LuxCoreRender Forums

happyboy wrote: ↑Tue Aug 13, 2019 2:02 am

Dade wrote: ↑Sun Aug 11, 2019 10:54 am This is, hand down, the best stuff out of SIGGRAPH 2019: "Path Guiding in Production" (https://jo.dreggn.org/path-tracing-in-p ... index.html)

Having the author's implementation based on a well-known codebase (Mitsuba) is great, and I'm really looking forward to see it implemented in LuxCore

One word of caution though if anyone wants to implement it in LuxCore. You cannot reuse or copy parts of the source code.
The original implementation from Thomas Müller for Mitsuba and Mitsuba itself are licensed under GPLv3 while LuxCore is Apache v2.0 licensed.

I quote from the Mistuba homepage:
Remark: Being a "viral" license, the GPL automatically applies to all derivative work. Amongst other things, this means that without express permission, Mitsuba's source code is off-limits to those who develop rendering software not distributed under a compatible license.
Apache states: "GPLv3 software cannot be included in Apache projects. The licenses are incompatible".

We had these discussions in appleseed and our implementation (a running GSoC project) does not reuse Mitsuba code but is a unique implementation of the algorithms from the research papers.

Mango3 wrote: ↑Tue Aug 13, 2019 9:46 am We had these discussions in appleseed and our implementation (a running GSoC project) does not reuse Mitsuba code but is a unique implementation of the algorithms from the research papers.

Haha, actually I wanted to ask you about this on appleseed forum but I was just too lazy to register... Thanks for clafying!! Still, author's code is great for comparing result (and intermediate result).

BTW: I've been watching the development for several weeks. Once it's completed, I'll definitely give it a try (the current version of appleseed is too slow for our use case)

Dade wrote: ↑Sun Aug 11, 2019 10:54 am This is, hand down, the best stuff out of SIGGRAPH 2019: "Path Guiding in Production" (https://jo.dreggn.org/path-tracing-in-p ... index.html)

This path guiding + Vertex merging will open a wide window of possibility for jewellery and complexe lighting animation shots. for me this have priority over Shading rework.

But pathguiding is for cpu only, right?

lacilaci wrote: ↑Wed Aug 28, 2019 11:52 am But pathguiding is for cpu only, right?

Yes (and, for instance, for indirect light, PhotonGI is a lot faster than any path guiding can ever be).

Dade wrote: ↑Wed Aug 28, 2019 1:00 pm Yes (and, for instance, for indirect light, PhotonGI is a lot faster than any path guiding can ever be).

hmmm... I also found that lately. So what is the reason you think it's the best thing in SIGGRAPH 2019? Because PhotonGI is biased and you thnk it's good to have path guiding in LuxCore if someone prefer unbiased rendering? Currently rendering time is very important for us, do you think we can still benefit from path guiding in some way?

Some comments on this:
The beauty of path guiding is it allows to keep the simplicity of path tracer without running into issues like, for example, light leaks associated with photons, yet it is capable of rendering complex specular-diffuse-specular paths.
It is unbiased (no systematic errors introduced and consistent) means it converges to the correct solution and works with say moving light sources in animations without introducing artifacts. Path guiding just learns the radiative distribution in the scene and guides the paths to the important parts, thus making it less wasteful.

What Dade stated about render speed is true, cached GI solutions are generally faster and for the typical archviz-interior scenes hard to beat (speed wise). That's why V-Ray and Corona are so popular among archviz professionals.

Simple scenes don't benefit much from path guiding and for difficult lighting (except the sds paths) LuxCore user can use bidirectional path tracing.

All light transport methods have their pros/cons. Depends what type of scenes one wants to render which method works best.
For more animation/vfx focused renderer, like our appleseed, it is a very good addition to have.

Mango3 wrote: ↑Thu Aug 29, 2019 5:12 am Some comments on this:
The beauty of path guiding is it allows to keep the simplicity of path tracer without running into issues like, for example, light leaks associated with photons, yet it is capable of rendering complex specular-diffuse-specular paths.
It is unbiased (no systematic errors introduced and consistent) means it converges to the correct solution and works with say moving light sources in animations without introducing artifacts. Path guiding just learns the radiative distribution in the scene and guides the paths to the important parts, thus making it less wasteful.

What Dade stated about render speed is true, cached GI solutions are generally faster and for the typical archviz-interior scenes hard to beat (speed wise). That's why V-Ray and Corona are so popular among archviz professionals.

Simple scenes don't benefit much from path guiding and for difficult lighting (except the sds paths) LuxCore user can use bidirectional path tracing.

All light transport methods have their pros/cons. Depends what type of scenes one wants to render which method works best.
For more animation/vfx focused renderer, like our appleseed, it is a very good addition to have.

Well you're comparing caching and guiding as if they're competing for which does a better job.

Afaik these features aren't mutually exclusive, corona does pathguiding and uses caching. Also both vray's lightcache and corona's uhd cache don't suffer from lightleaks and can be used without problems for animations. They are both valuable, especially if they can be used both at the same time.

Biggest issue is pathguiding not being able to run on gpus. So unless pathguiding can bring same priced cpu ahead of same priced gpu in same generation in terms of performance, it just might be worth to explore other ways for getting photongi better and faster for example...

On another hand, luxcore already can already do hybrid rendering where cpu does lighttracing independently for caustics. Maybe having pathguiding for the cpu lighttracing part could give us caustics+sds on cpu while gpu does pathtracing?

Sadly of course in luxcore I've noticed heavy problems with leaking and odd reflections in more complex interiors with photongi.
Very thin objects (thin walls and floorboards on ground or wall decorations) can show a lot of problems no matter the settings.
And reflections of distant objects also tend to show weird variable bright spots.

Ondra Karlik (corona) on caustics:
https://www.youtube.com/watch?v=OEU-Ksg9wls

We badly need a solution for SDS-paths in LuxCore as well as faster unbiased rendering for technical renders (laser, volumes etc).
I don't know how fast BiDirVM will be once it works but if path guiding can help with that it will be very welcome for sure.

Also I think there is much more potential in hybrid rendering, that is splitting the render tasks along "ray classes" or something and have different devices have a go at it with different algorithms.