Added Transform.inverse() as a standard operation.

src/main/java/com/sk89q/worldedit/math/transform/CombinedTransform.java

@@ -21,8 +21,10 @@ package com.sk89q.worldedit.math.transform;
 
 import com.sk89q.worldedit.Vector;
 
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.List;
 
 import static com.google.common.base.Preconditions.checkNotNull;
 
@@ -60,6 +62,15 @@ public class CombinedTransform implements Transform {
         return vector;
     }
 
+    @Override
+    public Transform inverse() {
+        List<Transform> list = new ArrayList<Transform>();
+        for (int i = transforms.length - 1; i >= 0; i--) {
+            list.add(transforms[i].inverse());
+        }
+        return new CombinedTransform(list);
+    }
+
     @Override
     public Transform combine(Transform other) {
         checkNotNull(other);

src/main/java/com/sk89q/worldedit/math/transform/Identity.java

@@ -31,6 +31,11 @@ public class Identity implements Transform {
         return vector;
     }
 
+    @Override
+    public Transform inverse() {
+        return this;
+    }
+
     @Override
     public Transform combine(Transform other) {
         if (other instanceof Identity) {

src/main/java/com/sk89q/worldedit/math/transform/Transform.java

@@ -27,6 +27,13 @@ import com.sk89q.worldedit.Vector;
  */
 public interface Transform extends Function<Vector, Vector> {
 
+    /**
+     * Create a new inverse transform.
+     *
+     * @return a new inverse transform
+     */
+    Transform inverse();
+
     /**
      * Create a new {@link Transform} that combines this transform with another.
      *