Carve terrain on demand

- eager terrain window covers the replayed object sources plus one chunk of footprint (radius 13 instead of 19 for overworld)
- content writers generate a chunk's missing terrain components before handing it out, so reads past the window stay identical
- getEagerInputRadius replaces isInputGenerationLazy

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

@@ -55,8 +55,12 @@ public interface MantleComponent extends Comparable<MantleComponent> {
         return getInputRadius();
     }
 
-    default boolean isInputGenerationLazy() {
+    /**
-        return false;
+     * The part of {@code inputRadius} generated before this component runs. Content writers generate the
+     * terrain of any chunk read beyond it on first access, so this sizes the eager window, not what may be read.
+     */
+    default int getEagerInputRadius(int inputRadius) {
+        return inputRadius;
     }
 
     default IrisData getData() {

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

@@ -67,8 +67,8 @@ public final class MantleHydrologyComponent extends IrisMantleComponent {
     }
 
     @Override
-    public boolean isInputGenerationLazy() {
+    public int getEagerInputRadius(int inputRadius) {
-        return true;
+        return 0;
     }
 
     @Override

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

@@ -128,6 +128,11 @@ public class MantleObjectComponent extends IrisMantleComponent {
         return calculateInputRadius(getRadius(), hasCollisionRules());
     }
 
+    @Override
+    public int getEagerInputRadius(int inputRadius) {
+        return Math.min(inputRadius, calculateEagerInputRadius(getRadius(), hasCollisionRules()));
+    }
+
     @Override
     public void hotload() {
         super.hotload();
@@ -272,6 +277,17 @@ public class MantleObjectComponent extends IrisMantleComponent {
         return radius > 0 ? Math.ceilDiv(radius, 16) : 0;
     }
 
+    /**
+     * Every replayed source chunk plus one chunk of placement footprint. Larger footprints read past it and
+     * get their terrain generated on first access.
+     */
+    static int calculateEagerInputRadius(int radius, boolean sourceAnchoredCollisions) {
+        int normalizedRadius = Math.max(0, radius);
+        long sourceLegs = sourceAnchoredCollisions ? 2L : 1L;
+        long inputRadius = (sourceChunkRadius(normalizedRadius) * 16L * sourceLegs) + Math.min(normalizedRadius, 16) + 1L;
+        return inputRadius >= Integer.MAX_VALUE ? Integer.MAX_VALUE : (int) inputRadius;
+    }
+
     static int calculateInputRadius(int radius, boolean sourceAnchoredCollisions) {
         int normalizedRadius = Math.max(0, radius);
         long sourceChunkRadius = sourceChunkRadius(normalizedRadius);

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

@@ -35,10 +35,12 @@ import art.arcane.iris.world.history.TransitionGenerationPlan;
 import art.arcane.iris.generation.noise.IrisGeneratorStyle;
 import art.arcane.iris.pack.value.IrisPosition;
 import art.arcane.iris.generation.block.TileData;
+import art.arcane.iris.generation.context.ChunkContext;
 import art.arcane.iris.generation.hydrology.cave.HydrologyCaveCell;
 import art.arcane.volmlib.util.collection.KSet;
 import art.arcane.volmlib.util.documentation.ChunkCoordinates;
 import art.arcane.volmlib.util.function.Function3;
+import art.arcane.volmlib.util.mantle.flag.MantleFlag;
 import art.arcane.volmlib.util.mantle.runtime.Mantle;
 import art.arcane.volmlib.util.mantle.runtime.MantleChunk;
 import art.arcane.volmlib.util.math.RNG;
@@ -90,6 +92,15 @@ public class MantleWriter implements ObjectPassPlacer, AutoCloseable {
     private final ThreadLocal<Integer> activeComponentPriority = new ThreadLocal<>();
     @Getter(AccessLevel.NONE)
     private final ThreadLocal<ObjectPlacementCapture> objectPlacementCapture = new ThreadLocal<>();
+    @Getter(AccessLevel.NONE)
+    @EqualsAndHashCode.Exclude
+    @ToString.Exclude
+    private final boolean[] terrainReady;
+    @Getter(AccessLevel.NONE)
+    @Setter(AccessLevel.NONE)
+    @EqualsAndHashCode.Exclude
+    @ToString.Exclude
+    private TerrainAccess terrainAccess;
 
