It’s something I’ve been thinking about for some time now, nothing extraordinary but cool at times.
The height of a scanline as well as the refresh rate can be set, by default a scanline height equals the height of a pixel of the game. You can for instance have a scanline height that is exactly 1 pixel high according your screen, instead. (a scenario is explained in the shader documentation)
find it here: https://github.com/aybe/RetroArch-shaders (officially my shader repository :D)
(a .GIF animation example can be seen in the repository)