Ian Rich

Turn, Turn, Turn - Life of a Maya Script, Part 1

My colleague at work had a folder full of models that needed to be rotated to face in the Z-positive direction, to match Unity's orientation. He asked me if there was a way to get that done without having to open up every file and do it manually. My eyes lit up and I was like, "Ooh, ooh, let me script that for you!" I had just begun working through Practical Maya Programming by Rob Galanakis and was thrilled that a real-world case study just fell into my lap.

I then went and made a 'Case Studies' section in my Workflowy notes for the book and outlined my anticipated program flow:

  • Load FBX
  • Get to the root transform of the model
  • Rotate it
  • Export a new FBX

I could have just had that all in my head, this isn't a crazy complicated scenario, but I knew there would be nuances to add so I might as well start laying out the 'skeleton' of the script in this way.

The first, and most important, thing to figure out was the name of the script, thus rotateEmAll.py was born! (Just be thankful I didn't go with gottaRotateEmAll;)

I began by inspecting one of the FBX files in Maya to see how the models were set up and figuring out what nodes were at play. Then it was just a matter of finding the relevant PyMEL functions or MEL commands I'd need to execute to get to the root transform. My first thought was to do ls(type='transform') which would give me a list of all the transforms, then I'd just need to find the one with no parent and that'd be my root. What I found was that that command had grabbed the transforms of all the cameras as well, so I needed to filter those out. The strategy I eventually landed on was to just select all the meshes in the scene; meshes = ls(type='mesh') whose parents just happen to be their Transform nodes. A little list comprehension would slurp those out: transforms = [m.getParent() for m in meshes]. Then I just needed to get the root transform, which would be the one with no parent: root = [t for t in transforms if t.getParent()==None][0] (This list comprehension would return a list with one item, so I index it out with [0] so that root is a Transform node, not a list). If I wanted to be a clever boy, I could have done that all in one statement, like: root = [t.getParent() for t in pmc.ls(type='mesh') if t.getParent().getParent()==None][0] but why sacrifice readability to reduce a mere two lines of code, eh?

Finally, the rotation could happen: root.setRotation([0.0,180.0,0.0], space='world'). Then, to make sure I was being Mr. Clean, I wanted to 'Freeze Transformations' on this model so it'd be spic-n-span upon import into the engine. To discover this command I used the classic method of performing it in the Maya GUI and looking at the script window to see what MEL command was executed. I saw 'makeIdentity', so I looked up the corresponding PyMEL syntax, thus: pmc.makeIdentity(apply=True). Makes sense, because an 'Identity Matrix' would be zero rotation and translation with a scale of one - nice and 'frozen!'

So here is the code for the full operation:

    meshes = pmc.ls(type='mesh')
    transforms = [m.getParent() for m in meshes]
    root = [t for t in transforms if t.getParent()==None][0]
    root.setRotation([0.0,180.0,0.0], space='world')
    pmc.makeIdentity(apply=True) # Freeze Transformations

Then it was a matter of doing this on multiple files... To be continued in:

Life's a Batch: Small Batch Artisinal File Processing - Life of a Maya Script, Part 2

P.S. Earlier I said it was, "just a matter of finding the relevant PyMEL functions.." which was not as straightforward as it sounds. Maybe I'll write about that special slice of the process later :)