Need help with sampleF()

[paco]

I'm currently at work so don't have time to code it - but will do so when I get a chance and post the diff.

Basically I just hard coded the layeredmatial getBSDF (?createBSDF) method to return a multiBSDF which contained both a specular reflector and a lambertian.

Then I altered the getWeight function in the specularReflection BxDF - and you can see the brightness fluctuate significantly when they are rendered (bidir + MLT). I spent a while looking at it and the multiBSDF methods look fine to me - and are similar to what I do in the layered mat. I suspect it's a bidir issue- but got lost looking through that code!

[paco]

Sorry for the delay - i'm away for work and have limited access to my files.

Attached is the patch and a sample scene - you might need to fix up some of the paths and supply your own hdri.

Here's the original result :

And here's what you get with a weight of 10.0f :

As you can see there is considerable darkening of the diffuse component.

[jeanphi]

Hi,

I might have spotted the issue.

Jeanphi

[paco]

Just noticed an update to MultiBSDF in the repo - does this fix the problem?

[jeanphi]

Hi,

I've not yet had time to test it, but it could.

Jeanphi

[paco]

Hi jeanphi,

any luck hunting down the bug?

[jeanphi]

Hi,

I haven't had time to test if the change fixed the issue, have you?

Jeanphi

[paco]

Just tested it, same result :

My gut feeling is that it's a weighting issue in bidir somewhere - i'm guessing one of the sample calls doesn't account for the pdf that gets returned, but I could be (and am often) wrong.