onRotateBegin
Responds to the beginning of a scaling gesture.
Reported by new pointers going down.
Return
Whether or not the detector should continue recognizing this gesture. For example, if a gesture is beginning with a focal point outside of a region where it makes sense, onRotateBegin() may return false to ignore the rest of the gesture.
Parameters
detector
The detector reporting the event - use this to retrieve extended info about event state.