Page 918 - Kitab3DsMax

Part VIII: Advanced Animation Techniques
Using Expression Controllers
You can use expressions to control the transforms of objects. You can access these transforms from the
Track View or from the Motion panel. You can also use expressions to control object parameters such as a
box’s length or material properties such as the amount of illumination applied to a material. You can access
all these parameters from the Track View.
Animating transforms with the Expression controller
After you assign a controller to a transform track, the Expression pane in the Expression Controller dialog
box includes the current values of the selected object. Position transforms display the X, Y, and Z coordi-
nates of the object; Rotation transforms display the rotation value in radians; and Scale transforms display
values describing the relative scaling values for each axis.
Note
Radians are another way to measure angles. A full revolution equals 360 degrees, which equates to 2 × pi radians.
The Expression dialog box includes the degToRad and radToDeg functions to convert back and forth between
these two measurement systems. n
Animating parameters with the Float Expression controller
To assign the Float Expression controller, select an object with a parameter or Modifier applied and open
the Track View. Find the track for the parameter that you want to change, and click the Assign Controller
button. Select the Float Controller from the list, and click OK.

Note
The actual controller type depends on the parameter selected. Many parameters use float expressions, but some
use Transform controllers. n

After you assign the Expression controller, the Expression Controller dialog box opens, or you can open it
by right-clicking the track and selecting Properties from the pop-up menu to load the dialog box. Within
this dialog box, the Expression pane includes the current value of the selected parameter.

Tutorial: Inflating a balloon
The Push Modifier mimics filling a balloon with air by pushing all its vertices outward. In this tutorial,
you’ll use a balloon model created by Zygote Media to see how you can use the Float Expression controller
to control the parameters of a modifier.
To inflate a balloon using the Float Expression controller, follow these steps:
1. Open the Balloon and pump.max file from the Chap 35 directory on the DVD.
This file includes a pump created from primitives and the balloon model with the Push modifier
applied.
2. Next, open the Track View by choosing Graph Editors ➪ Track View—Curve Editor. Select the
balloon and navigate the balloon object’s tracks until you find the Push Value track (found under

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