Hybrid Back/Forward path tracing (aka BiDir without MIS)

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B.Y.O.B.
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Re: Hybrid Back/Forward path tracing (aka BiDir without MIS)

Post by B.Y.O.B. »

Some quick tests.
Total Rendertime: 2 min per image (including cache building where necessary, cache build time was around 30 sec)
Hardware: Ryzen 7 2700x, RTX 2080
PhotonGI used default settings, apart from adjusted caustic photon radius.

I was surprised to see that the hybrid method can be used in addition to the caustic cache (middle image). However it is probably not intended, since the render seems incorrect to me (brighter caustics).

Note that the images with caustic photon cache show some extremely bright fireflies (with values around 100,000,000,000). Looks like a bug to me (nan/inf?). They also totally throw off the denoiser, producing complete garbage images.
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Hybrid Back/Forward
Hybrid Back/Forward
Hybrid Back/Forward + PhotonGI (indirect + caustic cache)
Hybrid Back/Forward + PhotonGI (indirect + caustic cache)
PhotonGI (indirect + caustic cache)
PhotonGI (indirect + caustic cache)
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Re: Hybrid Back/Forward path tracing (aka BiDir without MIS)

Post by lacilaci »

So let's say in theory, I could make a glass house (true thick geometry) and use caustics with it.

and if I could at the same time disable shadows for glass for pathtracer I could get near perfect simulation with true glass and excellent performance...

Like: glass visible for lighttracer(caustics) invisible for shadow/gi in backwards pathtracer.
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Re: Hybrid Back/Forward path tracing (aka BiDir without MIS)

Post by Dade »

epilectrolytics wrote: Sun Jun 23, 2019 4:15 pm But (nearly) no SDS-paths is a problem for me, especially since we now have a solution for this since three days with periodic caustic cache.
I understand that no more development should be invested into caustic cache and this is fine with me but please let's keep this on board until there is another solution to the SDS problem.
The solution is a fully functional BiDirVM, something that can now happen but not in v2.2, we need to stop and release v2.2 or is never going to be finished if we continue to add features.
epilectrolytics wrote: Sun Jun 23, 2019 4:15 pm In Blender Cycles render tab there is an option to choose between supported and experimental feature set.
Can we use this in Luxcore to hide the caustic cache from the user instead of discarding it?
It sounds good.
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Re: Hybrid Back/Forward path tracing (aka BiDir without MIS)

Post by Dade »

B.Y.O.B. wrote: Sun Jun 23, 2019 4:42 pm I was surprised to see that the hybrid method can be used in addition to the caustic cache (middle image). However it is probably not intended, since the render seems incorrect to me (brighter caustics).
Yes, you can (I want to remove caustic cache) but it doesn't make sense because you are computing the same solutoion 2 times (in different ways but 2 times).

P.S. if someone pop up and asks to render SDS paths with caustic cache, normal caustics with light paths and everything else with eye paths ... I will start to use the big axe I keep in my car box (for some wood work) to put some sense in people heads :mrgreen:
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Re: Hybrid Back/Forward path tracing (aka BiDir without MIS)

Post by Dade »

lacilaci wrote: Sun Jun 23, 2019 5:23 pm So let's say in theory, I could make a glass house (true thick geometry) and use caustics with it.

and if I could at the same time disable shadows for glass for pathtracer I could get near perfect simulation with true glass and excellent performance...

Like: glass visible for lighttracer(caustics) invisible for shadow/gi in backwards pathtracer.
If you use "path.hybridbackforward.partition = 0.0" (to trace only caustic light paths), it literally produces a "Caustic AOV" that can be used for many composing tricks.
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Re: Hybrid Back/Forward path tracing (aka BiDir without MIS)

Post by Dade »

B.Y.O.B. wrote: Sun Jun 23, 2019 4:42 pm Some quick tests.
In your rendering I see a bug I need to fix: "ES*L" paths (eye => any number of only specular bounces => light are not rendered at the moment in Hybrid Back/Forward).
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Re: Hybrid Back/Forward path tracing (aka BiDir without MIS)

Post by B.Y.O.B. »

Dade, did you see my question on the last page?
B.Y.O.B. wrote: Sun Jun 23, 2019 4:21 pm One question: does it make sense to use this for CPU-only rendering, or will Bidir still win there?
Dade wrote: Sun Jun 23, 2019 5:29 pm P.S. if someone pop up and asks to render SDS paths with caustic cache, normal caustics with light paths and everything else with eye paths ... I will start to use the big axe I keep in my car box (for some wood work) to put some sense in people heads :mrgreen:
I was definitely not thinking about that. :P
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Re: Hybrid Back/Forward path tracing (aka BiDir without MIS)

Post by B.Y.O.B. »

What I like most about this feature is that it's really easy to use - just enable it and you're done. Crazy simple compared to the caustic cache.

I rendered a quick animation with it: 90 frames with 40 sec rendertime per frame.
https://youtu.be/MXKYdekMgSE
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Re: Hybrid Back/Forward path tracing (aka BiDir without MIS)

Post by lacilaci »

amazing results, easy to use, i love it.
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Re: Hybrid Back/Forward path tracing (aka BiDir without MIS)

Post by Sharlybg »

Wonderfull !

For non technical like me.

Can we do this:
casa_naborana_led.jpg

And this (tyre rim caustics) :
0cb9ba48355409.5895b80bad27d.jpg

With this features ? #1 one Yes as example show but what about #2 ?
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