Knife tool shows questionable behavior when cutting through split edges #44492

New Issue

Gaia Clary · 2015-04-23T07:55:04+02:00

Gaia Clary commented

2015-04-23 07:55:04 +02:00

System Information
Windows 7
nvidia Titan

Blender Version
Broken: current development version
Works in 2.73 (just confirmed)

Short description of error

Make a knife cut through a split edge, then parts of the expected cut will be silently ignored. IMHO The tool should cut both split edges and not only one of them.

Exact steps for others to reproduce the error

Here is the demo blend file: knife_tool.blend and here is a very short demo video
https://www.youtube.com/watch?v=Lxfq7JBiG5k

**System Information** Windows 7 nvidia Titan **Blender Version** Broken: current development version Works in 2.73 (just confirmed) **Short description of error** Make a knife cut through a split edge, then parts of the expected cut will be silently ignored. IMHO The tool should cut both split edges and not only one of them. **Exact steps for others to reproduce the error** Here is the demo blend file: [knife_tool.blend](https://archive.blender.org/developer/F166145/knife_tool.blend) and here is a very short demo video https://www.youtube.com/watch?v=Lxfq7JBiG5k

Gaia Clary commented

2015-04-23 07:55:04 +02:00

Changed status to: 'Open'

Gaia Clary commented

2015-04-23 07:55:04 +02:00

Added subscriber: @GaiaClary

perfection cat commented

2015-04-23 08:09:44 +02:00

Added subscriber: @sindra1961

perfection cat commented

2015-04-23 08:09:44 +02:00

Because I can cut it definitely in 2.73a, I think that it is a bug.

Antonis Ryakiotakis commented

2015-04-23 14:41:47 +02:00

Added subscribers: @howardt, @ideasman42, @Psy-Fi

Antonis Ryakiotakis commented

2015-04-23 14:41:47 +02:00

Maybe @ideasman42 or @howardt can check things here?

Howard Trickey self-assigned this 2015-04-23 15:23:54 +02:00

Howard Trickey commented

2015-04-23 15:23:54 +02:00

Yes, it is a bug. I will look at it now.

Howard Trickey commented

2015-04-23 18:18:53 +02:00

I have diagnosed the problem, but need to think about a good fix.

Note to myself and Campbell:
The problem is that knife_find_line_hits, when looking for edge hits, uses

  point_is_visible(kcd, p_cage, sint, &mats, bm_elem_from_knife_edge(kfe))

which asks if the candidate hit KnifeEdge kfe is visible without hitting any face except possibly the one containing kfe itself.
Unfortunately here, when considering one of the split edges (e13), the visibility test finds a hit on the face containing the
other split edge (e10).

Campbell, maybe you have an idea for a good fix?
For convenience, here is a modified test file knife_tool_2.blend that you only need to run "knife project" on to tickle the bug.

I have diagnosed the problem, but need to think about a good fix. Note to myself and Campbell: The problem is that knife_find_line_hits, when looking for edge hits, uses ``` point_is_visible(kcd, p_cage, sint, &mats, bm_elem_from_knife_edge(kfe)) ``` which asks if the candidate hit KnifeEdge kfe is visible without hitting any face except possibly the one containing kfe itself. Unfortunately here, when considering one of the split edges (e13), the visibility test finds a hit on the face containing the other split edge (e10). Campbell, maybe you have an idea for a good fix? For convenience, here is a modified test file [knife_tool_2.blend](https://archive.blender.org/developer/F166327/knife_tool_2.blend) that you only need to run "knife project" on to tickle the bug.

Carlo Andreacchio commented

2015-04-24 01:47:32 +02:00

Added subscriber: @candreacchio

Carlo Andreacchio commented

2015-04-24 01:47:32 +02:00

Pretty sure this isnt a bug... pretty sure you need to either enable 'cut through' on either tool (z for knife cut or enabling it in the toolbox for knife project)

perfection cat commented

2015-04-24 02:11:58 +02:00

It surely works definitely if I enable 'cut through' option.
However, it is different from the reported meaning.
However, it may be useful information.

Cut through: Allow the cut tool to cut through to obscured faces, instead of only the visible ones.

It surely works definitely if I enable 'cut through' option. However, it is different from the reported meaning. However, it may be useful information. Cut through: Allow the cut tool to cut through to obscured faces, instead of only the visible ones.

blender-admin commented

2015-04-24 13:29:45 +02:00

This issue was referenced by c2f861453e

This issue was referenced by c2f861453e3eb9e3cbb7840066fc074e015dfc87

Howard Trickey commented

2015-04-24 13:32:51 +02:00

Knife, in non-cut-through mode, is supposed to cut "visible" things. Whether or not this is a bug depends on whether or not one thinks that two coincident edges (created by a split) obscure each other. This is a bit of an edge case, but reasonable people would probably say "no, they don't obscure each other -- both are 'visible'". On that theory, I call this a bug and have programmed a fix, which I am about to commit.

Howard Trickey commented

2015-04-24 13:34:23 +02:00

Changed status from 'Open' to: 'Resolved'

Howard Trickey closed this issue

2015-04-24 13:34:23 +02:00

Howard Trickey commented

2015-04-24 13:34:23 +02:00

Closed by commit c2f861453e.

Closed by commit c2f861453e.

Sign in to join this conversation.

No Label

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Knife tool shows questionable behavior when cutting through split edges #44492