Allow parallelisation of masks (#636)

* Allow parallelisation of masks
Increasing performance improvement with increased masking complexity and edit size.

* Address comments
 - Rename Mask#clone to Mask#copy
 - Rename Mask2D#copy to Mask2D#copy2D
 - Correct formatting

* cx -> centerX

* Make various operations relying on a single SingleThreadQueueExtent instance (mainly brushes) thread safe

worldedit-core/src/main/java/com/boydti/fawe/beta/implementation/blocks/CharBlocks.java

@@ -17,7 +17,7 @@ public abstract class CharBlocks implements IBlocks {
     };
     public static final Section EMPTY = new Section() {
         @Override
-        public final char[] get(CharBlocks blocks, int layer) {
+        public synchronized final char[] get(CharBlocks blocks, int layer) {
             char[] arr = blocks.blocks[layer];
             if (arr == null) {
                 arr = blocks.blocks[layer] = blocks.update(layer, null);

worldedit-core/src/main/java/com/boydti/fawe/beta/implementation/filter/MaskFilter.java

@@ -6,6 +6,7 @@ import com.boydti.fawe.beta.implementation.filter.block.FilterBlock;
 import com.sk89q.worldedit.function.mask.AbstractExtentMask;
 import com.sk89q.worldedit.function.mask.Mask;
 
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Supplier;
 
 /**
@@ -16,7 +17,7 @@ import java.util.function.Supplier;
 public class MaskFilter<T extends Filter> extends DelegateFilter<T> {
     private final Supplier<Mask> supplier;
     private final Mask mask;
-    private int changes;
+    private final AtomicInteger changes;
 
     public MaskFilter(T other, Mask mask) {
         this(other, () -> mask);
@@ -27,9 +28,14 @@ public class MaskFilter<T extends Filter> extends DelegateFilter<T> {
     }
 
     public MaskFilter(T other, Supplier<Mask> supplier, Mask root) {
+        this(other, supplier, root, new AtomicInteger());
+    }
+
+    public MaskFilter(T other, Supplier<Mask> supplier, Mask root, AtomicInteger changes) {
         super(other);
         this.supplier = supplier;
         this.mask = root;
+        this.changes = changes;
     }
 
     @Override
@@ -37,11 +43,11 @@ public class MaskFilter<T extends Filter> extends DelegateFilter<T> {
         if (mask instanceof AbstractExtentMask) {
             if (((AbstractExtentMask) mask).test(block, block)) {
                 getParent().applyBlock(block);
-                this.changes++;
+                this.changes.incrementAndGet();
             }
         } else if (mask.test(block)) {
             getParent().applyBlock(block);
-            this.changes++;
+            this.changes.incrementAndGet();
         }
     }
 
@@ -51,11 +57,16 @@ public class MaskFilter<T extends Filter> extends DelegateFilter<T> {
      * @return number of blocks which passed the Mask test and were applied to
      */
     public int getBlocksApplied(){
-        return this.changes;
+        return this.changes.get();
     }
 
     @Override
-    public MaskFilter newInstance(Filter other) {
+    public MaskFilter<?> newInstance(Filter other) {
         return new MaskFilter<>(other, supplier);
     }
+
+    @Override
+    public Filter fork() {
+        return new MaskFilter<>(getParent().fork(), mask::copy, mask.copy(), changes);
+    }
 }

worldedit-core/src/main/java/com/boydti/fawe/beta/implementation/processors/MultiBatchProcessor.java

@@ -1,18 +1,26 @@
 package com.boydti.fawe.beta.implementation.processors;
 
+import com.boydti.fawe.FaweCache;
+import com.boydti.fawe.beta.Filter;
 import com.boydti.fawe.beta.IBatchProcessor;
 import com.boydti.fawe.beta.IChunk;
 import com.boydti.fawe.beta.IChunkGet;
 import com.boydti.fawe.beta.IChunkSet;
 import com.boydti.fawe.util.StringMan;
+import com.google.common.cache.LoadingCache;
 import com.sk89q.worldedit.extent.Extent;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
+import java.util.function.Supplier;
 
 public class MultiBatchProcessor implements IBatchProcessor {
     private IBatchProcessor[] processors;
+    private final LoadingCache<Class<?>, Map<Long, Filter>> classToThreadIdToFilter =
+        FaweCache.IMP.createCache((Supplier<Map<Long, Filter>>) HashMap::new);
 
     public MultiBatchProcessor(IBatchProcessor... processors) {
         this.processors = processors;
@@ -56,14 +64,20 @@ public class MultiBatchProcessor implements IBatchProcessor {
     @Override
     public IChunkSet processSet(IChunk chunk, IChunkGet get, IChunkSet set) {
         try {
+            IChunkSet chunkSet = set;
             for (int i = processors.length - 1; i >= 0; i--) {
                 IBatchProcessor processor = processors[i];
-                set = processor.processSet(chunk, get, set);
+                if (processor instanceof Filter) {
-                if (set == null) {
+                    chunkSet = ((IBatchProcessor) classToThreadIdToFilter.getUnchecked(processor.getClass())
+                        .computeIfAbsent(Thread.currentThread().getId(), k -> ((Filter) processor).fork())).processSet(chunk, get, chunkSet);
+                } else {
+                    chunkSet = processor.processSet(chunk, get, chunkSet);
+                }
+                if (chunkSet == null) {
                     return null;
                 }
             }
-            return set;
+            return chunkSet;
         } catch (Throwable e) {
             e.printStackTrace();
             throw e;

worldedit-core/src/main/java/com/boydti/fawe/beta/implementation/queue/SingleThreadQueueExtent.java

@@ -24,6 +24,7 @@ import it.unimi.dsi.fastutil.longs.Long2ObjectLinkedOpenHashMap;
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
+import java.util.concurrent.locks.ReentrantLock;
 
 /**
  * Single threaded implementation for IQueueExtent (still abstract) - Does not implement creation of
@@ -52,6 +53,8 @@ public class SingleThreadQueueExtent extends ExtentBatchProcessorHolder implemen
 
     private boolean fastmode = false;
 
+    private final ReentrantLock getChunkLock = new ReentrantLock();
+
     /**
      * Safety check to ensure that the thread being used matches the one being initialized on. - Can
      * be removed later
@@ -217,6 +220,8 @@ public class SingleThreadQueueExtent extends ExtentBatchProcessorHolder implemen
 
     @Override
     public final IQueueChunk getOrCreateChunk(int x, int z) {
+        getChunkLock.lock();
+        try {
             final long pair = (long) x << 32 | z & 0xffffffffL;
             if (pair == lastPair) {
                 return lastChunk;
@@ -261,6 +266,9 @@ public class SingleThreadQueueExtent extends ExtentBatchProcessorHolder implemen
             lastChunk = chunk;
 
             return chunk;
+        } finally {
+            getChunkLock.unlock();
+        }
     }
 
     @Override

worldedit-core/src/main/java/com/boydti/fawe/object/brush/ImageBrush.java

@@ -1,5 +1,6 @@
 package com.boydti.fawe.object.brush;
 
+import com.boydti.fawe.object.brush.mask.ImageBrushMask;
 import com.boydti.fawe.object.collection.SummedColorTable;
 import com.boydti.fawe.object.mask.SurfaceMask;
 import com.boydti.fawe.util.TextureUtil;
@@ -8,18 +9,14 @@ import com.sk89q.worldedit.LocalSession;
 import com.sk89q.worldedit.MaxChangedBlocksException;
 import com.sk89q.worldedit.command.tool.brush.Brush;
 import com.sk89q.worldedit.extent.Extent;
-import com.sk89q.worldedit.function.mask.AbstractExtentMask;
 import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.function.operation.Operations;
 import com.sk89q.worldedit.function.pattern.Pattern;
 import com.sk89q.worldedit.function.visitor.RecursiveVisitor;
 import com.sk89q.worldedit.math.BlockVector3;
-import com.sk89q.worldedit.math.MutableVector3;
-import com.sk89q.worldedit.math.Vector3;
 import com.sk89q.worldedit.math.transform.AffineTransform;
 import com.sk89q.worldedit.util.Location;
 import com.sk89q.worldedit.world.block.BlockState;
-import com.sk89q.worldedit.world.block.BlockType;
 
 import java.awt.image.BufferedImage;
 import java.io.IOException;
@@ -30,8 +27,8 @@ public class ImageBrush implements Brush {
     private final SummedColorTable table;
     private final int width;
     private final int height;
-    private final double centerX;
+    private final double centerImageX;
-    private final double centerZ;
+    private final double centerImageZ;
 
     private final ColorFunction colorFunction;
 
@@ -40,8 +37,8 @@ public class ImageBrush implements Brush {
         this.table = new SummedColorTable(image, alpha);
         this.width = image.getWidth();
         this.height = image.getHeight();
-        this.centerX = width / 2d;
+        this.centerImageX = width / 2d;
-        this.centerZ = height / 2d;
+        this.centerImageZ = height / 2d;
 
         if (alpha) {
             colorFunction = (x1, z1, x2, z2, extent, pos) -> {
@@ -65,17 +62,12 @@ public class ImageBrush implements Brush {
         }
     }
 
-    private interface ColorFunction {
+    public interface ColorFunction {
         int call(int x1, int z1, int x2, int z2, Extent extent, BlockVector3 pos);
     }
 
