function returns the root window the pointer is logically on and the pointer
coordinates relative to the root windows origin.
the pointer is not on the same screen as the specified window, and
to child_return and zero to win_x_return and win_y_return.
the pointer coordinates returned to win_x_return and win_y_return
are relative to the origin of the specified window.
In this case,
returns the child that contains the pointer, if any,
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.