Detecting rotate gestures

A common gesture for manipulating objects on the screen is to use the twist or rotate gesture. This is often more natural than entering a rotation value or dragging a cursor.

How to do it...

Another multifinger gesture that is very common is the rotate gesture. For a two-finger rotate, we can do something very similar to what we would do when implementing the ScaleGestureDetector instance. However, we do have to create a RotateGestureDetector instance ourselves as this is not currently provided by the framework. We will create RotateGestureDetector by preforming the following steps:

1. First, we need an interface that represents our gesture detector's events:

   public interface IOnRotateGestureListener {
     bool OnRotateBegin(RotateGestureDetector detector);
     void OnRotate(RotateGestureDetector detector);
     void OnRotateEnd(RotateGestureDetector detector);
   }

2. Then, we create the gesture detector type:

   public class RotateGestureDetector {
     private float oldX2, oldY2,...