Error with rendering attribute pixelCenter (Object already exists)

[morinnicolas8944]

I need to get the current position in the image when rendering my material node in MPxNode::compute in order to export the rendering results to an image file.

I plan to use the rendering attribute pixelCenter, defined in Maya Developer Help - Appendix B.

http://help.autodesk.com/view/MAYAUL/2017/ENU/?guid=__files_Appendices_Appendix_C_Rendering_attribut...

I add the attribute to my node, as I do with other rendering attributes, in the node's initialize() with the following code.

aPixelCenterX = nAttr.create("pixelCenterX", "pcx", MFnNumericData::kFloat, 0, &status);
CHECK_MSTATUS(status);
CHECK_MSTATUS(nAttr.setStorable(true));
CHECK_MSTATUS(nAttr.setKeyable(true));
CHECK_MSTATUS(nAttr.setDefault(0.0f));

aPixelCenterY = nAttr.create("pixelCenterY", "pcy", MFnNumericData::kFloat, 0, &status);
CHECK_MSTATUS(status);
CHECK_MSTATUS(nAttr.setStorable(true));
CHECK_MSTATUS(nAttr.setKeyable(true));
CHECK_MSTATUS(nAttr.setDefault(0.0f));

aPixelCenter = nAttr.create("pixelCenter", "pc", aPixelCenterX, aPixelCenterY);
CHECK_MSTATUS(nAttr.setStorable(true));
CHECK_MSTATUS(nAttr.setKeyable(true));
CHECK_MSTATUS(nAttr.setDefault(0.0f, 0.0f));
CHECK_MSTATUS(nAttr.setHidden(true));
CHECK_MSTATUS(addAttribute(aPixelCenter));

But the last line fails with error ": (kInvalidParameter): Object already exists".

It appears to work if I change the brief names of the attributes to ones that are different from the ones specified in Appendix B.

I observed the problem with Maya 2017 Update 2. I did not try yet with other versions of Maya.

[Anonymous · Accepted solution]

Do you maybe add another attribute to your node, which is using the short name "pc" already?

[morinnicolas8944]

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@Anonymous wrote:

Do you maybe add another attribute to your node, which is using the short name "pc" already?

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You're right, I only checked my custom attributes so I didn't notice it, but I was also using "pc" for pointCamera!

Setting the short name for pointCamera to "p" fixed the problem.

Now I feel silly

Thanks for your help!

[Anonymous]

Happen to all of us from time to time 🙂