Attribute name `temperature` returns incorrect values for shading #110716

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opened 2023-08-02 12:55:17 +02:00 by Simon Thommes · 7 comments

Simon Thommes commented

2023-08-02 12:55:17 +02:00

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System Information
Operating system: Linux-5.17.15-76051715-generic-x86_64-with-glibc2.35 64 Bits, X11 UI
Graphics card: Quadro RTX 6000/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 515.48.07

Blender Version
Broken: version: 3.6.1, branch: blender-v3.6-release, commit date: 2023-07-21 12:59, hash: c284cfcd0830
Worked: (newest version of Blender that worked as expected)

Short description of error

Due to some special handling an attribute written to the name temperature is not read correctly by Cycles and Eevee in the shader. Eevee returns a third of the actual value, while Cycles simply returns 0.

Exact steps for others to reproduce the error
temperature_attribute_shader_handling.blend

write attribute named temperature to mesh
try to use it in the shader

**System Information** Operating system: Linux-5.17.15-76051715-generic-x86_64-with-glibc2.35 64 Bits, X11 UI Graphics card: Quadro RTX 6000/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 515.48.07 **Blender Version** Broken: version: 3.6.1, branch: blender-v3.6-release, commit date: 2023-07-21 12:59, hash: `c284cfcd0830` Worked: (newest version of Blender that worked as expected) **Short description of error** ![Screenshot from 2023-08-02 12-50-33.png](/attachments/751ebb4d-a30c-4572-a3bb-339fc2e56809) Due to some special handling an attribute written to the name `temperature` is not read correctly by Cycles and Eevee in the shader. Eevee returns a third of the actual value, while Cycles simply returns 0. **Exact steps for others to reproduce the error** [temperature_attribute_shader_handling.blend](/attachments/e99b4205-4481-415c-9a68-fc506b6177ce) - write attribute named `temperature` to mesh - try to use it in the shader

Screenshot from 2023-08-02 12-50-33.png

550 KiB

temperature_attribute_shader_handling.blend

872 KiB

Simon Thommes added the

labels 2023-08-02 12:55:17 +02:00

Iliya Katushenock commented

2023-08-02 12:58:34 +02:00

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It's a built-in render attribute, no?

It's a built-in render attribute, no?

Iliya Katushenock added the

EEVEE & Viewport

Nodes & Physics

Render & Cycles

labels 2023-08-02 12:58:46 +02:00

Simon Thommes commented

2023-08-02 13:09:19 +02:00

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Member

Just checked and you can indeed also retrieve it with the Volume Info node, but that has the same issue that the values are inaccurate and it's probably not how it should work.

Just checked and you can indeed also retrieve it with the `Volume Info` node, but that has the same issue that the values are inaccurate and it's probably not how it should work.

Iliya Katushenock commented

2023-08-02 13:11:27 +02:00

Member

The volume doesn't inherit the mesh's attributes, does it?

The volume doesn't inherit the mesh's attributes, does it?

Simon Thommes commented

2023-08-02 13:45:48 +02:00

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Member

There is no volume involved in this at all, I'm just writing to a temperature attribute on a mesh. Previously without user created generic attributes that was only used on volumes for fire simulations but now this is a quite arbitrary distinction that is not at all obvious and results in what looks a lot like a bug to me.

There is no volume involved in this at all, I'm just writing to a `temperature` attribute on a mesh. Previously without user created generic attributes that was only used on volumes for fire simulations but now this is a quite arbitrary distinction that is not at all obvious and results in what looks a lot like a bug to me.

Pratik Borhade commented

2023-08-03 06:58:19 +02:00

Member

I guess @mod_moder is right. Function of attribute node (node_shader_gpu_attribute) checks for built in color/temprature attribute and uses their shader functions: https://projects.blender.org/blender/blender/src/branch/main/source/blender/nodes/shader/nodes/node_shader_attribute.cc#L50

Though I'm not entirely sure about the working here. Forwarding to devs.

I guess @mod_moder is right. Function of attribute node (`node_shader_gpu_attribute`) checks for built in color/temprature attribute and uses their shader functions: https://projects.blender.org/blender/blender/src/branch/main/source/blender/nodes/shader/nodes/node_shader_attribute.cc#L50 Though I'm not entirely sure about the working here. Forwarding to devs.

Pratik Borhade added

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labels 2023-08-03 06:58:34 +02:00

Iliya Katushenock added

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labels 2023-08-03 10:48:55 +02:00

Simon Thommes commented

2023-08-03 11:46:28 +02:00

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I already mentioned this to @JacquesLucke before making the report. Could you leave your input here as well?

I already mentioned this to @JacquesLucke before making the report. Could you leave your input here as well?

Jacques Lucke commented

2023-08-03 12:25:23 +02:00

Member

Looked into this a bit more than I did originally now. Looks like the temperature not only has some special code on the CPU but also on the GPU. There are a bunch of attr_load_temperature_post functions, some of which shift the temperature range around. That seems to be related to the "max temperature" and "flame ignition" in fluid settings.
There is this comment: /* Output is such that 0..1 maps to 0..1000K */

Maybe the problem could also be addressed by not leaving y and z at 0 in node_attribute_temperature but to use the same value that is used for x.

Looked into this a bit more than I did originally now. Looks like the temperature not only has some special code on the CPU but also on the GPU. There are a bunch of `attr_load_temperature_post` functions, some of which shift the temperature range around. That seems to be related to the "max temperature" and "flame ignition" in fluid settings. There is this comment: `/* Output is such that 0..1 maps to 0..1000K */` Maybe the problem could also be addressed by not leaving y and z at 0 in `node_attribute_temperature` but to use the same value that is used for x.

Jacques Lucke referenced a pull request that will close this issue

2023-08-03 17:01:57 +02:00

Fix #110716: temperature attribute in eevee is divided by three #110768

Pratik Borhade referenced this issue

2023-08-04 08:49:44 +02:00

Fix #110716: temperature attribute in eevee is divided by three #110768

Jacques Lucke referenced this issue from a commit

2023-08-04 16:37:28 +02:00

Fix: temperature attribute in eevee is divided by three

Jacques Lucke closed this issue

2023-08-04 16:37:30 +02:00

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labels 2023-08-04 16:37:31 +02:00

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