Transform Script Controller

A Transform Script controller contains all of the information contained in a Position/Rotation/Scale (PRS) controller in one scripted matrix value. Instead of having three separate tracks for position, rotation, and scale, you can access all three values simultaneously from a single script controller dialog. Because a script defines the transform values, they are easier to animate.

The value of the controller script must be a matrix3 value. A matrix3 value is a 4x3 3D transformation matrix. For more information, see the Matrix3 Values topic in the MAXScript Help.

Writing Controller Scripts

3ds Max interprets the text you type into the Script text box as the body of a MAXScript block expression. You can type as many expressions as you want on as many lines as you want, and they are evaluated in turn. The value of the last expression is taken as the controller value. This value must yield the right type for the controller: float for Float, point3 for Position, quat for Rotation, matrix3 for Transform, and so on.

Because the text is inside a block expression, you can declare local variables that are visible only within the script and are temporary for one evaluation. You can also declare or access global variables that are shared with all other scripts in MAXScript and hold their values from one evaluation to the next.

A controller is always evaluated by 3ds Max with respect to a specific animation time. This might be the current time slider or incrementing frame time if an animation is playing, or a rendering is under way. In the case of Script controllers, the time being evaluated is used to establish an automatic "at time" context around the controller script, so any properties you access (outside of other explicit “at time” expressions) yield the correct values for the current controller evaluation time. This means you don't have to do anything special in your scripts to work at the correct time. You can access the evaluation time with the standard MAXScript variable, currentTime. You can also reference scene property values at other times by using "at time" expressions in your scripts, as in regular MAXScript programming.

Assign Nodes and Tracks to Variables

When you need to refer to nodes in your scene or to animation tracks, it is recommended that you use the Script controller variable toolset to create variables to assign to any particular node or controller track. This way, if you decide to later on rename your scene objects, the script controllers using these objects are preserved because the variables maintain the link to the nodes.

Otherwise, if you assign, for example, a node to a variable manually in the dialog's Expression window, that link becomes broken as soon as you rename that particular node.

Procedures

Example: To keep an object centered relative to other objects in the scene during an animation:

1. Name the object that should remain centered foo and assign a Script controller to its Position track.
2. Enter foo in the Name field and click Create.

   The new variable is automatically added to the Variables list.

3. With the variable highlighted, click Assign Node.

   The Track View Pick dialog opens, listing the contents of your scene.

4. Expand the Objects hierarchy until you locate foo. Highlight it and click OK.

   The foo node is assigned to your variable.

5. Enter the following script in the Script Controller dialog's Expression window:

   local pos=[0,0,0]

   for o in objects where o != foo do

   pos += o.pos

   pos / (objects.count - 1)

   This script computes the average position of all objects, except the current one (written as foo here) by setting up a local, iterating over all objects except foo, accumulating a total position vector, and computing the average in the last line, which is the final result of the script.

To use a Transform Script controller:

1. Select an object.
2. Right-click to open the quad menu.
3. In the Transform quadrant, click Curve Editor.
4. Select the Transform track of the selected object in Track View.
5. Select Transform Script from the Assign Transform Controller dialog and click OK.

   The Script Controller dialog opens.

6. Edit the matrix3 value in the Script Controller dialog, and click Evaluate when you are finished.

Interface

Assigning a Script controller automatically opens a Script Controller dialog where you can enter a script. You can open the dialog subsequently by right-clicking the track on the Motion panel or in the Track View hierarchy and choosing Properties, or clicking the Properties button on the Track View toolbar.