Occurs when the user presses a mouse button with the mouse pointer over a control.
Use the OnMouseDown event handler to implement any special processing that should occur as a result of pressing a mouse button.
The OnMouseDown event handler can respond to left, right, or center mouse button presses and shift key plus mouse-button combinations. Shift keys are the Shift, Ctrl, and Alt keys. X and Y are the pixel coordinates of the mouse pointer in the client area of the Sender.