Blender crash in bmesh.to_mesh() while using it to modify weights (fixed in 3.6, only relevant for 3.3 LTS) #71585

New Issue

Erik Abrahamsson · 2019-11-14T21:29:50+01:00

Erik Abrahamsson commented

2019-11-14 21:29:50 +01:00

System Information
Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.70

Blender Version
Broken: version: 2.82 (sub 1), branch: master, commit date: 2019-10-27 17:59, hash: dd904f6761
Worked: (optional)

Short description of error
Crash in bmesh.to_mesh() if using it to modify weights in weightpainting while playing animation

Exact steps for others to reproduce the error
*Remove any lights or cameras, keep just one cube in the scene (for the simple script to work).
*Subdivide it 5 times and apply the modifier.
*Add the script below to the script editor and run it
*Go to weight paint mode for the cube
*Run the animation and try to paint. If you just click the left mouse button it will paint a dot and the script will work, but if you hold and drag, Blender crashes.

import bpy, bmesh


def add_handler():
    # remove existing handlers
    old_handlers = []
    for h in bpy.app.handlers.frame_change_post:
        if "paint_test" in str(h):
            old_handlers.append(h)
    for h in old_handlers: bpy.app.handlers.frame_change_post.remove(h)
    # add new handler
    bpy.app.handlers.frame_change_post.append(paint_test)

def paint_test(scene):
    for ob in scene.objects:
        me = ob.data
        
        print(str(scene.frame_current) + ": Creating Bmesh")
        bm = bmesh.new()
        bm.from_mesh(me)
        
        group_index = ob.vertex_groups.active_index
        dvert_lay = bm.verts.layers.deform.active
            
        for vert in bm.verts:
            dvert = vert[dvert_lay]
            try: dvert[group_index] -= 0.1
            except: pass            
        
        print(str(scene.frame_current) + ": Writing Bmesh")
        bm.to_mesh(me)
        bm.free()
        
add_handler()

**System Information** Operating system: Windows-10-10.0.18362 64 Bits Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.70 **Blender Version** Broken: version: 2.82 (sub 1), branch: master, commit date: 2019-10-27 17:59, hash: `dd904f6761` Worked: (optional) **Short description of error** Crash in bmesh.to_mesh() if using it to modify weights in weightpainting while playing animation **Exact steps for others to reproduce the error** *Remove any lights or cameras, keep just one cube in the scene (for the simple script to work). *Subdivide it 5 times and apply the modifier. *Add the script below to the script editor and run it *Go to weight paint mode for the cube *Run the animation and try to paint. If you just click the left mouse button it will paint a dot and the script will work, but if you hold and drag, Blender crashes. ``` import bpy, bmesh def add_handler(): # remove existing handlers old_handlers = [] for h in bpy.app.handlers.frame_change_post: if "paint_test" in str(h): old_handlers.append(h) for h in old_handlers: bpy.app.handlers.frame_change_post.remove(h) # add new handler bpy.app.handlers.frame_change_post.append(paint_test) def paint_test(scene): for ob in scene.objects: me = ob.data print(str(scene.frame_current) + ": Creating Bmesh") bm = bmesh.new() bm.from_mesh(me) group_index = ob.vertex_groups.active_index dvert_lay = bm.verts.layers.deform.active for vert in bm.verts: dvert = vert[dvert_lay] try: dvert[group_index] -= 0.1 except: pass print(str(scene.frame_current) + ": Writing Bmesh") bm.to_mesh(me) bm.free() add_handler() ```

Erik Abrahamsson commented

2019-11-14 21:29:50 +01:00

Added subscriber: @erik85

Erik Abrahamsson commented

2019-11-19 03:02:32 +01:00

This is where the crash occurs:

This is where the crash occurs: ![bild.png](https://archive.blender.org/developer/F8136231/bild.png)

Jacques Lucke commented

2020-01-08 16:47:47 +01:00

Added subscriber: @JacquesLucke

Jacques Lucke commented

2020-01-08 16:47:47 +01:00

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

Jacques Lucke commented

2020-01-08 16:47:47 +01:00

I can reproduce the issue. Not sure if there is an easy fix. You could try to update the vertex weights without bmesh.

Bastien Montagne commented

2020-01-15 16:02:43 +01:00

Added subscribers: @Sergey, @ideasman42, @mont29

Bastien Montagne commented

2020-01-15 16:02:43 +01:00

@JacquesLucke (and obviously @erik85) please always attach minimal .blend file to help reproducing the issue, this saves time for everybody who would want to investigate further.

That handler callback will basically re-allocate all data inside of the Mesh data-block, not knowing enough about handler system to be sure without actual investigation, but I would bet that that is not supposed to happen (and hence not expected to work), @Sergey, @ideasman42 ?

@JacquesLucke (and obviously @erik85) please always attach minimal .blend file to help reproducing the issue, this saves time for everybody who would want to investigate further. That handler callback will basically re-allocate all data inside of the Mesh data-block, not knowing enough about handler system to be sure without actual investigation, but I would bet that that is not supposed to happen (and hence not expected to work), @Sergey, @ideasman42 ?

Philipp Oeser commented

2020-01-15 16:28:08 +01:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2020-01-15 16:28:08 +01:00

Not sure what I am doing "wrong", but this is not crashing for me:
#71585.blend

Not sure what I am doing "wrong", but this is **not** crashing for me: [#71585.blend](https://archive.blender.org/developer/F8279825/T71585.blend)

Jacques Lucke commented

2020-01-15 16:31:48 +01:00

@lichtwerk, it crashes for me when I add one more subdivision level to the cube.

Philipp Oeser removed the

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Blender crash in bmesh.to_mesh() while using it to modify weights (fixed in 3.6, only relevant for 3.3 LTS) #71585