getElements from MFnSingleIndexedComponent

[ynedelin]

Hey guys
I do not use OpenMaya very often so I need an advise here, I am writing a few functions to deal with skin weights and all works great as long as I do not change the components. I would like to change components for the setWeights.

Right now I create the variables I need and then run the MFnSkinCluster.getWeights.
 
So it looks sort of like this:

apiComponents = om.MFnSingleIndexedComponent().create(om.MFn.kMeshVertComponent)
skinCluster = omAnim.MFnSkinCluster(om.MObject())

skinCluster.getWeights(
                skinPath,
                apiComponents,
                weights,
                influenceCount)

Good!

Now I would like to know what is inside the apiComponents, and hopefully change it. I assume this is MFnSingleIndexedComponent object, therefore I should be able to run something like

vertexIndexList = om.MIntArray()
apiComponents.getElements(vertexIndexList)


But I get this error
#     self.apiComponents.getElements(vertexIndexList)
#   File "c:\buildforge\Maya_2013_Win64\build\work\Release\runTime\Python\Lib\site-packages\maya\OpenMaya.py", line 1529, in <lambda>
#   File "c:\buildforge\Maya_2013_Win64\build\work\Release\runTime\Python\Lib\site-packages\maya\OpenMaya.py", line 54, in _swig_getattr
# AttributeError: getElements #

please shed some light on how this supposed to work .

thank you

Yury

[ynedelin]

After keep looking into this I realized that my apiComponents is actually a MObject, but how can I use it?

[Paul Molodowitch]

The relationship between MObjects + MFn function sets is one of the stranger features of the OpenMaya API, and can be hard to wrap your head around.  Basically, the mobject represents the actual "data", is is generally what is passed into / from the various methods, while the MFns can be thought of as classes used to "decode" the data, so that you can actually interact with them.  Therefore, before you can actually do anything with an MObject, you will often need to cast it into the appropriate MFn function set.

In your case, since MFnSingleIndexedComponent.create returns an MObject, you need to then immediately turn around and cast that MObject into an MFnSingleIndexedComponent object (or set an an existing MFnSingleIndexedComponent to point to it).

Also, note that since the apiComponents arg to getWeights is an INPUT parameter, you will need to modify / set it BEFORE calling getWeights.

- Paul

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[yury nedelin]

Thank you Paul

It works. Awesome!

yury

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