vsync - Waits for a vertical retrace to begin. Allegro game programming library.

       Waits  for  a  vertical  retrace to begin. The retrace happens when the electron beam in your monitor has
       reached the bottom of the screen and is moving back to the top ready for another scan. During this  short
       period  the  graphics  card isn't sending any data to the monitor, so you can do things to it that aren't
       possible at other times, such as altering the palette without causing  flickering  (snow).  Allegro  will
       automatically  wait for a retrace before altering the palette or doing any hardware scrolling, though, so
       you don't normally need to bother with this function.

       vsync - Waits for a vertical retrace to begin. Allegro game programming library.

set_palette(3alleg4), scroll_screen(3alleg4)

Allegro                                           version 4.4.3                                   vsync(3alleg4)

#include<allegro.h>voidvsync();