LPE issue with Light cache usage.

[haike_ivanicova]

Hello all,
I am trying to create custom light select render elements via Light pass expressions.
It seems that LPE doesn't work properly with Light cache. When i set secondary GI to Bruteforce, outputs are 100% correct.

Here is 2 very simple examples to show the problem:
01. Scene with only self illumination object without lights. LPE is: C.*O .
02. Scene with one Vray light. LPE: C.*L

Of cource, my LPEs used in real scenarios are more complex/specific, but in this examples are better vissible the differences.
There are missing GI rays when i used Light cache.
In the second example in the middle, i turned off "store direct Light" in light cache. Results are better here, but very far from 100%.

My question is whether it's a technical limitation or a bug?
In documentation there is no mention about light cache limitation.
Rendered in vray 5.2.

Thanks for your ideas.

[^Lele^]

Thanks for the heads up, will poke the devs and open a ticket if needed.
It's generally best to use brute force GI, indeed, when LPEs are to be used.
They are generally not playing well with light caching (IRMap too, f.e.), as some paths are grouped together inside the cache, and can't be unraveled later.
We'll make sure to make a note of this in the docs.
I'll let you know if this is to be considered a bug, or a limitation like the one with IRMap.

In the while, try CD*[LOB], which should grab all the diffuse lighting from all sources (this works with the LC.)
You can use the LPE builder to create your own expressions: samples presented by the UI are old, and perhaps need a refresh.

[haike_ivanicova]

Thank for your answer,
My plan was to use LPEs as light selects for individual lights and at the same time combine multiple elements to reduce number of files. For Example:
-DirectLight + SSS + GI: C<T[SG]>*<[TR]D>.*L
-Direct + Indirect reflection: C<T[SG]>*<R[GS]>.*L
....so i cannot really use [LOB]
Brute Force is much more expensive in my scenes unfortunately, likely i cannot use it.

[^Lele^]

We have been finding out a few little niggles here and there with LPEs.
The devs are looking into them to figure out what can be fixed, and what not, and how to make the user experience, and functionalities, a bit better.

For now, you only have the option to use BF with LPEs to ensure you can split the paths out as you need.
We'll let you know as there will be updates and new insight into this.

[haike_ivanicova]

Great, looking forward , thank you very much.