set_write_alpha_blender (3alleg4)

#include <allegro.h>

void set_write_alpha_blender();

Enables the special alpha-channel editing mode, which is used for drawing alpha channels over the top of an existing 32-bit RGB sprite, to turn it into an RGBA format image. After calling this function, you can set the drawing mode to DRAW_MODE_TRANS and then write draw color values (0-255) onto a 32-bit image. This will leave the color values unchanged, but alter the alpha to whatever values you are writing. After enabling this mode you can also use draw_trans_sprite() to superimpose an 8-bit alpha mask over the top of an existing 32-bit sprite.

set_alpha_blender(3alleg4), draw_trans_sprite(3alleg4), drawing_mode(3alleg4), exalpha(3alleg4), extrans(3alleg4)