XQueryPointer - get pointer coordinates
Bool XQueryPointer(Display *display, Window w,
    Window *root_return, Window *child_return, int
    *root_x_return, int *root_y_return, int *win_x_return,
    int *win_y_return, unsigned int *mask_return);
  - child_return
- Returns the child window that the pointer is located in, if any.
- display
- Specifies the connection to the X server.
- mask_return
- Returns the current state of the modifier keys and pointer buttons.
- root_return
- Returns the root window that the pointer is in.
- root_x_return
- 
    
 
- root_y_return
- Return the pointer coordinates relative to the root window's origin.
- w
- Specifies the window.
- win_x_return
- 
    
 
- win_y_return
- Return the pointer coordinates relative to the specified window.
The XQueryPointer function returns the root window the pointer is
  logically on and the pointer coordinates relative to the root window's origin.
  If XQueryPointer returns False, the pointer is not on the same
  screen as the specified window, and XQueryPointer returns None
  to child_return and zero to win_x_return and win_y_return. If
  XQueryPointer returns True, the pointer coordinates returned to
  win_x_return and win_y_return are relative to the origin of the specified
  window. In this case, XQueryPointer returns the child that contains the
  pointer, if any, or else None to child_return.XQueryPointer returns the current logical state of the
    keyboard buttons and the modifier keys in mask_return. It sets mask_return
    to the bitwise inclusive OR of one or more of the button or modifier key
    bitmasks to match the current state of the mouse buttons and the modifier
    keys.
XQueryPointer can generate a BadWindow error.
  - BadWindow
- A value for a Window argument does not name a defined Window.
XGetWindowAttributes(3), XQueryTree(3)
Xlib - C Language X Interface