Material appears as black in cycles #103066

New Issue

quvr · 2022-12-09T12:57:24+01:00

quvr commented

2022-12-09 12:57:24 +01:00

System Information
Operating system: Windows 10
Graphics card: AMD

Blender Version
Broken: 3.4
Worked: none

Short description of error
After updating blender to 3.4 I've been working on optimizing my complex shader to use the newly introduced mix float and mix vector modes in the mix node. However I noticed that my shader shows as black in Cycles after changing all mix color nodes to float and vector where appropriate. I stripped down everything to investigate the cause and came up with a simple file that shows the problem.

What I think is causing problems is the lack of optimizations for mix float, mix vector, and map range nodes as described here

When executing shaders, a special optimization is applied to Mix Shader nodes. If Factor evaluates to 0 or 1, any nodes that are only reachable via the unused branch of the mix are not evaluated.

This can substantially reduce the performance cost of combining multiple materials in one shader with a Color Attribute, texture, or other input used as a switch.

Screenshots of the issue
Mix float - shows black

Map Range - Nothing

Mix Color - Texture is visible

Lowering factor - Shows black as on other nodes

Besides, If i remove "separate rgb" nodes the bug disappears.
In real scenario I'm using those mix nodes to switch between 20 different textures so the mix factor is always 0 or 1 and do not mixes anything. The mentioned optimization helps with this drastically.
In the file I left only 2 image texture nodes just to showcase

Also I'm testing all of this on a 4gb ram laptop so maybe i hit some hardware limit. But that doesn't explain why everything works fine if using mix color nodes everywhere.

Exact steps for others to reproduce the error
bug.blend
Open the file, switch to rendered view in Cycles
It should be displayed as black as on the screenshots.

Go into the "Texture" node group and switch the output from the mix float node to map range, then to the mix color
If output connected to the mix color, texture should be visible as it should
In the "Sample" node group you can switch mix vector to mix color and bug will disappear too.

**System Information** Operating system: Windows 10 Graphics card: AMD **Blender Version** Broken: 3.4 Worked: none **Short description of error** After updating blender to 3.4 I've been working on optimizing my complex shader to use the newly introduced mix float and mix vector modes in the mix node. However I noticed that my shader shows as black in Cycles after changing all mix color nodes to float and vector where appropriate. I stripped down everything to investigate the cause and came up with a simple file that shows the problem. What I think is causing problems is the lack of optimizations for mix float, mix vector, and map range nodes as described [here ](https://docs.blender.org/manual/en/latest/render/cycles/optimizations/nodes.html#run-time-optimizations) > When executing shaders, a special optimization is applied to Mix Shader nodes. If Factor evaluates to 0 or 1, any nodes that are only reachable via the unused branch of the mix are not evaluated. > > This can substantially reduce the performance cost of combining multiple materials in one shader with a Color Attribute, texture, or other input used as a switch. **Screenshots of the issue** Mix float - shows black ![1670585414.png](https://archive.blender.org/developer/F14046553/1670585414.png) Map Range - Nothing ![1670585418.png](https://archive.blender.org/developer/F14046554/1670585418.png) Mix Color - Texture is visible ![1670585422.png](https://archive.blender.org/developer/F14046556/1670585422.png) Lowering factor - Shows black as on other nodes ![1670585425.png](https://archive.blender.org/developer/F14046555/1670585425.png) Besides, If i remove "separate rgb" nodes the bug disappears. In real scenario I'm using those mix nodes to switch between 20 different textures so the mix factor is always 0 or 1 and do not mixes anything. The mentioned optimization helps with this drastically. In the file I left only 2 image texture nodes just to showcase Also I'm testing all of this on a 4gb ram laptop so maybe i hit some hardware limit. But that doesn't explain why everything works fine if using mix color nodes everywhere. **Exact steps for others to reproduce the error** [bug.blend](https://archive.blender.org/developer/F14046582/bug.blend) Open the file, switch to rendered view in Cycles It should be displayed as black as on the screenshots. Go into the "Texture" node group and switch the output from the mix float node to map range, then to the mix color If output connected to the mix color, texture should be visible as it should In the "Sample" node group you can switch mix vector to mix color and bug will disappear too.

quvr commented

2022-12-09 12:57:24 +01:00

Added subscriber: @Quver

Omar Emara commented

2022-12-09 14:34:32 +01:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-12-09 14:34:32 +01:00

Changed status from 'Needs Triage' to: 'Archived'

Omar Emara closed this issue

2022-12-09 14:34:32 +01:00

Omar Emara commented

2022-12-09 14:34:32 +01:00

Cycles: out of SVM stack space, shader "Material.001" too big.

Your shader exceeded its maximum complexity. This is a known limitation. Your only option is to try to simplify the shader.

> Cycles: out of SVM stack space, shader "Material.001" too big. Your shader exceeded its maximum complexity. This is a known limitation. Your only option is to try to simplify the shader.

quvr commented

2022-12-09 15:41:22 +01:00

It works fine if you use mix color nodes instead of float. It's said in the description. It's weird that mixing floats turns out heavier than mixing colors...
Also it's far from complex because the original shader uses 20 image texture nodes inside each node group and it works too.

It works fine if you use mix color nodes instead of float. It's said in the description. It's weird that mixing floats turns out heavier than mixing colors... Also it's far from complex because the original shader uses 20 image texture nodes inside each node group and it works too.

Omar Emara commented

2022-12-09 16:16:10 +01:00

Added subscriber: @brecht

Omar Emara commented

2022-12-09 16:16:10 +01:00

I see what you mean. That's because only the Color Mix node implements constant folding in Cycles. But still, that's not exactly a bug.
@brecht Would you say this should be confirmed?

I see what you mean. That's because only the Color Mix node implements constant folding in Cycles. But still, that's not exactly a bug. @brecht Would you say this should be confirmed?

blender-admin commented

2022-12-12 17:28:59 +01:00

This issue was referenced by 0b706237b0

This issue was referenced by 0b706237b09006f59a1a3b619d69d49d3c80b482

blender-admin commented

2022-12-12 17:28:59 +01:00

This issue was referenced by 312e42708f

This issue was referenced by 312e42708f8073ef0882d11376c30dee5ac1aef8

Brecht Van Lommel commented

2022-12-12 17:38:36 +01:00

I'll improve the constant folding since it's simple.