GPencil: Scripting weight_get cannot retrieve weights of certain vertex groups #96799

New Issue

Keny Chatain · 2022-03-26T13:25:48+01:00

Keny Chatain commented

2022-03-26 13:25:48 +01:00

System Information
Operating system: Kubuntu 21.04
Graphics card: AMD Radeon Vega 6 Graphics

Blender Version
Broken: 3.2.0.Alpha (branch: master, commit hash : 6bf51ab03a, commit date: Fri, 25 Mar 2022 9:33 PM)

Short description of error

When points of a stroke belong to just one vertex group and the index of that vertex group is not zero, Python API weight_get cannot retrieve weight assigned to points.

Not resolved after #91511.

Exact steps for others to reproduce the error

Run script in attached .blend file (bug.blend).

Draw two strokes.
Create two vertex groups.
Assign all points in first stroke to first vertex group group.
Assign all points in second stroke to second vertex group.
Call to stroke.points.weight_get(0, 0) results in -1.0
Call to stroke.points.weight_get(1, 0) throws Groups: index out of range

It seems that the code in rna_GPencilStrokePoints_weight_get interprets vertex_group_index in two different ways: index in dw array MDeformVert and index of vertex group in object. It checks bounds wrt totweight but gives weights associated. I have a fix ; I'll see if I can figure out how to attach it here.

**System Information** Operating system: Kubuntu 21.04 Graphics card: AMD Radeon Vega 6 Graphics **Blender Version** Broken: 3.2.0.Alpha (branch: master, commit hash : 6bf51ab03a066f8cf37a061ceb8d5c12bd6ea88d, commit date: Fri, 25 Mar 2022 9:33 PM) **Short description of error** When points of a stroke belong to just one vertex group and the index of that vertex group is not zero, Python API `weight_get` cannot retrieve weight assigned to points. Not resolved after [#91511](https://developer.blender.org/T91511). **Exact steps for others to reproduce the error** Run script in attached .blend file ([bug.blend](https://archive.blender.org/developer/F12948172/bug.blend)). - Draw two strokes. - Create two vertex groups. - Assign all points in first stroke to first vertex group group. - Assign all points in second stroke to second vertex group. - Call to `stroke.points.weight_get(0, 0)` results in -1.0 - Call to `stroke.points.weight_get(1, 0)` throws `Groups: index out of range` It seems that the code in `rna_GPencilStrokePoints_weight_get` interprets `vertex_group_index` in two different ways: index in `dw` array `MDeformVert` and index of vertex group in object. It checks bounds wrt `totweight` but gives weights associated. I have a fix ; I'll see if I can figure out how to attach it here.

Keny Chatain commented

2022-03-26 13:25:48 +01:00

Added subscriber: @KenyC

Pratik Borhade commented

2022-03-28 07:57:45 +02:00

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

Pratik Borhade commented

2022-03-28 07:57:47 +02:00

Added subscriber: @PratikPB2123

Antonio Vazquez commented

2022-03-29 10:53:56 +02:00

Added subscriber: @antoniov

Antonio Vazquez commented

2022-03-29 10:53:56 +02:00

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

Antonio Vazquez commented

2022-03-29 10:53:56 +02:00

I cannot reproduce. I guess you are mixing things in your script. I have done a test file to verify the weight API.

BugWeightAPI.blend

This blend file has a stroke with two vertex group. The first vertex group has assigned a weight of 1.0 to all points. The second vertex group has a 0.5 value for all points. Running the script you get this:

I cannot reproduce. I guess you are mixing things in your script. I have done a test file to verify the weight API. ![image.png](https://archive.blender.org/developer/F12953615/image.png) [BugWeightAPI.blend](https://archive.blender.org/developer/F12953617/BugWeightAPI.blend) This blend file has a stroke with two vertex group. The first vertex group has assigned a weight of `1.0` to all points. The second vertex group has a `0.5` value for all points. Running the script you get this: ![image.png](https://archive.blender.org/developer/F12953619/image.png)

Antonio Vazquez commented

2022-03-29 11:14:20 +02:00

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

Antonio Vazquez self-assigned this 2022-03-29 11:14:20 +02:00

Antonio Vazquez commented

2022-03-29 11:14:20 +02:00

I looked again and I was testing the wrong thing.

Keny Chatain commented

2022-03-29 11:18:44 +02:00

Indeed, the problem does not arise when there is just one stroke. Looking at the code, the one stroke vs. two strokes difference makes sense. As I understand it, weight_get checks bounds on vertex_group_index wrt totweight, which is the total number of vertex groups associated with the stroke, not the object.

Indeed, the problem does not arise when there is just one stroke. Looking at the code, the one stroke vs. two strokes difference makes sense. As I understand it, `weight_get` checks bounds on `vertex_group_index` wrt `totweight`, which is the total number of vertex groups associated with the *stroke*, not the *object*.

Antonio Vazquez commented

2022-03-29 11:22:56 +02:00

In #96799#1331389, @KenyC wrote:
Indeed, the problem does not arise when there is just one stroke. Looking at the code, the one stroke vs. two strokes difference makes sense. As I understand it, weight_get checks bounds on vertex_group_index wrt totweight, which is the total number of vertex groups associated with the stroke, not the object.

Yes, this is the problem... Fixing it!

> In #96799#1331389, @KenyC wrote: > Indeed, the problem does not arise when there is just one stroke. Looking at the code, the one stroke vs. two strokes difference makes sense. As I understand it, `weight_get` checks bounds on `vertex_group_index` wrt `totweight`, which is the total number of vertex groups associated with the *stroke*, not the *object*. Yes, this is the problem... Fixing it!

blender-admin commented

2022-03-29 11:25:18 +02:00

This issue was referenced by 343fc38b8d

This issue was referenced by 343fc38b8d646735f42c88dd9de8a33feaf3cb7f

blender-admin commented

2022-03-29 11:25:18 +02:00

This issue was referenced by 9450057b43

This issue was referenced by 9450057b43cb278e6b8003f54ec0705dae599165

Antonio Vazquez commented

2022-03-29 11:27:16 +02:00

Changed status from 'Confirmed' to: 'Resolved'

Antonio Vazquez closed this issue

2022-03-29 11:27:16 +02:00

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GPencil: Scripting weight_get cannot retrieve weights of certain vertex groups #96799