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Maniphest T48323

VRML2 export bug and fix
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Description

System Information
Fedora Linux 21, GeForce GT 240

Blender Version
Broken: 2.74

Short description of error
When exporting objects with complex faces (concave etc) sometimes the exported object is broken. This happens because the VRML2 export plugin first invokes bmesh.transform(), and after that does bmesh.ops.triangulate(). If we change the order of these calls, all works fine.

This looks more like a Blender bug rather than a export plugin bug; still, the workaround is attached.

Exact steps for others to reproduce the error
Load the attached .blend file, enable the VRML2 plugin and and export it to *.WRL. Then look at it with e.g. freewrl viewer. You'll see a rectangle rather than the U-shaped face from the example.

If you apply the fix, the U-shaped face is exported ok.

Revisions and Commits

rBA Blender Add-ons
rBA08eb51821ce3 Fix T48323: VRML2 tessellation fails in some cases

Event Timeline

Andrey Zabolotnyi (anpaza) created this task.Apr 30 2016, 11:21 PM
Andrey Zabolotnyi (anpaza) raised the priority of this task from to 90.
Andrey Zabolotnyi (anpaza) updated the task description. (Show Details)
Andrey Zabolotnyi (anpaza) added a project: BF Blender.
Andrey Zabolotnyi (anpaza) edited a custom field.
Andrey Zabolotnyi (anpaza) added a subscriber: Andrey Zabolotnyi (anpaza).
Andrey Zabolotnyi (anpaza) added a comment.Apr 30 2016, 11:23 PM

The .blend file demonstrating the problem

test.blend89 KBDownload

The fix
vrml2-export-fix.diff505 BDownload

Aaron Carlisle (Blendify) edited projects, added Add-ons (Community), Import/Export; removed BF Blender.May 1 2016, 12:22 AM
Sergey Sharybin (sergey) assigned this task to Campbell Barton (campbellbarton).May 2 2016, 10:19 AM
Sergey Sharybin (sergey) added subscribers: Campbell Barton (campbellbarton), Sergey Sharybin (sergey).

@Andrey Zabolotnyi (anpaza), the workaround is arbitrary: it might make some cases to work and other to prevent working. Imagine situation when you'll apply transform on your object in Blender (on the mesh itself) and then transform object back. That situation wouldn't work correct after your fix.

@Campbell Barton (campbellbarton) might have a look into a traingulation issue. However triangulating concave faces is always a pain.

Sergey Sharybin (sergey) lowered the priority of this task from 90 to Normal.May 2 2016, 10:19 AM
Campbell Barton (campbellbarton) changed the task status from Unknown Status to Resolved by committing rBA08eb51821ce3: Fix T48323: VRML2 tessellation fails in some cases.May 3 2016, 8:25 AM
Campbell Barton (campbellbarton) added a commit: rBA08eb51821ce3: Fix T48323: VRML2 tessellation fails in some cases.
Campbell Barton (campbellbarton) added a comment.May 3 2016, 8:27 AM

Applied the patch.

Applying the matrix will typically move the mesh away from having its zero centered origin. Its more likely the triangulation will have worse precision.

In any case, triangulating first will match the view-port result, so its preferred.

Andrey Zabolotnyi (anpaza) added a comment.May 4 2016, 1:21 PM

This case is not about losing precision. You can apply the transforms before export with Ctrl+A, nothing changes.
At the same time, triangulation in Blender Ctrl+T works fine.