title: android:two finger zoom in/out
body: <p>I draw an object (rectangle) on the screen and now I want to add two finger zooming to the viewport . I find some tutorial that was for zooming into an image , I changed/added that to my app , it runs but zoom in/out does not work! There's no error also ! 
  could you help me fixing that ? is this agood way to zoom in/out of view port?</p>
  
  <pre><code>public class android1 extends Activity implements OnTouchListener {
      /** Called when the activity is first created. */
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          this.requestWindowFeature(Window.FEATURE_NO_TITLE);
          getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                  WindowManager.LayoutParams.FLAG_FULLSCREEN);
          GLSurfaceView view = new GLSurfaceView(this);
          view.setRenderer(new OpenGLRenderer());
          setContentView(view);
          view.setOnTouchListener(this);
      }
  
     private static final String TAG = "Touch";
     // These matrices will be used to move and zoom image
     Matrix matrix = new Matrix();
     Matrix savedMatrix = new Matrix();
  
     // We can be in one of these 3 states
     static final int NONE = 0;
     static final int ZOOM = 2;
     int mode = NONE;
  
     // Remember some things for zooming
     PointF start = new PointF();
     PointF mid = new PointF();
     float oldDist = 1f;
  
  
     public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction() &amp; MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN:
           savedMatrix.set(matrix);
           start.set(event.getX(), event.getY());
           Log.d(TAG, "mode=DRAG");
  
           break;
        case MotionEvent.ACTION_POINTER_DOWN:
           oldDist = spacing(event);
           Log.d(TAG, "oldDist=" + oldDist);
           if (oldDist &gt; 10f) {
              savedMatrix.set(matrix);
              midPoint(mid, event);
              mode = ZOOM;
              Log.d(TAG, "mode=ZOOM");
           }
           break;
        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_POINTER_UP:
           mode = NONE;
           Log.d(TAG, "mode=NONE");
           break;
        case MotionEvent.ACTION_MOVE:
  
            if (mode == ZOOM) {
              float newDist = spacing(event);
              Log.d(TAG, "newDist=" + newDist);
              if (newDist &gt; 10f) {
                 matrix.set(savedMatrix);
                 float scale = newDist / oldDist;
                 matrix.postScale(scale, scale, mid.x, mid.y);
              }
           }
           break;
        }
  
        return true; // indicate event was handled
     }
  
     /** Show an event in the LogCat view, for debugging */
     private void dumpEvent(MotionEvent event) {
        String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE",
              "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };
        StringBuilder sb = new StringBuilder();
        int action = event.getAction();
        int actionCode = action &amp; MotionEvent.ACTION_MASK;
        sb.append("event ACTION_").append(names[actionCode]);
        if (actionCode == MotionEvent.ACTION_POINTER_DOWN
              || actionCode == MotionEvent.ACTION_POINTER_UP) {
           sb.append("(pid ").append(
                 action &gt;&gt; MotionEvent.ACTION_POINTER_ID_SHIFT);
           sb.append(")");
        }
        sb.append("[");
        for (int i = 0; i &lt; event.getPointerCount(); i++) {
           sb.append("#").append(i);
           sb.append("(pid ").append(event.getPointerId(i));
           sb.append(")=").append((int) event.getX(i));
           sb.append(",").append((int) event.getY(i));
           if (i + 1 &lt; event.getPointerCount())
              sb.append(";");
        }
        sb.append("]");
        Log.d(TAG, sb.toString());
     }
  
     /** Determine the space between the first two fingers */
     private float spacing(MotionEvent event) {
        float x = event.getX(0) - event.getX(1);
        float y = event.getY(0) - event.getY(1);
        return FloatMath.sqrt(x * x + y * y);
     }
  
     /** Calculate the mid point of the first two fingers */
     private void midPoint(PointF point, MotionEvent event) {
        float x = event.getX(0) + event.getX(1);
        float y = event.getY(0) + event.getY(1);
        point.set(x / 2, y / 2);
     }
  }
  </code></pre>