MAXScript - Baking Animation Transforms

A colleague of mine, Amer Yassine, who manages the awesome 3ds Max YouTube learning channel recently asked me how to bake world space transforms to helper objects.

Amer provided me the example of an arm with three bones and three helper objects. Each helper object was parented to the bone and the bones were animated using an IK solution. When he collapsed the transform controllers on the point helpers it would create keyframes for the helpers but with 0 values. So when he unlinked the helper objects they were no longer animated. This makes sense because the position of helpers was in local space relative to the parent object, but what Amer wanted were position/rotation keys for the helpers based on the world-space data.

My first thought was to try and find some scripts on ScriptSpot.com to do what he wanted. However none seemed to work and at first I wasn't quite clear on what the precise problem we needed to solve was. Eventually I found a thread on CGSociety.com where a similar question was framed in a way that explained what Amer and I were looking for except it applied to a camera:

I have been fumbling around trying to find a way to bake out some animation I have on a camera. The camera is animated via three dummies in a hierarchy and I need to 'bake' in the animation at every keyframe in worldspace. Currently every method/script I have found bakes the animation in local space so when the dummies/point helpers have been deleted the camera does not retain any of the animation, yet I have a keyframes at every frame. Is there a way to create keyframes that would take the position/rotation of the camera in worldspace at everyframe and allow me to delete everything but the camera and retain all animation?

http://forums.cgsociety.org/archive/index.php/t-740206.html

Now I was getting somewhere, because I finally understood the problem! The ensuing thread didn't make much sense to either of us, but going back to first principles, I created a basic script that:

1. Un-parented the helper from the bone.
2. Created a key-frame for the helper object at each frame based on the bones position/rotation/scale.

The resulting solution is quite elegant using MAXScript:

-- Create keys for the selected objects from the world space transforms taken from the parents (bones). 
-- Also unlink each object from the parent. 
startTime = 0
endTime = 100
nthFrame = 5
-- For all selected objects 
for obj in $ do 
(
  -- Get the current parent (a bone) and unlink the object. 
  bone = obj.parent
  obj.parent = undefined
  -- Create animation keys
  for t in startTime to endTime by nthFrame do (
    animate on at time t (
      obj.transform = at time t bone.transform
    )
  )              
)

The magic in this script occurs in the "animate" context expression. Check out the MAXScript documentation on the animate keyword to learn how it works. In short it acts like the "autokey" mode in 3ds Max. Any animatable property you change (such as the transform) is automatically associated with a new key.

I hope the rest of the script is sufficiently clear for you to use and modify for your own work. It did the trick for Amer. :-)

By the way, if you use 3ds Max at all you should check out Amer's tutorial on rigging a character for games that he just recently started posting. It is an amazing tutorial series that will have 40 parts once it is all online!