Inconsistensy between two vertex extrusion methods (skin modifier) Bug? #87174

New Issue

Vyacheslav Kobozev · 2021-04-03T20:08:58+02:00

2021-04-03 20:08:58 +02:00

System Information
Operating system: Windows-8.1-6.3.9600-SP0 64 Bits
Graphics card: GeForce GTX 660 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 461.40

Blender Version
Broken: Since 2.79b and later (tested with latest 2.93.0 Alpha, branch: master, commit date: 2021-04-01 15:32, hash: 76cdcc2bca)

Short description of error
When I use E, skin root moves with extrusion. When I use Ctrl+RMB, root remains at 1st vertex.
I expect keeping root in both cases.

skin extrude.mp4

If it is intended, I can`t see the difference between two extrusions.

**System Information** Operating system: Windows-8.1-6.3.9600-SP0 64 Bits Graphics card: GeForce GTX 660 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 461.40 **Blender Version** Broken: Since 2.79b and later (tested with latest 2.93.0 Alpha, branch: master, commit date: 2021-04-01 15:32, hash: `76cdcc2bca`) **Short description of error** When I use E, skin root moves with extrusion. When I use Ctrl+RMB, root remains at 1st vertex. I expect keeping root in both cases. [skin extrude.mp4](https://archive.blender.org/developer/F9919120/skin_extrude.mp4) If it is intended, I can`t see the difference between two extrusions.

Vyacheslav Kobozev commented

2021-04-03 20:08:58 +02:00

Added subscriber: @Vyach

Falk David commented

2021-04-07 09:51:21 +02:00

Added subscriber: @filedescriptor

Falk David commented

2021-04-07 09:51:21 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Falk David commented

2021-04-07 09:51:21 +02:00

I can confirm this on the latest 2.93.0 Alpha, branch: master, commit date: 2021-04-07 05:32, hash: 2fbee4598c.

I can confirm this on the latest 2.93.0 Alpha, branch: master, commit date: 2021-04-07 05:32, hash: `2fbee4598c`.

Falk David commented

2021-04-07 10:56:01 +02:00

Added subscriber: @ideasman42

Falk David commented

2021-04-07 10:56:01 +02:00

Took a look at this. Here is what I found.
So the two operations use different operators. MESH_OT_extrude_verts_indiv by pressing E and MESH_OT_dupli_extrude_cursor with Ctrl+RMB.

MESH_OT_extrude_verts_indiv will duplicate the vert (which will also copy the MVERT_SKIN_ROOT flag) and then remove the flag from the original vert. So the fact that the root "moves" along when extruding seems to be very much intended.
This is the crucial part of the code (bmo_extrude_vert_indiv_exec in blender/source/blender/bmesh/operators/bmo_extrude.c:244):

dupev = BM_vert_create(bm, v->co, v, BM_CREATE_NOP); // `v` is the original vertex, `dupev` the duplicated vertex
[...]

if (has_vskin) {
  bm_extrude_disable_skin_root(bm, v); // <-- Notice that we disable the flag on the original vertex `v`
}

MESH_OT_dupli_extrude_cursor will call bmo_extrude_face_region_exec instead. Here the vertices also get duplicated, but the bm_extrude_disable_skin_root will be called on "geom.out" which I belive will remove the flag from the duplicated vertices.
This is the crucial part of the code (bmo_extrude_face_region_exec in blender/source/blender/bmesh/operators/bmo_extrude.c:423):

/* disable root flag on all new skin nodes */
if (CustomData_has_layer(&bm->vdata, CD_MVERT_SKIN)) {
  BMO_ITER (v, &siter, dupeop.slots_out, "geom.out", BM_VERT) { // <-- notice that we remove the flag from the vertices of the output of dupeop
    bm_extrude_disable_skin_root(bm, v);
  }
}

In summary: Both bmo_extrude_face_region_exec and bmo_extrude_edge_only_exec seem to remove the flag on the duplicate verts. bmo_extrude_vert_indiv_exec will remove it on the original vert.

@ideasman42 Do you think this inconsistency should be fixed? Would this classify as a bug?

Took a look at this. Here is what I found. So the two operations use different operators. `MESH_OT_extrude_verts_indiv` by pressing `E` and `MESH_OT_dupli_extrude_cursor` with Ctrl+RMB. `MESH_OT_extrude_verts_indiv` will duplicate the vert (which will also copy the `MVERT_SKIN_ROOT` flag) and then **remove the flag from the original vert**. So the fact that the root "moves" along when extruding seems to be very much intended. This is the crucial part of the code (`bmo_extrude_vert_indiv_exec` in `blender/source/blender/bmesh/operators/bmo_extrude.c:244`): ``` dupev = BM_vert_create(bm, v->co, v, BM_CREATE_NOP); // `v` is the original vertex, `dupev` the duplicated vertex [...] if (has_vskin) { bm_extrude_disable_skin_root(bm, v); // <-- Notice that we disable the flag on the original vertex `v` } ``` `MESH_OT_dupli_extrude_cursor` will call `bmo_extrude_face_region_exec` instead. Here the vertices also get duplicated, but the `bm_extrude_disable_skin_root` will be called on "geom.out" which I belive will **remove the flag from the duplicated vertices**. This is the crucial part of the code (`bmo_extrude_face_region_exec` in `blender/source/blender/bmesh/operators/bmo_extrude.c:423`): ``` /* disable root flag on all new skin nodes */ if (CustomData_has_layer(&bm->vdata, CD_MVERT_SKIN)) { BMO_ITER (v, &siter, dupeop.slots_out, "geom.out", BM_VERT) { // <-- notice that we remove the flag from the vertices of the output of dupeop bm_extrude_disable_skin_root(bm, v); } } ``` In summary: Both `bmo_extrude_face_region_exec` and `bmo_extrude_edge_only_exec` seem to remove the flag on the duplicate verts. `bmo_extrude_vert_indiv_exec` will remove it on the original vert. @ideasman42 Do you think this inconsistency should be fixed? Would this classify as a bug?

Philipp Oeser removed the

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Inconsistensy between two vertex extrusion methods (skin modifier) Bug? #87174