Applying Vertex Weight Mix modifier invalidates existing references to Vertex Groups #98751

New Issue

Mysteryem · 2022-06-10T02:43:02+02:00

Mysteryem commented

2022-06-10 02:43:02 +02:00

System Information
Operating system: Windows-10-10.0.19043-SP0 64 Bits
Graphics card: NVIDIA GeForce GTX 1070 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.11

Blender Version
Broken: 3.0.0, 3.2.0, 3.3.0 Alpha (branch: master, commit date: 2022-06-07 18:08, hash: 173a15bcda)
Worked: 2.93.9

Short description of error
After applying a Vertex Weight Mix modifier, any existing references to Vertex Groups on the object the modifier was applied to become invalid, appearing to no longer reference the correct data in memory.

Exact steps for others to reproduce the error

Add vertex groups to the default cube (the more vertex groups there are, the more likely for there to be issues, 10 or more recommended for ease of reproduction)
Add a Vertex Weight Mix modifier to the cube
Set Vertex Group A and B in the modifier to any two vertex groups on the cube (they can be the same)
Select the cube so that is is the active object
In a Python Console window, run all_vg = bpy.context.object.vertex_groups[:]
Apply the Vertex Weight Mix modifier
In the same Python Console as before, run [v.name for v in all_vg]
It is likely that a UnicodeDecodeError will occur, some names will end up as the name of a different vertex group or something else entirely, some names will be empty or rarely, that Blender will crash
Performing other actions in Blender before running [v.name for v in all_vg], such as changing the Properties space from Modifier Properties to Material Properties is likely to cause issues even when there are only very few vertex groups on the cube.
An alternative to running [v.name for v in all_vg] in the Python Console, that may make the issue clearer, would be to instead run the following code as it will catch the UnicodeDecodeErrors:

for vg in all_vg:

try:
names.append(vg.name)
except UnicodeDecodeError:
names.append('error')


print(names)```
Provided that you enable the System Console for viewing the output and select the default cube as the active object first, the following script can be run from Blender's Text Editor to go through each of the steps (more vertex groups are added because it is much more likely for issues to not occur)

import bpy

cube = bpy.context.object
for _ in range(100):
cube.vertex_groups.new()

mod = cube.modifiers.new('Vertex Weight Mix', 'VERTEX_WEIGHT_MIX')
mod.vertex_group_a = cube.vertex_groups[0].name
mod.vertex_group_b = cube.vertex_groups[1].name

all_vg = cube.vertex_groups[:]

bpy.ops.object.modifier_apply(modifier=mod.name)

names = []
for vg in all_vg:
try:
names.append(vg.name)
except UnicodeDecodeError:
names.append('error')

print(names)

The following lines are to make it easier to repeatedly run the script, they are not required

print()
bpy.context.object.vertex_groups.clear()```

**System Information** Operating system: Windows-10-10.0.19043-SP0 64 Bits Graphics card: NVIDIA GeForce GTX 1070 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.11 **Blender Version** Broken: 3.0.0, 3.2.0, 3.3.0 Alpha (branch: master, commit date: 2022-06-07 18:08, hash: `173a15bcda`) Worked: 2.93.9 **Short description of error** After applying a Vertex Weight Mix modifier, any existing references to Vertex Groups on the object the modifier was applied to become invalid, appearing to no longer reference the correct data in memory. **Exact steps for others to reproduce the error** - Add vertex groups to the default cube (the more vertex groups there are, the more likely for there to be issues, 10 or more recommended for ease of reproduction) - Add a Vertex Weight Mix modifier to the cube - Set Vertex Group A and B in the modifier to any two vertex groups on the cube (they can be the same) - Select the cube so that is is the active object - In a Python Console window, run `all_vg = bpy.context.object.vertex_groups[:]` - Apply the Vertex Weight Mix modifier - In the same Python Console as before, run `[v.name for v in all_vg]` - It is likely that a UnicodeDecodeError will occur, some names will end up as the name of a different vertex group or something else entirely, some names will be empty or rarely, that Blender will crash Performing other actions in Blender before running `[v.name for v in all_vg]`, such as changing the Properties space from Modifier Properties to Material Properties is likely to cause issues even when there are only very few vertex groups on the cube. An alternative to running `[v.name for v in all_vg]` in the Python Console, that may make the issue clearer, would be to instead run the following code as it will catch the UnicodeDecodeErrors: ```names = [] for vg in all_vg: ``` try: names.append(vg.name) except UnicodeDecodeError: names.append('error') ``` print(names)``` Provided that you enable the System Console for viewing the output and select the default cube as the active object first, the following script can be run from Blender's Text Editor to go through each of the steps (more vertex groups are added because it is much more likely for issues to not occur) ``` import bpy cube = bpy.context.object for _ in range(100): cube.vertex_groups.new() mod = cube.modifiers.new('Vertex Weight Mix', 'VERTEX_WEIGHT_MIX') mod.vertex_group_a = cube.vertex_groups[0].name mod.vertex_group_b = cube.vertex_groups[1].name all_vg = cube.vertex_groups[:] bpy.ops.object.modifier_apply(modifier=mod.name) names = [] for vg in all_vg: try: names.append(vg.name) except UnicodeDecodeError: names.append('error') print(names) # The following lines are to make it easier to repeatedly run the script, they are not required print() bpy.context.object.vertex_groups.clear()```

