Avoid creating SliceShape when retrieving Voxelshape faces

SliceShape is not always the ideal shape, as sometimes the
face result is empty or full cube - but is represented as
SliceShape. Additionally, sometimes SliceShape should be
empty but isEmpty() is false.

fabric/src/main/java/ca/spottedleaf/moonrise/fabric/mixin/command/ClientSuggestionProviderMixin.java

@@ -9,12 +9,12 @@ import org.spongepowered.asm.mixin.Mixin;
 @Mixin(ClientSuggestionProvider.class)
 abstract class ClientSuggestionProviderMixin implements CommandClientCommandSource, FabricClientCommandSource {
     @Override
-    public void moonrise$sendSuccess(final Component message) {
+    public final void moonrise$sendSuccess(final Component message) {
         this.sendFeedback(message);
     }
 
     @Override
-    public void moonrise$sendFailure(final Component message) {
+    public final void moonrise$sendFailure(final Component message) {
         this.sendError(message);
     }
 }

neoforge/src/main/java/ca/spottedleaf/moonrise/neoforge/NeoForgeHooks.java

@@ -2,7 +2,6 @@ package ca.spottedleaf.moonrise.neoforge;
 
 import ca.spottedleaf.moonrise.common.PlatformHooks;
 import ca.spottedleaf.moonrise.common.util.CoordinateUtils;
-import ca.spottedleaf.moonrise.patches.chunk_system.scheduling.ChunkHolderManager;
 import ca.spottedleaf.moonrise.patches.chunk_system.scheduling.NewChunkHolder;
 import net.minecraft.core.BlockPos;
 import net.minecraft.nbt.CompoundTag;
@@ -15,7 +14,6 @@ import net.minecraft.world.level.ChunkPos;
 import net.minecraft.world.level.EmptyBlockGetter;
 import net.minecraft.world.level.Explosion;
 import net.minecraft.world.level.Level;
-import net.minecraft.world.level.LevelAccessor;
 import net.minecraft.world.level.block.state.BlockState;
 import net.minecraft.world.level.chunk.ChunkAccess;
 import net.minecraft.world.level.chunk.ImposterProtoChunk;

neoforge/src/main/java/ca/spottedleaf/moonrise/neoforge/mixin/command/ClientCommandSourceStackMixin.java

@@ -25,12 +25,12 @@ abstract class ClientCommandSourceStackMixin extends CommandSourceStack implemen
     public abstract void sendSuccess(Supplier<Component> message, boolean sendToAdmins);
 
     @Override
-    public void moonrise$sendFailure(final Component message) {
+    public final void moonrise$sendFailure(final Component message) {
         this.sendFailure(message);
     }
 
     @Override
-    public void moonrise$sendSuccess(final Component message) {
+    public final void moonrise$sendSuccess(final Component message) {
         this.sendSuccess(() -> message, true);
     }
 }

src/main/java/ca/spottedleaf/moonrise/mixin/chunk_system/ServerChunkCache$MainThreadExecutorMixin.java

@@ -11,9 +11,9 @@ import org.spongepowered.asm.mixin.Shadow;
 @Mixin(ServerChunkCache.MainThreadExecutor.class)
 abstract class ServerChunkCache$MainThreadExecutorMixin extends BlockableEventLoop<Runnable> {
 
-    @Shadow(aliases = "this$0")
+    @Shadow(aliases = "this$0") // Neoforge
     @Final
-    ServerChunkCache field_18810;
+    ServerChunkCache field_18810; // Fabric
 
     protected ServerChunkCache$MainThreadExecutorMixin(String string) {
         super(string);

src/main/java/ca/spottedleaf/moonrise/mixin/chunk_system/StructureTemplate$PaletteMixin.java

