Attempting to optimize, I’m looking at the impact of Roughness on performance - and what I’m finding is very surprising!
FPS drops **from 180 to 65 (!!) **as I’m changing **only **the roughness in my material!
My test scene is:
- Using **only **static lights, baked lighting
- Postprocess with SSR disabled
- Several Reflection Captures with 512k resolution
My material is:
- On a low-poly object with just one material assigned
- Using 2K Roughness, Diffuse, Normal maps, a very basic material
- Using no bump-mapping, no parallax, no ambient occlusion, no specular map
- Blend mode: Opaque, Shading model: default lit, Single sided.
I’ve tried a number of things to understand the problem:
- Getting similar results for DX11/DX12 and Forward/Deferred rendering
- Using less Reflection Captures in the scene lowers the impact, however I’m nowhere close to reaching memory limits and I see an impact even when reflection captures that are out-of-range are removed
- The <docs> on Reflection Environments explicitly state that Roughness should not have noticeable impact on performance
So what’s going on here? Is this normal behavior?
Here’s two screenshots with the stats from High/Low roughness: