Improvements of the class:
- angle returned is total since rotation has begun
- removing unnecessary functions
- simplification
- get position of first pointer only after second pointer is down
public class RotationGestureDetector {
private static final int INVALID_POINTER_ID = -1;
private float fX, fY, sX, sY;
private int ptrID1, ptrID2;
private float mAngle;
private OnRotationGestureListener mListener;
public float getAngle() {
return mAngle;
}
public RotationGestureDetector(OnRotationGestureListener listener){
mListener = listener;
ptrID1 = INVALID_POINTER_ID;
ptrID2 = INVALID_POINTER_ID;
}
public boolean onTouchEvent(MotionEvent event){
switch (event.getActionMasked()) {
case MotionEvent.ACTION_DOWN:
ptrID1 = event.getPointerId(event.getActionIndex());
break;
case MotionEvent.ACTION_POINTER_DOWN:
ptrID2 = event.getPointerId(event.getActionIndex());
sX = event.getX(event.findPointerIndex(ptrID1));
sY = event.getY(event.findPointerIndex(ptrID1));
fX = event.getX(event.findPointerIndex(ptrID2));
fY = event.getY(event.findPointerIndex(ptrID2));
break;
case MotionEvent.ACTION_MOVE:
if(ptrID1 != INVALID_POINTER_ID && ptrID2 != INVALID_POINTER_ID){
float nfX, nfY, nsX, nsY;
nsX = event.getX(event.findPointerIndex(ptrID1));
nsY = event.getY(event.findPointerIndex(ptrID1));
nfX = event.getX(event.findPointerIndex(ptrID2));
nfY = event.getY(event.findPointerIndex(ptrID2));
mAngle = angleBetweenLines(fX, fY, sX, sY, nfX, nfY, nsX, nsY);
if (mListener != null) {
mListener.OnRotation(this);
}
}
break;
case MotionEvent.ACTION_UP:
ptrID1 = INVALID_POINTER_ID;
break;
case MotionEvent.ACTION_POINTER_UP:
ptrID2 = INVALID_POINTER_ID;
break;
case MotionEvent.ACTION_CANCEL:
ptrID1 = INVALID_POINTER_ID;
ptrID2 = INVALID_POINTER_ID;
break;
}
return true;
}
private float angleBetweenLines (float fX, float fY, float sX, float sY, float nfX, float nfY, float nsX, float nsY)
{
float angle1 = (float) Math.atan2( (fY - sY), (fX - sX) );
float angle2 = (float) Math.atan2( (nfY - nsY), (nfX - nsX) );
float angle = ((float)Math.toDegrees(angle1 - angle2)) % 360;
if (angle < -180.f) angle += 360.0f;
if (angle > 180.f) angle -= 360.0f;
return angle;
}
public static interface OnRotationGestureListener {
public void OnRotation(RotationGestureDetector rotationDetector);
}
}
How to use it:
- Put the above class in a separate file
RotationGestureDetector.java
- create a private field
mRotationDetector
of typeRotationGestureDetector
in your activity class and create a new instance of the detector during the initialization (onCreate
method for example) and give as parameter a class implementing theonRotation
method (here theactivity = this
). - In the method
onTouchEvent
, send the touch events received to the gesture detector with ‘mRotationDetector.onTouchEvent(event);
‘ - Implements
RotationGestureDetector.OnRotationGestureListener
in your activity and add the method ‘public void OnRotation(RotationGestureDetector rotationDetector)
‘ in the activity. In this method, get the angle withrotationDetector.getAngle()
Example:
public class MyActivity extends Activity implements RotationGestureDetector.OnRotationGestureListener {
private RotationGestureDetector mRotationDetector;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mRotationDetector = new RotationGestureDetector(this);
}
@Override
public boolean onTouchEvent(MotionEvent event){
mRotationDetector.onTouchEvent(event);
return super.onTouchEvent(event);
}
@Override
public void OnRotation(RotationGestureDetector rotationDetector) {
float angle = rotationDetector.getAngle();
Log.d("RotationGestureDetector", "Rotation: " + Float.toString(angle));
}
}
Note:
You can also use the RotationGestureDetector
class in a View
instead of an Activity
.