@@ -27,7 +27,7 @@ abstract class StructureTemplate$PaletteMixin {
                     value = "RETURN"
             )
     )
-    private <K, V> void makeCacheCHM(final CallbackInfo ci) {
+    private void makeCacheCHM(final CallbackInfo ci) {
         this.cache = new ConcurrentHashMap<>();
     }
 }

src/main/java/ca/spottedleaf/moonrise/mixin/collisions/BlockStateBaseMixin.java

@@ -65,13 +65,19 @@ abstract class BlockStateBaseMixin extends StateHolder<Block, BlockState> implem
     private AABB constantAABBCollision;
 
     @Unique
-    private static void initCaches(final VoxelShape shape) {
+    private static void initCaches(final VoxelShape shape, final boolean neighbours) {
         ((CollisionVoxelShape)shape).moonrise$isFullBlock();
         ((CollisionVoxelShape)shape).moonrise$occludesFullBlock();
         shape.toAabbs();
         if (!shape.isEmpty()) {
             shape.bounds();
         }
+        if (neighbours) {
+            for (final Direction direction : DIRECTIONS_CACHED) {
+                initCaches(Shapes.getFaceShape(shape, direction), false);
+                initCaches(shape.getFaceShape(direction), false);
+            }
+        }
     }
 
     /**
@@ -98,17 +104,13 @@ abstract class BlockStateBaseMixin extends StateHolder<Block, BlockState> implem
             this.occludesFullBlock = ((CollisionVoxelShape)collisionShape).moonrise$occludesFullBlock();
             this.emptyCollisionShape = collisionShape.isEmpty();
             // init caches
-            initCaches(collisionShape);
-            if (collisionShape != Shapes.empty() && collisionShape != Shapes.block()) {
-                for (final Direction direction : DIRECTIONS_CACHED) {
-                    // initialise the directional face shape cache as well
-                    final VoxelShape shape = Shapes.getFaceShape(collisionShape, direction);
-                    initCaches(shape);
-                }
+            initCaches(collisionShape, true);
+            if (this.constantCollisionShape != null) {
+                initCaches(this.constantCollisionShape, true);
             }
             if (this.cache.occlusionShapes != null) {
                 for (final VoxelShape shape : this.cache.occlusionShapes) {
-                    initCaches(shape);
+                    initCaches(shape, false);
                 }
             }
         } else {

src/main/java/ca/spottedleaf/moonrise/mixin/collisions/DiscreteVoxelShapeMixin.java

@@ -60,7 +60,7 @@ abstract class DiscreteVoxelShapeMixin implements CollisionDiscreteVoxelShape {
             }
         }
 
-        final boolean hasSingleAABB = sizeX == 1 && sizeY == 1 && sizeZ == 1 && !isEmpty && discreteVoxelShape.isFull(0, 0, 0);
+        final boolean hasSingleAABB = sizeX == 1 && sizeY == 1 && sizeZ == 1 && !isEmpty && (voxelSet[0] & 1L) != 0L;
 
         final int minFullX = discreteVoxelShape.firstFull(Direction.Axis.X);
         final int minFullY = discreteVoxelShape.firstFull(Direction.Axis.Y);

src/main/java/ca/spottedleaf/moonrise/mixin/collisions/VoxelShapeMixin.java

@@ -23,7 +23,6 @@ import net.minecraft.world.phys.shapes.BooleanOp;
 import net.minecraft.world.phys.shapes.DiscreteVoxelShape;
 import net.minecraft.world.phys.shapes.OffsetDoubleList;
 import net.minecraft.world.phys.shapes.Shapes;
-import net.minecraft.world.phys.shapes.SliceShape;
 import net.minecraft.world.phys.shapes.VoxelShape;
 import org.spongepowered.asm.mixin.Final;
 import org.spongepowered.asm.mixin.Mixin;
@@ -208,13 +207,13 @@ abstract class VoxelShapeMixin implements CollisionVoxelShape {
 
