main.dart

@override
void onScaleStart(ScaleStartInfo info) {
  _startZoom = camera.viewfinder.zoom;
}

@override
void onScaleUpdate(ScaleUpdateInfo info) {
  if (currentScale.isIdentity()) {
    _processDrag(info);
  }
}

void _processDrag(ScaleUpdateInfo info) {
  final delta = info.delta.global;
  final zoomDragFactor = 1.0 / _startZoom;
  final currentPosition = camera.viewfinder.position;

  camera.viewfinder.position = currentPosition.translated(
    -delta.x * zoomDragFactor,
    -delta.y * zoomDragFactor,
  );
}