Stacking label on glass-material changes glass-material

[Ironscavenger]

Hey,
I have experienced the following buggy behaviour of Corona when working with labels on glass-materials:

1) I create a glass-type material for a bottle, mug etc. (Reflection+Refraction channel active, IOR both 1.52, reflectance glossiness 0.9).

2) I create a label material (Some diffuse color, alpha-map in opacity channel).

3) I apply both glass- and label-material to the bottle. Label material is set to flat-projection, no tiling, and adjusted using the material-tag's coordinates.

4) Rendering results in a strange behaviour of the glass-material as if the IOR is now totally different. Also it is visible where the label-projection's outlines are.

5) When removing the label-material-tag from the bottle the glass looks normal again, as it should be.


I attached 4 screenshots to show different behaviours of Corona:

1) "Bug1 (Simple Stack)" - This was the original bug, where the glass changes as described above.

2) "Bug2 (2 Objects, Label as front sides only)" - Someone on Facebook said he had the same problem. His workaround was to have two identical objects; one with glass-material and the other one with the label only. I tried to reproduce this and ended up with this image.

3) "Bug3 (Layer Material)" - Tried out a layer material with glass as base-layer and the label on top of it. This worked! But I cannot really position the label that way...

4) "Bug4 (2 Objects, Label projects on both sides)" - I tried step 2 again (workaround with 2 objects) but this time with the label set to project on both sides. Now the glass material appears only inside the bordes of the label-projection.


I also attached a *.c4d-file where this happens so you can check it yourselves. My current system data and info about the Corona version is listed below (I also had this error on my PC at home which I can't acces at this moment).

Corona:
Full-speed non-debug version
Build timestamp: Feb  5 2018 10:39:45
Version: B1  (core 1.7)
Cinema version: CINEMA 4D Studio R18.057 S
Plugin status: initialized successfully

System:
Microsoft Windows 10 Home (10.0.17134 Build 17134)
Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz, 2592 MHz
NVIDIA GeForce GTX 960M
16,0 GB RAM

Thanks in advance!
Greetings

Patrick

[Silverwing]

Hi there,

I found this interesting so I tried this myself and came to the same conclusion.
I have a couple attachments as well as the C4D scene.

I think that there seems to be a problem with the shading normals of the object when using stacking or multiple materials so the inside wall is not seen as a refraction where the rays leave the glass, but as another glass boundary where the rays enter another object.

Cheers,
Raphael

[iacdxb]

I am not a big master in this tips and trick but I think label with stacking on glass works fine to me.
Few month back I did one label with stack it was also fine. last option is without liquid.

...

[HFPatzi]

Hi!

just stumbled over this thread and since i have pretty much a similar problem with labels stacked onto anoter material. If still interesting for you, can either raphael or patrick try to do a multipass render with different material IDs for the label and the underlying material and tell me what appears in the mask channels? In my case i have no mask at all for that specific object on wich these two materials are stacked.

Cheers,
Moritz

[Beanzvision]

This has been reported before here: https://forum.corona-renderer.com/index.php?topic=21363.0 So we are aware of it already. Please try to do a quick search before posting. Saves filling up our forum with duplicates ;)

[HFPatzi]

I'm sorry for that. Didn't find it on my search.

[Beanzvision]

I'm sorry for that. Didn't find it on my search.

No need to be sorry. This serves as a good reminder for us. And thanks for your scene too. We'll look into it also. ;)

[tennet]

Hi! Maybe this doesn't solve your problem, but I find it much easier to create most labels as "separate meshes" and then use an alpha/opacity mask to cut it into shape. See attached image and C4D scene (update of your example "bugscene").

So I just selected some polys on the bottle to (for the label) and then used 'Split' to make an exact copy of these polys. Then you need to move these polygons just a tiny bit along their normals (Normal Move ~0,1mm) so you don't get polygons intersecting/overlapping each other. Then you can texture this label as you like using Flat projection or UVs, no need to mix materials.. Hope this helps!