Added Tweens.cycle() and Tweens.invert() methods (#1849)

Cycle is used for running delegate tween back and force and Invert is used to run delegate tween backward.

jme3-core/src/main/java/com/jme3/anim/tween/Tweens.java

@@ -213,6 +213,28 @@ public class Tweens {
         return new Loop(sequence(delegates), duration);
     }
 
+    /**
+     * Creates a tween that inverts the specified delegate tween.
+     *
+     * @param delegate the desired tween
+     * @return a new instance
+     */
+    public static Tween invert(Tween delegate) {
+        return new Invert(delegate);
+    }
+
+    /**
+     * Creates a tween that will cycle back and forth the specified delegate tween.
+     * When reaching the end, the tween will play backwards from the end until it
+     * reaches the start.
+     *
+     * @param delegate the desired tween
+     * @return a new instance
+     */
+    public static Tween cycle(Tween delegate) {
+        return sequence(delegate, invert(delegate));
+    }
+
     private static interface CurveFunction {
         public double curve(double input);
     }
@@ -761,4 +783,29 @@ public class Tweens {
             return getClass().getSimpleName() + "[delegate=" + delegate[0] + ", length=" + length + "]";
         }
     }
+
+    private static class Invert extends AbstractTween implements ContainsTweens {
+
+        private final Tween[] delegate = new Tween[1];
+
+        public Invert( Tween delegate ) {
+            super(delegate.getLength());
+            this.delegate[0] = delegate;
+        }
+
+        @Override
+        protected void doInterpolate(double t) {
+            delegate[0].interpolate((1.0 - t) * getLength());
+        }
+
+        @Override
+        public Tween[] getTweens() {
+            return delegate;
+        }
+
+        @Override
+        public String toString() {
+            return getClass().getSimpleName() + "[delegate=" + delegate[0] + ", length=" + getLength() + "]";
+        }
+    }
 }

jme3-examples/src/main/java/jme3test/model/anim/TestAnimMigration.java

@@ -32,6 +32,7 @@
 package jme3test.model.anim;
 
 import com.jme3.anim.*;
+import com.jme3.anim.tween.Tweens;
 import com.jme3.anim.tween.action.*;
 import com.jme3.anim.util.AnimMigrationUtils;
 import com.jme3.app.ChaseCameraAppState;
@@ -244,8 +245,11 @@ public class TestAnimMigration extends SimpleApplication {
 
             composer.action("Walk").setSpeed(-1);
 
+            composer.addAction("WalkCycle", new BaseAction(Tweens.cycle(composer.makeAction("Walk"))));
+
             composer.makeLayer("LeftArm", ArmatureMask.createMask(sc.getArmature(), "shoulder.L"));
 
+            anims.addFirst("WalkCycle");
             anims.addFirst("Blend");
             anims.addFirst("Sequence2");
             anims.addFirst("Sequence1");