     @Override
-    public void build(EditSession editSession, BlockVector3 position, Pattern pattern, double sizeDouble) throws MaxChangedBlocksException {
+    public void build(EditSession editSession, BlockVector3 center, Pattern pattern, double sizeDouble) throws MaxChangedBlocksException {
-        TextureUtil texture = session.getTextureUtil();
-
-        final int cx = position.getBlockX();
-        final int cy = position.getBlockY();
-        final int cz = position.getBlockZ();
         final Mask solid = new SurfaceMask(editSession);
 
         double scale = Math.max(width, height) / sizeDouble;
@@ -85,56 +77,11 @@ public class ImageBrush implements Brush {
         float pitch = loc.getPitch();
         AffineTransform transform = new AffineTransform().rotateY((-yaw) % 360).rotateX((pitch - 90) % 360).inverse();
 
-        RecursiveVisitor visitor = new RecursiveVisitor(new AbstractExtentMask(editSession) {
+        RecursiveVisitor visitor = new RecursiveVisitor(
-            private final MutableVector3 mutable = new MutableVector3();
+            new ImageBrushMask(solid, center, transform, scale, centerImageX, centerImageZ, width, height, colorFunction, editSession,
-
+                session.getTextureUtil()), vector -> true, Integer.MAX_VALUE);
-            @Override
-            public boolean test(Extent extent, BlockVector3 vector) {
-                return test(vector);
-            }
-
-            @Override
-            public boolean test(BlockVector3 vector) {
-                if (solid.test(vector)) {
-                    int dx = vector.getBlockX() - cx;
-                    int dy = vector.getBlockY() - cy;
-                    int dz = vector.getBlockZ() - cz;
-
-                    Vector3 pos1 = transform.apply(mutable.setComponents(dx - 0.5, dy - 0.5, dz - 0.5));
-                    int x1 = (int) (pos1.getX() * scale + centerX);
-                    int z1 = (int) (pos1.getZ() * scale + centerZ);
-
-                    Vector3 pos2 = transform.apply(mutable.setComponents(dx + 0.5, dy + 0.5, dz + 0.5));
-                    int x2 = (int) (pos2.getX() * scale + centerX);
-                    int z2 = (int) (pos2.getZ() * scale + centerZ);
-                    if (x2 < x1) {
-                        int tmp = x1;
-                        x1 = x2;
-                        x2 = tmp;
-                    }
-                    if (z2 < z1) {
-                        int tmp = z1;
-                        z1 = z2;
-                        z2 = tmp;
-                    }
-
-                    if (x1 >= width || x2 < 0 || z1 >= height || z2 < 0) return false;
-
-
-                    int color = colorFunction.call(x1, z1, x2, z2, editSession, vector);
-                    if (color != 0) {
-                        BlockType block = texture.getNearestBlock(color);
-                        if (block != null) {
-                            editSession.setBlock(vector, block.getDefaultState());
-                        }
-                    }
-                    return true;
-                }
-                return false;
-            }
-        }, vector -> true, Integer.MAX_VALUE);
         visitor.setDirections(Arrays.asList(visitor.DIAGONAL_DIRECTIONS));
-        visitor.visit(position);
+        visitor.visit(center);
         Operations.completeBlindly(visitor);
     }
 

worldedit-core/src/main/java/com/boydti/fawe/object/brush/LayerBrush.java

@@ -1,22 +1,20 @@
 package com.boydti.fawe.object.brush;
 
+import com.boydti.fawe.object.brush.mask.LayerBrushMask;
 import com.boydti.fawe.object.collection.BlockVectorSet;
 import com.boydti.fawe.object.mask.AdjacentAnyMask;
 import com.boydti.fawe.object.mask.RadiusMask;
 import com.sk89q.worldedit.EditSession;
 import com.sk89q.worldedit.MaxChangedBlocksException;
 import com.sk89q.worldedit.command.tool.brush.Brush;
-import com.sk89q.worldedit.extent.Extent;
-import com.sk89q.worldedit.function.mask.AbstractExtentMask;
 import com.sk89q.worldedit.function.mask.BlockMask;
-import com.sk89q.worldedit.function.mask.Mask;
+import com.sk89q.worldedit.function.mask.MaskIntersection;
 import com.sk89q.worldedit.function.mask.SolidBlockMask;
 import com.sk89q.worldedit.function.operation.Operations;
 import com.sk89q.worldedit.function.pattern.Pattern;
 import com.sk89q.worldedit.function.visitor.BreadthFirstSearch;
 import com.sk89q.worldedit.function.visitor.RecursiveVisitor;
 import com.sk89q.worldedit.math.BlockVector3;
-import com.sk89q.worldedit.math.MutableBlockVector3;
 import com.sk89q.worldedit.world.block.BlockState;
 import com.sk89q.worldedit.world.block.BlockTypes;
 
@@ -26,7 +24,6 @@ public class LayerBrush implements Brush {
 
     private final BlockState[] layers;
     private RecursiveVisitor visitor;
-    private MutableBlockVector3 mutable = new MutableBlockVector3();
 
     public LayerBrush(BlockState[] layers) {
         this.layers = layers;
@@ -37,48 +34,12 @@ public class LayerBrush implements Brush {
         final AdjacentAnyMask adjacent = new AdjacentAnyMask(new BlockMask(editSession).add(BlockTypes.AIR, BlockTypes.CAVE_AIR, BlockTypes.VOID_AIR));
         final SolidBlockMask solid = new SolidBlockMask(editSession);
         final RadiusMask radius = new RadiusMask(0, (int) size);
-        visitor = new RecursiveVisitor(new Mask() {
+        visitor = new RecursiveVisitor(new MaskIntersection(adjacent, solid, radius), function -> true);
-            @Override
-            public boolean test(BlockVector3 vector) {
-                return solid.test(vector) && radius.test(vector) && adjacent.test(vector);
-            }
-        }, function -> true);
         visitor.visit(position);
         visitor.setDirections(Arrays.asList(BreadthFirstSearch.DIAGONAL_DIRECTIONS));
         Operations.completeBlindly(visitor);
         BlockVectorSet visited = visitor.getVisited();
-        visitor = new RecursiveVisitor(new AbstractExtentMask(editSession) {
+        visitor = new RecursiveVisitor(new LayerBrushMask(editSession, visitor, layers, adjacent), pos -> {
-            @Override
-            public boolean test(Extent extent, BlockVector3 vector) {
-                return test(vector);
-            }
-
-            @Override
-            public boolean test(BlockVector3 pos) {
-                int depth = visitor.getDepth() + 1;
-                if (depth > 1) {
-                    boolean found = false;
-                    BlockState previous = layers[depth - 1];
-                    BlockState previous2 = layers[depth - 2];
-                    for (BlockVector3 dir : BreadthFirstSearch.DEFAULT_DIRECTIONS) {
-                        mutable.setComponents(pos.getBlockX() + dir.getBlockX(), pos.getBlockY() + dir.getBlockY(), pos.getBlockZ() + dir.getBlockZ());
-                        if (visitor.isVisited(mutable) && editSession.getBlock(mutable.getBlockX(), mutable.getBlockY(), mutable.getBlockZ()) == previous) {
-                            mutable.setComponents(pos.getBlockX() + dir.getBlockX() * 2, pos.getBlockY() + dir.getBlockY() * 2, pos.getBlockZ() + dir.getBlockZ() * 2);
-                            if (visitor.isVisited(mutable) && editSession.getBlock(mutable.getBlockX(), mutable.getBlockY(), mutable.getBlockZ()) == previous2) {
-                                found = true;
-                                break;
-                            } else {
-                                return false;
-                            }
-                        }
-                    }
-                    if (!found) {
-                        return false;
-                    }
-                }
-                return !adjacent.test(pos);
-            }
-        }, pos -> {
             int depth = visitor.getDepth();
             BlockState currentPattern = layers[depth];
             return currentPattern.apply(editSession, pos, pos);

worldedit-core/src/main/java/com/boydti/fawe/object/brush/SplatterBrush.java

@@ -1,11 +1,10 @@
 package com.boydti.fawe.object.brush;
 
+import com.boydti.fawe.object.brush.mask.SplatterBrushMask;
 import com.boydti.fawe.object.collection.LocalBlockVectorSet;
 import com.boydti.fawe.object.mask.SurfaceMask;
 import com.sk89q.worldedit.EditSession;
 import com.sk89q.worldedit.MaxChangedBlocksException;
-import com.sk89q.worldedit.extent.Extent;
-import com.sk89q.worldedit.function.mask.AbstractExtentMask;
 import com.sk89q.worldedit.function.operation.Operations;
 import com.sk89q.worldedit.function.pattern.Pattern;
 import com.sk89q.worldedit.function.visitor.BreadthFirstSearch;
@@ -13,7 +12,6 @@ import com.sk89q.worldedit.function.visitor.RecursiveVisitor;
 import com.sk89q.worldedit.math.BlockVector3;
 
 import java.util.Arrays;
-import java.util.concurrent.ThreadLocalRandom;
 
 public class SplatterBrush extends ScatterBrush {
     private final boolean solid;
@@ -36,23 +34,8 @@ public class SplatterBrush extends ScatterBrush {
         final int size2 = (int) (size * size);
         SurfaceMask surface = new SurfaceMask(editSession);
 
