Regression: Vertex colors are now broken in hair strands #98803

New Issue

happysmash27 · 2022-06-12T00:59:54+02:00

happysmash27 commented

2022-06-12 00:59:54 +02:00

System Information
Operating system: Gentoo Linux kernel 5.18.0-gentoo
Graphics card: RX 480

Blender Version
Broken: 3.2.0, 3.3.0
Worked: 3.1.0

Caused by b9799dfb8a

Short description of error

Vertex colors are strange and patchy when moving from 3.1.0 to 3.2.0 or later:

Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).

Make something with vertex colours and a hair system which utilises them in Blender 3.1.0. In my instance I used geometry nodes to generate them; this may differ when making them manually as one of my other projects which does it manually does not seem to exhibit this issue.
Open file in Blender 3.2.0.

I created the following .blend file to demonstrate the issue: Color_test_3s.blend

**System Information** Operating system: Gentoo Linux kernel 5.18.0-gentoo Graphics card: RX 480 **Blender Version** Broken: 3.2.0, 3.3.0 Worked: 3.1.0 Caused by b9799dfb8a **Short description of error** Vertex colors are strange and patchy when moving from 3.1.0 to 3.2.0 or later: ![2022-06-11-155614_1280x998_scrot.png](https://archive.blender.org/developer/F13147533/2022-06-11-155614_1280x998_scrot.png) ![2022-06-11-155621_1280x998_scrot.png](https://archive.blender.org/developer/F13147532/2022-06-11-155621_1280x998_scrot.png) **Exact steps for others to reproduce the error** Based on the default startup or an attached .blend file (as simple as possible). 1. Make something with vertex colours and a hair system which utilises them in Blender 3.1.0. In my instance I used geometry nodes to generate them; this may differ when making them manually as one of my other projects which does it manually does not seem to exhibit this issue. 2. Open file in Blender 3.2.0. I created the following .blend file to demonstrate the issue: [Color_test_3s.blend](https://archive.blender.org/developer/F13147536/Color_test_3s.blend)

happysmash27 commented

2022-06-12 00:59:54 +02:00

Added subscriber: @27Anonymous

Jesse Yurkovich commented

2022-06-13 06:07:15 +02:00

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

Jesse Yurkovich commented

2022-06-13 06:07:52 +02:00

Added subscribers: @JacquesLucke, @deadpin

Jesse Yurkovich commented

2022-06-13 06:07:52 +02:00

CC @JacquesLucke seems like b9799dfb8a has caused this issue.

CC @JacquesLucke seems like b9799dfb8a has caused this issue.

Pratik Borhade commented

2022-06-13 06:40:34 +02:00

Added subscriber: @PratikPB2123

Jacques Lucke commented

2022-06-13 13:07:24 +02:00

There seem to be multiple issues:

Using geometry nodes with the old particle system is not well supported generally (also with regard to instancing for example).
The hair system only supports byte-color face-corner attributes, but not (float-)color attributes. In the provided file, then behavior of the geometry nodes modifier changed a little bit. Previously, it would write the new attribute values into the existing byte-color attribute (because it was presented to geometry nodes as a float-color attribute internally). Now, the modifier deletes the byte-color attribute and creates a float-color attribute with the same name. This attribute can't be used with hair particles.
Not exactly sure what it does, but the hair drawing code uses some (random?) attribute when it does not find the attribute that was requested by the shader.
There seem to be missing updates when the color attribute type changes, not sure at which level that happens exactly..
Maybe due to the subdivision or maybe due to some other reason, the hair attachment information of the curves seems to be somewhat wrong.

You can try using the Store Named Attribute node to manually create the Byte-Color Face-Corner attribute, I had some limited success with that. Maybe try to avoid overwriting an existing attribute and just create a new one instead.

Overall, I can't really justify spending more time on this right now, because it relates to code that we are planning to replace fairly soon anyway (D14942). Also because to reproduce the bug, one has to use a combination of geometry nodes and end-of-life features (particles).

There seem to be multiple issues: * Using geometry nodes with the old particle system is not well supported generally (also with regard to instancing for example). * The hair system only supports byte-color face-corner attributes, but not (float-)color attributes. In the provided file, then behavior of the geometry nodes modifier changed a little bit. Previously, it would write the new attribute values into the existing byte-color attribute (because it was presented to geometry nodes as a float-color attribute internally). Now, the modifier deletes the byte-color attribute and creates a float-color attribute with the same name. This attribute can't be used with hair particles. * Not exactly sure what it does, but the hair drawing code uses some (random?) attribute when it does not find the attribute that was requested by the shader. * There seem to be missing updates when the color attribute type changes, not sure at which level that happens exactly.. * Maybe due to the subdivision or maybe due to some other reason, the hair attachment information of the curves seems to be somewhat wrong. You can try using the Store Named Attribute node to manually create the Byte-Color Face-Corner attribute, I had some limited success with that. Maybe try to avoid overwriting an existing attribute and just create a new one instead. Overall, I can't really justify spending more time on this right now, because it relates to code that we are planning to replace fairly soon anyway ([D14942](https://archive.blender.org/developer/D14942)). Also because to reproduce the bug, one has to use a combination of geometry nodes and end-of-life features (particles).

happysmash27 commented

2022-06-13 15:23:03 +02:00

@JacquesLucke THANK YOU SO MUCH! Deleting and re-creating the vertex colour and using Store Named Attribute node seems to have fixed it:

And much more importantly, also fixes it in the avatar project that I need to complete by the 17th (for an event):

Which means that I will not have to convert the fur to an object manually to preview it (I have a node setup that replicates the geometry and materials for the purpose of baking, but converting everything still takes time) and can work much faster, desperately needed when I only have a few days left.

It doesn't technically fix the bug, but absolutely fixes the problem of needing to get hair system preview working again in the next couple days by any and all means necessary.

I didn't convey the urgency in the original post but getting this response today is extremely, incredibly helpful and helps SO MUCH!

THANK YOU to an extreme degree! This workaround really makes a massive difference!

@JacquesLucke THANK YOU SO MUCH! Deleting and re-creating the vertex colour and using Store Named Attribute node seems to have fixed it: ![2022-06-13-061019_1280x998_scrot.png](https://archive.blender.org/developer/F13156196/2022-06-13-061019_1280x998_scrot.png) And much more importantly, also fixes it in the avatar project that I need to complete by the 17th (for an event): ![2022-06-13-061555_1280x998_scrot.png](https://archive.blender.org/developer/F13156214/2022-06-13-061555_1280x998_scrot.png) Which means that I will not have to convert the fur to an object manually to preview it (I have a node setup that replicates the geometry and materials for the purpose of baking, but converting everything still takes time) and can work much faster, desperately needed when I only have a few days left. It doesn't technically fix the bug, but absolutely fixes the problem of needing to get hair system preview working again in the next couple days by any and all means necessary. I didn't convey the urgency in the original post but getting this response today is extremely, incredibly helpful and helps SO MUCH! THANK YOU to an extreme degree! This workaround really makes a massive difference!

Philipp Oeser removed the

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Regression: Vertex colors are now broken in hair strands #98803