Skin Modifier - topology changes randomly when entering and exiting edit mode #42893
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Reference: blender/blender#42893
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System Information
Win7 x64
Blender Version
Broken: c51ca1b
Short description of error
Generated mesh topology changes randomly when changing modes
Exact steps for others to reproduce the error
Open file, hit Tab a bunch of times
skinBug.blend
Changed status to: 'Open'
Added subscriber: @MatthewHeimlich
Added subscriber: @JulianEisel
This seems to be a gooseberry only bug. We currently don't have a project dedicated to that, but I don't like having gooseberry branch bugs set to #bf_blender. Will check with others if it's worth adding a "BF Blender: Gooseberry" project.
Changed status from 'Open' to: 'Archived'
Okay, so in todays meeting we decided to not allow gooseberry branch bugs. I'd recommend to get in contact with the gooseberry developers in those cases.
But as always: thanks for the report @MatthewHeimlich :)
@MatthewHeimlich asked for reopening on IRC, since the bug seems to appear on master too.
I still cann't confirm here, but he said some people on #blender did.
Changed status from 'Archived' to: 'Open'
Added subscriber: @karja
Hey,
can confirm this - Skin is working continously and not consistent on branched edges.
Want to add that this topology changes occur for nearly every action that can change position or geometry of the skin object (except G/R/S in object mode).
Objects that are related somehow to the skin object (= modifier target, constraints, linked mesh) also cause this problem.
Further examples:
Added subscribers: @NicholasBishop, @kevindietrich
Some steps to easily reproduce using @MatthewHeimlich file:
To quote some comments in MOD_skin.c :
As the glitch actually appears in one of those concave regions, it might be that this case is not handled properly. @NicholasBishop care to have a quick glance here?
Hmm, I've found another comment that could lead us in the right direction:
And that's exactly what appears to be going on:
Added subscriber: @ideasman42
Assigning to Nicholas to increase pressure a bit ;) Also @ideasman42 might have some input.
Added subscriber: @numarul7
I can`t reproduce on standard 2.71 build from blender.org install (I know I know ...i wait for the OpenGL :D refactor ) :)
Added subscriber: @MarcClintDion
For the following .gif, I removed the mirror and moved the model in Object mode then applied the Object's Location using Ctrl+a.
I then used Undo and Redo repeatedly to see if this was possibly due to the GPU doing internal triangulation differently based on how Object Mode vs. Edit Mode are passing info to OpenGL .
That is a known nuisance but apparently not the issue here because it's only a slight shading issue that presents itself when that is happening.
For this Skin Modifier problem, the geometry is actually being visually moved to different places in 3D space and the results are often very different just by Undoing and Redoing. After doing that about 20 times, I ended up seeing about 5-6 different configurations of the geometry.
That's very unusual since Undoing and Redoing repeatedly should give identical results for every iteration.
Something weird is happening here. It can be seen in the following animation.
@NicholasBishop, @ideasman42, did anybody find the time to look into this?
Added subscriber: @brecht
This bug was caused by
92733179ae
.I can see that
hull_merge_triangles
uses the normal, so presumably some intermediate recalc normal operations are necessary for that. Also, is it ok to useBMO_push
andbmesh_edit_begin
withoutBMO_pop
andbmesh_edit_end
?Maybe the fix looks something like this, it works but I'm not sure it's correct.
This issue was referenced by
abd68c6e45
Changed status from 'Open' to: 'Resolved'
Closed by commit
abd68c6e45
.