Slightly improve FlatRegion iteration

src/main/java/com/sk89q/worldedit/regions/CylinderRegion.java

@@ -368,6 +368,11 @@ public class CylinderRegion extends AbstractRegion implements FlatRegion {
         return false;
     }
 
+    @Override
+    public Iterator<BlockVector> iterator() {
+        return new FlatRegion3DIterator(this);
+    }
+
     @Override
     public Iterable<Vector2D> asFlatRegion() {
         return new Iterable<Vector2D>() {

src/main/java/com/sk89q/worldedit/regions/FlatRegion3DIterator.java

@@ -0,0 +1,63 @@
+package com.sk89q.worldedit.regions;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+import com.sk89q.worldedit.BlockVector;
+import com.sk89q.worldedit.Vector2D;
+
+public class FlatRegion3DIterator implements Iterator<BlockVector> {
+
+    private Iterator<Vector2D> flatIterator;
+    private int minY;
+    private int maxY;
+
+    private Vector2D next2D;
+    private int nextY;
+
+    public FlatRegion3DIterator(FlatRegion region, Iterator<Vector2D> flatIterator) {
+        this.flatIterator = flatIterator;
+        this.minY = region.getMinimumY();
+        this.maxY = region.getMaximumY();
+
+        if (flatIterator.hasNext()) {
+            this.next2D = flatIterator.next();
+        } else {
+            this.next2D = null;
+        }
+        this.nextY = minY;
+    }
+
+    public FlatRegion3DIterator(FlatRegion region) {
+        this(region, region.asFlatRegion().iterator());
+    }
+
+    @Override
+    public boolean hasNext() {
+        return next2D != null;
+    }
+
+    @Override
+    public BlockVector next() {
+        if (!hasNext()) {
+            throw new NoSuchElementException();
+        }
+
+        BlockVector current = new BlockVector(next2D.getBlockX(), nextY, next2D.getBlockZ());
+        if (nextY < maxY) {
+            nextY++;
+        } else if (flatIterator.hasNext()) {
+            next2D = flatIterator.next();
+            nextY = minY;
+        } else {
+            next2D = null;
+        }
+
+        return current;
+    }
+
+    @Override
+    public void remove() {
+        throw new UnsupportedOperationException();
+    }
+}

src/main/java/com/sk89q/worldedit/regions/Polygonal2DRegion.java

@@ -492,7 +492,7 @@ public class Polygonal2DRegion extends AbstractRegion implements FlatRegion {
      */
     @Override
     public Iterator<BlockVector> iterator() {
-        return new RegionIterator(this);
+        return new FlatRegion3DIterator(this);
     }
 
     @Override