Hello there @aimbotRaz!
Checking around the community, this issue has popped up from time to time, and it boils down to the way Megalights is operating.
The feature doesn’t calculate lighting on every single frame. Instead, it casts multiple rays, then stacks multiple frames together to smooth out the shadows. So, when your camera is perfectly still, UE will just keep stacking frames on top of each other. And since grass blades and hair strands are quite thin, lighting will tend to bounce wrong, and generate the artifacts you are seeing. Then, when you move, the engine discards the frames and starts over, making the blue stuff dissapear.
To fix the problem, there are a few parameters to test around:
-
Changing the lighting data format to either Float16 RGBA or Float32 RGBA, using
r.MegaLights.LightingDataFormat 1or2 -
You can combine this change with
r.MegaLights.DownsampleMode 1, to clear up any remaining artifacts -
There’s also the option to adjust Megalights’ sample count, test with
r.MegaLights.NumSamplesPerPixel 2
-
Outside of Megalights, it’s worth testing to adjust your scene’s current AA setting. Go to Project Settings > Rendering, and test with both TSR and TAA.
If the issue persists, for further reading, please check the related case below: