
             fixture.generateAndCheckCleanup();
             verify(engine, times(1)).captureGenerationRuntimeBinding();
-            verify(engine, times(4)).openGenerationRuntimeScope(fixture.binding);
+            verify(engine, times(1)).openGenerationRuntimeScope(fixture.binding);
-            assertEquals(4, fixture.closedScopes.get());
+            assertEquals(1, fixture.closedScopes.get());
         }
     }
 
@@ -84,13 +84,13 @@ public class IrisDepositModifierContextTest {
             assertSame(failure, assertThrows(IllegalStateException.class, () ->
                     fixture.modifier.modify(32, -48, Hunk.newArrayHunk(16, 16, 16), true, fixture.context)));
             verify(fixture.chunk).release();
-            assertEquals(4, fixture.closedScopes.get());
+            assertEquals(1, fixture.closedScopes.get());
             assertNull(IrisContext.get());
         }
     }
 
     @Test
-    public void callerPlanFailureStillDrainsWorkersAndRestoresContext() throws Exception {
+    public void callerPlanFailureQueuesNoWorkAndRestoresContext() throws Exception {
         try (Fixture fixture = new Fixture(mock(IrisEngine.class, RETURNS_DEEP_STUBS), true)) {
             IllegalStateException failure = new IllegalStateException("caller deposit plan failed");
             doThrow(failure).when(fixture.biomeDeposit).getSpawnChance();
@@ -102,25 +102,24 @@ public class IrisDepositModifierContextTest {
                 assertEquals(19L, IrisContext.require().getGenerationSessionId());
             }
             verify(fixture.chunk).release();
-            assertEquals(3, fixture.closedScopes.get());
+            assertEquals(0, fixture.closedScopes.get());
-            assertEquals(10, fixture.completed.get());
+            assertEquals(0, fixture.completed.get());
             assertNull(IrisContext.get());
         }
     }
 
     @Test
-    public void callerFailureRetainsDistinctWorkerFailuresAfterDraining() throws Exception {
+    public void distinctWorkerFailuresAreRetainedAfterDraining() throws Exception {
         try (Fixture fixture = new Fixture(mock(IrisEngine.class, RETURNS_DEEP_STUBS), true)) {
-            IllegalStateException caller = new IllegalStateException("caller failure");
             IllegalArgumentException firstWorker = new IllegalArgumentException("first worker failure");
             UnsupportedOperationException secondWorker = new UnsupportedOperationException("second worker failure");
+            when(fixture.dimensionDeposit.getMinPerChunk()).thenReturn(200);
+            when(fixture.dimensionDeposit.getMaxPerChunk()).thenReturn(200);
             doThrow(firstWorker, secondWorker).when(fixture.dimensionDeposit).getClump(any(), any(), any());
-            doThrow(caller).when(fixture.biomeDeposit).getSpawnChance();
+            assertSame(firstWorker, assertThrows(IllegalArgumentException.class, () ->
-            assertSame(caller, assertThrows(IllegalStateException.class, () ->
                     fixture.modifier.modify(32, -48, Hunk.newArrayHunk(16, 16, 16), true, fixture.context)));
-            assertEquals(2, caller.getSuppressed().length);
+            assertEquals(1, firstWorker.getSuppressed().length);
-            assertSame(firstWorker, caller.getSuppressed()[0]);
+            assertSame(secondWorker, firstWorker.getSuppressed()[0]);
-            assertSame(secondWorker, caller.getSuppressed()[1]);
             verify(fixture.chunk).release();
             assertEquals(3, fixture.closedScopes.get());
             assertNull(IrisContext.get());

core/src/test/java/art/arcane/iris/generation/stage/IrisDepositModifierOrderingTest.java

@@ -79,16 +79,16 @@ public class IrisDepositModifierOrderingTest {
 
     @Test
     public void reverseWorkerCompletionKeepsDimensionRegionBiomePlacementOrder() throws Exception {
-        try (Fixture fixture = new Fixture(true, 1)) {
+        try (Fixture fixture = new Fixture(true, 96, true)) {
             fixture.generate();
-            assertEquals(List.of("biome", "region", "dimension"), fixture.completed);
+            assertEquals(List.of("biome", "region", "dimension"), fixture.firstCompletions());
             fixture.assertBiomeWins();
         }
     }
 