-        RecursiveVisitor visitor = new RecursiveVisitor(new AbstractExtentMask(editSession) {
+        RecursiveVisitor visitor = new RecursiveVisitor(new SplatterBrushMask(editSession, position, size2, surface, placed),
-            @Override
+            vector -> editSession.setBlock(vector, finalPattern), recursion);
-            public boolean test(Extent extent, BlockVector3 vector) {
-                return test(vector);
-            }
-
-            @Override
-            public boolean test(BlockVector3 vector) {
-                double dist = vector.distanceSq(position);
-                if (dist < size2 && !placed.contains(vector) && ThreadLocalRandom.current().nextInt(5) < 2
-                        && surface.test(vector)) {
-                    placed.add(vector);
-                    return true;
-                }
-                return false;
-            }
-        }, vector -> editSession.setBlock(vector, finalPattern), recursion);
         visitor.setMaxBranch(2);
         visitor.setDirections(Arrays.asList(BreadthFirstSearch.DIAGONAL_DIRECTIONS));
         visitor.visit(position);

worldedit-core/src/main/java/com/boydti/fawe/object/brush/StencilBrush.java

@@ -1,26 +1,21 @@
 package com.boydti.fawe.object.brush;
 
 import com.boydti.fawe.object.brush.heightmap.HeightMap;
-import com.boydti.fawe.util.MathMan;
+import com.boydti.fawe.object.brush.mask.StencilBrushMask;
 import com.sk89q.worldedit.EditSession;
 import com.sk89q.worldedit.MaxChangedBlocksException;
-import com.sk89q.worldedit.extent.Extent;
 import com.sk89q.worldedit.extent.clipboard.Clipboard;
-import com.sk89q.worldedit.function.mask.AbstractExtentMask;
 import com.sk89q.worldedit.function.mask.SolidBlockMask;
 import com.sk89q.worldedit.function.operation.Operations;
 import com.sk89q.worldedit.function.pattern.Pattern;
 import com.sk89q.worldedit.function.visitor.BreadthFirstSearch;
 import com.sk89q.worldedit.function.visitor.RecursiveVisitor;
 import com.sk89q.worldedit.math.BlockVector3;
-import com.sk89q.worldedit.math.MutableVector3;
-import com.sk89q.worldedit.math.Vector3;
 import com.sk89q.worldedit.math.transform.AffineTransform;
 import com.sk89q.worldedit.util.Location;
 
 import java.io.InputStream;
 import java.util.Arrays;
-import java.util.concurrent.ThreadLocalRandom;
 
 public class StencilBrush extends HeightBrush {
     private final boolean onlyWhite;
@@ -31,10 +26,7 @@ public class StencilBrush extends HeightBrush {
     }
 
     @Override
-    public void build(EditSession editSession, BlockVector3 position, Pattern pattern, double sizeDouble) throws MaxChangedBlocksException {
+    public void build(EditSession editSession, BlockVector3 center, Pattern pattern, double sizeDouble) throws MaxChangedBlocksException {
-        final int cx = position.getBlockX();
-        final int cy = position.getBlockY();
-        final int cz = position.getBlockZ();
         int size = (int) sizeDouble;
         int size2 = (int) (sizeDouble * sizeDouble);
         int maxY = editSession.getMaxY();
@@ -55,42 +47,11 @@ public class StencilBrush extends HeightBrush {
         AffineTransform transform = new AffineTransform().rotateY((-yaw) % 360).rotateX(pitch - 90).inverse();
 
         double scale = (yscale / sizeDouble) * (maxY + 1);
-        RecursiveVisitor visitor = new RecursiveVisitor(new AbstractExtentMask(editSession) {
+        RecursiveVisitor visitor =
-            @Override
+            new RecursiveVisitor(new StencilBrushMask(editSession, solid, center, transform, size2, map, scale, add, cutoff, maxY, pattern),
-            public boolean test(Extent extent, BlockVector3 vector) {
+                vector -> true, Integer.MAX_VALUE);
-                return test(vector);
-            }
-
-            private final MutableVector3 mutable = new MutableVector3();
-            @Override
-            public boolean test(BlockVector3 vector) {
-                if (solid.test(vector)) {
-                    int dx = vector.getBlockX() - cx;
-                    int dy = vector.getBlockY() - cy;
-                    int dz = vector.getBlockZ() - cz;
-
-                    Vector3 srcPos = transform.apply(mutable.setComponents(dx, dy, dz));
-                    dx = MathMan.roundInt(srcPos.getX());
-                    dz = MathMan.roundInt(srcPos.getZ());
-
-                    int distance = dx * dx + dz * dz;
-                    if (distance > size2 || Math.abs(dx) > 256 || Math.abs(dz) > 256) return false;
-
-                    double raise = map.getHeight(dx, dz);
-                    int val = (int) Math.ceil(raise * scale) + add;
-                    if (val < cutoff) {
-                        return true;
-                    }
-                    if (val >= 255 || ThreadLocalRandom.current().nextInt(maxY) < val) {
-                        editSession.setBlock(vector.getBlockX(), vector.getBlockY(), vector.getBlockZ(), pattern);
-                    }
-                    return true;
-                }
-                return false;
-            }
-        }, vector -> true, Integer.MAX_VALUE);
         visitor.setDirections(Arrays.asList(BreadthFirstSearch.DIAGONAL_DIRECTIONS));
-        visitor.visit(position);
+        visitor.visit(center);
         Operations.completeBlindly(visitor);
     }
 }

worldedit-core/src/main/java/com/boydti/fawe/object/brush/mask/ImageBrushMask.java

@@ -0,0 +1,107 @@
+package com.boydti.fawe.object.brush.mask;
+
+import com.boydti.fawe.object.brush.ImageBrush;
+import com.boydti.fawe.util.TextureUtil;
+import com.sk89q.worldedit.EditSession;
+import com.sk89q.worldedit.extent.Extent;
+import com.sk89q.worldedit.function.mask.AbstractExtentMask;
+import com.sk89q.worldedit.function.mask.Mask;
+import com.sk89q.worldedit.math.BlockVector3;
+import com.sk89q.worldedit.math.MutableVector3;
+import com.sk89q.worldedit.math.Vector3;
+import com.sk89q.worldedit.math.transform.Transform;
+import com.sk89q.worldedit.world.block.BlockType;
+
+public class ImageBrushMask extends AbstractExtentMask {
+
+    private final MutableVector3 mutable = new MutableVector3();
+    private final Mask solid;
+    private final BlockVector3 center;
+    private final Transform transform;
+    private final double scale;
+    private final double centerImageX;
+    private final double centerImageZ;
+    private final int width;
+    private final int height;
+    private final ImageBrush.ColorFunction colorFunction;
+    private final EditSession session;
+    private final TextureUtil texture;
+
+    public ImageBrushMask(Mask solid,
+                          BlockVector3 center,
+                          Transform transform,
+                          double scale,
+                          double centerImageX,
+                          double centerImageZ,
+                          int width,
+                          int height,
+                          ImageBrush.ColorFunction colorFunction,
+                          EditSession session,
+                          TextureUtil texture) {
+        super(session);
+        this.solid = solid;
+        this.center = center;
+        this.transform = transform;
+        this.scale = scale;
+        this.centerImageX = centerImageX;
+        this.centerImageZ = centerImageZ;
+        this.width = width;
+        this.height = height;
+        this.colorFunction = colorFunction;
+        this.session = session;
+        this.texture = texture;
+    }
+
+    @Override
+    public boolean test(Extent extent, BlockVector3 vector) {
+        return test(vector);
+    }
+
+    @Override
+    public boolean test(BlockVector3 vector) {
+        if (solid.test(vector)) {
+            int dx = vector.getBlockX() - center.getBlockX();
+            int dy = vector.getBlockY() - center.getBlockY();
+            int dz = vector.getBlockZ() - center.getBlockZ();
+
+            Vector3 pos1 = transform.apply(mutable.setComponents(dx - 0.5, dy - 0.5, dz - 0.5));
+            int x1 = (int) (pos1.getX() * scale + centerImageX);
+            int z1 = (int) (pos1.getZ() * scale + centerImageZ);
+
+            Vector3 pos2 = transform.apply(mutable.setComponents(dx + 0.5, dy + 0.5, dz + 0.5));
+            int x2 = (int) (pos2.getX() * scale + centerImageX);
+            int z2 = (int) (pos2.getZ() * scale + centerImageZ);
+            if (x2 < x1) {
+                int tmp = x1;
+                x1 = x2;
+                x2 = tmp;
+            }
+            if (z2 < z1) {
+                int tmp = z1;
+                z1 = z2;
+                z2 = tmp;
+            }
+
+            if (x1 >= width || x2 < 0 || z1 >= height || z2 < 0) {
+                return false;
+            }
+
+
+            int color = colorFunction.call(x1, z1, x2, z2, session, vector);
+            if (color != 0) {
+                BlockType block = texture.getNearestBlock(color);
+                if (block != null) {
+                    session.setBlock(vector, block.getDefaultState());
+                }
+            }
+            return true;
+        }
+        return false;
+    }
+
+    @Override
+    public Mask copy() {
+        return new ImageBrushMask(solid.copy(), center.toImmutable(), transform, scale, centerImageX, centerImageZ, width, height, colorFunction,
+            session, texture);
+    }
+}

worldedit-core/src/main/java/com/boydti/fawe/object/brush/mask/LayerBrushMask.java

