Allegro 5 api
#include <allegro5/allegro.h> void al_set_separate_blender(int op, int src, int dst, int alpha_op, int alpha_src, int alpha_dst)
Like al_set_blender(3alleg5), but allows specifying a separate blending operation for the alpha channel. This is useful if your target bitmap also has an alpha channel and the two alpha channels need to be combined in a different way than the color components.
al_set_blender(3alleg5), al_get_blender(3alleg5), al_get_separate_blender(3alleg5)