osx man page for geta

getr(3alleg4)							  Allegro manual						     getr(3alleg4)

NAME

       getr, getg, getb, geta - Extract a color component from the current pixel format. Allegro game programming library.

SYNOPSIS

       #include <allegro.h>

       int getr(int c);

       int getg(int c);

       int getb(int c);

       int geta(int c);

DESCRIPTION

       Given  a color in the format being used by the current video mode, these functions extract one of the red, green, blue, or alpha components
       (ranging 0-255), calling the preceding 8, 15, 16, 24, or 32-bit get functions as appropriate. The alpha part is only meaningful for  32-bit
       pixels. Example:

	  int r, g, b, color_value;

	  color_value = getpixel(screen, 100, 100);
	  r = getr(color_value);
	  g = getg(color_value);
	  b = getb(color_value);

SEE ALSO

       getr8(3alleg4), getr_depth(3alleg4), makecol(3alleg4), set_color_depth(3alleg4), exalpha(3alleg4)

Allegro 							   version 4.4.2						     getr(3alleg4)