Page 913 - Kitab3DsMax

Chapter 35: Animating with the Expression Controller and Wiring Parameters
Before you can use the Expression controller on a track, you must assign it to a track. You can assign con-
trollers to the Position, Rotation, and Scale tracks using the Motion panel or the Track View or you can
apply a controller by right-clicking on a track in the Track View and selecting the Assign Controller option.
After you assign a controller, the Expression Controller dialog box immediately opens, or you can access
this dialog box at any time by right-clicking the track and selecting Properties from the pop-up menu. For
example, select an object in your scene, open the Motion panel, and select the Position track. Then click the
Assign Controller button at the top of the Assign Controller rollout, and select Position Expression from the
list of Controllers. This causes the Expression Controller dialog box to appear.
You can use this dialog box to define variables and write expressions. The dialog box, shown in Figure
35.2, includes four separate panes used to display a list of Scalar and Vector variables, build an expression,
and enter a description of the expression.
FIGURE 35.2
You can use the Expression controller to build expressions and define their results.

Defining variables
Variables are placeholders for different values. For example, creating a variable for a sphere’s radius called
“r” would simplify an expression for doubling its size from “take the sphere’s radius and multiply it by two,”
to simply “r times 2.”
To add variables to the list panes in the Expression Controller dialog box, type a name in the Name field,
select the Scalar or Vector option type, and click the Create button; the new variable appears in the Scalars
or Vectors list. To delete a variable, select it from the list and click the Delete button. The Tick Offset value
is the time added to the current time and can be used to delay variables.
You can assign any new variable either to a constant or to a controller. Assigning a variable to a constant
does the same thing as typing the constant’s value in the expression. Constant variables are simply for con-
venience in writing expressions. The Assign to Controller button opens the Track View Pick dialog box,
shown in Figure 35.3, where you can select the specific controller track for the variable, such as the posi-
tion of an object.

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