Material glitches at joints when using Bevel modifier #97000

New Issue

George Hawkins · 2022-04-03T14:22:43+02:00

George Hawkins commented

2022-04-03 14:22:43 +02:00

System Information
Operating system: Ubuntu 20.04.3 LTS
Graphics card: GeForce RTX 2060

Blender Version
Broken: 3.1.2, cc66d1020c, master, 2022-03-31
Worked:

Short description of error

I know people experience no end of unexpected Bevel behavior due to issues with their geometry. But I think this is a genuine bug - as do people who responded to my Blender SE question: https://blender.stackexchange.com/q/258493/124535

Robin Betts commented there that "it looks like a bug. But at least a consistent, and therefore traceable bug. It seems to be in the 'Automatic' (-1) material offset setting, which should split the bevel down the middle at material boundaries. It's getting the boundary 1-off at the end of a patch/arc spread of faces."

At joints where two materials meet, the Bevel modifier seems to miscalculate which faces of the bevel should contain one material and which the other, as shown here:

If I apply the modifier, I can then correct the issue by hand.

The above picture is from Blender 3.1.2. The problem seems to have been there for a long time, things look different but are still incorrect in 2.93.7:

The complete mesh is fairly simple (I cut it out of a larger object for this bug report) and I've confirmed there are no overlapping vertices etc.:

I actually started with a much simpler mesh but converted to triangles to ensure the issue wasn't somehow n-gon related (it isn't):

Exact steps for others to reproduce the error

Create a simple shape like the one shown in the last image above and use two different materials for your object, e.g. above, I've applied one material to the darker colored faces and the other to the lighter colored faces.

Then apply a Bevel modifier and then look at the object in a Viewport Shading mode that shows materials, e.g. Material Preview or Rendered (you can even see the issue with Solid viewport shading if you set the Viewport Display for one of the materials to be a different color to the default grey).

Here are two small .blend files - the first created in Blender 3.1.2 and the second in Blender 2.93.7:

bevel-3.1.2.blend

bevel-2.93.7.blend

You can find a larger .blend file containing the original full mesh in my Blender SE question: https://blender.stackexchange.com/q/258493/124535

**System Information** Operating system: Ubuntu 20.04.3 LTS Graphics card: GeForce RTX 2060 **Blender Version** Broken: 3.1.2, cc66d1020c3b, master, 2022-03-31 Worked: **Short description of error** I know people experience no end of unexpected Bevel behavior due to issues with their geometry. But I think this is a genuine bug - as do people who responded to my Blender SE question: https://blender.stackexchange.com/q/258493/124535 Robin Betts commented there that "it looks like a bug. But at least a consistent, and therefore traceable bug. It seems to be in the 'Automatic' (-1) material offset setting, which should split the bevel down the middle at material boundaries. It's getting the boundary 1-off at the end of a patch/arc spread of faces." At joints where two materials meet, the Bevel modifier seems to miscalculate which faces of the bevel should contain one material and which the other, as shown here: ![image.png](https://archive.blender.org/developer/F12966244/image.png) If I apply the modifier, I can then correct the issue by hand. The above picture is from Blender 3.1.2. The problem seems to have been there for a long time, things look different but are still incorrect in 2.93.7: ![image.png](https://archive.blender.org/developer/F12966264/image.png) The complete mesh is fairly simple (I cut it out of a larger object for this bug report) and I've confirmed there are no overlapping vertices etc.: ![image.png](https://archive.blender.org/developer/F12966270/image.png) I actually started with a much simpler mesh but converted to triangles to ensure the issue wasn't somehow n-gon related (it isn't): ![image.png](https://archive.blender.org/developer/F12966292/image.png) **Exact steps for others to reproduce the error** Create a simple shape like the one shown in the last image above and use two different materials for your object, e.g. above, I've applied one material to the darker colored faces and the other to the lighter colored faces. Then apply a *Bevel* modifier and then look at the object in a *Viewport Shading* mode that shows materials, e.g. *Material Preview* or *Rendered* (you can even see the issue with *Solid* viewport shading if you set the *Viewport Display* for one of the materials to be a different color to the default grey). Here are two small `.blend` files - the first created in Blender 3.1.2 and the second in Blender 2.93.7: [bevel-3.1.2.blend](https://archive.blender.org/developer/F12966314/bevel-3.1.2.blend) [bevel-2.93.7.blend](https://archive.blender.org/developer/F12966315/bevel-2.93.7.blend) You can find a larger `.blend` file containing the original full mesh in my Blender SE question: https://blender.stackexchange.com/q/258493/124535

George Hawkins commented

2022-04-03 14:22:43 +02:00

Added subscriber: @GeorgeHawkins

Omar Emara commented

2022-04-04 13:27:36 +02:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-04-04 13:27:36 +02:00

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

Omar Emara commented

2022-04-04 13:27:36 +02:00

Minimal file to reproduce the issue. Defaults with Miter Outer -> Arc.

bevelMaterialBleed.blend

Minimal file to reproduce the issue. Defaults with Miter Outer -> Arc. [bevelMaterialBleed.blend](https://archive.blender.org/developer/F12969254/bevelMaterialBleed.blend)

Cathal McNally commented

2022-06-21 18:48:01 +02:00

Added subscriber: @thefoofighter

Cathal McNally commented

2022-06-21 19:00:48 +02:00

This issue is still present in 3.2

As mentioned it only appears to happen when Miter Outer is set to Arc

This issue is still present in 3.2 As mentioned it only appears to happen when **Miter Outer** is set to **Arc** ![image.png](https://archive.blender.org/developer/F13213138/image.png) ![image.png](https://archive.blender.org/developer/F13213144/image.png)

Philipp Oeser removed the

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Material glitches at joints when using Bevel modifier #97000