Glass Solid/Dielectric/Plastic Transparent - Not Rendering Correctly

[dan.spore]

Hello -

I am baffled here. I start with a scene using a Glass Material for a tweeter dome. It is a transparent dome with a blue diffusor behind it which should show through the dome material. I am using physical lights in the scene. All is well when I start the scene, but when I began animating, the material stops rendering correctly. The blue diffusor now appears black.

-I have adjusted Global Illumination (from the default product mode) to 256 (just to be crazy) and it does nothing.
-I’ve turned GI on an off. I’ve moved between GPU and CPU modes.
-Tried turning on caustics. Nothing.
-Glass Basic works (although no roughness control), but no other transparent materials work.
-When I activate an HDRI at default brightness (1), it works again.

Any ideas? Is this a bug? It’s holding me up on this animation under deadline, unfortunately.

The images attached are:

1. Blue diffusor showing correctly - HDRI with default brightness and no physical area lights.
2. Blue diffusor showing as black - HDRI with 0.1 brightness and physical area lights.
   
   
   
   
   

[oliver.yu]

What type of transparent material are you using?

Basically, Glass (just regular glass not solid) is the only true transparent material, that works with alpha.

Then you have all the other transparent materials. Cloudy Plastic and Transparent Plastic work pretty well, but if you are rending in GPU mode and if it is a contrasty scene, it will require upward of 800-1000 samples per frame so it doesn’t make your lighting go crazy.

All the other materials like Dielectic and Solid Glass, from my experience, have the inner parts of the transparent material turn up black unless using CPU mode.

You said you tried CPU mode animation already? How many samples per frame are you rendering your animation?

[dan.spore]

Thanks for the reply, @oliver.yu.

I am using Glass Solid. The odd thing is that it does work in GPU mode and CPU mode, but not with physical lighting - only with HDRI. Even more odd, is that it worked initially with physical lighting (until it didn’t) I’m not sure at what point or from what change in the scene it stopped working.

Since I am animating, though, I am using physical lighting for more control over the individual light sources and I cannot turn up the brightness of the HDRI.

With physical lights in CPU mode, I can let it run up to 512 samples with no change. 1000+ samples in GPU with no change.

All very odd.

[oliver.yu]

That make sense. When I am using the transparent materials, it is generally for video game controllers that are transparent overall and there are LED lighting within the controller that I use Area Lights to convey so anything aside from Glass, Transparent Plastic, and Cloudy Plastic work in GPU mode. This has left me using only those material types for the most part for my still product renderings as GPU renders way faster than CPU mode, even at 250 samples per frame which I generally use for still images.

With that said, transparent materials is currently something I feel all 3D software kind of struggle with, which our outside vendors use Unreal engine to create some of our more complicated animations and they are not sure they can do transparent materials very well.

Have you tried using Cloudy Plastic or Transparent plastic materials to see if you can get a similar look? Sometimes I will use Cloudy Plastic and set the cloudiness to white and turn the transparency distance to near max to get similar looks to the other materials.

[dan.spore]

Hi, @oliver.yu. Thank you. Yes, I have tried all other transparent options - plastic, cloudy plastic, translucent, dielectric. Nothing worked. I just reopened the scene anew from the original package I generated and the transparent material was working as expected. I did update geometry at one point and I wonder if something changed at that point.

For now my workaround is to use Glass Basic with Refraction turned on. It looks good and will have to suffice for now. I just don’t have roughness control so I will used the bump map to adjust that as needed.

[dan.spore]

Here is the same image with Glass Basic in use and Refraction turned on. So, I’m able to proceed now, though still perplexed.

[oscar.rottink]

All the other materials like Dielectic and Solid Glass, from my experience, have the inner parts of the transparent material turn up black unless using CPU mode.

@oliver.yu I’m guessing a bit what you mean but I think that’s caused by the lighting presets.

This is a red plastic sphere inside solid glass (on the left) and a dielectric (on the right) rendered with GPU but top is the result if you’ve the lighting preset at basic/interior and bottom one when you select ‘product’ as lighting preset. But again, not sure if you’re meaning this.

[oliver.yu]

@oscar.rottink Thanks for the samples, but it doesn’t seem to make a difference with the lighting presets.

But once you turn off GPU mode and run in CPU mode, it works just fine.

[oscar.rottink]

Hey that’s weird! The back side does look right but the front doesn’t. I’m not sure how the solid material gets treated but could it be the ‘solid’ materials like the glass also need a ‘solid’ object, so with out any holes but with an actual thickness?

Again, just a guess but since the front has a lot of shapes cut out I can imagine it might not be a solid part anymore. Especially since the back of the controller looks good, the black you see there is just the reflection of the black front.

[oliver.yu]

Oh it is because I was lazy and just changed the front plate material and left the back material as transparent plastic. The front and back of the controllers are two separate pieces and since different designs and textures are on the front and back, they are not linked.

Edit: I changed the front and back to the Solid Glass and this is what I got.

GPU:

CPU:

[oscar.rottink]

I think it’s weird, this is a grabcad model so not nearly as nice but no problems at all with solid glass.

[oliver.yu]

@oscar.rottink I think the issue maybe tied to what Dan was saying about physical lights causing the issue. Are you using just a HDRI lighting as it apparently works properly when just using HDRI and no physical lights like area lights, etc?

[oscar.rottink]

I tried to add a lot of different lights but can’t replicate the problem Dan has.

@dan.spore is the scale of the speaker matching the real life scale? I did notice when I made the controller like 100x smaller light starts to do weird things although it got mainly way to bright.

If you want you can send me a PM with the scene (maybe just problematic parts), I’d like to see if I notice something off but I can imagine you’re not able to send such product scenes.

[dan.spore]

@oscar.rottink - thank you for your reply. The scale in the scene is 1:1. Initially the scene was working for me as well with physical lights - but something changed along the way. I updated the geometry at one point through the Rhino plugin and I wonder if that caused an issue somehow.

I am sorry, I am not able to send the scene to you.

[oscar.rottink]

No worries, totally understand you can’t send the file. I’m currently testing a lot in KeyShot Beta so I’ll try to keep an eye on problems like the one you mentioned.

It’s not that you updated the model and there are suddenly two parts of the same geometry on top of each other? I’ve that sometimes when I changed materials in the 3D modelling tool and there suddenly will be another part with exactly the same geometry in the scene (maybe blocking light at all)

[dan.spore]

@oscar.rottink - good thought on duplicate geometry. This did not happen in my case, but has happened before if I change a layer name before syncing in Keyshot.