     @Test
     public void inlinePreparationUsesTheSameOverlappingHostRules() throws Exception {
-        try (Fixture fixture = new Fixture(false, 1)) {
+        try (Fixture fixture = new Fixture(false, 1, false)) {
             fixture.generate();
             assertEquals(List.of("dimension", "region", "biome"), fixture.completed);
             fixture.assertBiomeWins();
@@ -107,7 +107,7 @@ public class IrisDepositModifierOrderingTest {
         Collections.sort(expectedSamples);
 
         for (boolean parallel : new boolean[]{false, true}) {
-            try (Fixture fixture = new Fixture(parallel, 25)) {
+            try (Fixture fixture = new Fixture(parallel, 25, false)) {
                 fixture.generate();
                 Collections.sort(fixture.samples);
                 assertEquals(expectedSamples, fixture.samples);
@@ -290,11 +290,13 @@ public class IrisDepositModifierOrderingTest {
         private final MantleChunk<Matter> chunk;
         private final boolean parallel;
         private final int attempts;
+        private final boolean reverse;
 
         @SuppressWarnings("unchecked")
-        private Fixture(boolean parallel, int attempts) {
+        private Fixture(boolean parallel, int attempts, boolean reverse) {
             this.parallel = parallel;
             this.attempts = attempts;
+            this.reverse = reverse;
             IrisBiome biome = mock(IrisBiome.class, withSettings().stubOnly());
             IrisRegion region = mock(IrisRegion.class, withSettings().stubOnly());
             ChunkedDataCache<IrisBiome> biomes = new ChunkedDataCache<>(
@@ -348,11 +350,9 @@ public class IrisDepositModifierOrderingTest {
                 }
             }
             when(generator.getClump(any(), any(), any())).thenAnswer(invocation -> {
-                assertTrue("Placement must release the first clump window before more are prepared",
+                if (reverse && name.equals("dimension")) {
-                        samples.size() < 32 || output.get(0, 4, 0) != stone);
-                if (parallel && attempts == 1 && name.equals("dimension")) {
                     assertTrue(regionReady.await(10, TimeUnit.SECONDS));
-                } else if (parallel && attempts == 1 && name.equals("region")) {
+                } else if (reverse && name.equals("region")) {
                     assertTrue(biomeReady.await(10, TimeUnit.SECONDS));
                 }
                 RNG rng = invocation.getArgument(1);
@@ -376,6 +376,18 @@ public class IrisDepositModifierOrderingTest {
             verify(chunk).release();
         }
 
+        private List<String> firstCompletions() {
+            List<String> order = new ArrayList<>();
+            synchronized (completed) {
+                for (String name : completed) {
+                    if (!order.contains(name)) {
+                        order.add(name);
+                    }
+                }
+            }
+            return order;
+        }
+
         private void assertBiomeWins() {
             for (int x = 0; x < 16; x++) {
                 for (int z = 0; z < 16; z++) {

core/src/test/java/art/arcane/iris/generation/stage/IrisDepositModifierParityTest.java

@@ -8,6 +8,7 @@ import art.arcane.iris.generation.biome.IrisBiome;
 import art.arcane.iris.generation.decoration.IrisDepositBiomeScope;
 import art.arcane.iris.generation.decoration.IrisDepositGenerator;
 import art.arcane.iris.generation.decoration.IrisDepositHeightDistribution;
+import art.arcane.iris.generation.decoration.IrisDepositPlacementScope;
 import art.arcane.iris.generation.decoration.IrisDepositShape;
 import art.arcane.iris.generation.decoration.IrisDepositVariant;
 import art.arcane.iris.generation.terrain.IrisDimension;
@@ -129,6 +130,56 @@ public class IrisDepositModifierParityTest {
         assertEquals(0, clumps.get());
     }
 
