TControl.ClientToScreen
From OpenEUO
ME ClientToScreen(nX,nY) Translates a given point from client area coordinates to global screen coordinates.
Use ClientToScreen to convert a point whose coordinates are expressed locally to the control to the corresponding point in screen coordinates. In client area coordinates (0,0) corresponds to the upper left corner of the control's client area. In screen coordinates (0,0) corresponds to the upper left corner of the screen. Use ScreenToClient along with ClientToScreen to convert from one control's coordinate system to another control's coordinate system.
