HWND pascal DetermineClickOwner(int row, int col)

  This function determines which window a mouse click or mouse
movement corresponds to. If multiple windows occupy a point, the
window which is on top will be returned. If a window has set the mouse
capture by calling SetCapture(), then all mouse messages will be sent
to this window.

Parameters
  row and col are the 0-based screen coordinates of the mouse click.

Returns
  The handle of the window where the mouse was clicked, or NULLHWND if
either no window encompassed that point, or if the window was hidden
or disabled.