How to add a quaternion attribute on a node?

[yaoys]

Hi all,
I'm going to add an attribute of MQuaternion type on my custom node, but I don't know how to do it? Could anyone give me any clue? Thank you in advance.

Cheers
yao

[Rick Silliker]

I could be wrong, but couldn't you just use MFnNumericAttribute and when you create it declare a MFnNumericData.k4Double type?

[Joe Weidenbach]

That would be the right way as far as I can see, you can feed the four float values into a new MQuaternion in your node, or output them, depending on the intended result.

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[yaoys]

But the problem is how to set the value with MDataHandle?
e.g.
MDataHandle dh = datablock.outputValue(myNode.aQuaternion)
dh.set?(...) # there is not interfaces for set double4 or quaternion
dh.setClean()

Cheers
yao

[Joe Weidenbach]

Ok, I see where you're going, and you're correct, there's no double4 output.

You could make an array of doubles, but my question is why you'd want a Quaternion as an output--to my knowledge, Maya does process rotations internally as a Quaternion, but it converts those to Euler's before it outputs, and I don't know of any plugs that take a Quaternion.

When I've used Quaternions, I normally build my Quaternion internally, use it, and then output as a float3 after converting to a Euler with the appropriate rotation order.

You can do this pretty easily with MEulerRotation--it has asQuaternion(), and MQuaternion has asEulerRotation.

Once you've converted to a MEulerRotation, it's pretty straightforward to put it into a rotation data set.

You basically will need to set up three attributes (rotationX, rotationY, rotationZ) as MFnUnitAttributes with a type of MFnUnitAttribute::kAngle, and then a MFnNumericAttribute (rotation) with the three rotation attributes.  At least that's how I do it--the setup looks something like this in c++ (but Python's very similar), in the initialize() function:

    MFnNumericAttribute nAttr;
    MFnUnitAttribute uAttr;
   
    aRotX = uAttr.create("rotateX", "rx", MFnUnitAttribute::kAngle);
    uAttr.setWritable(false);
    uAttr.setStorable(false);
    aRotY = uAttr.create("rotateY", "ry", MFnUnitAttribute::kAngle);
    uAttr.setWritable(false);
    uAttr.setStorable(false);
    aRotZ = uAttr.create("rotateZ", "rz", MFnUnitAttribute::kAngle);
    uAttr.setWritable(false);
    uAttr.setStorable(false);
    aOutRotation = nAttr.create("outRotation", "or", aRotX, aRotY, aRotZ);
    nAttr.setWritable(false);
    nAttr.setStorable(false);
    nAttr.setArray(true);

Then you just use set3Double to set them.

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