Glass refraction inside an object works not as expected #98633

New Issue

Anton Aparin · 2022-06-06T23:00:10+02:00

Anton Aparin commented

2022-06-06 23:00:10 +02:00

System Information
Operating system: Windows 11 Pro
Graphics card: NVIDIA GeForce RTX 3060 Ti

Blender Version: 2.83.21

If you put a glass object inside another glass object with the same IOR, the object inside is still clearly visible. I should have only been visible if the IOR were different.

Steps to reproduce:

Create 2 objects.
Set transmission to 1
Set IOR to 1.5 (glass IOR) (1.33 = water IOR)
put one object inside the other
Set renderer to cycles

Result:
The object inside is clearly visible

Broken (Cycles):

Correct (Eevee):

**System Information** Operating system: Windows 11 Pro Graphics card: NVIDIA GeForce RTX 3060 Ti Blender Version: 2.83.21 If you put a glass object inside another glass object with the same IOR, the object inside is still clearly visible. I should have only been visible if the IOR were different. Steps to reproduce: * Create 2 objects. * Set transmission to 1 * Set IOR to 1.5 (glass IOR) (1.33 = water IOR) * put one object inside the other * Set renderer to cycles Result: The object inside is clearly visible Broken (Cycles): ![glass-bug.png](https://archive.blender.org/developer/F13135537/glass-bug.png) Correct (Eevee): ![glass-bug-eevee.png](https://archive.blender.org/developer/F13135550/glass-bug-eevee.png)

Anton Aparin commented

2022-06-06 23:00:10 +02:00

Added subscriber: @Antosser

Alaska commented

2022-06-07 05:32:46 +02:00

Added subscribers: @brecht, @Alaska

Alaska commented

2022-06-07 05:32:46 +02:00

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Alaska commented

2022-06-07 05:32:46 +02:00

I can confirm this issue in Blender 3.3, and the physics of the real world which is the reasoning behind @Antosser's report is correct. Assuming that I'm remembering my physics classes properly.

However, I believe this might just be a limitation of how most ray tracers like Cycles works? Luxcore has the same issue.
So I will wait for someone like @brecht to comment on the matter.

I can confirm this issue in Blender 3.3, and the physics of the real world which is the reasoning behind @Antosser's report is correct. Assuming that I'm remembering my physics classes properly. However, I believe this might just be a limitation of how most ray tracers like Cycles works? Luxcore has the same issue. So I will wait for someone like @brecht to comment on the matter.

Brecht Van Lommel commented

2022-06-07 12:07:18 +02:00

Changed status from 'Needs Developer To Reproduce' to: 'Archived'

Brecht Van Lommel closed this issue

2022-06-07 12:07:18 +02:00

Brecht Van Lommel commented

2022-06-07 12:07:18 +02:00

That's how it's designed to work. The IOR does not define the properties of the interior volume of the object, but rather the difference between the interior and exterior volumes at the surface separating them. It would be convenient if it worked differently but that's outside the scope of the bug tracker.

Anton Aparin commented

2022-06-07 18:00:59 +02:00

In #98633#1369764, @brecht wrote:
That's how it's designed to work. The IOR does not define the properties of the interior volume of the object, but rather the difference between the interior and exterior volumes at the surface separating them. It would be convenient if it worked differently but that's outside the scope of the bug tracker.

That means it's working incorrectly in Eevee.

> In #98633#1369764, @brecht wrote: > That's how it's designed to work. The IOR does not define the properties of the interior volume of the object, but rather the difference between the interior and exterior volumes at the surface separating them. It would be convenient if it worked differently but that's outside the scope of the bug tracker. That means it's working incorrectly in Eevee.

Brecht Van Lommel commented

2022-06-07 18:09:56 +02:00

Refraction in Eevee is only approximate, see:
https://docs.blender.org/manual/en/latest/render/eevee/limitations.html#screen-space-refraction

Only one refraction event is correctly modeled.

Refraction in Eevee is only approximate, see: https://docs.blender.org/manual/en/latest/render/eevee/limitations.html#screen-space-refraction > Only one refraction event is correctly modeled.

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Glass refraction inside an object works not as expected #98633