protected override void MouseDown(MapDocument document, MapViewport viewport, PerspectiveCamera camera, ViewportEvent e)
{
if (viewport != ActiveViewport)
{
return;
}
if (e.Button != MouseButtons.Left || _mouseOver == CircleType.None)
{
return;
}
_mouseDown = _mouseOver;
_mouseDownPoint = new Vector3(e.X, e.Y, 0);
_mouseMovePoint = null;
e.Handled = true;
viewport.AquireInputLock(this);
}