MPxNode Plug-in Crashing Maya

[Alec Fredericks]

Hi there.

I wanted to finally start writing plug-ins for Maya using Python. To start, I created a template for myself that just takes a matrix as an input and outputs the same matrix -- basically, a compute devoid of any computing.

When I plug the matrix of one object into it and connect the output of the matrix (via a decompose matrix node for the time being -- I'll output constituent transform data later) to the translation of another object, I get the expected output. Object 2 follows object 1.

The problem is that after wiggling object 1 around for a little bit, Maya crashes eventually, giving me an error similar to this: undo of command caused reentrant call to undo manager

I guess it could be that I need to add some undo code in there.

I threw my code up on pastebin if anyone has a moment to look at it to see what I did wrong. I'll keep poking at it, too, and maybe adding a debugger to the mix.

https://pastebin.com/vMeaJME5

Thanks,

Alec

[Ravi Jagannadhan]

What's your crash's stack trace?

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[Alec Fredericks]

Sorry I didn't provide that. Once I get home tonight, I'll dig that up and post it, too.

[Chad Vernon]

Try getting rid of some of your constructors which are unnecessary:

Instead of 

matrixOutDataHandle = om.MDataHandle(pDataBlock.outputValue(TransformHistory.matrixOutputAttribute))

just write

matrixOutDataHandle = pDataBlock.outputValue(TransformHistory.matrixOutputAttribute)

Instead of 

inputMatrix = om.MMatrix(matrixInDataHandle.asMatrix())

just write

inputMatrix = matrixInDataHandle.asMatrix()

[Chad Vernon]

You also need to set the plug or data handle clean.

matrixOutDataHandle.setClean()

or 

pDataBlock.setClean(pPlug)

[Alec Fredericks]

Hi. After trying a little bit to sort this out, I still can't figure out why it's crashing. It's choking on foundation.dll and I've discovered that it's sometimes a permissions error that causes it.

Anyway, I've attached the crash log and dump files. I've also updated the plug-in template a little so it represents the latest.

https://pastebin.com/yZn9vUz5

Thanks,

Alec

On Monday, October 30, 2017 at 11:40:46 AM UTC-7, Ravi Jagannadhan wrote:

[Balazs Pataki]

You are incorrectly creating matrix attributes:

eg.: The input matrix is created as 

TransformHistory.matrixInputAttribute = matrixAttributeFn.create('inMatrix', 'inMatrix', om.MFnMatrixData.kMatrix)

but it should be  

TransformHistory.matrixInputAttribute = matrixAttributeFn.create('inMatrix', 'inMatrix', om.MFnMatrixAttribute.kDouble) # or om.MFnMatrixAttribute.kFloat depends what you want

(Also your output matrix suffers from the same problem)

The last parameter is just an enum value(in this case om.MFnMatrixData.kMatrix which holds the value 5 and om.MFnMatrixAttribute.kDouble what equals to 1) but since we don't know the underlying implementation is, putting in undocumented values is questionable.

But how do we know that what values are supported? It's in the Python API documentation or also in the C API.

[Alec Fredericks]

Wow, I think that did it! Thanks for the suggestion, Balazs. I've been trying to get it to crash but so far so good. I think your tip, and probably the other suggestions by Chad, stabilized everything. I'll read the docs more clearly next time.

Alec