Dialog procedure drawing boxes onto the screen. allegro game programming library.
#include <allegro.h>
int d_box_proc(int msg, DIALOG *d, int c);
int d_shadow_box_proc(int msg, DIALOG *d, int c);
These draw boxes onto the screen, with or without a shadow.
exgui(3alleg4), exrgbhsv(3alleg4)