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Emitter in glass - mystery bug? Incorrect approach?

Posted: Wed Feb 06, 2019 4:45 am
by SarahC
Here's the scene if you want to look for yourself:
http://untamed.co.uk/miscFolder/bugExample.scn.zip (705 KB)

I rendered it, and saw that the lighting of the filament was wrong. I figured Thea was likely treating the bulb as a solid volume of glass so to fix it I realised I'd need to add the glass as a container for the emitting filament.

But the light continued to be rendered incorrectly!

I'm using TR1 rendering - and a sample limit of 4096 - so I don't think it's because I'm running out of "light bounces".

EDIT: Turning off "Shadow caster" for the glass itself solves the problem! What does this mean!?
http://kb.thearender.com/thea-studio-v1 ... scenes/#03 Doesn't mention shadows being turned off!
I'm just wondering why the shadows are the thing to destroy the rendered images?

Here is the image showing the filament light source not being visible through the bulb from light reflected on the floor.
2_Bug1.jpg
2_Bug1.jpg (61.58 KiB) Viewed 882 times

I can work around this by adding an "invisible" emitter BELOW the glass bulb below the glass, outside of its volume.
The light then correctly appears through the bulb - but for close ups and other angles, the specular reflection will come from the wrong angle.
1_Bug2.jpg
1_Bug2.jpg (46.07 KiB) Viewed 882 times
What's going on!?

Re: Emitter in glass - mystery bug? Incorrect approach?

Posted: Wed Feb 06, 2019 7:48 am
by SandroS
haven't got time to check scene as i'm heading out but there should be no need for the workarounds you suggest with this, and also no need for containers.

if your glass bulb is modelled as a solid then that is the problem.

to solve it model the bulb as in real life - the glass should have a thickness to and in so doing it creates a hollow inside where the filaments go. be sure also to avoid intersections of any kind, especially with the glass and filaments.

Re: Emitter in glass - mystery bug? Incorrect approach?

Posted: Wed Feb 06, 2019 5:42 pm
by Hieru
I'm not seeing a bug.

What you have is a high(ish)-poly emitter inside a clear glass object (with thickness). Both of these cause renders to take a long time to resolve and what looks like a bug is just the caustics forming inside the glass material.

Unless a bulb is the main focus of a scene, you should be able to get good results with thin glass, or thin glass blended with another material (single sided SSS if you are still using V1.5). Even then you'll still get some noise, but nowhere near the number of issues seen with your current setup.

Re: Emitter in glass - mystery bug? Incorrect approach?

Posted: Sat Feb 23, 2019 2:27 am
by SarahC
Thank you both for the important tips!

They get me much better results.

I noticed something - if I turn off "Project shadows" for the bulb glass, the "shadow on the inside" goes away too....

Very strange!

Re: Emitter in glass - mystery bug? Incorrect approach?

Posted: Sat Feb 23, 2019 5:10 pm
by Hieru
I can't really comment on things like disabling projected shadows. My focus is always photorealism so I tend to avoid 'cheating' techniques.