set_dissolve_blender - Man Page

#include <allegro.h>

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

Enables a dissolve blender mode for combining translucent or lit  truecolor pixels. Randomly replaces the colours of some pixels in the  destination image with those of the source image. The number of pixels  replaced depends on the alpha value (higher value, more pixels replaced;  you get the idea :).

set_trans_blender(3), drawing_mode(3)

set_trans_blender(3).