Bezier curve to mesh creates duplicate vertices / edges #40171

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Frank Olthuis · 2014-05-13T00:51:31+02:00

Frank Olthuis commented

2014-05-13 00:51:31 +02:00

Blender Version
Broken: 2.70a

Short description of error
The curve to mesh function creates duplicate vertices and/or edges, which by many other function is considered invalid geometry.

Exact steps for others to reproduce the error
See #40139 where I reported an issue with the boolean operator. The issue was diagnosed as not-a-bug because the mesh contained duplicate vertices. I did not add those vertices though. It was the curve-to-mesh function that did that. I realize that as a workaround I can manually execute the remove doubles function, but in my view this is something the curve-to-mesh function should take care of itself.

Before you close this as not-a-bug as well, please bear in mind that duplicate vertices are not that easy to spot, not even for the more technically inclined. as proven by the fact that mont29, who was assigned to the aforementioned bug, also failed to notice them. Moreover, with the increasing importance of 3D printing, it becomes increasingly important for Blender to be able to generate manifold surfaces, because this is a requirement for the correct export to STL format.

**Blender Version** Broken: 2.70a **Short description of error** The curve to mesh function creates duplicate vertices and/or edges, which by many other function is considered invalid geometry. **Exact steps for others to reproduce the error** See [#40139](https://developer.blender.org/T40139) where I reported an issue with the boolean operator. The issue was diagnosed as not-a-bug because the mesh contained duplicate vertices. I did not add those vertices though. It was the curve-to-mesh function that did that. I realize that as a workaround I can manually execute the remove doubles function, but in my view this is something the curve-to-mesh function should take care of itself. Before you close this as not-a-bug as well, please bear in mind that duplicate vertices are not that easy to spot, not even for the more technically inclined. as proven by the fact that mont29, who was assigned to the aforementioned bug, also failed to notice them. Moreover, with the increasing importance of 3D printing, it becomes increasingly important for Blender to be able to generate manifold surfaces, because this is a requirement for the correct export to STL format.

Frank Olthuis commented

2014-05-13 00:51:31 +02:00

Changed status to: 'Open'

Frank Olthuis commented

2014-05-13 00:51:31 +02:00

Added subscriber: @Fury

Willi commented

2014-05-13 01:17:58 +02:00

Added subscriber: @willi-2

Willi commented

2014-05-13 01:17:58 +02:00

Please provide a blend file with the original curve object.

Sergey Sharybin commented

2014-05-13 10:25:20 +02:00

Added subscriber: @Sergey

Sergey Sharybin commented

2014-05-13 10:25:20 +02:00

As mentioned, it always helps a lot when having .blend with which the issue might be easily reproduced.

Frank Olthuis commented

2014-05-14 22:25:39 +02:00

Here are five files.
The first is the initial bezier curve.
The last is the resulting mesh, where I've applied a boolean operation with a cube that goes wrong, which according to you guys (#40139) is because the mesh contains duplicates
BezierTriangle0.blend
BezierTriangle1.blend
BezierTriangle2.blend
BezierTriangle3.blend
BezierTriangle4.blend

Here are five files. The first is the initial bezier curve. The last is the resulting mesh, where I've applied a boolean operation with a cube that goes wrong, which according to you guys (#40139) is because the mesh contains duplicates [BezierTriangle0.blend](https://archive.blender.org/developer/F88976/BezierTriangle0.blend) [BezierTriangle1.blend](https://archive.blender.org/developer/F88977/BezierTriangle1.blend) [BezierTriangle2.blend](https://archive.blender.org/developer/F88978/BezierTriangle2.blend) [BezierTriangle3.blend](https://archive.blender.org/developer/F88979/BezierTriangle3.blend) [BezierTriangle4.blend](https://archive.blender.org/developer/F88980/BezierTriangle4.blend)

Frank Olthuis commented

2014-05-14 22:33:01 +02:00

BTW, I realize my control points overlap, but in my understanding of Bezier curves this should play no role. Moreover, if I move the vertices of the initial curve away from each other so that the control points no longer overlap, I keep seeing the same issue.

Willi commented

2014-05-14 23:00:13 +02:00

If the curve's Fill property is set to None, there are no double vertices. Makes sense to improve this - if possible.

Sergey Sharybin self-assigned this 2014-05-15 10:30:38 +02:00

Sergey Sharybin commented

2014-05-15 10:30:38 +02:00

Will have a look.

Sergey Sharybin commented

2014-05-15 15:37:46 +02:00

Changed status from 'Open' to: 'Archived'

Sergey Sharybin closed this issue

2014-05-15 15:37:46 +02:00

Sergey Sharybin commented

2014-05-15 15:37:46 +02:00

So it's not "convert curve to mesh" which gives you duplicates, but converting bevelled curve to mesh gives duplicates. This would indeed give you duplicates in areas where side meets the caps. For most operations it's rather harmless, for boolean you just need to be aware how it behaves. Making it so every tool generates geometry which is compatible with any other tool is possible, but would slow lots of things down.

This is all known behavior of curves and wouldn't consider this is a bug.

So it's not "convert curve to mesh" which gives you duplicates, but converting bevelled curve to mesh gives duplicates. This would indeed give you duplicates in areas where side meets the caps. For most operations it's rather harmless, for boolean you just need to be aware how it behaves. Making it so every tool generates geometry which is compatible with any other tool is possible, but would slow lots of things down. This is all known behavior of curves and wouldn't consider this is a bug.

Frank Olthuis commented

2014-05-16 01:10:27 +02:00

Great to hear the user is taken seriously again. Sorry for being sarcastic, but really, this is very basic functionality that just doesn't work correctly. Your'e being very unprofessional.

Sergey Sharybin commented

2014-05-16 10:28:11 +02:00

Curve to mesh conversions just converts internal reprsesenation of tessellated curve to mesh datablock. And tessellating caps and sides separately is just the simplest way to make vertex normals work in all circumstances. It's used, for example, in BI renderer to make text have smooth caps and sides and also have sharp corner between them. Now, when we've got split normals implemented for meshes, we can make it so curve-to-mesh would benefit of this as well, but it'll take some time.

Blender might not do what people expect, but solving that is our regular day job. But bugs are issues where the code doesn't do what developer wants it to do. Here the code does exactly what it is intended to do, so it's being handled outside of the bug tracker. We already had a TODO item to improve text/curve tessellation (see http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/Tools#Curves). Now i made sure this report is also listed there,

Curve to mesh conversions just converts internal reprsesenation of tessellated curve to mesh datablock. And tessellating caps and sides separately is just the simplest way to make vertex normals work in all circumstances. It's used, for example, in BI renderer to make text have smooth caps and sides and also have sharp corner between them. Now, when we've got split normals implemented for meshes, we can make it so curve-to-mesh would benefit of this as well, but it'll take some time. Blender might not do what people expect, but solving that is our regular day job. But bugs are issues where the code doesn't do what developer wants it to do. Here the code does exactly what it is intended to do, so it's being handled outside of the bug tracker. We already had a TODO item to improve text/curve tessellation (see http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/Tools#Curves). Now i made sure this report is also listed there,

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Bezier curve to mesh creates duplicate vertices / edges #40171