I was just doing some experiments with lightmass when I noticed something very surprising. I was testing how well volumetric lightmaps work to capture light bounced off of landscape for moving objects, and I noticed that lightmass completely ignores UV mapping of the landscape, be it modified or default, and instead samples the textures on landscape in some arbitrary random UV space, which doesn’t match the actual UV mapping you see. Here are some examples:
I tried some modifications to both TextureCoordinate and LandscapeCoords, like rotations, different sizes, and they did affect the result of volumetric lightmap every time, but also, they never actually matched the surroundings.
What this pretty much means is that everyone who ever used volumetric lightmap on landscapes ever since this broken has likely got a very wrong results
So the volumetric lightmap itself works, but when it comes to landscapes, it samples something completely weird. It definitely doesn’t sample the result you see.
I am surprised people have so little interest in something so breaking. I guess game people don’t really give a ■■■■ about if indirect lighting is right or not
That’s my plan. But I want to first verify I did not make any mistake on my side, because I just struggle to believe no one noticed something so crucial to game visuals yet so broken. Once someone independently verifies it’s really not an user/setup mistake, I’ll make the bug report.
The person on the other end did not even bother to read it carefully enough to realize it’s not a volumetric light probe placement issue, but issue with the colors that the light probes gather. So obviously bCullBricksBelowLandscape does nothing.
So, in the end, there is currently no way to use volumetric lightmass with landscape in UE4. Which means there is currently no way to get proper indirect illumination from the landscape on any movable objects. And this issue probably won’t be solved anytime soon, if ever. Ultimately, if you have any project which includes landscape and movable objects, you can forget about indirect illumination. Even baked lightmass one.
So apparently the issue goes even deeper than that. I’ve made one of the objects on the landscape static, and the baked lighting on it has wrong bounce color as well.
So this doesn’t only affect volumetric lightmass bounces from landscape, but all bounced light from landscape, including baked one on static objects. But I would still very much appreciate if someone grabbed the project and verified it independently https://drive.google.com/open?id=1Xb…Qt5re7D6eyISIi because I am not that experienced with lightmass.
Since GPULightmass also relies on the original Lightmass’s material export, I modified GPULightmass to let it output diffuse channel to the lightmap, and this is how the material is exported:
Hmm… if I remember correctly, landscape is being broken into separate components before sent to lightmass. So I guess the issue is that the separate components are then starting their own UV coordinates from their local corners instead of the global UV coordinates of the entire landscape component array.
Thank you! Unfortunately I am not technically skilled to trust myself to touch the engine source code, but hopefully someone else will find it useful before (if) it gets the official fix
@Luoshuang
By the way there were some rumors that you are an Epic employee. Do you think you could pull some strings to make sure this doesn’t get into final 4.22, since my bug report got rejected?
Here are some examples:
Once someone independently verifies it’s really not an user/setup mistake, I’ll make the bug report.
Ultimately, if you have any project which includes landscape and movable objects, you can forget about indirect illumination. Even baked lightmass one.
I don’t have older ones installed, but I’ll have to bite the bullet.