### Light Expression Help with refractions

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I am trying to get a direct refract through LPEs.

I did get the whole refraction result with:

C<TG>.*

Can anyone help me to just the direct refraction?

Thanks.
Edited by mzigaib - Sept. 23, 2020 17:28:26
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Actually I would like like to understand to how to split it in to direct and indirect refraction.

Thanks.
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Hi. The distinction between direct and indirect is the number of scattering events. If there's only one between the camera and the light, then it's direct. If there's more, then it's indirect.

So, direct refraction could be:
C<TG>L

Indirect refraction:
C<TG>.+L

You could substitute `[LO]`for `L`if you want to count emissive objects as lights.
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should be something like this
direct -> lpe:C<TG>L
indirect -> lpe:C<TG>.+L
combined -> lpe:C<TG>.*

EDIT:a bit too late to the party
Edited by tamte - Sept. 24, 2020 16:16:27
Tomas Slancik
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dlee
Hi. The distinction between direct and indirect is the number of scattering events. If there's only one between the camera and the light, then it's direct. If there's more, then it's indirect.

So, direct refraction could be:
C<TG>L

Indirect refraction:
C<TG>.+L

You could substitute `[LO]`for `L`if you want to count emissive objects as lights.

Closed form solids are unlikely to have any direct refract events reach the camera. I've found a good substitute for ‘direct’ scatter in the pathtracer's definition is for direct from an artist's perspective. Where the path is defined as a ray that interacts with the refractive surfaces only before reaching a light source. This way light coming through a window or glints in a rain drop would be described by this event. The question is, do you also put internal reflections in this bucket? As gemstone ‘fire’ is more of an internal reflection that's transmitted back through, i.e. TRT, or TRRT etc.
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Dudes! Thank you very much for the feedback.

That seems to work but it seems that mantra works differently in the direct refraction I don't get the blueish color that I have in my interior volume and speculars are a little different even using the same shader and lighting but I think that is normal.

Anyway thanks again for the help.
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jsmack
I've found a good substitute for ‘direct’ scatter in the pathtracer's definition is for direct from an artist's perspective. Where the path is defined as a ray that interacts with the refractive surfaces only before reaching a light source.
so you mean something like
```lpe:C<TG>+L
```
how would you define the complementary lightpaths starting with single <TG> event? To me it sounds like that any path that after first <TG> event has any non <TG> event and then zero or more of anything until it reaches the light. Tried
```lpe:C<TG>[^<TG>].*L
```
, but that's not the correct syntax, what would be the correct way to describe it?

EDIT: embedded lpes as code as they were not showing correctly
Edited by tamte - Sept. 25, 2020 11:37:48
Tomas Slancik
FX Supervisor
Method Studios, NY