main.dart

@override
void onScaleUpdate(ScaleUpdateInfo info) {
  final currentScale = info.scale.global;

  if (currentScale.isIdentity()) {
    _processDrag(info);
  } else {
    _processScale(info, currentScale);
  }
}

void _processScale(ScaleUpdateInfo info, Vector2 currentScale) {
  final newZoom = _startZoom * ((currentScale.y + currentScale.x) / 2.0);
  camera.viewfinder.zoom = newZoom.clamp(_minZoom, _maxZoom);
}