Performance issues with emissive material and large scatter

[tombyrom]

Hello,
I am seeing huge performance issues even on an extremely simple scene when using an emissive material on a large forestpack scatter. Not sure if it has anything to do with ForestPack or just an issue with Octane and using large amounts of an instanced objects with an emissive material.

See video, but effectively performance drops off a cliff the minute you add an emissive texture/black body etc to the Universal emissive slot. Prior to adding the emissive texture the responsiveness is really good. After adding the emissive performance is unusable with dense scatter.

Scene updates go from 500ms to like 30 seconds!

Video - https://drive.google.com/file/d/1JflWrI ... sp=sharing

I also noticed that my hard drive storage went down by about 20gbs in some cases on a separate scene! And I didn't come back until I restarted my computer.

What's happening here?

Octane 2025 16.01
ForestPack Pro 9.1.1

[paride4331]

Hi tombyrom,
I've done some testing, and while I'm not entirely sure, I imagine there is a limit to how many objects can be instantiated. I’m also not certain if there's a limit on the number of emitters, but if you remove the subdivision tool or convert the original pyramid with subdivision into a mesh, everything runs smoothly and feels fluid. I managed to get up to 10m in the distribution unit with minimal lag. However, going beyond that threshold causes issues, and at that point, the developers would need to step in to figure out what's going wrong.
In any case issue with subdivision could makes sense because every polygon on the surface increases not only the geometry but especially the weight and performance of the emitter, leading to artifacts, noise, etc. So unless you have a specific need, it's better to stick to the simplest geometries possible. Instead, use the same logic as low-poly: the real geometry has one emitter just for rendering and a simple, invisible geometry for actual lighting, or even better, an Octane light.
Regards
Paride

[tombyrom]

Thanks paride, in my original scene the material was on a flower mesh, with the emission coming from the flower petals. So each flower had a number of faces that would effectively emit light. I added the subdiv to the test pyramid to try and create a similar setup.

It is as you say much better the moment you remove the subdiv.

So it looks like you need to be very efficient when using emission on a material and make sure any mesh using the material is as optimized as possible because the moment you instance it and use it in a large scatter there is a huge multiplier in rendering cost.

I'll see if I can optimize the original flower mesh to reduce the amount of individual faces emitting light.

Coming from Vray I have created Tyflow particle systems with hundreds of thousands of particles/meshes with an emissive material and never had an issue - so just was not sure if something was wrong in Octane. I found some other Octane posts and emissive materials are very expensive on rendering...

[paride4331]

Hi tombyrom,
Here is an example of how to avoid issue using complex geometries with emitter
viewtopic.php?f=27&t=60648&p=310376&hilit=+bulb#p310376
Regards
Paride