SDL_UnlockSurface — Unlocks a previously locked surface.
#include "SDL.h"
| void
            SDL_UnlockSurface( | SDL_Surface * | surface ); | 
Surfaces that were previously locked using SDL_LockSurface must be unlocked with
      SDL_UnlockSurface. Surfaces
      should be unlocked as soon as possible.
It should be noted that since 1.1.8, surface locks are
      recursive. See SDL_LockSurface.