This method is called in response to the left mouse button being pressed on a component. The designer overrides the base form of this method to provide a "lasso" selection mechanism for components within the control.
You can pass a point in screen coordinates to the System.Windows.Forms.Control.PointToClient(System.Drawing.Point) method of the System.Windows.Forms.Control class to obtain the coordinates of the point relative to the upper-left corner of the control.