Crash when using to_mesh() on a depsgraph object in a driver #84117
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Reference: blender/blender#84117
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System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 457.30
Blender Version
Broken: version: 2.91.0, branch: master, commit date: 2020-11-25 08:34, hash:
0f45cab862Short description of error
Blender crashes when we use the following driver for a bone's X position:
Exact steps for others to reproduce the error
crashTest.blend
Added subscriber: @KevinHays
Added subscriber: @rjg
I can reproduce a crash, but I'm not sure if this use of the Python API in the driver is permitted. I'm confirming this for now, so that the Data, Assets & I/O module can take a closer look.
Addressable: 00
Partially addressable: 01 02 03 04 05 06 07
Heap left redzone: fa
Freed heap region: fd
Stack left redzone: f1
Stack mid redzone: f2
Stack right redzone: f3
Stack after return: f5
Stack use after scope: f8
Global redzone: f9
Global init order: f6
Poisoned by user: f7
Container overflow: fc
Array cookie: ac
Intra object redzone: bb
ASan internal: fe
Left alloca redzone: ca
Right alloca redzone: cb
Shadow gap: cc
Changed status from 'Needs Triage' to: 'Confirmed'
Added subscriber: @mont29
This can crash in several different places... Here is another ASAN backtrace:
I think that this code cannot work in a driver because depsgraph is not aware of the dependency from the Object to its mesh evaluation then?
But even with adding manually explicit dependencies over
Cube.001mesh and object (through unused driver variables)......it still crashes, although with a slithly different backtrace:
In any case, this is for the depsgraph & animation department, not really related to Data & IO module...
Added subscriber: @dr.sybren
@KevinHays converting an object to a mesh may not be the most elegant approach here. What is your use case for this code? Why not use something like a Hook constraint, for example? What kind of object are you converting to a mesh?
Changed status from 'Confirmed' to: 'Needs User Info'
So when I encountered this crash, I was working on a facial mocap system. I have footage of a face with dots painted on it, and tracked those dots to give me motion-tracked empties. My goal was to use those empty positions to drive the bone positions of a rigged character.
However there's not a 1:1 mapping from tracker dots to character bone positions. I wrote some python code to figure out the best character bone positions based on the input tracker data.
Unfortunately my code had poor results when relying solely on tracker locations as input data, so I created a mesh that connects the tracker dots: https://i.imgur.com/JeAJUYe.gif
The idea was to use edge lengths and edge angles as input data for my code that calculates the character bone positions. My code was able to produce better, less-jittery bone positions using the edge data, but also but also crashed often (hence the bug report).
I admit this is probably a pretty obscure use case, but it crashes consistently which is why I decided to report the bug.
I ended up going with an off-line approach by calculating bone positions for each frame, and inserting a keyframe of my calculated bone location (as opposed to relying on drivers to give me the correct bone positions for the current frame).
Changed status from 'Needs User Info' to: 'Needs Triage'
Added subscriber: @lichtwerk
Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'
@dr.sybren : since there is new information here: how would you classify this then?
I still don't understand why
.to_mesh()is called. The cube object is already a mesh, so there should be no need to do this conversion.Changed status from 'Needs Developer To Reproduce' to: 'Archived'
I looked at the code for
BKE_object_to_mesh()(the C function that's called when you call.to_mesh()from Python), and it looks like it's not made for being called on evaluated data-blocks. As such this is simply a design limitation, and not a bug.