set_multiply_blender - Man Page

#include <allegro.h>

void set_multiply_blender(int r, int g, int b, int a);

Enables a multiply blender mode for combining translucent or lit  truecolor pixels. Combines the source and destination images, multiplying  the colours to produce a darker colour. If a colour is multiplied by  white it remains unchanged; when multiplied by black it also becomes  black.

set_trans_blender(3), drawing_mode(3), exalpha(3)

exalpha(3), set_trans_blender(3).