scroll_screen - Requests a hardware scroll request. Allegro game programming library.

       Attempts  to  scroll  the hardware screen to display a different part of the virtual screen (initially it
       will be positioned at 0, 0, which is the top left corner). You can use this to move  the  screen  display
       around  in a large virtual screen space, or to page flip back and forth between two non-overlapping areas
       of the virtual screen. Note that to draw outside the original position in the screen bitmap you will have
       to alter the clipping rectangle with set_clip_rect().

       Mode-X scrolling is reliable and will work on any card, other drivers may not work or not work  reliably.
       See the platform-specific section of the docs for more information.

       Allegro  will  handle  any  necessary  vertical retrace synchronisation when scrolling the screen, so you
       don't need to call vsync() before it. This means that scroll_screen() has the same time delay effects  as
       vsync().

       scroll_screen - Requests a hardware scroll request. Allegro game programming library.

       Returns  zero  on success. Returns non-zero if the graphics driver can't handle hardware scrolling or the
       virtual screen is not large enough.

set_gfx_mode(3alleg4),                show_video_bitmap(3alleg4),                request_scroll(3alleg4),
       request_video_bitmap(3alleg4), exscroll(3alleg4)

Allegro                                           version 4.4.3                           scroll_screen(3alleg4)

#include<allegro.h>intscroll_screen(intx,inty);