onScaleUpdate method
Implementation
void onScaleUpdate(double focalX, double canvasWidth, double scale) {
if (_disposed) return;
if (!constraints.enablePinchZoom) return;
if (canvasWidth <= 0 || !canvasWidth.isFinite || !focalX.isFinite) return;
final s = scale.clamp(0.1, 10.0);
value = value.zoomAroundCanvas(focalX, canvasWidth, s);
_applyConstraints();
}