         if (direction.getAxisDirection() == Direction.AxisDirection.POSITIVE) {
             if (DoubleMath.fuzzyEquals(this.max(axis), 1.0, CollisionUtil.COLLISION_EPSILON)) {
-                ret = tryForceBlock(new SliceShape((VoxelShape)(Object)this, axis, this.shape.getSize(axis) - 1));
+                ret = CollisionUtil.sliceShape((VoxelShape)(Object)this, axis, this.shape.getSize(axis) - 1);
             } else {
                 ret = Shapes.empty();
             }
         } else {
             if (DoubleMath.fuzzyEquals(this.min(axis), 0.0, CollisionUtil.COLLISION_EPSILON)) {
-                ret = tryForceBlock(new SliceShape((VoxelShape)(Object)this, axis, 0));
+                ret = CollisionUtil.sliceShape((VoxelShape)(Object)this, axis, 0);
             } else {
                 ret = Shapes.empty();
             }
@@ -225,24 +224,6 @@ abstract class VoxelShapeMixin implements CollisionVoxelShape {
         return ret;
     }
 
-    @Unique
-    private static VoxelShape tryForceBlock(final VoxelShape other) {
-        if (other == Shapes.block()) {
-            return other;
-        }
-
-        final AABB otherAABB = ((CollisionVoxelShape)other).moonrise$getSingleAABBRepresentation();
-        if (otherAABB == null) {
-            return other;
-        }
-
-        if (((CollisionVoxelShape)Shapes.block()).moonrise$getSingleAABBRepresentation().equals(otherAABB)) {
-            return Shapes.block();
-        }
-
-        return other;
-    }
-
     @Unique
     private boolean computeOccludesFullBlock() {
         if (this.isEmpty) {
@@ -353,6 +334,115 @@ abstract class VoxelShapeMixin implements CollisionVoxelShape {
         return this.isEmpty;
     }
 
+    /**
+     * @author Spottedleaf
+     * @reason Use cached bounds
+     */
+    @Overwrite
+    public VoxelShape singleEncompassing() {
+        if (this.isEmpty) {
+            return Shapes.empty();
+        }
+        return Shapes.create(this.bounds());
+    }
+
+    /**
+     * @author Spottedleaf
+     * @reason Optimise implementation to avoid indirection
+     */
+    @Overwrite
+    protected double get(final Direction.Axis axis, final int idx) {
+        switch (axis) {
+            case X: {
+                return this.rootCoordinatesX[idx] + this.offsetX;
+            }
+            case Y: {
+                return this.rootCoordinatesY[idx] + this.offsetY;
+            }
+            case Z: {
+                return this.rootCoordinatesZ[idx] + this.offsetZ;
+            }
+            default: {
+                throw new IllegalStateException("Unknown axis: " + axis);
+            }
+        }
+    }
+
+    /**
+     * @author Spottedleaf
+     * @reason Optimise implementation to avoid indirection
+     */
+    @Overwrite
+    public int findIndex(final Direction.Axis axis, final double value) {
+        switch (axis) {
+            case X: {
+                final double[] values = this.rootCoordinatesX;
+                return CollisionUtil.findFloor(
+                    values, value - this.offsetX, 0, values.length - 1
+                );
+            }
+            case Y: {
+                final double[] values = this.rootCoordinatesY;
+                return CollisionUtil.findFloor(
+                    values, value - this.offsetY, 0, values.length - 1
+                );
+            }
+            case Z: {
+                final double[] values = this.rootCoordinatesZ;
+                return CollisionUtil.findFloor(
+                    values, value - this.offsetZ, 0, values.length - 1
+                );
+            }
+            default: {
+                throw new IllegalStateException("Unknown axis: " + axis);
+            }
+        }
+    }
+
+    @Unique
+    private VoxelShape calculateFaceDirect(final Direction direction, final Direction.Axis axis, final double[] coords, final double offset) {
+        if (coords.length == 2 &&
+            DoubleMath.fuzzyEquals(coords[0] + offset, 0.0, CollisionUtil.COLLISION_EPSILON) &&
+            DoubleMath.fuzzyEquals(coords[1] + offset, 1.0, CollisionUtil.COLLISION_EPSILON)) {
+            return (VoxelShape)(Object)this;
+        }
+
+        final boolean positiveDir = direction.getAxisDirection() == Direction.AxisDirection.POSITIVE;
+
+        // see findIndex
+        final int index = CollisionUtil.findFloor(
+            coords, (positiveDir ? (1.0 - CollisionUtil.COLLISION_EPSILON) : (0.0 + CollisionUtil.COLLISION_EPSILON)) - offset,
+            0, coords.length - 1
+        );
+
+        return CollisionUtil.sliceShape(
+            (VoxelShape)(Object)this, axis, index
+        );
+    }
+
+    /**
+     * @author Spottedleaf
+     * @reason Avoid creating SliceShape
+     */
+    @Overwrite
+    public VoxelShape calculateFace(final Direction direction) {
+        final Direction.Axis axis = direction.getAxis();
+        switch (axis) {
+            case X: {
+                return this.calculateFaceDirect(direction, axis, this.rootCoordinatesX, this.offsetX);
+            }
+            case Y: {
+                return this.calculateFaceDirect(direction, axis, this.rootCoordinatesY, this.offsetY);
+            }
+            case Z: {
+                return this.calculateFaceDirect(direction, axis, this.rootCoordinatesZ, this.offsetZ);
+            }
+            default: {
+                throw new IllegalStateException("Unknown axis: " + axis);
+            }
+        }
+    }
+
     /**
      * @author Spottedleaf
      * @reason Route to optimized collision method
@@ -382,11 +472,12 @@ abstract class VoxelShapeMixin implements CollisionVoxelShape {
     }
 
