debian man page for gui_mouse_b

gui_mouse_x(3alleg4)						  Allegro manual					      gui_mouse_x(3alleg4)

NAME
       gui_mouse_x,  gui_mouse_y,  gui_mouse_z, gui_mouse_b - Hook functions used by the GUI routines to access the mouse state. Allegro game pro-
       gramming library.

SYNOPSIS
       #include <allegro.h>

       extern int (*gui_mouse_x)();

       extern int (*gui_mouse_y)();

       extern int (*gui_mouse_z)();

       extern int (*gui_mouse_b)();

DESCRIPTION
       Hook functions, used by the GUI routines whenever they need to access the mouse state. By default these just return copies of the  mouse_x,
       mouse_y,  mouse_z,  and	mouse_b  variables,  but  they could be used to offset or scale the mouse position, or read input from a different
       source entirely.

Allegro 							   version 4.4.2					      gui_mouse_x(3alleg4)