Gamescope, the microcompositor from Valve that is used on the Steam Deck that can also be used on desktop Linux, just got a major upgrade.

What exactly does Gamescope do? Think of it like a piece of software that handles display output. So for the Steam Deck, it's what actually displays your games in Gaming Mode. For desktop Linux you can use it to run games directly to force resolution, AMD FSR, NVIDIA Image Scaling, border-less window, full-screen window and more.

Developer Joshua Ashton has been hacking away on HDR support, some of which has shipped in SteamOS 3.5 Preview but another fun addition recently is work on support for ReShade. 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".

On their Fediverse social media page, they mentioned with some screenshots:

I got Reshade shaders working under Gamescope/SteamOS today! Which means we can get Lilium/EndlesslyFlowering's amazing HDR Analysis shaders to work on all HDR games on SteamOS. This will be super useful for users and developers.