set_alpha_blender - Man Page

#include <allegro.h>

void set_alpha_blender();

Enables the special alpha-channel blending mode, which is used for  drawing 32-bit RGBA sprites. After calling this function, you can use  draw_trans_sprite() or draw_trans_rle_sprite() to draw a 32-bit source  image onto any hicolor or truecolor destination. The alpha values will be  taken directly from the source graphic, so you can vary the solidity of  each part of the image. You can't use any of the normal translucency  functions while this mode is active, though, so you should reset to one  of the normal blender modes (eg. set_trans_blender()) before drawing  anything other than 32-bit RGBA sprites.

set_trans_blender(3), draw_trans_sprite(3), draw_trans_rle_sprite(3), set_write_alpha_blender(3), exalpha(3), exrotscl(3), extrans(3)

draw_trans_rle_sprite(3), draw_trans_sprite(3), exalpha(3), exrotscl(3), extrans(3), makeacol(3), makeacol32(3), make_trans_font(3), set_blender_mode_ex(3), set_trans_blender(3), set_write_alpha_blender(3).