For example, the SDL2 wiki "SDL_GetWindowSurface" sample code

	https://wiki.libsdl.org/SDL_GetWindowSurface

doesn't work with directfb unless there is a hardware accelerator AFAIK.  With "software" only, it exits with an error.  

The source code (SDL2/src/video/SDL_video.c)  call stack shown below shows why:

 #1 SDL_GetWindowSurface
 #2 SDL_CreateWindowFramebuffer
 #3 _this->CreateWindowFramebuffer == SDL_CreateWindowTexture for directFB
 #3 SDL_CreateWindowTexture
 #4 SDL_GetWindowData 

SDL_CreateWindowTexture executes the following code (SDL_video.c)  
        if (!renderer) {
            for (i = 0; i < SDL_GetNumRenderDrivers(); ++i) {
                SDL_RendererInfo info;
                SDL_GetRenderDriverInfo(i, &info);
                if (SDL_strcmp(info.name, "software") != 0) {
                    renderer = SDL_CreateRenderer(window, i, 0);
                    if (renderer) {
                        break;
                    }
                }
            }
        }
        if (!renderer) {
            return SDL_SetError("No hardware accelerated renderers available");

        /* Create the data after we successfully create the renderer (bug #1116) */


SDL_CreateRenderer() which calls SW_CreateRenderer() for "software" also does not work because SDL_GetWindowSurface gets called in the process. 

I am quite sure this all used to work in earlier versions of SDL2. Also Buildroot creates SDL2 with directfb used to work and no longer does (which is why I am writing this note).  Hence I am assuming this is a bug.   Not sure if bug #1116 commented in the source code is related or not.