Working emissive materials in RTGI (with screenshots)

[TommyBear]

@Juan_Canada

Hi Tommy,

Sorry for your frustration, you deserve a more detailed explanation that what we provided initially. The reason we decided not integrate this pull request is because we have plans to modify that area significantly to make it more performant. Your pull request is indeed correct and adds funcionality that surely users will find welcome. In fact, your implementation is familiar to us: we do pretty much the same in the reference path tracer (pathtracing.ush) for dealing with emissive geometry.

That technique is suitable for interactive rendering but slow for real time, where ray budgets are very low. In fact as you saw yourself you need to increase the amount of samples a lot, cranking it up to 30spp or more to get good results in simple scenes. We have plans to improve our light sampling techniques in the 4.24-4.25 time frame and these improvement will bring this funtionality together with other enhancements. We prefer not to integrate pull request that could collide with the changes we are already working on this particular area. Of course, you all are very welcome to integrate this pull request into your code base in the meantime.

Again, thanks so much for your pull request and sorry for not giving you a more detailed answer before.

Regards,

Juan

Perfect. Thank you Juan for the explanation This makes sense. Is the intention to handle sampling of material light contributions also, not just emissive geometry? It’s a distinction for me because of the detail you can get from any animated material light source versus a large flat light geo light.

Anyway, thank you very much for replying. All the best!

Tommy.

[Dan_Govier]

Hi Tommy, I’d just like to say a massive thank you for making this possible. I make heavy use of emissive lighting in my projects, and it was really disappointing that the stock Ray Tracing implementation doesn’t support it. I have a couple of quick questions if that’s ok?

Does this support GI bounce for emissive lighting? I think I’m only seeing direct lighting from emissives.

I get no Ray Tracing at all on spline meshes (not even path tracing), which I’m assuming is something Epic need to add to the RT engine itself?

Thanks again, and I’ve included I scene I’m working on which is lit 100% by RT emissives

Dan Govier

[TommyBear]

@Dan_Govier

Does this support GI bounce for emissive lighting? I think I’m only seeing direct lighting from emissives.

GI bounces count should affect this. The original code was taken from the RT-PT path and is almost identical to it

@Dan_Govier

I get no Ray Tracing at all on spline meshes (not even path tracing), which I’m assuming is something Epic need to add to the RT engine itself?

For 4.23, BSP brushes and Splines are not supported for RT. I’m sure Epic will add support soon.

@Dan_Govier

Thanks again, and I’ve included I scene I’m working on which is lit 100% by RT emissives

Hey no problem! Looks cool. Glad it was useful.

Tommy

[Leo_Rakes]

@TommyBear

GI bounces count should affect this. The original code was taken from the RT-PT path and is almost identical to it

For 4.23, BSP brushes and Splines are not supported for RT. I’m sure Epic will add support soon.

Hey no problem! Looks cool. Glad it was useful.

Tommy

This is really beautiful. We have been looking for ways to use self illumination materials to illuminate the scene in the virtual engine. We have tried vxgi before, but the effect is not so good.

This function is really great. Unfortunately, epic didn’t add it to the engine. I’m not very familiar with programming, but I want to add this function to the engine I use. Can you give me some simple help? For example, what steps should I use to add this cool feature to the engine I use?

I don’t have much programming skills. I’ve only used vs to build some versions of the unreal engine, and I’m currently using 4.23 and 4.24.

Thank you for your help

[jakealexdun]

@TommyBear

Okay it is a pull request for Master now, so 4.24 if Epic like it. If you are interested in integrating it into your own build, you can find the pull request here:
https://github.com/EpicGames/UnrealEngine/pull/6193

Good luck!

Tommy.

The link seems to be down, is there any other way I can get it to test out?

[archviz84]

@TommyBear Hi i am struggling to get emissive lighting with raytracing.
It will be great help if you show step by step process of achieving it.

[PorcoRosso87]

TommyBear Hi i am struggling to get emissive lighting with raytracing.
It will be great help if you show step by step process of achieving it.

Yeah, that would be awsome, i’ve faced many issues with emissive lights.
Unreal documentation isn’t useful about emissive lights with RT.

[Tim_Hobson]

@PorcoRosso87

Unreal documentation isn’t useful about emissive lights with RT.

That’s because it’s not yet a supported feature. It’s currently being worked on but I’m not sure if it’ll land in 4.26 or not.

Once the feature is part of a release, I’ll add it to the Ray Tracing documentation with additional details.

Tim

[Turbo_Papok]

Hey!

Is there a possibility to use this feature on the launcher version of the engine? As a plugin or something?

[Kelheor]

Actually, you can add support for it even in Epic Games Launcher’s build, just modify only shader code (in this case you won’t have a console switch to turn off this feature, but since it works only with brute force method (which is too heavy for real-time, but good for making screenshots/movies) and not in final gather, it still could be useful.

If you don’t have access to GitHub, here’s the modified version of the shader: RayTracingGlobalIlluminationRGS.usf - Google Drive
Put it here (editor should be closed): Epic Games\UE_4.25\Engine\Shaders\Private\RayTracing
Tested on UE 4.25

[Pellaaa93]

compilation error in 4.26… no way to use it?