android - How to rotate an Actor with pinch gesture

Question

I'm trying to rotate an actor using the pinch gesture. The actor is actually rotating but there are times that the rotation is "stucked". I logged the deltaRotDeg (delta rotation in degrees) and there are times when the values jump. For example it's rotating in -42.25918 degrees then it will jump to 317.7408 degrees. I followed the rotation math here http://www.codeproject.com/Articles/319401/Simple-Gestures-on-Android

And here's my code. Is my math wrong or there's something wrong in the code?

public ActorGestureListener gestureListener = new ActorGestureListener() {
 @Override
    public void pinch(InputEvent event, Vector2 initialPointer1, Vector2 initialPointer2, Vector2 pointer1, Vector2 pointer2)  {
        Actor actor = event.getListenerActor();
        if(actor.getName().equals("valve")){
            Vector2 a = initialPointer2.sub(initialPointer1);
            Vector2 b = pointer2.sub(pointer1);
            a = a.nor();
            b = b.nor();
            float deltaRot = (float)(Math.atan2(b.y,b.x) - Math.atan2(a.y,a.x));
            float deltaRotDeg = (float)((deltaRot*180)/Math.PI);
            world.getValve().rotate(deltaRotDeg);
        }
    }

Answer 1

代替

float deltaRotDeg = (float)((deltaRot*180)/Math.PI);

和

float deltaRotDeg = (float)(((deltaRot*180)/Math.PI + 360) % 360);