STL: faces not normalized correctly when exporting multiple meshes #47490

New Issue

Matthias Urlichs · 2016-02-19T13:50:18+01:00

Matthias Urlichs commented

2016-02-19 13:50:18 +01:00

Blender Version
Broken: 2.74

Short description of error

STL export applies normalization inconsistently

Exact steps for others to reproduce the error

See the attached file. It consists of three objects. When exporting to STL and re-importing, one or two of these objects are inverted.

BorroPart2.blend

Other STL importers ,like the one in Slic3r, require consistent face orientation and cannot deal with that.

**Blender Version** Broken: 2.74 **Short description of error** STL export applies normalization inconsistently **Exact steps for others to reproduce the error** See the attached file. It consists of three objects. When exporting to STL and re-importing, one or two of these objects are inverted. [BorroPart2.blend](https://archive.blender.org/developer/F283922/BorroPart2.blend) Other STL importers ,like the one in Slic3r, require consistent face orientation and cannot deal with that.

Matthias Urlichs commented

2016-02-19 13:50:18 +01:00

Changed status to: 'Open'

Matthias Urlichs commented

2016-02-19 13:50:18 +01:00

Added subscriber: @MatthiasU

Campbell Barton commented

2016-02-19 17:48:47 +01:00

Added subscriber: @ideasman42

Campbell Barton commented

2016-02-19 17:48:47 +01:00

Changed status from 'Open' to: 'Archived'

Campbell Barton closed this issue

2016-02-19 17:48:47 +01:00

Campbell Barton self-assigned this 2016-02-19 17:48:47 +01:00

Campbell Barton commented

2016-02-19 17:48:47 +01:00

The models have a negative scaled axis, blender's viewport accounts for this but currently exporters dont.

Apply scale then flip normals - or remove negative scale.

We could support negative scale correction, but this is more a TODO then a bug.
If we support this, we should try support this for all exporters eventually.

The models have a negative scaled axis, blender's viewport accounts for this but currently exporters dont. Apply scale then flip normals - or remove negative scale. We could support negative scale correction, but this is more a TODO then a bug. If we support this, we should try support this for all exporters eventually.

Bastien Montagne commented

2016-02-19 18:40:15 +01:00

Added subscriber: @mont29

Bastien Montagne commented

2016-02-19 18:40:15 +01:00

Uh… Issue here is with negative transform matrix (i.e. when scale is negative along one or three axes), this effectively inverts the winding of faces, hence their normals.

@ideasman42 think BKE_mesh_transform() should flip faces' winding (i.e. loops) in this case? Will prepare a patch, this could be useful in other cases too (some modifiers e.g.).

Uh… Issue here is with negative transform matrix (i.e. when scale is negative along one or three axes), this effectively inverts the winding of faces, hence their normals. @ideasman42 think `BKE_mesh_transform()` should flip faces' winding (i.e. loops) in this case? Will prepare a patch, this could be useful in other cases too (some modifiers e.g.).

Matthias Urlichs commented

2016-02-20 08:00:56 +01:00

I just discovered that the problem also manifests when using a mirrored object in Boolean operations. "intersect" and "difference" swap their meaning and "union", fascinatingly, behaves like "reverse difference" (i.e. the result is subtracting the source from the target, not vice versa).

Please do not close this bug as "invalid". In my "real" project I need to keep some meshes linked with their mirrors for symmetry (you try to replicate a free-hand edit on both sides of a world …), thus I cannot work around the problem by applying the transform or inverting the faces.

I just discovered that the problem also manifests when using a mirrored object in Boolean operations. "intersect" and "difference" swap their meaning and "union", fascinatingly, behaves like "reverse difference" (i.e. the result is subtracting the source from the target, not vice versa). Please do not close this bug as "invalid". In my "real" project I need to keep some meshes linked with their mirrors for symmetry (you try to replicate a free-hand edit on both sides of a world …), thus I cannot work around the problem by applying the transform or inverting the faces.

Matthias Urlichs commented

2016-02-20 08:02:40 +01:00

@mont29: does your patch fix this?

Bastien Montagne commented

2016-02-20 09:43:43 +01:00

@MatthiasU no, patch does not fix booleans, those are using a custom code (from Carve lib) currently. Issue is exactly the same though (transforming mesh's coordinates by object matrix, which flips the mesh in case matrix is negative). Think we can wait for final BMesh boolean code here, though, not worth spending time on carve anymore.

blender-admin commented

2016-02-28 16:48:08 +01:00

This issue was referenced by blender/blender-addons@0f2f0e4951

This issue was referenced by blender/blender-addons@0f2f0e49517612db379f7f2958b1d1967e7e9e19

Bastien Montagne commented

2016-02-28 16:50:24 +01:00

Changed status from 'Archived' to: 'Resolved'

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STL: faces not normalized correctly when exporting multiple meshes #47490