     @Unique
-    private static DoubleList offsetList(final DoubleList src, final double by) {
-        if (src instanceof OffsetDoubleList offsetDoubleList) {
-            return new OffsetDoubleList(offsetDoubleList.delegate, by + offsetDoubleList.offset);
+    private static DoubleList offsetList(final double[] src, final double by) {
+        final DoubleArrayList wrap = DoubleArrayList.wrap(src);
+        if (by == 0.0) {
+            return wrap;
         }
-        return new OffsetDoubleList(src, by);
+        return new OffsetDoubleList(wrap, by);
     }
 
     /**
@@ -401,9 +492,9 @@ abstract class VoxelShapeMixin implements CollisionVoxelShape {
 
         final ArrayVoxelShape ret = new ArrayVoxelShape(
             this.shape,
-                offsetList(this.getCoords(Direction.Axis.X), x),
-                offsetList(this.getCoords(Direction.Axis.Y), y),
-                offsetList(this.getCoords(Direction.Axis.Z), z)
+            offsetList(this.rootCoordinatesX, this.offsetX + x),
+            offsetList(this.rootCoordinatesY, this.offsetY + y),
+            offsetList(this.rootCoordinatesZ, this.offsetZ + z)
         );
 
         final CachedToAABBs cachedToAABBs = this.cachedToAABBs;
@@ -416,10 +507,12 @@ abstract class VoxelShapeMixin implements CollisionVoxelShape {
 
     @Unique
     private List<AABB> toAabbsUncached() {
-        final List<AABB> ret = new ArrayList<>();
+        final List<AABB> ret;
         if (this.singleAABBRepresentation != null) {
+            ret = new ArrayList<>(1);
             ret.add(this.singleAABBRepresentation);
         } else {
+            ret = new ArrayList<>();
             final double[] coordsX = this.rootCoordinatesX;
             final double[] coordsY = this.rootCoordinatesY;
             final double[] coordsZ = this.rootCoordinatesZ;
@@ -718,6 +811,11 @@ abstract class VoxelShapeMixin implements CollisionVoxelShape {
 
         final List<AABB> aabbs = this.toAabbs();
 
