Raytracing GI lighting incorrectly

Axemeister · Jun 2019

I've been trying out some RTX GI in an environment i'm working on, for the most part it looks really good, but on some specific meshes (walls and roofs) they're being completely lit up, unlike the other side of the room which looks fine. Below in the images you can see the wall in the first one being lit completely different to the adjecent wall/roof. And in the second the roof is inaccurate. I have already tried different lightmap resolutions, adding thicker geometry to walls etc.

My lighting setup is just one directional light using RTX indirect lighting.

I was wondering if anyone knows what could be causing this?

Thanks in advance, I aoreciate any help with this

Image: https://i.gyazo.com/3195f4575d95ae933eb43bc5aaba9484.jpg

Image: https://i.gyazo.com/ddb42c75d1a1238cd1e02d9bca80ecfd.jpg

Obscura · Jun 2019

Lightmap resolution is irrelevant when you use ray traced lighting. I would need more info. Show the settings of the light please. Make sure the light is set to movable, and ray traced shadows are enables. Also make sure that under the world settings, "force no precomputed shadows" is enabled. Also make sure that "r.raytracing.shadows.enabletwosidedgeometry" is set to 1.

Axemeister · Jun 2019

Hey Obscura, thanks for the reply. My light was already set to movable with rtx shadows. When changing the Force no precomputed shadows option it comes up with an error saying to build lighting once to change it. But after I enable that nothing happens when I build my lighting, as in it won't even build the lighting at all. Any ideas what could cause that? I really appreciate the help by the way man.

Image: https://i.gyazo.com/297dcfa36773ce035928489443336be4.png

Obscura · Jun 2019

When that checkbox is enabled, it forces the scene to use dynamic lighting so you don't need to build it anymore. That first build is to remove existing static lighting. Do you have that console command for 2 sided geometry enabled?

Axemeister · Jun 2019

Yes I put that console command on too

Obscura · Jun 2019

Can you give more details please? What does the scene look like without rtgi? Do you have a ray traced skylight in the scene? Whats the angle of the directional light? Can you reproduce the error in a simple scene populated with boxes?Anything would help. Its kinda hard to tell whats going on based only on this picture.

Axemeister · Jun 2019

I do not have a skylight in the scene. This is the scene as it currently is:

Image: https://i.gyazo.com/3ad96696ac7793ef12dc97b590b28e93.jpg

This its the scene with indirect lighting turned off:

Image: https://i.gyazo.com/ae2befcab6558ce408053e4e1840ee17.png

And this is the light angle: (Pointing towards the back right hand side of the room from above)

Image: https://i.gyazo.com/f40b82f85025b320f901a86705843132.jpg

Obscura · Jul 2019

Can you reproduce the error with a simple box layout? Also, is it possible that something is wrong with the vertex normals? How does the world normal pass looks like?

Axemeister · Jul 2019

The issue still remains with simple UE4 boxes, so it does not appear to be an issue with the meshes themselves. The left corner even lights up as though there is a point light there, which of course there isn't, there is only one directional light in my scene.

Image: https://i.gyazo.com/cd77525a742a8fbbc8279c7eabbdedb2.png

And here's the Normal pass, which to me doesn't seem to have any glaring issues

Image: https://i.gyazo.com/29f4fa105412f64af1a3e32863c0882c.jpg

Obscura · Jul 2019

Yep the normal pass looks correct. I will try to recreate your scene with boxes when I get home and see myself what happens. To clear things up a little bit, I also have an rtx card and I use the rtx features in Unreal as well, and I haven't run into this issue. I'll report back with my results later today.

Axemeister · Jul 2019

Thanks man, I really appreciate it. Also to clarify, I also have an RTX 2070 so raytracing shouldnt be an issue for my pc setup to run

Obscura · Jul 2019

Alright, I did some tests and your results looks very different from mine:

Image: https://us.v-cdn.net/5021068/uploads/editor/j8/ghqgto4ze7c6.png

Your one lacks the shadow detail in indirect lighting, and also the noise. It almost looks like you don't have some ray tracing setting enabled. GI always gives me some noise even on higher sample count (2 bounces and 5 samples in this case). It isn't this much visible on textured assets though. I still don't have much idea about whats going on in your scene. If you want, I can take a look at your project file.

Axemeister · Jul 2019

I'll start by going over my raytracing settings again. It's obviously working to a certain degree, there may be a setting I have missed somewhere that I haven't enabled. This was the tutorial I followed on how to set it up

https://youtu.be/ZzJ7QDixzoI?t=1497

Axemeister · Jul 2019

I just figured out that putting the light behind a wall is causing the same glowing/lighting up effect, as though light is bleeding through the mesh. The walls already have some geometry/thickness to them, they are not just flat planes. Does this narrow down the problem for you in any way?

Image: https://i.gyazo.com/f00b85f2f28feebd0b135715641c50d0.png

Obscura · Jul 2019

Not really, that is absolutely strange, since directional light doesn't really have a location

Axemeister · Jul 2019

Well by behind, I mean the light is shining in that direction with shadows turned on, meaning that wall should be in shadow theoretically

cupsster · Jul 2019

You might want to try to add some occluder object behind that wall if it is not solid object. Looks like it is not, like it was paper thin.. That might cause issues.

Ikatar · Jul 2020

EDIT

For anyone having the same issue:
Change skylight from movable to static. Not sure why that helps but it does.

Raytracing GI lighting incorrectly

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