[GZDoom 4.0.0] Glitchy rendering with FXAA on

[_mental_]

I see. What should we do with my "workaround" then?

[dpJudas]

Your fix is correct - removing the discard keyword solves the problem. I do wonder in which situations the discard would work, though. Maybe the FXAA shader was originally made with the assumption the last shader would be rendering into the original frame buffer image. Probably under the assumption the game engine used a more classical setup where all postprocess ends up in the swap chain backbuffer.

Maybe also why they made it optional with that define?

[_mental_]

Here is the description for this #define in the original source code.
Probably, I got it wrong during addition of FXAA. Or maybe it worked by occasion, and I left it defined.

[Graf Zahl]

I strongly suspect most image transitions do nothing on NVidia, which means the original contents were probably just the contents from last render (like with the OpenGL backend).

I once read in a technical paper from NVidia that they do not have different image layouts and therefore transitioning is a no-op on their current hardware.