+        if (aabbs.isEmpty()) {
+            // We are a SliceShape, which does not properly fill isEmpty for every case
+            return Shapes.empty();
+        }
+
         if (aabbs.size() == 1) {
             final AABB singleAABB = aabbs.get(0);
             final VoxelShape ret = Shapes.create(singleAABB);

src/main/java/ca/spottedleaf/moonrise/mixin/serverlist/ServerAddressResolverMixin.java

@@ -4,8 +4,6 @@ import net.minecraft.client.multiplayer.resolver.ServerAddressResolver;
 import org.spongepowered.asm.mixin.Mixin;
 import org.spongepowered.asm.mixin.injection.At;
 import org.spongepowered.asm.mixin.injection.Redirect;
-import java.net.Inet4Address;
-import java.net.Inet6Address;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
 
@@ -29,9 +27,10 @@ interface ServerAddressResolverMixin {
     private static InetAddress eliminateRDNS(final String name) throws UnknownHostException {
         final InetAddress ret = InetAddress.getByName(name);
 
-        if (ret instanceof Inet4Address || ret instanceof Inet6Address) {
+        final byte[] address = ret.getAddress();
+        if (address != null) {
             // pass name to prevent rDNS
-            return InetAddress.getByAddress(name, ret.getAddress());
+            return InetAddress.getByAddress(name, address);
         }
 
         return ret;

src/main/java/ca/spottedleaf/moonrise/patches/collisions/CollisionUtil.java

@@ -35,9 +35,11 @@ import net.minecraft.world.phys.shapes.DiscreteVoxelShape;
 import net.minecraft.world.phys.shapes.EntityCollisionContext;
 import net.minecraft.world.phys.shapes.OffsetDoubleList;
 import net.minecraft.world.phys.shapes.Shapes;
+import net.minecraft.world.phys.shapes.SliceShape;
 import net.minecraft.world.phys.shapes.VoxelShape;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Objects;
 import java.util.function.BiPredicate;
 import java.util.function.Predicate;
 
@@ -162,7 +164,8 @@ public final class CollisionUtil {
 
     // startIndex and endIndex inclusive
     // assumes indices are in range of array
-    private static int findFloor(final double[] values, final double value, int startIndex, int endIndex) {
+    public static int findFloor(final double[] values, final double value, int startIndex, int endIndex) {
+        Objects.checkFromToIndex(startIndex, endIndex + 1, values.length);
         do {
             final int middle = (startIndex + endIndex) >>> 1;
             final double middleVal = values[middle];
@@ -177,6 +180,214 @@ public final class CollisionUtil {
         return startIndex - 1;
     }
 
