Point-based animation applied while rendering

[Nicolas Castagne]

Dear all,

I am new to this group, and somewhat new to Maya, and I am looking for directions to start a new Maya Python script.

On the one side, I have large files encoding the sampled movement of a large number of 3D points.
These movements can be parsed using Python - no problem here.

My goal is to let these "moving 3D points" control various Maya objects (points, locaters, clusters, nurbs's control points, polygons, etc).

I know that, for each of the moving points, I could attach a keyframe to a node, and pre-load all the movement as keyframes.

However, since I am not interested in keyframes, I would like to set up a system that, while runing the Maya animation, on each frame :
- reads the current points' positions in the file
- applies the new position to the Maya scene (eg move chosen "points", eg locators, in the Maya scene)
- then, and only then, starts the frame's rendering pipeline

Hence, to some extend, I would need to "hook" into Maya's in-time loop.

Since I am very new to Maya-Python, I hardly figure out where to start.

Would you have any advice, examples, or entries in the API ?

Thank you very much in advance,
Nicolas & team

[Manuel Macha]

It seems to me that what you describe as Maya's 'in-time' loop could be achieved using expressions.

Have a look at Maya's-Online help for expressions and see if you can make sense of it.

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[Marcus Ottosson]

Hi Nicolas, and welcome.

Have a look at the script node. It’ll let you run Python on a per-frame basis and you should be able to apply your data from there.
http://download.autodesk.com/global/docs/maya2013/en_us/Nodes/script.html

It does however sound quite taxing from a performance perspective and for that you might be better off writing a plug-in in either C++ or C#

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[Nicolas Castagne]

Hello all,

Thanks for your answers Manuel and Marcus.

The notion of "Script Node" is apparently very appropriate, with a "on software frame render" setting.
Thank you Marcus.


However, it raises two question we could not solve so far.

First question :
Is it possible to pass a Python variable to a Script Node ?
My idea is :
   1/ open my motion file BEFORE launching Maya's loop (parse the file header, check a series of things, etc)
   2/ pass a File object to the script node, so that on each Maya frame the corresponding data are read in the file.
However, I then need to let my scipt node access the File variable...

More generally, I think there is probably a mean to let a script node access parameters (Python variables, etc). But which is it ?


Second question :
Apparently, a "script nodes" deletes itself when executed. Well... This sound a bit strange to me... Is there a mean to let a "on software frame render" script node be permanent, and be executed on each frame ?


Thank you very much for your upcoming answers,
best-

Nicolas (& colleagues)

[Nicolas Castagne]

Auto-answer to my own message : I got time to look arround myself and got some success.

Execute the following Maya script :

testVar=5

cmds.scriptNode( n='test script node R', bs='print "current time is %f" %maya.cmds.currentTime(q=1); print "value of testVar : %i" %testVar;', st=7, stp='python' )

Note that the "st" flag is 7 => "Execute on time changed"

(see http://download.autodesk.com/global/docs/maya2014/en_us/CommandsPython/scriptNode.html#flagbeforeScript for the documentation of the script Node Command)

Then play the animation. 

It outputs :

current time is 1.000000

value of testVar : 5

current time is 2.000000

value of testVar : 5

... and so forth.

Rational : 

1/ python script node has access to the interpreter's global variables

2/ when set as "Execute on time changed", a script node is not auto-deleted once executed.

just the behaviour we were looking for.

[Nicolas Castagne]

Yet another small new question...

Is there a mean to pass a value to a Python script node (as we pass a value to a function) ?

Thanks,

Nicolas