     public MantleWriter(EngineMantle engineMantle, Mantle<Matter> mantle, int x, int z, int radius, boolean multicore) {
         this(engineMantle, mantle, x, z, radius, radius * 2, multicore);
@@ -104,17 +115,7 @@ public class MantleWriter implements ObjectPassPlacer, AutoCloseable {
             int accessRadius,
             boolean multicore
     ) {
-        this.engineMantle = engineMantle;
+        this(engineMantle, mantle, x, z, accessRadius);
-        this.mantle = mantle;
-        this.radius = accessRadius;
-        this.x = x;
-        this.z = z;
-        IrisComplex complex = engineMantle.getComplex();
-        this.transitionGenerationPlan = complex == null ? null : complex.getTransitionGenerationPlan();
-        // Every coordinate acquireChunk accepts lives in this window, so a flat array replaces the
-        // boxed per-block map lookup on the placement and carve hot paths.
-        this.windowSide = (this.radius * 2) + 1;
-        this.window = new AtomicReferenceArray<>(windowSide * windowSide);
 
         final boolean foliaMaintenance = J.isFolia()
                 && WorldMaintenance.isWorldMaintenanceActive(engineMantle.getEngine().getWorld().identity());
@@ -142,6 +143,42 @@ public class MantleWriter implements ObjectPassPlacer, AutoCloseable {
         }
     }
 
+    private MantleWriter(EngineMantle engineMantle, Mantle<Matter> mantle, int x, int z, int accessRadius) {
+        this.engineMantle = engineMantle;
+        this.mantle = mantle;
+        this.radius = accessRadius;
+        this.x = x;
+        this.z = z;
+        IrisComplex complex = engineMantle.getComplex();
+        this.transitionGenerationPlan = complex == null ? null : complex.getTransitionGenerationPlan();
+        // Every coordinate acquireChunk accepts lives in this window, so a flat array replaces the
+        // boxed per-block map lookup on the placement and carve hot paths.
+        this.windowSide = (this.radius * 2) + 1;
+        this.window = new AtomicReferenceArray<>(windowSide * windowSide);
+        this.terrainReady = new boolean[windowSide * windowSide];
+    }
+
+    /**
+     * A writer over one already loaded chunk, for generating that chunk's terrain components without a
+     * prefetch.
+     */
+    static MantleWriter forChunk(EngineMantle engineMantle, Mantle<Matter> mantle, MantleChunk<Matter> chunk,
+                                 int chunkX, int chunkZ) {
+        MantleWriter writer = new MantleWriter(engineMantle, mantle, chunkX, chunkZ, 0);
+        writer.window.set(0, chunk.use());
+        return writer;
+    }
+
+    /**
+     * From now on every chunk this writer hands out has its terrain components generated first. Called once
+     * the terrain passes of the window are done and before any content pass reads or writes.
+     */
+    void requireTerrainOnAccess(List<MantleComponent> terrainComponents, ChunkContext context, IrisComplex complex) {
+        terrainAccess = terrainComponents.isEmpty()
+                ? null
+                : new TerrainAccess(terrainComponents.toArray(new MantleComponent[0]), context, complex);
+    }
+
     static int resolvePrefetchParallelism(boolean foliaMaintenance, boolean multicore, int availableProcessors) {
         if (foliaMaintenance) {
             return 1;
@@ -844,20 +881,24 @@ public class MantleWriter implements ObjectPassPlacer, AutoCloseable {
             return null;
         }
 
-        while (true) {
+        MantleChunk<Matter> chunk = window.get(index);
-            MantleChunk<Matter> chunk = window.get(index);
+        while (chunk == null) {
-            if (chunk != null) {
-                return chunk;
-            }
-
             // Losing this race must release our own use, never the winner's: the winner is already
             // writing through the chunk it published.
             MantleChunk<Matter> acquired = mantle.getChunk(cx, cz).use();
             if (window.compareAndSet(index, null, acquired)) {
-                return acquired;
+                chunk = acquired;
+            } else {
+                acquired.release();
+                chunk = window.get(index);
             }
-            acquired.release();
         }
+        TerrainAccess access = terrainAccess;
+        if (access != null && !terrainReady[index]) {
+            access.ensure(chunk, cx, cz);
+            terrainReady[index] = true;
+        }
+        return chunk;
     }
 
