Knife tool fails on a non-planar n-gon #84299

New Issue

Stanislav Blinov · 2021-01-01T01:13:32+01:00

Stanislav Blinov commented

2021-01-01 01:13:32 +01:00

Blender Version
Broken: 2.74 up to and including 2.92 master
Worked: 2.73 (yes, I bisected that far back ;) )

Short description of error

Knife tool fails to cut between verts in n-gons of certain configuration.

Exact steps for others to reproduce the error

Load the attached .blend and try to make a knife cut between the two selected verts (i.e. try to create an edge connecting them).

knife_fail.blend

(If you want to test in 2.73 yourself, copy the object from a running instance of 2.9x into 2.73 using ctrl+c/ctrl+v, then replace the mesh in another existing mesh object).

**Blender Version** Broken: 2.74 up to and including 2.92 master Worked: 2.73 (yes, I bisected that far back ;) ) **Short description of error** Knife tool fails to cut between verts in n-gons of certain configuration. **Exact steps for others to reproduce the error** Load the attached .blend and try to make a knife cut between the two selected verts (i.e. try to create an edge connecting them). [knife_fail.blend](https://archive.blender.org/developer/F9544216/knife_fail.blend) (If you want to test in 2.73 yourself, copy the object from a running instance of 2.9x into 2.73 using ctrl+c/ctrl+v, then replace the mesh in another existing mesh object).

Stanislav Blinov commented

2021-01-01 01:13:32 +01:00

Added subscriber: @Stan_Pancakes

blender-admin commented

2021-01-01 01:13:32 +01:00

#91356 was marked as duplicate of this issue

Robert Guetzkow commented

2021-01-01 14:24:47 +01:00

Added subscriber: @rjg

Robert Guetzkow commented

2021-01-01 14:24:47 +01:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Robert Guetzkow commented

2021-01-01 14:24:47 +01:00

When you say between do you mean that the knife cut cross the imaginary edge between the two vertices perpendicularly or that the knife cut connects the two? The former works for me, the latter doesn't. Tested with 2.92.0 Alpha, branch: master, commit date: 2020-12-31 13:25, hash: 8c135fa9a8.

When you say between do you mean that the knife cut cross the imaginary edge between the two vertices perpendicularly or that the knife cut connects the two? The former works for me, the latter doesn't. Tested with 2.92.0 Alpha, branch: master, commit date: 2020-12-31 13:25, hash: `8c135fa9a8`.

Stanislav Blinov commented

2021-01-01 14:34:07 +01:00

Sorry, I did mean connect the two verts with the knife. The workaround for this simplified case is of course to just use the Connect Vertex Path operator, which does work (so I think should the knife as well), but it becomes a speed bump on an actual mesh.

Robert Guetzkow commented

2021-01-09 14:35:47 +01:00

Changed status from 'Needs User Info' to: 'Confirmed'

Robert Guetzkow commented

2021-01-09 14:37:27 +01:00

I've confirmed this with low priority since this seems like an issue, but quite an edge case. The UI team that handles the tools & operators might not consider this a limitation and not a bug though.

Julian Eisel commented

2021-01-29 02:10:27 +01:00

Added subscriber: @JulianEisel

Julian Eisel commented

2021-01-29 02:10:27 +01:00

This seems to be more for the modeling module than the UI module.

Campbell Barton changed title from ~~Knife tool fails on an n-gon~~ to Knife tool fails on a non-planar n-gon

2021-01-29 11:10:47 +01:00

Campbell Barton commented

2021-01-29 11:11:34 +01:00

Added subscriber: @ideasman42

Campbell Barton commented

2021-01-29 11:11:34 +01:00

Note that the n-gon is quite distorted (non-planar), the error is likely caused by the non-planar triangulated data being used to compute the cut. Making the n-gon flat resolves this.

Pratik Borhade commented

2021-09-13 10:26:50 +02:00

Added subscribers: @RobertS, @PratikPB2123

Campbell Barton commented

2022-05-17 13:40:42 +02:00

Changing to a TODO, since very distorted N-gons don't define a surface that can necessarily be operated on usefully.

While some workarounds are possible I don't think it's an error in the logic of the knife tool that this fails.

Changing to a TODO, since very distorted N-gons don't define a surface that can necessarily be operated on usefully. While some workarounds are possible I don't think it's an error in the logic of the knife tool that this fails.

Philipp Oeser removed the

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Knife tool fails on a non-planar n-gon #84299