onDragStart method

@override bool onDragStart(Point<double> localPosition)

Implementation

@override
bool onDragStart(Point<double> localPosition) {
  if (chart == null) {
    return false;
  }

  super.onDragStart(localPosition);

  // Save the current scaling factor to make zoom events relative.
  _scalingFactor = chart!.domainAxis!.viewportScalingFactor;
  _isZooming = true;

  return true;
}