osx man page for get_color_depth

get_color_depth(3alleg4)					  Allegro manual					  get_color_depth(3alleg4)

NAME
       get_color_depth - Returns the current pixel color depth. Allegro game programming library.

SYNOPSIS
       #include <allegro.h>

       int get_color_depth(void);

DESCRIPTION
       Returns	the  current  pixel format. This can be very useful to know in order to write generic functions which select a different code path
       internally depending on the color depth being used.

       Note that the function returns whatever value you may have set previously with set_color_depth(), which can be different from  the  current
       color depth of the screen global variable. If you really need to know the color depth of the screen, use bitmap_color_depth().

SEE ALSO
       set_color_depth(3alleg4), bitmap_color_depth(3alleg4), exrgbhsv(3alleg4)

Allegro 							   version 4.4.2					  get_color_depth(3alleg4)