Env. Light Visibility Cache

[Dade]

Do you have any papers flying around or is this IT?

Nope, I think iRay was doing it but not sure.

[lacilaci]

So I was exploring a little what is causing such problems for luxcore in my scene and I kinda recreated the issue simplified..

It's basicaly poor performance with highly glossy bright object within a dark environment. For several reasons, but biggest problem is that the glossy object won't get much out of photonGI and then the reflections are super noisy with more complex scenes making things just worse. Some bug might be somewhere there too, I don't know...

I'm still not convinced about the env.cache visibility map thingy either.

first here's how the situation is handled by luxcore and cycles without any help (no visibility map for luxcore and no portals in cycles)

luxcore:

cycles:

very close performance here and everything pretty much looks as expected I think

then for luxcore I used env.cache and for cycles a portal and while the portal did a lot for cycles, visibility map just brings trouble for luxcore

Here's luxcore and visibility map:

and here even with PGI:

better a little bit, but look at cycles with portal:

note that cycles is withut any tricks, same bounces just brute force and portal...
Look also at the top of the box in luxcore version, it was ok without env.visibility cache...

So obviously to get some help for luxcore I can lower glossiness threshold to include the glossy objects in PGI:

This helps in this basic scene but could introduce problems in real world case. So now luxcore somewhat gets ahead but look at the top of the box. In cycles this is near clean but somehow luxcore cannot clean that part + some other smaller places...

So still some contact areas are noisy so I even lowered the bruteforce radius to 0:

this cleans some more noise but introduces problems even in this basic scene and still look at the top of the box or the area between the monkeys eyebrows down in the middle...

I assume this is partially a performance issue and maybe some bug aswell, not sure...

here's the scene:

luxcoreReflections.blend

(915.51 KiB) Downloaded 155 times

I don't know to what extent or even if it's related to env.cache but while portals do a lot for cycles even with glossy objects, env.cache and PGI won't help anything with highly glossy objects and things can look pretty bad in dark environment which makes the bright noise even more stand out.

[FarbigeWelt]

Nice test setup, it shows clearly what you want to show.
Maybe you are right and the noise in the mirror of the shoe shop, the noise around the tap of the kitchen and the noise here on the box‘ surface have something in common in the algorithms.

[zuljin3d]

lacilaci scene
300 samples+pgi+vis map cache

[FarbigeWelt]

lacilaci scene
300 samples+pgi+vis map cache

But the top of the box remains noisy...

[Dade]

So I was exploring a little what is causing such problems for luxcore in my scene and I kinda recreated the issue simplified..

There are 3 topics:

1) Env. Light Visibility Cache Vs. Portals direct light sampling

2) Indirect light sampling

3) Glossy materials with very low roughness (i.e. glossy nearly specular materials).

You should pick a single topic to investigate, may be a blend of 2 but looking into 3 at the same time is a perfect recipe for ending without a solution. To start I would keep #2 out of the picture because we already know PGI works well.

So, switch to direct light only renderings for testings. I'm going to check your scene (but with direct light only).

Another side note, I have the feeling the default BlendLuxCore values are wrong: https://github.com/LuxCoreRender/BlendL ... t-34530908

[Dade]

lacilaci scene
300 samples+pgi+vis map cache

But the top of the box remains noisy...

It is what I find puzzling and I'm looking into it.

[lacilaci]

Yeah, I'll try to keep it more focused next time. PGI is definitely not the source of problems here..

I think it's a combo of env. cache + glossy materials, or just env.cache problem.

[Dade]

It is what I find puzzling and I'm looking into it.

This is strange, with Env. Light Visibility Cache:

and without:

The material glossy roughness is under the threshold so the cache should not affect the rendering at all (!).

[lacilaci]

I think the same problem happens when you have a single object+hdri+env.cache enabled.. cause the reflections tend to look very noisy as well.
But it might be unrelated.