     @ChunkCoordinates
@@ -1509,6 +1550,44 @@ public class MantleWriter implements ObjectPassPlacer, AutoCloseable {
         }
     }
 
+    private final class TerrainAccess {
+        private final MantleComponent[] components;
+        private final ChunkContext context;
+        private final IrisComplex complex;
+
+        private TerrainAccess(MantleComponent[] components, ChunkContext context, IrisComplex complex) {
+            this.components = components;
+            this.context = context;
+            this.complex = complex;
+        }
+
+        private void ensure(MantleChunk<Matter> chunk, int chunkX, int chunkZ) {
+            if (chunk.isFlagged(MantleFlag.PLANNED) || complex != null && !complex.allowsMantleChunkWrite(chunkX, chunkZ)) {
+                return;
+            }
+            for (MantleComponent component : components) {
+                if (chunk.isFlagged(component.getFlag()) || !hasPrerequisites(chunk, component)) {
+                    continue;
+                }
+                chunk.raiseFlagSuspend(component.getFlag(), () -> {
+                    try (MantleWriter terrainWriter = forChunk(engineMantle, mantle, chunk, chunkX, chunkZ)) {
+                        terrainWriter.withComponentPriority(component.getPriority(),
+                                () -> component.generateLayer(terrainWriter, chunkX, chunkZ, context));
+                    }
+                });
+            }
+        }
+
+        private static boolean hasPrerequisites(MantleChunk<Matter> chunk, MantleComponent component) {
+            for (MantleFlag prerequisite : component.getPrerequisiteFlags()) {
+                if (!chunk.isFlagged(prerequisite)) {
+                    return false;
+                }
+            }
+            return true;
+        }
+    }
+
     public final class ObjectPlacementCapture implements AutoCloseable {
         private final ObjectContinuationBundle.PlacementKey key;
         private final Long2ObjectOpenHashMap<Matter> fragments = new Long2ObjectOpenHashMap<>();

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

@@ -90,7 +90,7 @@ public interface MatterGenerator {
         int prefetchRadius = passPlans[0].passChunkRadius();
         LongOpenHashSet partialChunks = new LongOpenHashSet();
         List<MantleComponent> requiredComponents = enabledComponents();
-        List<MantleFlag> terrainFlags = terrainFlags(requiredComponents);
+        boolean terrainOnAccess = false;
 
         try (MantleWriter writer = new MantleWriter(
                 getEngine().getMantle(),
@@ -129,6 +129,10 @@ public interface MatterGenerator {
                     if (enabledComponentCount == 0) {
                         continue;
                     }
+                    if (!terrainOnAccess && includesContent(enabledComponents, enabledComponentCount)) {
+                        writer.requireTerrainOnAccess(terrainComponents(requiredComponents), context, complex);
+                        terrainOnAccess = true;
+                    }
 
                     // Every multicore generation claims its components through the in-flight map.
                     // A caller outside the pool spreads its window across the pool; a pool thread
@@ -185,9 +189,6 @@ public interface MatterGenerator {
                                 continue;
                             }
 
-                            if (phase == MatterGenerationPhase.CONTENT) {
-                                requireTerrainPhase(chunk, passX, passZ, terrainFlags);
-                            }
                             int eligibleComponentCount = 0;
                             for (int componentIndex = 0; componentIndex < enabledComponentCount; componentIndex++) {
                                 MantleComponent component = enabledComponents[componentIndex];
@@ -303,9 +304,8 @@ public interface MatterGenerator {
                         : 0;
                 int componentInputRadius = component.getInputRadius(x, z, invocationChunkRadius, context);
                 passAccessInputRadius = Math.max(passAccessInputRadius, componentInputRadius);
-                if (!component.isInputGenerationLazy()) {
+                passGenerationInputRadius = Math.max(passGenerationInputRadius,
-                    passGenerationInputRadius = Math.max(passGenerationInputRadius, componentInputRadius);
+                        component.getEagerInputRadius(componentInputRadius));
-                }
             }
             int accessInvocationRadius = accessDownstreamBlockRadius + passBlockRadius;
             int generationInvocationRadius = generationDownstreamBlockRadius + passBlockRadius;
@@ -332,24 +332,23 @@ public interface MatterGenerator {
         return List.copyOf(components);
     }
 
