Dynamic padding is transparent

[Kirill Chibisov]

The dynamic padding around the window is transparent, since the gl:Clear is called with 0 alpha afaics, so it should be called with a proper background color and alpha. You may also do that in shader, but since clear is called also during display init, you should do it there as well(it'll be noticeable on X11 if you don't do that in clear during init).