Overlays

RetroArch

Overlays should be possible to add when using RetroArch cores. Broadly speaking overlays serve three purposes:

1. To fill the black areas of the screen while playing games that were developed for a different aspect ratio than the device uses (e.g 4:3 games on a 16:9 screen)
2. To simulate scan lines to improve how games originally developed for CRT monitors are displayed on low-powered devices. For high-powered devices you probably want to use a shader
3. To display buttons on devices with touch-screens

Instructions on how to use overlays can be found here: Libretro Overlays. Suggested sample configurations for different systems can be found in Retrogamecorps Overlay and Shaders guide.

The default selection of overlays in Retroarch is limited, additional overlays can be found on Github, see e.g Duimn Retroarch-Overlays for 16:9 systems or Ourigen Perfect Overlays for 4:3 screens.

Stand-Alone Emulators

Overlays are not supported for standalone emulators. That said, if you are interested in developing the support to add them please check out how to start contributing here.