set_invert_blender - Enables an invert blender mode. Allegro game programming library.
#include <allegro.h> void set_invert_blender(int r, int g, int b, int a);
Enables an invert blender mode for combining translucent or lit truecolor pixels. Blends the inverse (or negative) colour of the source with the destination.
set_trans_blender(3alleg), drawing_mode(3alleg)