I’ve been experimenting with hair for the past couple of weeks and I found a small issue with shadows. Basically what’s happening is that points lights seem to cast hair shadows in the opposite direction. It’s easier to understand if you see the image. This only seems to happen with point lights.
After rebuilding the level, the shadow is still there (it moves around if I move the character).
For me in 4.26 preview 7, the fix was in the point light’s advanced settings. When I turned off Cast Ray Tracing Shadows, the duplicate/opposite shadow went away. The expected shadow is still there and appears slightly softer.
The issue is when the Groom asset has Voxelize enabled, whether or not it also has Use Hair Raytracing Geometry enabled. The Cast Deep Shadow option on the point light also results in duplicate shadows, only they’re much more accurate than in the pictures with one raytracing pass on the light.
In both pictures, the Groom asset has Voxelize enabled and Use Hair Raytracing Geometry disabled. The only difference is the point light Cast Ray Tracing Shadows.