man geta32 (3): Extract the alpha component form a 32-bit pixel format color. Allegro game programming library.

geta32(3) Extract the alpha component form a 32-bit pixel format color. Allegro game programming library.

SYNOPSIS

#include <allegro.h>

int geta32(int c);

Given a color in a 32-bit pixel format, this function extracts the alpha component (ranging 0-255).