@@ -0,0 +1,66 @@
+package com.boydti.fawe.object.brush.mask;
+
+import com.sk89q.worldedit.EditSession;
+import com.sk89q.worldedit.extent.Extent;
+import com.sk89q.worldedit.function.mask.AbstractExtentMask;
+import com.sk89q.worldedit.function.mask.Mask;
+import com.sk89q.worldedit.function.visitor.BreadthFirstSearch;
+import com.sk89q.worldedit.function.visitor.RecursiveVisitor;
+import com.sk89q.worldedit.math.BlockVector3;
+import com.sk89q.worldedit.math.MutableBlockVector3;
+import com.sk89q.worldedit.world.block.BlockState;
+
+public class LayerBrushMask extends AbstractExtentMask {
+
+    private final EditSession editSession;
+    private final RecursiveVisitor visitor;
+    private final BlockState[] layers;
+    private final MutableBlockVector3 mutable = new MutableBlockVector3();
+    private final Mask adjacent;
+
+    public LayerBrushMask(EditSession editSession, RecursiveVisitor visitor, BlockState[] layers, Mask adjacent) {
+        super(editSession);
+        this.editSession = editSession;
+        this.visitor = visitor;
+        this.layers = layers;
+        this.adjacent = adjacent;
+    }
+
+    @Override
+    public boolean test(Extent extent, BlockVector3 vector) {
+        return test(vector);
+    }
+
+    @Override
+    public boolean test(BlockVector3 pos) {
+        int depth = visitor.getDepth() + 1;
+        if (depth > 1) {
+            boolean found = false;
+            BlockState previous = layers[depth - 1];
+            BlockState previous2 = layers[depth - 2];
+            for (BlockVector3 dir : BreadthFirstSearch.DEFAULT_DIRECTIONS) {
+                mutable.setComponents(pos.getBlockX() + dir.getBlockX(), pos.getBlockY() + dir.getBlockY(), pos.getBlockZ() + dir.getBlockZ());
+                if (visitor.isVisited(mutable) && editSession.getBlock(mutable.getBlockX(), mutable.getBlockY(), mutable.getBlockZ()) == previous) {
+                    mutable.setComponents(pos.getBlockX() + dir.getBlockX() * 2, pos.getBlockY() + dir.getBlockY() * 2,
+                        pos.getBlockZ() + dir.getBlockZ() * 2);
+                    if (visitor.isVisited(mutable)
+                        && editSession.getBlock(mutable.getBlockX(), mutable.getBlockY(), mutable.getBlockZ()) == previous2) {
+                        found = true;
+                        break;
+                    } else {
+                        return false;
+                    }
+                }
+            }
+            if (!found) {
+                return false;
+            }
+        }
+        return !adjacent.test(pos);
+    }
+
+    @Override
+    public Mask copy() {
+        return new LayerBrushMask(editSession, visitor, layers.clone(), adjacent.copy());
+    }
+}

worldedit-core/src/main/java/com/boydti/fawe/object/brush/mask/SplatterBrushMask.java

@@ -0,0 +1,49 @@
+package com.boydti.fawe.object.brush.mask;
+
+import com.boydti.fawe.object.collection.LocalBlockVectorSet;
+import com.sk89q.worldedit.EditSession;
+import com.sk89q.worldedit.extent.Extent;
+import com.sk89q.worldedit.function.mask.AbstractExtentMask;
+import com.sk89q.worldedit.function.mask.Mask;
+import com.sk89q.worldedit.math.BlockVector3;
+
+import java.util.concurrent.ThreadLocalRandom;
+
+public class SplatterBrushMask extends AbstractExtentMask {
+
+    private final BlockVector3 position;
+    private final int size2;
+    private final Mask surface;
+    private final LocalBlockVectorSet placed;
+
+    public SplatterBrushMask(EditSession editSession, BlockVector3 position, int size2, Mask surface, LocalBlockVectorSet placed) {
+        super(editSession);
+        this.position = position;
+        this.size2 = size2;
+        this.surface = surface;
+        this.placed = placed;
+    }
+
+    @Override
+    public boolean test(Extent extent, BlockVector3 vector) {
+        return test(vector);
+    }
+
+    @Override
+    public boolean test(BlockVector3 vector) {
+        double dist = vector.distanceSq(position);
+        synchronized (placed) {
+            if (dist < size2 && !placed.contains(vector) && ThreadLocalRandom.current().nextInt(5) < 2 && surface.test(vector)) {
+                placed.add(vector);
+                return true;
+            }
+        }
+        return false;
+    }
+
+    @Override
+    public Mask copy() {
+        // There should not be multiple instances to be thread safe
+        return this;
+    }
+}

worldedit-core/src/main/java/com/boydti/fawe/object/brush/mask/StencilBrushMask.java

@@ -0,0 +1,95 @@
+package com.boydti.fawe.object.brush.mask;
+
+import com.boydti.fawe.object.brush.heightmap.HeightMap;
+import com.boydti.fawe.util.MathMan;
+import com.sk89q.worldedit.EditSession;
+import com.sk89q.worldedit.extent.Extent;
+import com.sk89q.worldedit.function.mask.AbstractExtentMask;
+import com.sk89q.worldedit.function.mask.Mask;
+import com.sk89q.worldedit.function.pattern.Pattern;
+import com.sk89q.worldedit.math.BlockVector3;
+import com.sk89q.worldedit.math.MutableVector3;
+import com.sk89q.worldedit.math.Vector3;
+import com.sk89q.worldedit.math.transform.Transform;
+
+import java.util.concurrent.ThreadLocalRandom;
+
+public class StencilBrushMask extends AbstractExtentMask {
+
+    private final MutableVector3 mutable = new MutableVector3();
+    private final EditSession editSession;
+    private final Mask solid;
+    private final BlockVector3 center;
+    private final Transform transform;
+    private final int size2;
+    private final HeightMap map;
+    private final double scale;
+    private final int add;
+    private final int cutoff;
+    private final int maxY;
+    private final Pattern pattern;
+
+    public StencilBrushMask(EditSession editSession,
+                            Mask solid,
+                            BlockVector3 center,
+                            Transform transform,
+                            int size2,
+                            HeightMap map,
+                            double scale,
+                            int add,
+                            int cutoff,
+                            int maxY,
+                            Pattern pattern) {
+        super(editSession);
+        this.editSession = editSession;
+        this.solid = solid;
+        this.center = center;
+        this.transform = transform;
+        this.size2 = size2;
+        this.map = map;
+        this.scale = scale;
+        this.add = add;
+        this.cutoff = cutoff;
+        this.maxY = maxY;
+        this.pattern = pattern;
+    }
+
+    @Override
+    public boolean test(Extent extent, BlockVector3 vector) {
+        return test(vector);
+    }
+
+    @Override
+    public boolean test(BlockVector3 vector) {
+        if (solid.test(vector)) {
+            int dx = vector.getBlockX() - center.getBlockX();
+            int dy = vector.getBlockY() - center.getBlockY();
+            int dz = vector.getBlockZ() - center.getBlockZ();
+
+            Vector3 srcPos = transform.apply(mutable.setComponents(dx, dy, dz));
+            dx = MathMan.roundInt(srcPos.getX());
+            dz = MathMan.roundInt(srcPos.getZ());
+
+            int distance = dx * dx + dz * dz;
+            if (distance > size2 || Math.abs(dx) > 256 || Math.abs(dz) > 256) {
+                return false;
+            }
+
+            double raise = map.getHeight(dx, dz);
+            int val = (int) Math.ceil(raise * scale) + add;
+            if (val < cutoff) {
+                return true;
+            }
+            if (val >= 255 || ThreadLocalRandom.current().nextInt(maxY) < val) {
+                editSession.setBlock(vector.getBlockX(), vector.getBlockY(), vector.getBlockZ(), pattern);
+            }
+            return true;
+        }
+        return false;
+    }
+
+    @Override
+    public Mask copy() {
+        return new StencilBrushMask(editSession, solid.copy(), center.toImmutable(), transform, size2, map, scale, add, cutoff, maxY, pattern);
+    }
+}

worldedit-core/src/main/java/com/boydti/fawe/object/function/mask/AbstractDelegateMask.java

@@ -30,4 +30,9 @@ public class AbstractDelegateMask extends AbstractMask {
         return mask.toMask2D();
     }
 
+    @Override
+    public Mask copy() {
+        return new AbstractDelegateMask(mask.copy());
+    }
+
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/AdjacentAnyMask.java

@@ -1,6 +1,5 @@
 package com.boydti.fawe.object.mask;
 
-import com.sk89q.worldedit.extent.Extent;
 import com.sk89q.worldedit.function.mask.AbstractMask;
 import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.BlockVector3;
@@ -53,4 +52,9 @@ public class AdjacentAnyMask extends AbstractMask implements ResettableMask {
             return null;
         }
     }
+
+    @Override
+    public Mask copy() {
+        return new AdjacentAnyMask(mask.copy());
+    }
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/AdjacentMask.java

@@ -9,7 +9,7 @@ public class AdjacentMask extends AbstractMask {
     private final int min;
     private final int max;
     private final Mask mask;
-    private MutableBlockVector3 vector;
+    private final MutableBlockVector3 vector;
 
     public AdjacentMask(Mask mask, int requiredMin, int requiredMax) {
         this.mask = mask;
@@ -60,4 +60,9 @@ public class AdjacentMask extends AbstractMask {
         vector.mutZ(z);
         return count >= min && count <= max;
     }
+
+    @Override
+    public Mask copy() {
+        return new AdjacentMask(mask.copy(), min, max);
+    }
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/AirMask.java

