[Maya-Python] Can't read worldMatrix of custom Python API 2.0 node

[Marcus Ottosson]

Hi all,
I’ve been writing custom nodes in 1.0 and recently transitioned into 2.0, but found that one of the commands or methods of retrieving a matrix MPlug no longer works, returning a Unexpected Internal Failure, which isn’t very descriptive. I’m hoping you can help me spot what needs to change in order for this to work.

To reproduce:

1. Save the below to myplugin.py
2. Run the attached example

Any ideas?

Best,
Marcus

"""Can't read worldMatrix of custom node

Example:
    from maya import cmds
    from maya.api import OpenMaya as om

    cmds.loadPlugin(r"c:\path\to\myplugin.py")

    fn = om.MFnDagNode()
    parent = fn.create("transform", "myTransform")
    mobj = fn.create("myLocator", "myLoc", parent)
    plug = fn.findPlug("worldMatrix", False)
    plug = plug.elementByLogicalIndex(0)
    om.MFnMatrixData(plug.asMObject()).matrix()
    # RuntimeError: (kFailure): Unexpected Internal Failure

"""

from maya.api import OpenMaya as om, OpenMayaUI as omui

class MyLocator(omui.MPxLocatorNode):
    name = "myLocator"
    typeid = om.MTypeId(0x999999)
    classification = "drawdb/geometry/custom"

    @classmethod
    def creator(cls):
        return cls()

    @classmethod
    def init(cls):
        pass

maya_useNewAPI = True

def initializePlugin(obj):
    plugin = om.MFnPlugin(obj, "MyPlugin", "1.0", "Any")

    plugin.registerNode(MyLocator.name,
                        MyLocator.typeid,
                        MyLocator.creator,
                        MyLocator.init,
                        om.MPxNode.kLocatorNode,
                        MyLocator.classification)

def uninitializePlugin(obj):
    om.MFnPlugin(obj).deregisterNode(MyLocator.typeid)

[Tim Fowler]

Not sure what you're hitting.  That last line gives me...

om.MFnMatrixData(plug.asMObject()).matrix()

# Result: maya.api.OpenMaya.MMatrix(((1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1))) # 

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[Marcus Ottosson]

Wuw! What version of Maya is that, and what OS? I'm on Windows, Maya 2018. Hadn't considered it might be a version or OS thing, will have a look at that.

To view this discussion on the web visit https://groups.google.com/d/msgid/python_inside_maya/CALKD2Wpgj%2BgfVMAHRL3HW7T3Oz-qkoRLQxEoc6fLMxSfH5MhwQ%40mail.gmail.com.

[Tim Fowler]

Hmm...looks like I tried that on an unreleased version of Maya (and a Debug version too).  Just tried again in Maya 2018 and got the same error as you.  I'll take a quick look and see if I can figure out what fixed it, but I should warn you that API fixes can sometimes be tricky to get into Updates since those typically have to remain binary compatible.

-Tim

[Marcus Ottosson]

Mm, I'm looking to get a matrix out of Maya 2015 and above, so a patch would unfortunately not help me in this case. Do you know of another way of getting hold of that matrix?

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[Michael Boon]

Can you use fn.dagPath().inclusiveMatrix() ?

On Wednesday, 5 December 2018 02:02:25 UTC+11, Marcus Ottosson wrote:

Mm, I'm looking to get a matrix out of Maya 2015 and above, so a patch would unfortunately not help me in this case. Do you know of another way of getting hold of that matrix?

On Tue, 4 Dec 2018 at 14:50, Tim Fowler <tim.f...@gmail.com> wrote:

Hmm...looks like I tried that on an unreleased version of Maya (and a Debug version too).  Just tried again in Maya 2018 and got the same error as you.  I'll take a quick look and see if I can figure out what fixed it, but I should warn you that API fixes can sometimes be tricky to get into Updates since those typically have to remain binary compatible.

-Tim

On Tue, Dec 4, 2018 at 9:26 AM Marcus Ottosson <konstr...@gmail.com> wrote:

Wuw! What version of Maya is that, and what OS? I'm on Windows, Maya 2018. Hadn't considered it might be a version or OS thing, will have a look at that.

On Tue, 4 Dec 2018 at 14:14, Tim Fowler <tim.f...@gmail.com> wrote:

Not sure what you're hitting.  That last line gives me...

om.MFnMatrixData(plug.asMObject()).matrix()

# Result: maya.api.OpenMaya.MMatrix(((1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1))) # 

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[Marcus Ottosson]

> Can you use fn.dagPath().inclusiveMatrix() ?

Yes! That looks very promising (for completeness, it was `getPath()` rather than `dagPath()`). I worked around it this time around, by getting the parent of any shape, and fetching it's matrix instead. Not as neat, so will experiment with your suggestion as well.

Thank you!

On Tue, 4 Dec 2018 at 21:25, Michael Boon <boon...@gmail.com> wrote:

Can you use fn.dagPath().inclusiveMatrix() ?

On Wednesday, 5 December 2018 02:02:25 UTC+11, Marcus Ottosson wrote:

Mm, I'm looking to get a matrix out of Maya 2015 and above, so a patch would unfortunately not help me in this case. Do you know of another way of getting hold of that matrix?

On Tue, 4 Dec 2018 at 14:50, Tim Fowler <tim.f...@gmail.com> wrote:

Hmm...looks like I tried that on an unreleased version of Maya (and a Debug version too).  Just tried again in Maya 2018 and got the same error as you.  I'll take a quick look and see if I can figure out what fixed it, but I should warn you that API fixes can sometimes be tricky to get into Updates since those typically have to remain binary compatible.

-Tim

On Tue, Dec 4, 2018 at 9:26 AM Marcus Ottosson <konstr...@gmail.com> wrote:

Wuw! What version of Maya is that, and what OS? I'm on Windows, Maya 2018. Hadn't considered it might be a version or OS thing, will have a look at that.

On Tue, 4 Dec 2018 at 14:14, Tim Fowler <tim.f...@gmail.com> wrote:

Not sure what you're hitting.  That last line gives me...

om.MFnMatrixData(plug.asMObject()).matrix()

# Result: maya.api.OpenMaya.MMatrix(((1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1))) # 

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[Marcus Ottosson]

Back at this and, unlike an attribute query, turns out the `inclusiveMatrix` doesn't support being passed a `MDGContext`. That's a bummer, didn't realise I was so dependent on that.

The workaround has been working well. As it happens, it also enabled me to consolidate calls to matrices of each shape for a transform into a single call, saving on performance, which is particularly important in this case, as the calls I'm making are made each frame, in the range of 20-1,000 nodes, at all times on the timeline; not unlike a scene export.