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Caustics Question

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Caustics Question

Unread postby blazelet » Fri May 27, 2022 5:45 am

Are sharp caustics possible with Clarisse 4?

I am trying to do a caustics setup where a series of mirror panels are reflecting caustic light onto surrounding walls. I have quite a few panels, though, and they are maybe 1m square with 10cm gaps between them. I am using the dielectric material for the panels with reflective caustics enabled, and a standard diffuse material for the walls to pick up the reflection caustics.

My light source is a directional light with 0 degree angle. I've turned roughness off on the dielectric (0%) and the diffuse catcher also has no roughness. What I'm wanting is to get crisp caustic reflections on the surrounding surfaces, but they all come across with feathered edges - so much that it kind of looks more like a diffuse bounce (which I have disabled) because all the caustics are feathering together. I'd like to be able to see the gaps between the panels as occluding the caustics.

Interestingly, when I turn "specular reflection caustics only" on my caustics disappear, even though my materials are all 0% roughness. They are coming across as glossy reflection caustics and I don't understand why.

Can anyone help me make sense of what's happening? I can't share the scene but I can make a simpler sample scene if that would help. Thanks!
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Re: Caustics Question

Unread postby sam » Fri May 27, 2022 5:58 am

Hi there,

Caustics are resolved with material sampling since Clarisse is a unidirectional path tracer. If the angle of your light is 0 then there's no chance whatsoever to reach the light woth material sampling. So you can't get any caustics.

Then you should also have a look at that https://clarissewiki.com/5.0/roughness- ... ation.html

This alter roughness around the path to try to mitigate the sampling issue and fireflies.

Hope this helps,
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Re: Caustics Question

Unread postby blazelet » Fri May 27, 2022 6:03 am

Maybe it's possible, then, that I do have some diffuse bounce sneaking in? When I turn the dielectric reflection color to red, all my light in the scene turns red, and when I disable reflection caustics altogether the scene goes black ... so caustics definitely are doing something with a 0 degree angle and 0% roughness, but I bet its not doing what I think it is. Ill poke around and see if I can find it. Thank you Sam!
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Re: Caustics Question

Unread postby sam » Fri May 27, 2022 6:08 am

Try to set roughness noise optimization to 0
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Re: Caustics Question

Unread postby blazelet » Fri May 27, 2022 6:18 am

I just did that and it goes black. So now I think I understand, roughness noise optimization is essentially introducing roughness along the path ... being unidirectional, there's 0 chance for a material ray to hit a light with 0 radius since it's not tracing back to the light directly? And so the roughness noise optimization is causing the soft caustics, but is really necessary to render this is any reasonable amount of time ...

then specular caustic reflections are only possible with roughness noise optimization off, but then the light would have to have a physical size which will soften the caustics and resolve much more slowly?
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Re: Caustics Question

Unread postby sam » Fri May 27, 2022 6:19 am

Bingo! :)
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Re: Caustics Question

Unread postby blazelet » Fri May 27, 2022 6:20 am

Alright thank you for the clarification, frees me up to take another route :)
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Re: Caustics Question

Unread postby sam » Fri May 27, 2022 6:23 am

Well if you are a gamer you just unlocked an achievement/trophy "I know Clarisse's Path Tracer" ;)
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Re: Caustics Question

Unread postby blazelet » Fri May 27, 2022 5:22 pm

Ill take it! Life skill achieved. Thank you for helping me figure it out, these forums are great!
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Re: Caustics Question

Unread postby sam » Fri May 27, 2022 5:26 pm

Glad we can help! :)
And who knows, if you keep it up you'll end up getting the Platinum Trophy ;)
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