The patch I posted recreates the exact effect you posted on my windows machine upon loading. Perhaps I'm missing something or your patch isn't working properly on my machine. My impression was a slitscan samples a scanline of a picture shifts it to the left and then samples the same scanline and keeps shifting. Can you clarify this for me? I really liked your patch and it gave me a bunch of cool ideas for shaders.
I've been having fun with the tex_plane_t/s and figured out a super simple way of doing slitscan. It may not be the most versatile implementation, since it relies on jit.gl.render to have an erase_color 0 0 0 0 and fsaa 0 on your jit.window. But it's damn simple, that's for sure!!