@@ -1,7 +1,8 @@
-package com.boydti.fawe.function.mask;
+package com.boydti.fawe.object.mask;
 
 import com.sk89q.worldedit.extent.Extent;
 import com.sk89q.worldedit.function.mask.BlockMask;
+import com.sk89q.worldedit.function.mask.Mask;
 
 public class AirMask extends BlockMask {
 
@@ -10,4 +11,9 @@ public class AirMask extends BlockMask {
         add(state -> state.getMaterial().isAir());
     }
 
+    @Override
+    public Mask copy() {
+        return new AirMask(getExtent());
+    }
+
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/AngleMask.java

@@ -1,6 +1,7 @@
 package com.boydti.fawe.object.mask;
 
 import com.sk89q.worldedit.extent.Extent;
+import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.function.mask.SolidBlockMask;
 import com.sk89q.worldedit.math.BlockVector3;
 import com.sk89q.worldedit.math.MutableBlockVector3;
@@ -44,7 +45,6 @@ public class AngleMask extends SolidBlockMask implements ResettableMask {
         }
     }
 
-    protected transient int cacheCenX;
     protected transient int cacheCenZ;
     protected transient int cacheBotX = Integer.MIN_VALUE;
     protected transient int cacheBotZ = Integer.MIN_VALUE;
@@ -173,4 +173,9 @@ public class AngleMask extends SolidBlockMask implements ResettableMask {
         return testSlope(getExtent(), x, y, z);
     }
 
+    @Override
+    public Mask copy() {
+        return new AngleMask(getExtent(), min, max, overlay, distance);
+    }
+
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/CachedMask.java

@@ -65,4 +65,9 @@ public class CachedMask extends AbstractDelegateMask implements ResettableMask {
             return result;
         }
     }
+
+    @Override
+    public Mask copy() {
+        return new CachedMask(getMask().copy());
+    }
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/DataMask.java

@@ -2,6 +2,7 @@ package com.boydti.fawe.object.mask;
 
 import com.sk89q.worldedit.extent.Extent;
 import com.sk89q.worldedit.function.mask.AbstractExtentMask;
+import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.BlockVector3;
 
 public class DataMask extends AbstractExtentMask implements ResettableMask {
@@ -37,4 +38,9 @@ public class DataMask extends AbstractExtentMask implements ResettableMask {
         this.data = -1;
     }
 
+    @Override
+    public Mask copy() {
+        return new DataMask(getExtent());
+    }
+
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/ExtremaMask.java

@@ -1,6 +1,7 @@
 package com.boydti.fawe.object.mask;
 
 import com.sk89q.worldedit.extent.Extent;
+import com.sk89q.worldedit.function.mask.Mask;
 
 public class ExtremaMask extends AngleMask {
     public ExtremaMask(Extent extent, double min, double max, boolean overlay, int distance) {
@@ -62,4 +63,9 @@ public class ExtremaMask extends AngleMask {
         }
         return (lastHeight1 - base) + (lastHeight2 - base);
     }
+
+    @Override
+    public Mask copy() {
+        return new ExtremaMask(getExtent(), min, max, overlay, distance);
+    }
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/IdDataMask.java

@@ -2,6 +2,7 @@ package com.boydti.fawe.object.mask;
 
 import com.sk89q.worldedit.extent.Extent;
 import com.sk89q.worldedit.function.mask.AbstractExtentMask;
+import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.BlockVector3;
 
 public class IdDataMask extends AbstractExtentMask implements ResettableMask {
@@ -31,4 +32,9 @@ public class IdDataMask extends AbstractExtentMask implements ResettableMask {
         this.combined = -1;
     }
 
+    @Override
+    public Mask copy() {
+        return new IdDataMask(getExtent());
+    }
+
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/IdMask.java

@@ -2,6 +2,7 @@ package com.boydti.fawe.object.mask;
 
 import com.sk89q.worldedit.extent.Extent;
 import com.sk89q.worldedit.function.mask.AbstractExtentMask;
+import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.BlockVector3;
 
 public class IdMask extends AbstractExtentMask implements ResettableMask {
@@ -32,4 +33,9 @@ public class IdMask extends AbstractExtentMask implements ResettableMask {
         this.id = -1;
     }
 
+    @Override
+    public Mask copy() {
+        return new IdMask(getExtent());
+    }
+
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/LiquidMask.java

@@ -1,7 +1,8 @@
-package com.boydti.fawe.function.mask;
+package com.boydti.fawe.object.mask;
 
 import com.sk89q.worldedit.extent.Extent;
 import com.sk89q.worldedit.function.mask.BlockMask;
+import com.sk89q.worldedit.function.mask.Mask;
 
 public class LiquidMask extends BlockMask {
 
@@ -10,4 +11,9 @@ public class LiquidMask extends BlockMask {
         add(state -> state.getMaterial().isLiquid());
     }
 
+    @Override
+    public Mask copy() {
+        return new LiquidMask(getExtent());
+    }
+
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/PlaneMask.java

@@ -1,6 +1,7 @@
 package com.boydti.fawe.object.mask;
 
 import com.sk89q.worldedit.function.mask.AbstractMask;
+import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.BlockVector3;
 
 public class PlaneMask extends AbstractMask implements ResettableMask {
@@ -55,4 +56,9 @@ public class PlaneMask extends AbstractMask implements ResettableMask {
         mode = -1;
     }
 
+    @Override
+    public Mask copy() {
+        return new PlaneMask();
+    }
+
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/ROCAngleMask.java

@@ -1,6 +1,7 @@
 package com.boydti.fawe.object.mask;
 
 import com.sk89q.worldedit.extent.Extent;
+import com.sk89q.worldedit.function.mask.Mask;
 
 public class ROCAngleMask extends AngleMask {
 
@@ -31,4 +32,9 @@ public class ROCAngleMask extends AngleMask {
 
         return lastValue = slope >= min && slope <= max;
     }
+
+    @Override
+    public Mask copy() {
+        return new ROCAngleMask(getExtent(), min, max, overlay, distance);
+    }
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/RadiusMask.java

@@ -1,6 +1,7 @@
 package com.boydti.fawe.object.mask;
 
 import com.sk89q.worldedit.function.mask.AbstractMask;
+import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.BlockVector3;
 
 public class RadiusMask extends AbstractMask implements ResettableMask {
@@ -13,6 +14,11 @@ public class RadiusMask extends AbstractMask implements ResettableMask {
         this.maxSqr = max * max;
     }
 
+    private RadiusMask(Integer minSqr, Integer maxSqr) {
+        this.minSqr = minSqr;
+        this.maxSqr = maxSqr;
+    }
+
     @Override
     public void reset() {
         pos = null;
@@ -41,4 +47,9 @@ public class RadiusMask extends AbstractMask implements ResettableMask {
         return true;
     }
 
+    @Override
+    public Mask copy() {
+        return new RadiusMask(minSqr, maxSqr);
+    }
+
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/RandomMask.java

@@ -1,6 +1,7 @@
 package com.boydti.fawe.object.mask;
 
 import com.sk89q.worldedit.function.mask.AbstractMask;
+import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.BlockVector3;
 
 import java.util.SplittableRandom;
@@ -23,4 +24,9 @@ public class RandomMask extends AbstractMask implements ResettableMask {
     public void reset() {
         random = new SplittableRandom();
     }
+
+    @Override
+    public Mask copy() {
+        return new RandomMask(threshold);
+    }
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/SimplexMask.java

@@ -2,6 +2,7 @@ package com.boydti.fawe.object.mask;
 
 import com.boydti.fawe.object.random.SimplexNoise;
 import com.sk89q.worldedit.function.mask.AbstractMask;
+import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.BlockVector3;
 
 public class SimplexMask extends AbstractMask {
@@ -18,4 +19,10 @@ public class SimplexMask extends AbstractMask {
         double value = SimplexNoise.noise(vector.getBlockX() * scale, vector.getBlockY() * scale, vector.getBlockZ() * scale);
         return value >= min && value <= max;
     }
+
+    @Override
+    public Mask copy() {
+        // The mask is not mutable. There is no need to clone it.
+        return this;
+    }
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/SurfaceMask.java

@@ -3,10 +3,12 @@ package com.boydti.fawe.object.mask;
 import com.sk89q.worldedit.extent.Extent;
 import com.sk89q.worldedit.function.mask.AbstractExtentMask;
 import com.sk89q.worldedit.function.mask.BlockMaskBuilder;
+import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.BlockVector3;
 import com.sk89q.worldedit.world.block.BlockTypes;
 
 public class SurfaceMask extends AdjacentAnyMask {
+
     public SurfaceMask(Extent extent) {
         super(getMask(extent));
     }
@@ -22,4 +24,10 @@ public class SurfaceMask extends AdjacentAnyMask {
     public boolean test(BlockVector3 v) {
         return !getParentMask().test(v.getBlockX(), v.getBlockY(), v.getBlockZ()) && super.test(v);
     }
+
+    @Override
+    public Mask copy() {
+        // The mask is not mutable. There is no need to clone it.
+        return this;
+    }
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/WallMask.java

@@ -48,4 +48,9 @@ public class WallMask extends AbstractMask {
         v.mutZ(z);
         return count >= min && count <= max;
     }
+
+    @Override
+    public Mask copy() {
+        return new WallMask(mask.copy(), min, max);
+    }
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/XAxisMask.java

