The documentation for Gamescope has now been updated to note it supports a “subset of Reshade effects/shaders” and so this provides an easy way to layer “shader effects (ie. CRT shader, film grain, debugging HDR with histograms, etc) on top of whatever is being displayed in Gamescope without having to hook into the underlying process”.
To be clear, this functionality isn’t available in SteamOS yet but hopefully it will be coming soon.
This is awesome news! This means a shader could be applied regardless of game support. So say for example I’m playing an old 640x480 DirectDraw-era game, something that has no hardware-accelerated rendering at all. With this I could still apply a nice CRT shader over it regardless of rendering API support. And there’s countless games I’d always wished to do that to! This will really open the doors to something special.