-    private static List<MantleFlag> terrainFlags(List<MantleComponent> components) {
+    private static boolean includesContent(MantleComponent[] components, int count) {
-        List<MantleFlag> flags = new ArrayList<>();
+        for (int index = 0; index < count; index++) {
-        for (MantleComponent component : components) {
+            if (components[index].getGenerationPhase() == MatterGenerationPhase.CONTENT) {
-            if (component.getGenerationPhase() == MatterGenerationPhase.TERRAIN) {
+                return true;
-                flags.add(component.getFlag());
             }
         }
-        return List.copyOf(flags);
+        return false;
     }
 
-    private static void requireTerrainPhase(MantleChunk<Matter> chunk, int chunkX, int chunkZ,
+    private static List<MantleComponent> terrainComponents(List<MantleComponent> components) {
-                                            List<MantleFlag> flags) {
+        List<MantleComponent> terrain = new ArrayList<>();
-        for (MantleFlag flag : flags) {
+        for (MantleComponent component : components) {
-            if (!chunk.isFlagged(flag)) {
+            if (component.getGenerationPhase() == MatterGenerationPhase.TERRAIN) {
-                throw new IllegalStateException("Content generation at " + chunkX + "," + chunkZ
+                terrain.add(component);
-                        + " requires completed terrain component " + flag.name());
             }
         }
+        return terrain;
     }
 
     private static boolean hasCompletedComponents(MantleChunk<Matter> chunk, List<MantleComponent> components) {

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

@@ -45,6 +45,7 @@ import java.util.List;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.assertFalse;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyInt;
@@ -188,6 +189,23 @@ public class MantleObjectComponentBoundaryRadiusTest {
                 MantleObjectComponent.calculateInputRadius(Integer.MAX_VALUE, true));
     }
 
+    @Test
+    public void eagerInputRadiusCoversEverySourceChunkPlusOneChunkOfFootprint() {
+        assertEquals(129, MantleObjectComponent.calculateEagerInputRadius(103, false));
+        assertEquals(65, MantleObjectComponent.calculateEagerInputRadius(33, false));
+        assertEquals(113, MantleObjectComponent.calculateEagerInputRadius(33, true));
+        assertEquals(27, MantleObjectComponent.calculateEagerInputRadius(10, false));
+        assertEquals(1, MantleObjectComponent.calculateEagerInputRadius(0, false));
+        for (int radius = 0; radius < 300; radius++) {
+            for (boolean collisions : new boolean[]{false, true}) {
+                assertTrue(MantleObjectComponent.calculateEagerInputRadius(radius, collisions)
+                        <= MantleObjectComponent.calculateInputRadius(radius, collisions));
+            }
+        }
+        assertEquals(Integer.MAX_VALUE,
+                MantleObjectComponent.calculateEagerInputRadius(Integer.MAX_VALUE, true));
+    }
+
     @Test
     public void proceduralTreeTransformsContributeToRadius() {
         IrisObjectPlacement placement = new IrisObjectPlacement()

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

@@ -309,8 +309,8 @@ public class MatterGeneratorCarvePassRadiusTest {
         }
 
         @Override
-        public boolean isInputGenerationLazy() {
+        public int getEagerInputRadius(int inputRadius) {
-            return lazyInputGeneration;
+            return lazyInputGeneration ? 0 : inputRadius;
         }
 
