Screenspace global illumination

[Guest]

Recently I tested various Reshade shaders that use depth buffer in GZDoom. I was very impressed with the RTGI shader which can add some illumination from bright areas, for example, the terrain looks red if the sky is red on the map. Unfortunately, these Reshade shaders do not work perfectly in GZDoom, because all 2D sprites become transparent and you can properly play with these shaders with only using 3D models. Also, when capturing a buffer through a reshade in GZDoom, there are various artifacts that appear in the sky. So, couldn’t you just build a similar effect into the engine? As far as I know, this is just a post-processing effect like SSAO which is already in GZDoom and does not require rewriting the engine.

Before: https://postimg.cc/4njkgynr
After: https://postimg.cc/56vcNJCj

[Graf Zahl]

Doing this in screen space is never going to work without artifacts.Not even the bloom pass which is supposedly a lot simpler, has enough information to properly apply its effect and tends to cause problems with bright but unlit elements. This will inevitably suffer from similar issues.