+    @Test
+    public void terrainFootprintsAboveTheHighestSurfaceAreSkippedWithoutChangingOutput() {
+        long[] expected = {-681153659952315909L, 784L, 2118L, 53L, 67L, 10L};
+        for (boolean multicore : new boolean[]{false, true}) {
+            AtomicInteger skipped = new AtomicInteger();
+            long[] withSkipped = generateConfigured(101L, multicore, true, false, new AtomicInteger(), null, true,
+                    skyDeposit(47, skipped));
+            assertEquals(Arrays.toString(expected), Arrays.toString(withSkipped));
+            assertEquals(0, skipped.get());
+            AtomicInteger sampled = new AtomicInteger();
+            long[] withSampled = generateConfigured(101L, multicore, true, false, new AtomicInteger(), null, true,
+                    skyDeposit(46, sampled));
+            assertEquals(Arrays.toString(expected), Arrays.toString(withSampled));
+            assertTrue(sampled.get() > 0);
+        }
+    }
+
+    @Test
+    public void aboveTerrainDepositsWithoutHostsAreSkippedWithoutChangingOutput() {
+        long[] expected = {-681153659952315909L, 784L, 2118L, 53L, 67L, 10L};
+        for (boolean multicore : new boolean[]{false, true}) {
+            AtomicInteger vacant = new AtomicInteger();
+            long[] withoutHosts = generateConfigured(101L, multicore, true, false, new AtomicInteger(), null, true,
+                    floatingDeposit(vacant), false);
+            assertEquals(Arrays.toString(expected), Arrays.toString(withoutHosts));
+            assertEquals(0, vacant.get());
+            AtomicInteger hosted = new AtomicInteger();
+            generateConfigured(101L, multicore, true, false, new AtomicInteger(), null, true,
+                    floatingDeposit(hosted), true);
+            assertTrue(hosted.get() > 0);
+        }
+    }
+
+    private IrisDepositGenerator floatingDeposit(AtomicInteger clumps) {
+        return new CountingPaletteGenerator(state("andesite"), clumps)
+                .setShape(IrisDepositShape.VANILLA_ELLIPSOID).setMinSize(9).setMaxSize(9)
+                .setMinPerChunk(40).setMaxPerChunk(40).setMinHeight(0).setMaxHeight(47)
+                .setHeightDistribution(IrisDepositHeightDistribution.UNIFORM).setSurfaceClearance(0)
+                .setPlacementScope(IrisDepositPlacementScope.ABOVE_TERRAIN)
+                .setPerClumpSpawnChance(1D).setReplaceableBlocks(new KList<>("stone"));
+    }
+
+    private IrisDepositGenerator skyDeposit(int minimumHeight, AtomicInteger clumps) {
+        return new CountingPaletteGenerator(state("andesite"), clumps)
+                .setShape(IrisDepositShape.VANILLA_ELLIPSOID).setMinSize(17).setMaxSize(17)
+                .setMinPerChunk(60).setMaxPerChunk(60).setMinHeight(minimumHeight).setMaxHeight(400)
+                .setHeightDistribution(IrisDepositHeightDistribution.UNIFORM).setSurfaceClearance(0)
+                .setPerClumpSpawnChance(1D).setReplaceableBlocks(new KList<>("stone"));
+    }
+
     private long[] generateConfigured(long seed, boolean multicore) {
         return generateConfigured(seed, multicore, true, false, new AtomicInteger());
     }
@@ -143,10 +194,25 @@ public class IrisDepositModifierParityTest {
         return generateConfigured(seed, multicore, caveVariant, enumerablePack, caveBiomeLookups, unmatchableClumps, true);
     }
 
-    @SuppressWarnings("unchecked")
     private long[] generateConfigured(long seed, boolean multicore, boolean caveVariant, boolean enumerablePack,
                                       AtomicInteger caveBiomeLookups, AtomicInteger unmatchableClumps,
                                       boolean oreScaling) {
+        return generateConfigured(seed, multicore, caveVariant, enumerablePack, caveBiomeLookups, unmatchableClumps,
+                oreScaling, null, false);
+    }
+
+    private long[] generateConfigured(long seed, boolean multicore, boolean caveVariant, boolean enumerablePack,
+                                      AtomicInteger caveBiomeLookups, AtomicInteger unmatchableClumps,
+                                      boolean oreScaling, IrisDepositGenerator extraSurfaceDeposit) {
+        return generateConfigured(seed, multicore, caveVariant, enumerablePack, caveBiomeLookups, unmatchableClumps,
+                oreScaling, extraSurfaceDeposit, false);
+    }
+
+    @SuppressWarnings("unchecked")
+    private long[] generateConfigured(long seed, boolean multicore, boolean caveVariant, boolean enumerablePack,
+                                      AtomicInteger caveBiomeLookups, AtomicInteger unmatchableClumps,
+                                      boolean oreScaling, IrisDepositGenerator extraSurfaceDeposit,
+                                      boolean floatingHost) {
         Engine engine = mock(Engine.class, withSettings().stubOnly().defaultAnswer(RETURNS_DEEP_STUBS));
         ChunkContext context = mock(ChunkContext.class, withSettings().stubOnly().defaultAnswer(RETURNS_DEEP_STUBS));
         IrisDimension dimension = new IrisDimension();
@@ -189,6 +255,9 @@ public class IrisDepositModifierParityTest {
                     .setIncludedBiomes(new KList<>("elsewhere"));
             surface.getDeposits().add(unmatchable);
         }
+        if (extraSurfaceDeposit != null) {
+            surface.getDeposits().add(extraSurfaceDeposit);
+        }
         when(engine.getHeight()).thenReturn(48);
         when(engine.getMinHeight()).thenReturn(-64);
         when(engine.getSeedManager().getDeposit()).thenReturn(seed);
@@ -241,6 +310,9 @@ public class IrisDepositModifierParityTest {
                 }
             }
         }
+        if (floatingHost) {
+            terrain.set(8, 44, 8, state("stone"));
+        }
         MultiBurst burst = new MultiBurst("Deposit parity", () -> 4);
         when(engine.burst()).thenReturn(burst);
         try (MockedStatic<B> blocks = mockStatic(B.class, withSettings().stubOnly().defaultAnswer(CALLS_REAL_METHODS))) {