Bevel objects along 3D curves get distorted #50720

New Issue

Peter Romero · 2017-02-19T01:57:18+01:00

Peter Romero commented

2017-02-19 01:57:18 +01:00

System Information
Windows 10; Intel Iris Graphics 6100

Blender Version
Broken: 2.78; 4bb1e22

Short description of error
Size and shape of bevel object does not stay consistent when sweeping along a 3D path. Simple example: sweeping a square along a 3D path that consists only of orthogonal segments results in non-flat faces, strange hexagonal cross sections in spots and general non-rectilinear output.

Exact steps for others to reproduce the error
See attached .blend file.

3D Bevel.blend

**System Information** Windows 10; Intel Iris Graphics 6100 **Blender Version** Broken: 2.78; 4bb1e22 **Short description of error** Size and shape of bevel object does not stay consistent when sweeping along a 3D path. Simple example: sweeping a square along a 3D path that consists only of orthogonal segments results in non-flat faces, strange hexagonal cross sections in spots and general non-rectilinear output. **Exact steps for others to reproduce the error** See attached .blend file. [3D Bevel.blend](https://archive.blender.org/developer/F489358/3D_Bevel.blend)

Peter Romero commented

2017-02-19 01:57:18 +01:00

Changed status to: 'Open'

Peter Romero commented

2017-02-19 01:57:18 +01:00

Added subscriber: @aprilwine

Bastien Montagne commented

2017-02-19 09:28:23 +01:00

Added subscribers: @Sergey, @mont29

Sergey Sharybin was assigned by Bastien Montagne

2017-02-19 09:28:23 +01:00

Bastien Montagne commented

2017-02-19 09:28:23 +01:00

I don’t think there is any bug here, you are somewhat abusing the curve bevel feature, it’s not designed to handle that kind of things (it’s rather designed to handle rather smooth, organic shaping). Will let @Sergey decide here, though.

Peter Romero commented

2017-02-20 06:13:16 +01:00

My example was an extreme edge case to illustrate a more subtle problem. I think the issue here is that, regardless of the intended behavior, the curve bevel feature has created an expectation (a mathematical axiom) in the mind of the average user. The axiom is that a cross section normal to the curve at any point should be identical to the bevel object in shape and size. 2D curves always follow this axiom, but 3D curves only follow it part of the time. The way it is now, the tool cannot be used to create certain common shapes, like handrails, etc. See the attached .blend file for an example. If we don't want to break the existing functionality, maybe we should add an option to address this use case, like a checkbox on 3D curves called "Consistent Width" or "Handrail Mode" or something. Thoughts?

Axiom.blend

My example was an extreme edge case to illustrate a more subtle problem. I think the issue here is that, regardless of the intended behavior, the curve bevel feature has created an expectation (a mathematical axiom) in the mind of the average user. The axiom is that a cross section normal to the curve at any point should be identical to the bevel object in shape and size. 2D curves always follow this axiom, but 3D curves only follow it part of the time. The way it is now, the tool cannot be used to create certain common shapes, like handrails, etc. See the attached .blend file for an example. If we don't want to break the existing functionality, maybe we should add an option to address this use case, like a checkbox on 3D curves called "Consistent Width" or "Handrail Mode" or something. Thoughts? [Axiom.blend](https://archive.blender.org/developer/F490323/Axiom.blend)

Sergey Sharybin commented

2017-02-20 09:32:48 +01:00

Changed status from 'Open' to: 'Archived'

Sergey Sharybin closed this issue

2017-02-20 09:32:48 +01:00

Sergey Sharybin commented

2017-02-20 09:32:48 +01:00

Can see two cases here. First one is the bevel not being orthogonal in the first case. This is caused by the bevel object rotated according to the curve twist, which is currently set to Minimal Twist. Using Z-Up with some manual control over the bottom CV will fix this issue.

Second issue is caused by Blender's bevel is keeping constant shape of the "extruded" geometry. This works fine for such things s hair and wires, but fails for more technical usecase as you've got.

Not saying it's ideal, but that's how bevel is currently expected to work. Curves area did not change in ages and surely needs modernization.

Will consider it a TODO listed there: https://wiki.blender.org/index.php/Dev:Source/Development/Todo/Tools#Curves

Thanks for the report anyway!

Can see two cases here. First one is the bevel not being orthogonal in the first case. This is caused by the bevel object rotated according to the curve twist, which is currently set to `Minimal Twist`. Using `Z-Up` with some manual control over the bottom CV will fix this issue. Second issue is caused by Blender's bevel is keeping constant shape of the "extruded" geometry. This works fine for such things s hair and wires, but fails for more technical usecase as you've got. Not saying it's ideal, but that's how bevel is currently expected to work. Curves area did not change in ages and surely needs modernization. Will consider it a TODO listed there: https://wiki.blender.org/index.php/Dev:Source/Development/Todo/Tools#Curves Thanks for the report anyway!

Peter Romero commented

2017-02-20 18:11:39 +01:00

Sounds good! I think there's a typo in the link on the TODO page (TT instead of T).

Sergey Sharybin commented

2017-02-20 22:32:19 +01:00

Ah, you're right. We use mediawiki template for the link which adds T (which i always forget). Fixed now!

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Bevel objects along 3D curves get distorted #50720