@@ -1,8 +1,8 @@
-package com.boydti.fawe.function.mask;
+package com.boydti.fawe.object.mask;
 
-import com.boydti.fawe.object.mask.ResettableMask;
 import com.sk89q.worldedit.extent.Extent;
 import com.sk89q.worldedit.function.mask.AbstractMask;
+import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.BlockVector3;
 
 public class XAxisMask extends AbstractMask implements ResettableMask {
@@ -26,4 +26,9 @@ public class XAxisMask extends AbstractMask implements ResettableMask {
         this.layer = -1;
     }
 
+    @Override
+    public Mask copy() {
+        return new XAxisMask(null);
+    }
+
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/YAxisMask.java

@@ -1,8 +1,8 @@
-package com.boydti.fawe.function.mask;
+package com.boydti.fawe.object.mask;
 
-import com.boydti.fawe.object.mask.ResettableMask;
 import com.sk89q.worldedit.extent.Extent;
 import com.sk89q.worldedit.function.mask.AbstractMask;
+import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.BlockVector3;
 
 public class YAxisMask extends AbstractMask implements ResettableMask {
@@ -25,4 +25,9 @@ public class YAxisMask extends AbstractMask implements ResettableMask {
         this.layer = -1;
     }
 
+    @Override
+    public Mask copy() {
+        return new YAxisMask(null);
+    }
+
 }

worldedit-core/src/main/java/com/boydti/fawe/object/mask/ZAxisMask.java

@@ -1,7 +1,7 @@
-package com.boydti.fawe.function.mask;
+package com.boydti.fawe.object.mask;
 
-import com.boydti.fawe.object.mask.ResettableMask;
 import com.sk89q.worldedit.function.mask.AbstractMask;
+import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.BlockVector3;
 
 public class ZAxisMask extends AbstractMask implements ResettableMask {
@@ -24,4 +24,9 @@ public class ZAxisMask extends AbstractMask implements ResettableMask {
         this.layer = -1;
     }
 
+    @Override
+    public Mask copy() {
+        return new ZAxisMask();
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/EditSession.java

@@ -71,6 +71,7 @@ import com.sk89q.worldedit.function.mask.NoiseFilter2D;
 import com.sk89q.worldedit.function.mask.RegionMask;
 import com.sk89q.worldedit.function.mask.SingleBlockTypeMask;
 import com.sk89q.worldedit.function.mask.SolidBlockMask;
+import com.sk89q.worldedit.function.mask.WallMakeMask;
 import com.sk89q.worldedit.function.operation.ChangeSetExecutor;
 import com.sk89q.worldedit.function.operation.ForwardExtentCopy;
 import com.sk89q.worldedit.function.operation.Operations;
@@ -1406,15 +1407,7 @@ public class EditSession extends PassthroughExtent implements AutoCloseable {
         if (region instanceof CuboidRegion) {
             return makeCuboidWalls(region, pattern);
         } else {
-            replaceBlocks(region, new Mask() {
+            replaceBlocks(region, new WallMakeMask(region), pattern);
-                @Override
-                public boolean test(BlockVector3 position) {
-                    int x = position.getBlockX();
-                    int z = position.getBlockZ();
-                    return !region.contains(x, z + 1) || !region.contains(x, z - 1) || !region
-                        .contains(x + 1, z) || !region.contains(x - 1, z);
-                }
-            }, pattern);
         }
         return changes;
     }

worldedit-core/src/main/java/com/sk89q/worldedit/extension/factory/parser/mask/LiquidMaskParser.java

@@ -1,6 +1,6 @@
 package com.sk89q.worldedit.extension.factory.parser.mask;
 
-import com.boydti.fawe.function.mask.LiquidMask;
+import com.boydti.fawe.object.mask.LiquidMask;
 import com.google.common.collect.ImmutableList;
 import com.sk89q.worldedit.WorldEdit;
 import com.sk89q.worldedit.extension.input.ParserContext;

worldedit-core/src/main/java/com/sk89q/worldedit/extension/factory/parser/mask/XAxisMaskParser.java

@@ -19,7 +19,7 @@
 
 package com.sk89q.worldedit.extension.factory.parser.mask;
 
-import com.boydti.fawe.function.mask.XAxisMask;
+import com.boydti.fawe.object.mask.XAxisMask;
 import com.google.common.collect.ImmutableList;
 import com.sk89q.worldedit.WorldEdit;
 import com.sk89q.worldedit.extension.input.ParserContext;

worldedit-core/src/main/java/com/sk89q/worldedit/extension/factory/parser/mask/YAxisMaskParser.java

@@ -19,7 +19,7 @@
 
 package com.sk89q.worldedit.extension.factory.parser.mask;
 
-import com.boydti.fawe.function.mask.YAxisMask;
+import com.boydti.fawe.object.mask.YAxisMask;
 import com.google.common.collect.ImmutableList;
 import com.sk89q.worldedit.WorldEdit;
 import com.sk89q.worldedit.extension.input.ParserContext;

worldedit-core/src/main/java/com/sk89q/worldedit/extension/factory/parser/mask/ZAxisMaskParser.java

@@ -19,7 +19,7 @@
 
 package com.sk89q.worldedit.extension.factory.parser.mask;
 
-import com.boydti.fawe.function.mask.ZAxisMask;
+import com.boydti.fawe.object.mask.ZAxisMask;
 import com.google.common.collect.ImmutableList;
 import com.sk89q.worldedit.WorldEdit;
 import com.sk89q.worldedit.extension.input.ParserContext;

worldedit-core/src/main/java/com/sk89q/worldedit/extent/MaskingExtent.java

@@ -44,7 +44,7 @@ import static com.google.common.base.Preconditions.checkNotNull;
 public class MaskingExtent extends AbstractDelegateExtent implements IBatchProcessor, Filter {
 
     private Mask mask;
-    private LoadingCache<Long, ChunkFilterBlock> threadIdToFilter = FaweCache.IMP.createCache(() -> new CharFilterBlock(getExtent()));
+    private final LoadingCache<Long, ChunkFilterBlock> threadIdToFilter;
 
     /**
      * Create a new instance.
@@ -56,6 +56,14 @@ public class MaskingExtent extends AbstractDelegateExtent implements IBatchProce
         super(extent);
         checkNotNull(mask);
         this.mask = mask;
+        this.threadIdToFilter = FaweCache.IMP.createCache(() -> new CharFilterBlock(getExtent()));
+    }
+
+    private MaskingExtent(Extent extent, Mask mask, LoadingCache<Long, ChunkFilterBlock> threadIdToFilter) {
+        super(extent);
+        checkNotNull(mask);
+        this.mask = mask;
+        this.threadIdToFilter = threadIdToFilter;
     }
 
     /**
@@ -64,7 +72,7 @@ public class MaskingExtent extends AbstractDelegateExtent implements IBatchProce
      * @return the mask
      */
     public Mask getMask() {
-        return mask;
+        return this.mask;
     }
 
     /**
@@ -79,38 +87,40 @@ public class MaskingExtent extends AbstractDelegateExtent implements IBatchProce
 
     @Override
     public <B extends BlockStateHolder<B>> boolean setBlock(BlockVector3 location, B block) throws WorldEditException {
-        return mask.test(location) && super.setBlock(location, block);
+        return this.mask.test(location) && super.setBlock(location, block);
     }
 
     @Override
     public boolean setBiome(BlockVector2 position, BiomeType biome) {
-        return mask.test(position.toBlockVector3()) && super.setBiome(position, biome);
+        return this.mask.test(position.toBlockVector3()) && super.setBiome(position, biome);
     }
 
     @Override
     public boolean setBiome(int x, int y, int z, BiomeType biome) {
-        return mask.test(BlockVector3.at(x, y, z)) && super.setBiome(x, y, z, biome);
+        return this.mask.test(BlockVector3.at(x, y, z)) && super.setBiome(x, y, z, biome);
     }
 
     @Override
-    public IChunkSet processSet(IChunk chunk, IChunkGet get, IChunkSet set) {
+    public IChunkSet processSet(final IChunk chunk, final IChunkGet get, final IChunkSet set) {
-        ChunkFilterBlock filter = threadIdToFilter.getUnchecked(Thread.currentThread().getId());
+        final ChunkFilterBlock filter = threadIdToFilter.getUnchecked(Thread.currentThread().getId());
-        return filter.filter(chunk, get, set, this);
+        return filter.filter(chunk, get, set, MaskingExtent.this);
     }
 
     @Override
-    public void applyBlock(FilterBlock block) {
+    public void applyBlock(final FilterBlock block) {
-        //TODO: Find a way to make masking thread safe without having to synchonise the whole extent
+        if (!this.mask.test(block)) {
-        synchronized (this) {
-            if (!mask.test(block)) {
             block.setOrdinal(0);
         }
     }
-    }
 
     @Override
     public Extent construct(Extent child) {
         if (child == getExtent()) return this;
-        return new MaskingExtent(child, mask);
+        return new MaskingExtent(child, this.mask.copy(), this.threadIdToFilter);
+    }
+
+    @Override
+    public Filter fork() {
+        return new MaskingExtent(getExtent(), this.mask.copy(), this.threadIdToFilter);
     }
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/AbstractMask.java

@@ -19,9 +19,20 @@
 
 package com.sk89q.worldedit.function.mask;
 
