handleVerticalDragStart method
Implementation
void handleVerticalDragStart(DragStartDetails details) {
  if (!enablePanning) {
    return;
  }
  _previousMovedPosition = null;
  _updateZoomStartDetails();
}void handleVerticalDragStart(DragStartDetails details) {
  if (!enablePanning) {
    return;
  }
  _previousMovedPosition = null;
  _updateZoomStartDetails();
}