Does anyone know why this is happening and how to fix it? UE5.5 & UE5.4
This is with the light source facing the mesh.
This is on the backside where the light source is facing.
Simple material masked.
This is with RVT.
Tutorial I am following, also seems like most people have this issue.
There’s no weird black parts in UE 5.1. Not sure about the other ones not mentioned in this post.
Maybe a bug?
TLDR
5.4 and up show black areas even with shadows turned off.
5.3 and down does not show black areas (as long as two sided is turned off)
It could be contact shadows
In the RVT it seems like the normals are messed up. I’d need to see the material to say how, but most likely they are in the wrong space (world instead of tangent or something like that). Or you need to invert the normals on part of the grass using the two sided sign node.
In the first 2 pictures, this is the expected behavior. Forget about grass for a second, and imagine a wall. The side of the wall that faces the sun will be more brightly lit than the side that doesn’t. The side facing the sun may be brighter or darker than the terrain depending on how high the sun is in the sky.
The grass is like a ton of tiny walls, so naturally they have a dark side too. At least, by default. While this is technically accurate lighting for the geometry, it’s not really how we perceive surfaces like grass at a distance. So to better match the expectations of our perception (which is that the grass is lit in the same manner as the ground), grass is usually given the same normal vector as the underlying terrain.
One way to do this is to sample the RVT normals and use them instead. Which takes us to the third picture where I assume you’re doing just that? But if you do it wrong, it’ll mess the lighting up even worse.
