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); }