+import org.jetbrains.annotations.Nullable;
+
 /**
  * A base class of {@link Mask} that all masks should inherit from.
  */
 public abstract class AbstractMask implements Mask {
 
+    @Override
+    @Nullable
+    public Mask copy() {
+        try {
+            return (Mask) super.clone();
+        } catch (CloneNotSupportedException e) {
+            return null;
+        }
+    }
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BiomeMask.java

@@ -102,4 +102,9 @@ public class BiomeMask extends AbstractMask {
         return null;
     }
 
+    @Override
+    public Mask copy() {
+        return new BiomeMask(extent, new HashSet<>(biomes));
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BiomeMask2D.java

@@ -98,4 +98,9 @@ public class BiomeMask2D extends AbstractMask2D {
         return biomes.contains(biome);
     }
 
+    @Override
+    public Mask2D copy2D() {
+        return new BiomeMask2D(extent, new HashSet<>(biomes));
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BlockCategoryMask.java

@@ -56,4 +56,9 @@ public class BlockCategoryMask extends AbstractExtentMask {
     public Mask2D toMask2D() {
         return null;
     }
+
+    @Override
+    public Mask copy() {
+        return new BlockCategoryMask(getExtent(), category);
+    }
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BlockMask.java

@@ -328,4 +328,9 @@ public class BlockMask extends ABlockMask {
         }
         return new BlockMask(getExtent(), cloned);
     }
+
+    @Override
+    public Mask copy() {
+        return new BlockMask(getExtent(), ordinals.clone());
+    }
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BlockStateMask.java

@@ -28,6 +28,7 @@ import com.sk89q.worldedit.world.block.BlockState;
 import com.sk89q.worldedit.world.block.BlockType;
 import com.sk89q.worldedit.world.block.BlockTypes;
 
+import java.util.HashMap;
 import java.util.Map;
 import javax.annotation.Nullable;
 
@@ -82,4 +83,11 @@ public class BlockStateMask extends AbstractExtentMask {
     public Mask2D toMask2D() {
         return null;
     }
+
+    @Override
+    public Mask copy() {
+        Map<String, String> statesClone = new HashMap<>();
+        states.forEach(statesClone::put);
+        return new BlockStateMask(getExtent(), statesClone, strict);
+    }
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BlockTypeMask.java

@@ -70,6 +70,12 @@ public class BlockTypeMask extends AbstractExtentMask {
         }
     }
 
+    private BlockTypeMask(Extent extent, boolean[] types, boolean hasAir) {
+        super(extent);
+        this.types = types;
+        this.hasAir = hasAir;
+    }
+
     /**
      * Add the given blocks to the list of criteria.
      *
@@ -134,4 +140,9 @@ public class BlockTypeMask extends AbstractExtentMask {
         return null;
     }
 
+    @Override
+    public Mask copy() {
+        return new BlockTypeMask(getExtent(), types.clone(), hasAir);
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/BoundedHeightMask.java

@@ -57,4 +57,10 @@ public class BoundedHeightMask extends AbstractMask {
         return null;
     }
 
+    @Override
+    public Mask copy() {
+        // The mask is not mutable. There is no need to clone it.
+        return this;
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/ExistingBlockMask.java

@@ -55,4 +55,10 @@ public class ExistingBlockMask extends AbstractExtentMask {
         return null;
     }
 
+    @Override
+    public Mask copy() {
+        // The mask is not mutable. There is no need to clone it.
+        return this;
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/ExpressionMask.java

@@ -89,4 +89,9 @@ public class ExpressionMask extends AbstractMask {
         return new ExpressionMask2D(expression, timeout);
     }
 
+    @Override
+    public Mask copy() {
+        return new ExpressionMask(expression.clone(), timeout);
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/ExpressionMask2D.java

@@ -72,4 +72,9 @@ public class ExpressionMask2D extends AbstractMask2D {
         }
     }
 
+    @Override
+    public Mask2D copy2D() {
+        return new ExpressionMask2D(expression.clone(), timeout);
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/InverseMask.java

@@ -31,4 +31,9 @@ public class InverseMask extends AbstractMask {
     public Mask inverse() {
         return mask;
     }
+
+    @Override
+    public Mask copy() {
+        return new InverseMask(mask.copy());
+    }
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/InverseSingleBlockStateMask.java

@@ -18,6 +18,12 @@ public class InverseSingleBlockStateMask extends ABlockMask {
         this.ordinal = state.getOrdinalChar();
     }
 
+    private InverseSingleBlockStateMask(Extent extent, char ordinal, boolean isAir) {
+        super(extent);
+        this.ordinal = ordinal;
+        this.isAir = isAir;
+    }
+
     @Override
     public boolean test(BlockVector3 vector) {
         int test = getExtent().getBlock(vector).getOrdinal();
@@ -40,4 +46,9 @@ public class InverseSingleBlockStateMask extends ABlockMask {
     public Mask inverse() {
         return new SingleBlockStateMask(getExtent(), BlockState.getFromOrdinal(ordinal));
     }
+
+    @Override
+    public Mask copy() {
+        return new InverseSingleBlockStateMask(getExtent(), ordinal, isAir);
+    }
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/InverseSingleBlockTypeMask.java

@@ -27,4 +27,10 @@ public class InverseSingleBlockTypeMask extends ABlockMask {
     public BlockType getBlockType() {
         return BlockTypes.get(internalId);
     }
+
+    @Override
+    public Mask copy() {
+        // The mask is not mutable. There is no need to clone it.
+        return this;
+    }
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/Mask.java

@@ -100,4 +100,10 @@ public interface Mask {
     default boolean replacesAir() {
         return false;
     }
+
+    /**
+     * Returns a copy of the mask. Usually for multi-threaded operation
+     * @return a clone of the mask
+     */
+    Mask copy();
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/Mask2D.java

@@ -34,4 +34,6 @@ public interface Mask2D {
      */
     boolean test(BlockVector2 vector);
 
+    Mask2D copy2D();
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/MaskIntersection.java

@@ -33,6 +33,7 @@ import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
 import java.util.function.Function;
+import java.util.stream.Collectors;
 import javax.annotation.Nullable;
 
 import static com.google.common.base.Preconditions.checkNotNull;
@@ -45,9 +46,9 @@ import static org.slf4j.LoggerFactory.getLogger;
  */
 public class MaskIntersection extends AbstractMask {
 
-    private final Set<Mask> masks;
+    protected final Set<Mask> masks;
-    private Mask[] masksArray;
+    protected Mask[] masksArray;
-    private boolean defaultReturn;
+    protected boolean defaultReturn;
 
     /**
      * Create a new intersection.
@@ -60,6 +61,12 @@ public class MaskIntersection extends AbstractMask {
         formArray();
     }
 
+    protected MaskIntersection(Set<Mask> masks, Mask[] masksArray, boolean defaultReturn) {
+        this.masks = masks;
+        this.masksArray = masksArray;
+        this.defaultReturn = defaultReturn;
+    }
+
     public static Mask of(Mask... masks) {
         Set<Mask> set = new LinkedHashSet<>();
         for (Mask mask : masks) {
@@ -250,4 +257,11 @@ public class MaskIntersection extends AbstractMask {
         return new MaskIntersection2D(mask2dList);
     }
 
+    @Override
+    public Mask copy(){
+        Set<Mask> masks = this.masks.stream().map(Mask::copy).collect(Collectors.toSet());
+        Mask[] maskArray = (Mask[]) Arrays.stream(this.masksArray).map(Mask::copy).toArray();
+        return new MaskIntersection(masks, maskArray, this.defaultReturn);
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/MaskIntersection2D.java

@@ -25,6 +25,7 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.stream.Collectors;
 
 import static com.google.common.base.Preconditions.checkNotNull;
 
@@ -33,7 +34,7 @@ import static com.google.common.base.Preconditions.checkNotNull;
  */
 public class MaskIntersection2D implements Mask2D {
 
-    private final Set<Mask2D> masks = new HashSet<>();
+    protected final Set<Mask2D> masks = new HashSet<>();
 
     /**
      * Create a new intersection.
@@ -97,4 +98,10 @@ public class MaskIntersection2D implements Mask2D {
         return true;
     }
 
+    @Override
+    public Mask2D copy2D() {
+        Set<Mask2D> masksCopy = this.masks.stream().map(Mask2D::copy2D).collect(Collectors.toSet());
+        return new MaskIntersection2D(masksCopy);
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/MaskUnion.java

@@ -22,12 +22,14 @@ package com.sk89q.worldedit.function.mask;
 import com.sk89q.worldedit.math.BlockVector3;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map.Entry;
 import java.util.Set;
 import java.util.function.Function;
+import java.util.stream.Collectors;
 import javax.annotation.Nullable;
 
 /**
@@ -55,6 +57,10 @@ public class MaskUnion extends MaskIntersection {
         super(mask);
     }
 
+    private MaskUnion(Set<Mask> masks, Mask[] maskArray, boolean defaultReturn) {
+        super(masks, maskArray, defaultReturn);
+    }
+
     public static Mask of(Mask... masks) {
         Set<Mask> set = new LinkedHashSet<>();
         for (Mask mask : masks) {
@@ -111,4 +117,11 @@ public class MaskUnion extends MaskIntersection {
         }
         return new MaskUnion2D(mask2dList);
     }
+
+    @Override
+    public Mask copy() {
+        Set<Mask> masksCopy = masks.stream().map(Mask::copy).collect(Collectors.toSet());
+        Mask[] maskArray = (Mask[]) Arrays.stream(masksArray).map(Mask::copy).toArray();
+        return new MaskUnion(masksCopy, maskArray, defaultReturn);
+    }
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/MaskUnion2D.java

