Eevee - material gets darkened when shader is being mixed with itself using 'mix shader' #61704

New Issue

Marcin Twarowski · 2019-02-19T10:54:24+01:00

Marcin Twarowski commented

2019-02-19 10:54:24 +01:00

Windows 10, GTX 1080
Blender 2.80 2019-02-19 00:38 790cb7799d

See attached file. mix_shader_Eeevee_bug.blend

Shader is mixed with itself using 'mix shader' node. It's a simple mix so it should look the same whether it's 0 or 1. In Cycles it works correctly. In Eevee however it gets darkened.

Blender 2019.02.19 - 10.40.27.01.mp4

EDIT: I just noticed, that even when you mix two separate identical shaders there's still a difference in brightness. You can see that in the video in 00:25 on the lower right corner of the box, there's a slight variation in brightness. What is going is the second shader ignores Screen Space Reflections. If you turn SSR off they both look the same.

Windows 10, GTX 1080 Blender 2.80 2019-02-19 00:38 790cb7799dcf See attached file. [mix_shader_Eeevee_bug.blend](https://archive.blender.org/developer/F6657677/mix_shader_Eeevee_bug.blend) Shader is mixed with itself using 'mix shader' node. It's a simple mix so it should look the same whether it's 0 or 1. In Cycles it works correctly. In Eevee however it gets darkened. [Blender 2019.02.19 - 10.40.27.01.mp4](https://archive.blender.org/developer/F6657706/Blender_2019.02.19_-_10.40.27.01.mp4) EDIT: I just noticed, that even when you mix two separate identical shaders there's still a difference in brightness. You can see that in the video in 00:25 on the lower right corner of the box, there's a slight variation in brightness. What is going is the second shader ignores Screen Space Reflections. If you turn SSR off they both look the same.

Marcin Twarowski commented

2019-02-19 10:54:24 +01:00

Added subscriber: @MarcinTwarowski

Clément Foucault was assigned by William Reynish

2019-02-19 12:01:47 +01:00

Jacques Lucke commented

2019-02-19 12:51:42 +01:00

Added subscriber: @JacquesLucke

Jacques Lucke commented

2019-02-19 12:51:42 +01:00

mix_shader_Eeevee_bug_simplified.blend

[mix_shader_Eeevee_bug_simplified.blend](https://archive.blender.org/developer/F6658537/mix_shader_Eeevee_bug_simplified.blend)

Marcin Twarowski commented

2019-02-19 13:32:49 +01:00

I just noticed, that even when you mix two separate identical shaders there's still a difference in brightness. You can see that in the video in 00:25 on the lower right corner of the box, there's a slight variation in brightness. EDIT: What is going is the second shader ignores Screen Space Reflections. If you turn SSR off they both look the same.

Dalai Felinto commented

2019-02-19 22:15:25 +01:00

Added subscriber: @dfelinto

Dalai Felinto commented

2019-02-19 22:15:25 +01:00

The issue is on the ssr_data calculated in bsdf_common_lib.glsl:closure_mix().
Mainly it is mixing the ssr_data of closure 1 with (0,0,0,w) of closure2:

cl.ssr_data·=·mix(cl1.ssr_data.xyzw,·vec4(vec3(0.0),·cl1.ssr_data.w),·fac);·/*·do·not·blend·roughness·*/

The issue is on the `ssr_data` calculated in `bsdf_common_lib.glsl:closure_mix()`. Mainly it is mixing the ssr_data of closure 1 with (0,0,0,w) of closure2: ```cl.ssr_data·=·mix(cl1.ssr_data.xyzw,·vec4(vec3(0.0),·cl1.ssr_data.w),·fac);·/*·do·not·blend·roughness·*/```

Dalai Felinto commented

2019-02-19 22:54:49 +01:00

Changed status from 'Open' to: 'Archived'

Dalai Felinto closed this issue

2019-02-19 22:54:49 +01:00

Dalai Felinto commented

2019-02-19 22:54:49 +01:00

Okay, talked to Clément and this is working by design. Although mixing RGB is fine, there is no way to reasonably mix SSR data.

So we are (by design) reducing the specular intensity when using the mix shader node in EEVEE.

I added some comments on 0e7409d466 explaining what is going on.

Okay, talked to Clément and this is working by design. Although mixing RGB is fine, there is no way to reasonably mix SSR data. So we are (by design) reducing the specular intensity when using the mix shader node in EEVEE. I added some comments on 0e7409d466 explaining what is going on.

Marcin Twarowski commented

2019-02-20 07:42:37 +01:00

I don't get it. I can mix base color maps, metallic maps, roughness maps and normal maps using mix RGB nodes and screen space reflection works just fine. Why is mixing shaders any different?

Clément Foucault commented

2019-02-28 14:32:20 +01:00

@MarcinTwarowski Because when you are mixing shaders you are mixing the result of the lighting calculation (and/or some other internal data for SSR). Sometimes these cannot be mixed because it would break the SSR completely.

This is the difference between mixing inputs of a bsdfs and the outputs.

To better see what I mean, compare mixing 2 glossy shaders with different roughness and just mixing their roughness instead. And when I say mixing, it is with intermediate values (like 0.5), not 1.0 or 0.0.

@MarcinTwarowski Because when you are mixing shaders you are mixing the result of the lighting calculation (and/or some other internal data for SSR). Sometimes these cannot be mixed because it would break the SSR completely. This is the difference between mixing inputs of a bsdfs and the outputs. To better see what I mean, compare mixing 2 glossy shaders with different roughness and just mixing their roughness instead. And when I say mixing, it is with intermediate values (like 0.5), not 1.0 or 0.0.

Marcin Twarowski commented

2019-03-01 12:55:29 +01:00

Yes, I was wrong. Mixing glossy shaders is not the same as mixing roughness. Thank you for clarification.

Sign in to join this conversation.

No Label

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Eevee - material gets darkened when shader is being mixed with itself using 'mix shader' #61704