UIPinchGestureRecognizer is a concrete subclass of
UIGestureRecognizer that looks for pinching gestures involving two touches. When the user moves the two fingers toward each other, the conventional meaning is zoom-out; when the user moves the two fingers away from each other, the conventional meaning is zoom-in.
Pinching is a continuous gesture. The gesture begins (
began) when the two touches have moved enough to be considered a pinch gesture. The gesture changes (
changed) when a finger moves (with both fingers remaining pressed). The gesture ends (
ended) when both fingers lift from the view.
Interpreting the Pinching Gesture
var scale: CGFloat
The scale factor relative to the points of the two touches in screen coordinates.