+    private static VoxelShape sliceShapeVanilla(final VoxelShape src, final Direction.Axis axis,
+                                                final int index) {
+        return new SliceShape(src, axis, index);
+    }
+
+    private static DoubleList offsetList(final double[] src, final double by) {
+        final DoubleArrayList wrap = DoubleArrayList.wrap(src);
+        if (by == 0.0) {
+            return wrap;
+        }
+        return new OffsetDoubleList(wrap, by);
+    }
+
+    private static VoxelShape sliceShapeOptimised(final VoxelShape src, final Direction.Axis axis,
+                                                  final int index) {
+        // assume index in range
+        final double off_x = ((CollisionVoxelShape)src).moonrise$offsetX();
+        final double off_y = ((CollisionVoxelShape)src).moonrise$offsetY();
+        final double off_z = ((CollisionVoxelShape)src).moonrise$offsetZ();
+
+        final double[] coords_x = ((CollisionVoxelShape)src).moonrise$rootCoordinatesX();
+        final double[] coords_y = ((CollisionVoxelShape)src).moonrise$rootCoordinatesY();
+        final double[] coords_z = ((CollisionVoxelShape)src).moonrise$rootCoordinatesZ();
+
+        final CachedShapeData cached_shape_data = ((CollisionVoxelShape)src).moonrise$getCachedVoxelData();
+
+        // note: size = coords.length - 1
+        final int size_x = cached_shape_data.sizeX();
+        final int size_y = cached_shape_data.sizeY();
+        final int size_z = cached_shape_data.sizeZ();
+
+        final long[] bitset = cached_shape_data.voxelSet();
+
+        final DoubleList list_x;
+        final DoubleList list_y;
+        final DoubleList list_z;
+        final int shape_sx;
+        final int shape_ex;
+        final int shape_sy;
+        final int shape_ey;
+        final int shape_sz;
+        final int shape_ez;
+
+        switch (axis) {
+            case X: {
+                // validate index
+                if (index < 0 || index >= size_x) {
+                    return Shapes.empty();
+                }
+
+                // test if input is already "sliced"
+                if (coords_x.length == 2 && (coords_x[0] + off_x) == 0.0 && (coords_x[1] + off_x) == 1.0) {
+                    return src;
+                }
+
+                // test if result would be full box
+                if (coords_y.length == 2 && coords_z.length == 2 &&
+                    (coords_y[0] + off_y) == 0.0 && (coords_y[1] + off_y) == 1.0 &&
+                    (coords_z[0] + off_z) == 0.0 && (coords_z[1] + off_z) == 1.0) {
+                    // note: size_y == size_z == 1
+                    final int bitIdx = 0 + 0*size_z + index*(size_z*size_y);
+                    return (bitset[bitIdx >>> 6] & (1L << bitIdx)) == 0L ? Shapes.empty() : Shapes.block();
+                }
+
+                list_x = ZERO_ONE;
+                list_y = offsetList(coords_y, off_y);
+                list_z = offsetList(coords_z, off_z);
+                shape_sx = index;
+                shape_ex = index + 1;
+                shape_sy = 0;
+                shape_ey = size_y;
+                shape_sz = 0;
+                shape_ez = size_z;
+
+                break;
+            }
+            case Y: {
+                // validate index
+                if (index < 0 || index >= size_y) {
+                    return Shapes.empty();
+                }
+
+                // test if input is already "sliced"
+                if (coords_y.length == 2 && (coords_y[0] + off_y) == 0.0 && (coords_y[1] + off_y) == 1.0) {
+                    return src;
+                }
+
+                // test if result would be full box
+                if (coords_x.length == 2 && coords_z.length == 2 &&
+                    (coords_x[0] + off_x) == 0.0 && (coords_x[1] + off_x) == 1.0 &&
+                    (coords_z[0] + off_z) == 0.0 && (coords_z[1] + off_z) == 1.0) {
+                    // note: size_x == size_z == 1
+                    final int bitIdx = 0 + index*size_z + 0*(size_z*size_y);
+                    return (bitset[bitIdx >>> 6] & (1L << bitIdx)) == 0L ? Shapes.empty() : Shapes.block();
+                }
+
+                list_x = offsetList(coords_x, off_x);
+                list_y = ZERO_ONE;
+                list_z = offsetList(coords_z, off_z);
+                shape_sx = 0;
+                shape_ex = size_x;
+                shape_sy = index;
+                shape_ey = index + 1;
