LuxCoreRender Forums

@BruceXu There's a setting used in (.e.g) scenes/cornell/cornell-glass.cfg: path.hybridbackforward.enable = 1 which (when enabled) seems to cause the problem. It's not documented in the wiki, but it's definitely used in the code.

There is another setting in there: path.clamping.variance.maxvalue ...

Found the problem. I was using forward-backward tracing. When I switched to backward-only, it worked fine.

Which points to a bug in the forward-backward processing I think.

In the second case you are returning BLACK half of the times. How can the results be identical ?

Because the other half of the time I'm returning twice kt. 0.5 * kt * 2 + 0 == kt. Otherwise what is the point of glassmaterial multiplying its computed colour by pdfW?

MIS == Multiple Importance Sampling. Ah! Thank you.

I'd like, if I may, to show you some results I'm getting. First, what I think is the canonical case. Code (inside ::Sample() ) is:
const float threshold = 1.f;
if (passThroughEvent < threshold) {
// Transmit
*localSampledDir = -localFixedDir ...

Thanks for your advice.

I can confirm, I had ::IsDelta() set correctly. Didn't seem make a difference either way.

In the course of re-arranging my code to create a more obvious test case, suddenly it came right! As far as I can tell, it makes no difference to the result no matter how pdfW is set ...

Hi, Dade, thanks for the very quick reply.

#1: I just copied the GlassMaterial::Evaluate. It returns just Spectrum (). That being so, I don't understand where else my transmission colour is coming from.

#2: I'm trying to model a coated glass material whose properties have been measured physically ...

Hi.
I'm currently developing a modified glass material for Luxcore on behalf of a client of mine, but I'm getting some behaviour out of the Sample function which I don't understand, and I wonder if you can provide some advice?

Inside Sample, I have code like this (rather like that from glass.cpp ...