anchor.diff:     *  SDL_GL_DeleteContext()
      *}
   
  -  extern DECLSPEC SDL_GLContext SDLCALL SDL_GL_CreateContext(SDL_Window *
  -                                                             window);
  +  function SDL_GL_CreateContext(window: PSDLWindow): TSDLGLContext cdecl external {$IFDEF GPC} name 'SDL_GL_CreateContext' {$ELSE} SDL_LibName {$ENDIF};
   
     {**
      *  Set up an OpenGL context for rendering into an OpenGL window.
  
positive.code:    *  The context must have been created with a compatible window.
     *}
  
    function SDL_GL_MakeCurrent(window: PSDLWindow; context: TSDLGLContext): SInt32;
  
    {**
     *  Set the swap interval for the current OpenGL context.
  
negative.code:    *  SDL_GL_SetSwapInterval()
     *}
  
    function SDL_GL_GetSwapInterval: SInt32 cdecl external {$IFDEF GPC} name 'SDL_GL_GetSwapInterval' {$ELSE} SDL_LibName {$ENDIF};
  
    {**
     *  Swap the OpenGL buffers for a window, if double-buffering is
     *  supported.
     *}
  
    procedure SDL_GL_SwapWindow(window: PSDLWindow) cdecl external {$IFDEF GPC} name 'SDL_GL_SwapWindow' {$ELSE} SDL_LibName {$ENDIF};
  
    {**
     *  Delete an OpenGL context.
  