@@ -22,6 +22,8 @@ package com.sk89q.worldedit.function.mask;
 import com.sk89q.worldedit.math.BlockVector2;
 
 import java.util.Collection;
+import java.util.Set;
+import java.util.stream.Collectors;
 
 /**
  * Tests true if any contained mask is true, even if it just one.
@@ -59,4 +61,10 @@ public class MaskUnion2D extends MaskIntersection2D {
         return false;
     }
 
+    @Override
+    public Mask2D copy2D() {
+        Set<Mask2D> masksCopy = masks.stream().map(Mask2D::copy2D).collect(Collectors.toSet());
+        return new MaskUnion2D(masksCopy);
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/Masks.java

@@ -92,6 +92,11 @@ public final class Masks {
             public boolean test(BlockVector2 vector) {
                 return !mask.test(vector);
             }
+
+            @Override
+            public Mask2D copy2D() {
+                return Masks.negate(mask.copy2D());
+            }
         };
     }
 
@@ -113,6 +118,11 @@ public final class Masks {
             public Mask2D toMask2D() {
                 return mask;
             }
+
+            @Override
+            public Mask copy() {
+                return Masks.asMask(mask.copy2D());
+            }
         };
     }
 
@@ -143,6 +153,18 @@ public final class Masks {
             return this;
         }
 
+        // No need to properly clone an always true mask
+        @Override
+        public Mask copy() {
+            return new AlwaysTrue();
+        }
+
+        // No need to properly clone an always true mask
+        @Override
+        public Mask2D copy2D() {
+            return new AlwaysTrue();
+        }
+
     }
 
     protected static class AlwaysFalse implements Mask, Mask2D {
@@ -172,6 +194,18 @@ public final class Masks {
             return other;
         }
 
+        // No need to properly clone an always false mask
+        @Override
+        public Mask copy() {
+            return new AlwaysFalse();
+        }
+
+        // No need to properly clone an always true mask
+        @Override
+        public Mask2D copy2D() {
+            return new AlwaysFalse();
+        }
+
     }
 
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/NoiseFilter.java

@@ -96,4 +96,9 @@ public class NoiseFilter extends AbstractMask {
         return new NoiseFilter2D(getNoiseGenerator(), getDensity());
     }
 
+    @Override
+    public Mask copy() {
+        return new NoiseFilter(noiseGenerator, density);
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/NoiseFilter2D.java

@@ -87,4 +87,9 @@ public class NoiseFilter2D extends AbstractMask2D {
         return noiseGenerator.noise(pos.toVector2()) <= density;
     }
 
+    @Override
+    public Mask2D copy2D() {
+        return new NoiseFilter2D(noiseGenerator, density);
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/OffsetMask.java

@@ -105,4 +105,9 @@ public class OffsetMask extends AbstractMask {
         }
     }
 
+    @Override
+    public Mask copy() {
+        return new OffsetMask(mask.copy(), offset.toImmutable());
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/OffsetMask2D.java

@@ -92,4 +92,9 @@ public class OffsetMask2D extends AbstractMask2D {
         return getMask().test(mutable);
     }
 
+    @Override
+    public Mask2D copy2D() {
+        return new OffsetMask2D(mask.copy2D(), BlockVector2.at(offset.getX(), offset.getZ()));
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/RegionMask.java

@@ -72,4 +72,9 @@ public class RegionMask extends AbstractMask {
         return null;
     }
 
+    @Override
+    public Mask copy() {
+        return new RegionMask(region.clone());
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/SingleBlockStateMask.java

@@ -18,6 +18,12 @@ public class SingleBlockStateMask extends ABlockMask {
         this.ordinal = state.getOrdinalChar();
     }
 
+    private SingleBlockStateMask(Extent extent, char ordinal, boolean isAir) {
+        super(extent);
+        this.ordinal = ordinal;
+        this.isAir = isAir;
+    }
+
     @Override
     public boolean test(BlockVector3 vector) {
         int test = getExtent().getBlock(vector).getOrdinal();
@@ -50,4 +56,9 @@ public class SingleBlockStateMask extends ABlockMask {
         }
         return null;
     }
+
+    @Override
+    public Mask copy() {
+        return new SingleBlockStateMask(getExtent(), ordinal, isAir);
+    }
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/SingleBlockTypeMask.java

@@ -17,6 +17,12 @@ public class SingleBlockTypeMask extends ABlockMask {
         this.internalId = type.getInternalId();
     }
 
+    private SingleBlockTypeMask(Extent extent, int internalId, boolean isAir) {
+        super(extent);
+        this.internalId = internalId;
+        this.isAir = isAir;
+    }
+
     @Override
     public final boolean test(BlockState state) {
         return state.getBlockType().getInternalId() == internalId;
@@ -35,4 +41,9 @@ public class SingleBlockTypeMask extends ABlockMask {
     public boolean replacesAir() {
         return isAir;
     }
+
+    @Override
+    public Mask copy() {
+        return new SingleBlockTypeMask(getExtent(), internalId, isAir);
+    }
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/SolidBlockMask.java

@@ -35,4 +35,9 @@ public class SolidBlockMask extends BlockMask {
         return null;
     }
 
+    @Override
+    public Mask copy() {
+        return new SolidBlockMask(getExtent());
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/function/mask/WallMakeMask.java

@@ -0,0 +1,26 @@
+package com.sk89q.worldedit.function.mask;
+
+import com.sk89q.worldedit.math.BlockVector3;
+import com.sk89q.worldedit.regions.Region;
+
+public class WallMakeMask implements Mask {
+
+    private final Region region;
+
+    public WallMakeMask(Region region) {
+        this.region = region.clone();
+    }
+
+    @Override
+    public boolean test(BlockVector3 position) {
+        int x = position.getBlockX();
+        int z = position.getBlockZ();
+        return !region.contains(x, z + 1) || !region.contains(x, z - 1) || !region.contains(x + 1, z) || !region.contains(x - 1, z);
+    }
+
+    @Override
+    public Mask copy() {
+        return new WallMakeMask(region);
+    }
+
+}

worldedit-core/src/main/java/com/sk89q/worldedit/internal/expression/Expression.java

@@ -31,8 +31,10 @@ import org.antlr.v4.runtime.misc.ParseCancellationException;
 import org.antlr.v4.runtime.tree.ParseTreeWalker;
 
 import java.time.Instant;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Objects;
+import java.util.Set;
 
 /**
  * Compiles and evaluates expressions.
@@ -60,19 +62,55 @@ import java.util.Objects;
  * pass values for all slots specified while compiling.
  * To query slots after evaluation, you can use the {@linkplain #getSlots() slot table}.
  */
-public class Expression {
+public class Expression implements Cloneable {
 
     private final SlotTable slots = new SlotTable();
     private final List<String> providedSlots;
     private final ExpressionParser.AllStatementsContext root;
     private final Functions functions = Functions.create();
     private final CompiledExpression compiledExpression;
+    private final String initialExpression;
 
     public static Expression compile(String expression, String... variableNames) throws ExpressionException {
         return new Expression(expression, variableNames);
     }
 
     private Expression(String expression, String... variableNames) throws ExpressionException {
+        this.initialExpression = expression;
+
+        slots.putSlot("e", new LocalSlot.Constant(Math.E));
+        slots.putSlot("pi", new LocalSlot.Constant(Math.PI));
+        slots.putSlot("true", new LocalSlot.Constant(1));
+        slots.putSlot("false", new LocalSlot.Constant(0));
+
+        for (String variableName : variableNames) {
+            slots.initVariable(variableName)
+                .orElseThrow(() -> new ExpressionException(-1,
+                    "Tried to overwrite identifier '" + variableName + "'"));
+        }
+        this.providedSlots = ImmutableList.copyOf(variableNames);
+
+        CharStream cs = CharStreams.fromString(expression, "<input>");
+        ExpressionLexer lexer = new ExpressionLexer(cs);
+        lexer.removeErrorListeners();
+        lexer.addErrorListener(new LexerErrorListener());
+        CommonTokenStream tokens = new CommonTokenStream(lexer);
+        ExpressionParser parser = new ExpressionParser(tokens);
+        parser.removeErrorListeners();
+        parser.addErrorListener(new ParserErrorListener());
+        try {
+            root = parser.allStatements();
+            Objects.requireNonNull(root, "Unable to parse root, but no exceptions?");
+        } catch (ParseCancellationException e) {
+            throw new ParserException(parser.getState(), e);
+        }
+        ParseTreeWalker.DEFAULT.walk(new ExpressionValidator(slots.keySet(), functions), root);
+        this.compiledExpression = new ExpressionCompiler().compileExpression(root, functions);
+    }
+
+    private Expression(String expression, Set<String> variableNames) throws ExpressionException {
+        this.initialExpression = expression;
+
         slots.putSlot("e", new LocalSlot.Constant(Math.E));
         slots.putSlot("pi", new LocalSlot.Constant(Math.PI));
         slots.putSlot("true", new LocalSlot.Constant(1));
@@ -147,4 +185,8 @@ public class Expression {
         functions.setEnvironment(environment);
     }
 
+    public Expression clone() {
+        return new Expression(initialExpression, new HashSet<>(providedSlots));
+    }
+
 }