NAME

       SDL_LockSurface - Lock a surface for directly access.

SYNOPSIS

       #include "SDL.h"

       int SDL_LockSurface(SDL_Surface *surface);

DESCRIPTION

       SDL_LockSurface  sets  up  a  surface  for directly accessing the pixels. Between calls to
       SDL_LockSurface and 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 SDL_MUSTLOCK(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.

       No operating system or library calls should be made between lock/unlock pairs, as critical
       system locks may be held during this time.

       It  should be noted, that since SDL 1.1.8 surface locks are recursive. This means that you
       can lock a surface multiple times, but each lock must have a match unlock.

           .
           .
           SDL_LockSurface( surface );
           .
           /* Surface is locked */
           /* Direct pixel access on surface here */
           .
           SDL_LockSurface( surface );
           .
           /* More direct pixel access on surface */
           .
           SDL_UnlockSurface( surface );
           /* Surface is still locked */
           /* Note: Is versions < 1.1.8, the surface would have been */
           /* no longer locked at this stage                         */
           .
           SDL_UnlockSurface( surface );
           /* Surface is now unlocked */
           .
           .

RETURN VALUE

       SDL_LockSurface returns 0, or -1 if the surface couldn't be locked.

SEE ALSO

       SDL_UnlockSurface