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on EEVEE, Glass BSDF + procedural textures bug
Closed, InvalidPublic

Description

System Information
Windows 10 and Ubuntu 18.04
Radeon HD 7670m
Intel HD 4000

Blender Version
Broken: 2.80 faf43ff9ad8

on EEVEE, Glass BSDF + procedutal textures bug

Exact steps for others to reproduce the error
the bug occurs both on linux and on windows with both gpu.
bug 1 glass BSDF + procedural textures inconsistency when "show backside is enabled" (see the screenshots)
bug 2 when "Refraction Depth = 0" and "show backside" is off, the background object is only seen on one side of the cube

Event Timeline

Clément Foucault (fclem) changed the task status from Unknown Status to Invalid.Aug 13 2018, 11:58 AM

This is perfectly normal behaviour.

Bug 1 is when you disable the depth prepass (that's what the option) you have incorrect / inconsistent face ordering. This option is only recommended for aditive and multiplicative blending.
Bug 2 is because when set to 0 the refraction depth is only simulating one refraction event which totally change the refraction direction but the suzane can still be observed through all faces if you rotate the view correctly.

"bug1" ok in additive and multiplicative works correctly.
so in "alpha blend" a correct display of all the refracted textured faces with "show backside" is not possible ??
at the moment is inverted, the back textured face are shown first..
I'm a bit confused what is the use of the option "show backside" for alpha blend if the correct result is not obtained?

Well the "show backside" has a performance cost associated to it, and it is unnecessary for certain objects (think a simple glass plane).

The incorrect sorting of faces with "alpha blend" is the same as it was in the old 2.7 GLSL viewport. This is a limitation with traditional alpha blending in all "realtime" (Opengl, DirectX, etc...) engine.

thanks now I understand the motivation of this imperfection, even if it is a bit of a pity that the effect is not obtained in the correct way

Well the "show backside" has a performance cost associated to it, and it is unnecessary for certain objects (think a simple glass plane).

It would be great to have the option of sorting the faces for alpha objects, which could be turned off for certain objects to reduce the performance - ie correctness before speed ( https://realtimevfx.com/t/transparency-issues-in-unity/4337/2 - Sort per triangle prior to rendering ).

I found this issue even with a simple transparent cube, and when searching for a solution found this post.

Here's an example of the Eevee and then Cycles render of the cube from the back.