onDrag method

Implementation

onDrag(DragUpdateDetails details)
{
  if (widget.model.draggable == false) return;
  setState(()
  {
    dx = dx! + details.delta.dx;
    dy = dy! + details.delta.dy;
    if (widget.model.modal == true)
    {
      var viewport = MediaQuery.of(context).size;
      if (dx! < 0) dx = 0;
      if (dy! < 0) dy = 0;
      if (dx! + (width!  + (padding * 2)) > viewport.width)  dx = viewport.width  - (width!  + (padding * 2));
      if (dy! + (height! + (padding * 2)) > viewport.height) dy = viewport.height - (height! + (padding * 2));
    }

    lastDx = dx;
    lastDy = dy;
    lastWidth  = width;
    lastHeight = height;
  });
}