You, or in my case Me, would need PNG overlays for every machine, twice. One for scratch effect, one without. My Outrun zip would have 6 fairly large PNGs. But make a separate scratch PNG and you only need 4 PNG overlays, 3 for the machines and 1 small one for the scratches. Then, you can use the scratch PNG on ALL overlays without extra Photoshop work.
At the moment, I would need to edit over 150 overlays to add a scratch effect layer, save them out and re-do the lay files and archive them to zip.
The other great thing about a separate PNG is you can make up loads of effects without touching the original overlay. For example, I have made refection, light reflection, and arcade reflection PNGs that can be added to the lay without the need for Photoshop. Bring up the MAME menu and you now have a whole load of machines to choose from with different effects.
Rion, they may work in Retroarch but the user would need to do all the cfg files themselves, and the lining up of the emulated image.
The beauty of MAME is the shaders auto rotate with the image for horizontal or vertical. So, scanlines auto-rotate without having to do separate configs. You don’t need to worry about Integer on or off, the scanlines just work.
The Vectrex ones are finished in MAME only, and I doubt I will return to Retroarch because the vector shaders are night and day better in MAME.