Enabled fsr for downscaling

[ruanformigoni]

Hi,

This PR is related to issue #692, besides upscaling, FSR can yield good results for downscaling.

This is the current result of gamescope (from 5120x2160 to 2560x1080):

This is with fsr for downscaling (from 5120x2160 to 2560x1080):

The power lines, stage mounts, and everything else is better defined, with less jagged edges.

[vic-bay]

I tested this tweak, and this is the only "painless" way to get SSAA/DSR on linux for me. Works well on nvidia RTX 2070s.

gamescope -h 2160 -H 1080 -f -U --fsr-sharpness 20 -- %command%

Trees and grassblades:

Trees and obelisk sihoulette:

Grass blades:

Outer edge of the door frame:

[orowith2os]

Sorry to bug, but would you mind explaining how this works to me? How does FSR matter here for downscaling? Isn't downscaling directly from a higher resolution good enough for this case, or does it handle it differently, like by upscaling the original res to a higher res, and then downscaling?

[ruanformigoni]

Hi @orowith2os, as you can see by the screenshots, downscaling in gamescope does not produce good results due to a lack of a good downscaling algorithm. FSR makes the image smoother and less aliased, it is used as if it were a downscaling algorithm (although it is for upscaling).

[ruanformigoni]

Hey, I've implemented a proper bicubic algorithm for downscaling (from this source). To test it, please follow the instructions here. Thanks!

[rKsanu2MMYvypWePtQWM]

Since this PR request was made before #740, does it mean that the effect of this FSR "downscaling" is identical to enabling FSR on native resolution (since no actual downscaling is being performed)?

[ruanformigoni]

Hi @rKsanu2MMYvypWePtQWM , no. When rendering in a higher than native resolution FSR used bilinear filtering (I think, from reading the code) in the image before it was resized, so it looks smoother and less aliased. However I think that a dedicated shader for doing that is less of a hack. The usage of FSR from a higher resolution to native helps preserve detail that would not exist otherwise.