Ce Trivia

[Nicholas Ralabate]

What is the difference between exporting Ce in a Bind Export VOP, feeding a Constant VOP into the Ce input of Compute Lighting VOP and feeding the output of PBR Emission VOP into either the Ce or the layer input of the Compute Lighting VOP? 

 

It seems like even if I don't feed the Ce from a Bind Export VOP it into Compute Lighting it gets... combined/computed somehow (additively?).

 

The only other difference I notice is that I am only able to turn off emissive as light source when I use the PBR Emission VOP.  Is it possible to do the same if I am just using Bind Export VOP?

 

I am using PBR engine by the way...  super curious about what is going on under the hood.

Edited April 10, 2020 by xxyxxy

[anim]

not much difference, all of them in the end export Ce

6 minutes ago, xxyxxy said:

The only other difference I notice is that I am only able to turn off emissive as light source when I use the PBR Emission VOP.  Is it possible to do the same if I am just using Bind Export VOP?

because internally if the checkbox is off it only exports Ce for primary rays:

...
$Ce *= $illum || getraylevel() == 0;
...

so you can use similar logic yourself, either getraylevel() VEX function or Ray Bounce Level VOP

[Nicholas Ralabate]

Oh sweet, getraylevel() is new to me...  thanks for the reply!

I also found a few more details about how Ce is used on this page, but it made me wonder... since Compute Lighting VOP doesn't compute lighting in PBR mode, can it be essentially replaced with a layer unpack?

https://www.sidefx.com/docs/houdini/nodes/vop/computelighting.html

(Again, this is just for understanding purposes, not a production problem)

 

[anim]

2 minutes ago, xxyxxy said:

can it be essentially replaced with a layer unpack?

for the most part yes, I'm however not exactly familiar with how dispersion and nested dielectrict work in PBR, I'm under the impression PBR still needs those exports so Compute Lighting or at least guttet version with those exports may be important

[Nicholas Ralabate]

Ah, that's right I forgot about that checkbox on Mantra ROP... otherwise those exports aren't exported...  thanks!

 

I assume you meant transmission and nested dialectric though, I thought dispersion didn't need any additional exports...

 

 

(P.S. In the above network the Compute Lighting VOP is actually still exporting even when the Switch VOP isn't grabbing its input... so probably not the best test...  to use JUST the Unpack Layer VOP, you would also have to pipe Ce into a Bind Export VOP)

 

(P.P.S. You do in fact need to add a Layer Export VOP yourself if you want to use transmission...  there were a few of these inside Compute Lighting VOP dealing with transmission and nested dialectrics.  There was also one for dispersion, but this way seems to work without it...?)

 

 

Edited April 11, 2020 by xxyxxy