         @Override

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

@@ -387,27 +387,94 @@ public class MatterGeneratorConcurrencyTest {
     }
 
     @Test
-    public void contentPhaseRequiresTerrainEvenWhenItsExplicitPrerequisiteIsMissing() {
+    public void contentPhaseGeneratesTerrainOfEveryChunkBeforeItIsReadOrWritten() {
         GeneratorFixture fixture = new GeneratorFixture(true);
+        List<String> events = new ArrayList<>();
         RecordingComponent terrain = new RecordingComponent(ReservedFlag.CARVED, 0, 0) {
             @Override
             public MatterGenerationPhase getGenerationPhase() {
                 return MatterGenerationPhase.TERRAIN;
             }
+
+            @Override
+            public void generateLayer(MantleWriter writer, int x, int z, ChunkContext context) {
+                assertSame(fixture.mantle.getChunk(x, z), writer.acquireChunk(x, z));
+                events.add("terrain " + x + "," + z);
+            }
         };
         RecordingComponent content = new RecordingComponent(ReservedFlag.OBJECT, 1, 0) {
             @Override
             public MantleFlag[] getPrerequisiteFlags() {
                 return new MantleFlag[]{ReservedFlag.CARVED};
             }
+
+            @Override
+            public int getInputRadius() {
+                return 48;
+            }
+
+            @Override
+            public int getEagerInputRadius(int inputRadius) {
+                return 0;
+            }
+
+            @Override
+            public void generateLayer(MantleWriter writer, int x, int z, ChunkContext context) {
+                events.add("content " + x + "," + z);
+                assertSame(fixture.mantle.getChunk(x + 3, z), writer.acquireChunk(x + 3, z));
+                writer.acquireChunk(x + 3, z);
+                events.add("read " + (x + 3) + "," + z);
+            }
         };
         TestMatterGenerator generator = fixture.generator(List.of(
                 new MantlePass(List.of(terrain), 0, 0),
                 new MantlePass(List.of(content), 0, 0)));
 
-        assertThrows(IllegalStateException.class,
+        generator.generateTerrainMatter(0, 0, false, fixture.context);
-                () -> generator.generateContentMatter(0, 0, false, fixture.context));
+        assertEquals(List.of("terrain 0,0"), events);
-        assertFalse(fixture.mantle.getChunk(0, 0).isFlagged(MantleFlag.PLANNED));
+        generator.generateContentMatter(0, 0, false, fixture.context);
+
+        assertEquals(List.of("terrain 0,0", "content 0,0", "terrain 3,0", "read 3,0"), events);
+        assertTrue(fixture.mantle.getChunk(0, 0).isFlagged(MantleFlag.PLANNED));
+        assertTrue(fixture.mantle.getChunk(3, 0).isFlagged(ReservedFlag.CARVED));
+        assertFalse(fixture.mantle.getChunk(3, 0).isFlagged(ReservedFlag.OBJECT));
+    }
+
+    @Test
+    public void contentPhaseGeneratesMissingTerrainOfItsOwnChunk() {
+        GeneratorFixture fixture = new GeneratorFixture(true);
+        AtomicInteger terrainRuns = new AtomicInteger();
+        RecordingComponent terrain = new RecordingComponent(ReservedFlag.CARVED, 0, 0) {
+            @Override
+            public MatterGenerationPhase getGenerationPhase() {
+                return MatterGenerationPhase.TERRAIN;
+            }
+
+            @Override
+            public void generateLayer(MantleWriter writer, int x, int z, ChunkContext context) {
+                terrainRuns.incrementAndGet();
+            }
+        };
+        RecordingComponent content = new RecordingComponent(ReservedFlag.OBJECT, 1, 0) {
+            @Override
+            public MantleFlag[] getPrerequisiteFlags() {
+                return new MantleFlag[]{ReservedFlag.CARVED};
+            }
+
+            @Override
+            public void generateLayer(MantleWriter writer, int x, int z, ChunkContext context) {
+                assertEquals(1, terrainRuns.get());
+            }
+        };
+        TestMatterGenerator generator = fixture.generator(List.of(
+                new MantlePass(List.of(terrain), 0, 0),
+                new MantlePass(List.of(content), 0, 0)));
+
+        generator.generateContentMatter(0, 0, false, fixture.context);
+
+        assertEquals(1, terrainRuns.get());
+        assertTrue(fixture.mantle.getChunk(0, 0).isFlagged(ReservedFlag.OBJECT));
+        assertTrue(fixture.mantle.getChunk(0, 0).isFlagged(MantleFlag.PLANNED));
     }
 
     @Test