Simply put, when using DLSS or when turning on TAAU and reducing the Screen Percentage, any Post Process Material using the blend location After Tonemapping will produce strange results.
It’s most quickly visible by simply plugging in Absolute World Position into the Emissive slot on a PPM and applying it to the PostProcess. Normally it would produce this at 0,0,0 world origin:
However with DLSS enabled, or with TAAU enabled and reducing the screen percentage, due to this screen percentage reduction happening after the Temporal Upsampling, the World Position becomes offset, and swing around bizarrely as the camera turns. As well, it’s clearly pixelated from the upsampling.
Essentially, what’s happening is it’s sampling the world position to pixel at the wrong step, using the wrong resolution?
See “Post Process Material after Temporal Upsample” Screen Percentage with Temporal Upsample | Unreal Engine Documentation to see how to get the Viewport UV before and after the upsampling occurs, however I am at a loss as to how that can be used to get the right world position per pixel.
I tried to reconstruct World Position and maybe plug in the upsampled Viewport UV into scene depth but I don’t think that’s how it works. The reconstructed World Position sort of produces the same effect (works without upsampling, breaks just the same with it)
Anyone able to help me on this? Thanks!