+                shape_sz = 0;
+                shape_ez = size_z;
+
+                break;
+            }
+            case Z: {
+                // validate index
+                if (index < 0 || index >= size_z) {
+                    return Shapes.empty();
+                }
+
+                // test if input is already "sliced"
+                if (coords_z.length == 2 && (coords_z[0] + off_z) == 0.0 && (coords_z[1] + off_z) == 1.0) {
+                    return src;
+                }
+
+                // test if result would be full box
+                if (coords_x.length == 2 && coords_y.length == 2 &&
+                    (coords_x[0] + off_x) == 0.0 && (coords_x[1] + off_x) == 1.0 &&
+                    (coords_y[0] + off_y) == 0.0 && (coords_y[1] + off_y) == 1.0) {
+                    // note: size_x == size_y == 1
+                    final int bitIdx = index + 0*size_z + 0*(size_z*size_y);
+                    return (bitset[bitIdx >>> 6] & (1L << bitIdx)) == 0L ? Shapes.empty() : Shapes.block();
+                }
+
+                list_x = offsetList(coords_x, off_x);
+                list_y = offsetList(coords_y, off_y);
+                list_z = ZERO_ONE;
+                shape_sx = 0;
+                shape_ex = size_x;
+                shape_sy = 0;
+                shape_ey = size_y;
+                shape_sz = index;
+                shape_ez = index + 1;
+
+                break;
+            }
+            default: {
+                throw new IllegalStateException("Unknown axis: " + axis);
+            }
+        }
+
+        final int local_len_x = shape_ex - shape_sx;
+        final int local_len_y = shape_ey - shape_sy;
+        final int local_len_z = shape_ez - shape_sz;
+
+        final BitSetDiscreteVoxelShape shape = new BitSetDiscreteVoxelShape(local_len_x, local_len_y, local_len_z);
+
+        final int idx_off = shape_sz + shape_sy*size_z + shape_sx*(size_z*size_y);
+        for (int x = 0; x < local_len_x; ++x) {
+            boolean setX = false;
+            for (int y = 0; y < local_len_y; ++y) {
+                boolean setY = false;
+                for (int z = 0; z < local_len_z; ++z) {
+                    final int unslicedIdx = idx_off + z + y*size_z + x*(size_z*size_y);
+                    if ((bitset[unslicedIdx >>> 6] & (1L << unslicedIdx)) == 0L) {
+                        continue;
+                    }
+
+                    setY = true;
+                    setX = true;
+                    shape.zMin = Math.min(shape.zMin, z);
+                    shape.zMax = Math.max(shape.zMax, z + 1);
+
+                    shape.storage.set(
+                        z + y*local_len_z + x*(local_len_y*local_len_z)
+                    );
+                }
+
+                if (setY) {
+                    shape.yMin = Math.min(shape.yMin, y);
+                    shape.yMax = Math.max(shape.yMax, y + 1);
+                }
+            }
+            if (setX) {
+                shape.xMin = Math.min(shape.xMin, x);
+                shape.xMax = Math.max(shape.xMax, x + 1);
+            }
+        }
+
+        return shape.isEmpty() ? Shapes.empty() : new ArrayVoxelShape(
+            shape, list_x, list_y, list_z
+        );
+    }
+
+    private static final boolean DEBUG_SLICE_SHAPE = false;
+
+    public static VoxelShape sliceShape(final VoxelShape src, final Direction.Axis axis,
+                                        final int index) {
+        final VoxelShape ret = sliceShapeOptimised(src, axis, index);
+        if (DEBUG_SLICE_SHAPE) {
+            final VoxelShape vanilla = sliceShapeVanilla(src, axis, index);
+            if (!equals(ret, vanilla)) {
+                // special case: SliceShape is not empty when it should be!
+                if (areAnyFull(ret.shape) || areAnyFull(vanilla.shape)) {
+                    equals(ret, vanilla);
+                    sliceShapeOptimised(src, axis, index);
+                    throw new IllegalStateException("Slice shape mismatch");
+                }
+            }
+        }
+
+        return ret;
+    }
+
     public static boolean voxelShapeIntersectNoEmpty(final VoxelShape voxel, final AABB aabb) {
         if (voxel.isEmpty()) {
             return false;
@@ -1306,7 +1517,7 @@ public final class CollisionUtil {
             return true;
         } else if (isEmpty1 ^ isEmpty2) {
             return false;
-        }
+        } // else: isEmpty1 = isEmpty2 = false
 