Mysteryem commented

2022-06-10 02:43:02 +02:00

Added subscriber: @Mysteryem-2

Omar Emara commented

2022-06-10 09:55:20 +02:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-06-10 09:55:20 +02:00

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

Omar Emara commented

2022-06-10 09:55:20 +02:00

I can't reproduce on any of the listed versions for some reason, both in release and debug builds. Can you try this code instead:

import bpy

cube = bpy.context.object
for _ in range(100):
    cube.vertex_groups.new()

mod = cube.modifiers.new('Vertex Weight Mix', 'VERTEX_WEIGHT_MIX')
mod.vertex_group_a = cube.vertex_groups[0].name
mod.vertex_group_b = cube.vertex_groups[1].name

vertex_groups_copy = cube.vertex_groups[:]

bpy.ops.object.modifier_apply(modifier=mod.name)

for a, b in zip(reversed(vertex_groups_copy), cube.vertex_groups):
    print(a.name, a.as_pointer(), b.name, b.as_pointer())

print("=" * 40)

bpy.context.object.vertex_groups.clear()

Do any of the pointers change?

I can't reproduce on any of the listed versions for some reason, both in release and debug builds. Can you try this code instead: ``` import bpy cube = bpy.context.object for _ in range(100): cube.vertex_groups.new() mod = cube.modifiers.new('Vertex Weight Mix', 'VERTEX_WEIGHT_MIX') mod.vertex_group_a = cube.vertex_groups[0].name mod.vertex_group_b = cube.vertex_groups[1].name vertex_groups_copy = cube.vertex_groups[:] bpy.ops.object.modifier_apply(modifier=mod.name) for a, b in zip(reversed(vertex_groups_copy), cube.vertex_groups): print(a.name, a.as_pointer(), b.name, b.as_pointer()) print("=" * 40) bpy.context.object.vertex_groups.clear() ``` Do any of the pointers change?

Mysteryem commented

2022-06-10 10:48:06 +02:00

In #98751#1372106, @OmarEmaraDev wrote:
I can't reproduce on any of the listed versions for some reason, both in release and debug builds. Can you try this code instead:

[...]
Do any of the pointers change?

(I'm not sure the call to reversed() was supposed to be in your script, I removed it so that the vertex groups would line up).
Yes, on 3.0.0+, all the pointers change. On 2.93.9, the pointers remain the same

> In #98751#1372106, @OmarEmaraDev wrote: > I can't reproduce on any of the listed versions for some reason, both in release and debug builds. Can you try this code instead: > > [...] > Do any of the pointers change? (I'm not sure the call to reversed() was supposed to be in your script, I removed it so that the vertex groups would line up). Yes, on 3.0.0+, all the pointers change. On 2.93.9, the pointers remain the same ![image.png](https://archive.blender.org/developer/F13142953/image.png)

Omar Emara commented

2022-06-10 10:58:54 +02:00

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

Omar Emara commented

2022-06-10 10:58:54 +02:00

The pointers are the same for me in all versions, pre and post 3.0. Since I am on Linux, I will let someone on Windows to triage this and see if it can be confirmed there.

Omar Emara commented

2022-06-10 14:19:42 +02:00

Closed as duplicate of #93896

Omar Emara closed this issue

2022-06-10 14:19:42 +02:00

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Applying Vertex Weight Mix modifier invalidates existing references to Vertex Groups #98751

The following lines are to make it easier to repeatedly run the script, they are not required