I primarily use retroarch on retropie. And while it’s an outstanding solution for emulation, there’s not a lot of headroom for shaders. I decided to create a bunch of overlays using maths and grids etc.
You may find some you like, or not. Also, I’m working on creating non-grid versions of everything there, in case someone likes the overlay, but would rather add their own special effects. These are for 1080p displays only.