Set up a surface for directly accessing the pixels.
int SDL_LockSurface(SDL_Surface * surface);
the SDL_Surface structure to be locked
Returns 0 on success or a negative error code on failure; call SDL_GetError() for more information.
Between calls to SDL_LockSurface() / SDL_UnlockSurface(), you can write to and read from
surface->pixels, using the pixel format stored in
surface->format. Once you are done accessing the surface, you should use SDL_UnlockSurface() to release it.
Not all surfaces require locking. If
(surface) evaluates to 0, then you can read and write to the surface at any time, and the pixel format of the surface will not change.
/* Make the pixels pointer valid in the surface */ SDL_LockSurface(surface); /* Surface is locked */ /* Direct pixel access on surface here */ SDL_UnlockSurface(surface); /* Surface is now unlocked */