BDPT bugs

[anchovy]

Not sure if this has been fixed in a more current nightly build but in build 2.45.01 with the BDPT

1. Dispersion produces black glass and rainbow fireflies. no dispersive glass looks correct.
2. Glass with multiple interfaces produces different result if the diffuse is black or white. This is not the case in non BDPT setups. its very easy to see with a glass tube as a simple example.

Any chance these may be fixed prior to 3.0?

Thanks!

-Michael

www.morphographic.com

[AndresAhumada]

Were is that Build?

[Zdravko]

1. Dispersion produces black glass and rainbow fireflies. no dispersive glass looks correct.
2. Glass with multiple interfaces produces different result if the diffuse is black or white. This is not the case in non BDPT setups. its very easy to see with a glass tube as a simple example.

Could you please upload an example scene or send it to: support@chaosgroup.com

[anchovy]

Could you please upload an example scene or send it to: support@chaosgroup.com

Zdravko-

Ive sent a link to the sample file. Im thinking the dispersion bug is possibly related to the more general BDPT refraction issue that I'm seeing.

Here is the scene with a standard glass setup (black in the diffuse) using the PPTracer. The results are as I would expect.



Here is the same file rendered with the BDPT



Here is the same scene but now the diffuse in the glass has been set to white.



Ill show an example with dispersion next.

Thanks!

-Michael

www.morphographic.com

[Zdravko]

We reproduced the issue and add it in our bug tracking system.
Thnak you for your feedback.

[anchovy]

Zdravko-

As promised here are some test using the various rendering methods with dispersion. I have little doubt that the issues are related but it may help to see some of the combinations.

Here is a brute force test using a HDR in the dome light with dispersion off. This is as I would expect, transparency in the right places and appropriate shadows. noisy but about the best you can expect.



Here is the same setup but with dispersion switched on for the glass. You can see the shadow becomes opaque incorrectly as well as the base of the prism becomes black. Not to mention the dispersion fails to resolve.



With PPT and no dispersion we also get a reasonable image.



PPT with dispersion on has similar issues with the shadows.



Finally BDPT with dispersion is wrong not only with the glass but also the shadow and the dispersion.



So lots of interrelated things going on there. Im sure the dome light is part of it but ill look at that specifically next.

Thanks!

-Michael

www.morphographic.com

[Dariusz Makowski (Dadal)]

Very interesting tests and so on !! Thanks!

[vlado]

Will fix that...

Best regards,
Vlado

[anchovy]

Here are a couple more tests this time with the PPT and an area light vs the dome HDR.

Area light with dispersion off


Area light with dispersion on


-Michael

www.morphographic.com

[anchovy]

And for completeness sake here are the BDPT versions

Area light with dispersion off


Area light with dispersion on


-Michael

www.morphographic.com

[jacksc02]

Ha! I think they have picked up that there is an issue

[tashko.zashev]

Hi Michael,

Thank you for your examples, I have updated the corresponding issue in our bug tracker.