         if (cachedShapeData1.hasSingleAABB() != cachedShapeData2.hasSingleAABB()) {
             return false;
@@ -1327,6 +1538,12 @@ public final class CollisionUtil {
 
     // useful only for testing
     public static boolean equals(final VoxelShape shape1, final VoxelShape shape2) {
+        if (shape1.isEmpty() & shape2.isEmpty()) {
+            return true;
+        } else if (shape1.isEmpty() ^ shape2.isEmpty()) {
+            return false;
+        }
+
         if (!equals(shape1.shape, shape2.shape)) {
             return false;
         }
@@ -1336,6 +1553,84 @@ public final class CollisionUtil {
                 shape1.getCoords(Direction.Axis.Z).equals(shape2.getCoords(Direction.Axis.Z));
     }
 
+    public static boolean areAnyFull(final DiscreteVoxelShape shape) {
+        if (shape.isEmpty()) {
+            return false;
+        }
+
+        final int sizeX = shape.getXSize();
+        final int sizeY = shape.getYSize();
+        final int sizeZ = shape.getZSize();
+
+        for (int x = 0; x < sizeX; ++x) {
+            for (int y = 0; y < sizeY; ++y) {
+                for (int z = 0; z < sizeZ; ++z) {
+                    if (shape.isFull(x, y, z)) {
+                        return true;
+                    }
+                }
+            }
+        }
+
+        return false;
+    }
+
+    public static String shapeMismatch(final DiscreteVoxelShape shape1, final DiscreteVoxelShape shape2) {
+        final CachedShapeData cachedShapeData1 = ((CollisionDiscreteVoxelShape)shape1).moonrise$getOrCreateCachedShapeData();
+        final CachedShapeData cachedShapeData2 = ((CollisionDiscreteVoxelShape)shape2).moonrise$getOrCreateCachedShapeData();
+
+        final boolean isEmpty1 = cachedShapeData1.isEmpty();
+        final boolean isEmpty2 = cachedShapeData2.isEmpty();
+
+        if (isEmpty1 & isEmpty2) {
+            return null;
+        } else if (isEmpty1 ^ isEmpty2) {
+            return null;
+        } // else: isEmpty1 = isEmpty2 = false
+
+        if (cachedShapeData1.sizeX() != cachedShapeData2.sizeX()) {
+            return "size x: " + cachedShapeData1.sizeX() + " != " + cachedShapeData2.sizeX();
+        }
+        if (cachedShapeData1.sizeY() != cachedShapeData2.sizeY()) {
+            return "size y: " + cachedShapeData1.sizeY() + " != " + cachedShapeData2.sizeY();
+        }
+        if (cachedShapeData1.sizeZ() != cachedShapeData2.sizeZ()) {
+            return "size z: " + cachedShapeData1.sizeZ() + " != " + cachedShapeData2.sizeZ();
+        }
+
+        final StringBuilder ret = new StringBuilder();
+
+        final int sizeX = cachedShapeData1.sizeX();;
+        final int sizeY = cachedShapeData1.sizeY();
+        final int sizeZ = cachedShapeData1.sizeZ();
+
+        boolean first = true;
+
+        for (int x = 0; x < sizeX; ++x) {
+            for (int y = 0; y < sizeY; ++y) {
+                for (int z = 0; z < sizeZ; ++z) {
+                    final boolean isFull1 = shape1.isFull(x, y, z);
+                    final boolean isFull2 = shape2.isFull(x, y, z);
+
+                    if (isFull1 == isFull2) {
+                        continue;
+                    }
+
+                    if (first) {
+                        first = false;
+                    } else {
+                        ret.append(", ");
+                    }
+
+                    ret.append("(").append(x).append(",").append(y).append(",").append(z)
+                        .append("): shape1: ").append(isFull1).append(", shape2: ").append(isFull2);
+                }
+            }
+        }
+
+        return ret.isEmpty() ? null : ret.toString();
+    }
+
     public static AABB offsetX(final AABB box, final double dx) {
         return new AABB(box.minX + dx, box.minY, box.minZ, box.maxX + dx, box.maxY, box.maxZ);
     }