Ticket #8031: move_screen.cpp

void OSystem_SDL_Common::move_screen(int dx, int dy, int height) {

        if ((dx == 0) && (dy == 0))
                return;

        /* FIXME: undraw mouse only if the draw rect intersects with the mouse rect */
        if (_mouse_drawn)
                undraw_mouse();

        if (SDL_LockSurface(sdl_screen) == -1)
                error("SDL_LockSurface failed: %s.\n", SDL_GetError());

        int offset = dx + dy * SCREEN_WIDTH;
        byte *src;
        
        int w;
        int pitch;

        if (dy < 0)
                w = SCREEN_WIDTH + dy;
        else
                w = SCREEN_WIDTH - dy;
        
        if (offset > 0) {
                // bottom to top
                src = (byte *)sdl_screen->pixels + SCREEN_WIDTH * (SCREEN_HEIGHT - 1);
                pitch = -SCREEN_WIDTH;
        } else if (offset < 0) {
                // top to bottom
                src = (byte *)sdl_screen->pixels - offset;
                pitch = SCREEN_WIDTH;
        }

        do {
                memmove(src + offset, src, w);
                src += pitch;
        } while (--height);

        SDL_UnlockSurface(sdl_screen);
}