gui_set_screen - Man Page

#include <allegro.h>

void gui_set_screen(BITMAP *bmp);

This function can be used to change the bitmap surface the GUI routines draw to. This can be useful if you are using a double buffering or page  flipping system. Passing NULL will cause the default surface (screen) to be used again. Example:

   BITMAP *page[2];
   
   /* Allocate two pages of video memory */
   page[0] = create_video_bitmap(SCREEN_W, SCREEN_H);
   page[1] = create_video_bitmap(SCREEN_W, SCREEN_H);
   
   /* Page flip */
   show_video_bitmap(page[0]);
   gui_set_screen(page[0]);

gui_get_screen(3)

gui_get_screen(3).