Copy the window surface to the screen.
int SDL_UpdateWindowSurface(SDL_Window * window);
|window||the window to update|
Returns 0 on success or a negative error code on failure; call SDL_GetError() for more information.
This is the function you use to reflect any changes to the surface on the screen.
This function is equivalent to the SDL 1.2 API SDL_Flip().
This function is available since SDL 2.0.0.