makeacol32 - Man Page

#include <allegro.h>

int makeacol32(int r, int g, int b, int a);

Converts an RGBA color into a 32-bit display pixel format, which includes  an alpha (transparency) value. There are no versions of this routine for  other color depths, because only the 32-bit format has enough room to  store a proper alpha channel. You should only use RGBA format colors as  the input to draw_trans_sprite() or draw_trans_rle_sprite() after calling  set_alpha_blender(), rather than drawing them directly to the screen.

makeacol(3), set_alpha_blender(3), set_write_alpha_blender(3)

makecol8(3).