add_clip_rect - Intersects a bitmap's clipping rectangle with the given
area. Allegro game programming library.
#include <allegro.h>
void add_clip_rect(BITMAP *bitmap, int x1, int y1, int x2, int y2);
Sets the clipping rectangle of the specified bitmap as the intersection
of its current clipping rectangle and the rectangle described by the
four coordinates.
set_clip_rect(3alleg), get_clip_rect(3alleg), set_clip_state(3alleg),
get_clip_state(3alleg)