I've run into some retro-styled games lately that don't have any filters available. Specifically, Freedom Planet, Shantae: Risky's Revenge, and Shovel Knight. Shovel Knight looks pretty solid anyway - no scanlines but I think there is a filter - so I'm cool with that. But Shantae is low-res and blocky (DS port) so some scanlines would be really give those big old pixels some flair.
Now, I know that SweetFX has an Advanced CRT option. That does work with Freedom Planet, and I even made a tutorial on Steam
about getting it working. SweetFX doesn't seem to be compatible with Shovel Knight or Shantae, though. The former crashes, the latter process starts but can't be accessed.
So, are there any other options? It doesn't have to be anything complicated. I was looking to see if there was a general overlay you could use in Windows to add scanlines, since you could then run the games windowed borderless to get the effect in-game. But no luck. I know MAME and emulators have these options, but I don't know of any way to extract those effects and apply them to anything else.
So... any ideas?