Page 912 - Kitab3DsMax

Part VIII: Advanced Animation Techniques
FIGURE 35.1
The Numerical Expression Evaluator dialog box lets you enter expressions for a spinner.
To use this evaluator, just type the expression in the field; the result is displayed in the result field. The
result field is updated as you type the expression. If you make a mistake, the Result is blanked out. The
Paste button places the result value in the spinner, and the Cancel button closes the dialog box without a
change.
Tip
You can enter a relative value in a spinner by typing the letter R and a value. For example, if the Segments value
of a sphere object is 32, then typing R20 changes the value to 52 and R-20 changes the value to 12. n

Understanding the Expression Controller

Interface

The term expression refers to a mathematical expression or simple formula that computes a value based on
other values. These expressions can be simple, as with moving a bicycle based on the rotation of the pedals,
or they can be complex, as with computing the sinusoidal translation of a boat on the sea as a function of
the waves beneath it.
You can use almost any value as a variable in an expression, from object coordinates and modifier parame-
ters to light and material settings. The results of the expression are computed for every frame and used to
affect various parameters in the scene. You can include the number of frames and time variables in the
expression to cause the animation results to repeat for the entire sequence.

Note
Although it is not as powerful as the Script controller, the Expression controller is much faster than the Script con-
troller because it doesn’t require any compile time. n
Of all the controllers that are available, the Expression controller has limitless possibilities that could fill an
entire book. This section covers the basics of building expressions and includes several examples.

The Expression controller is just one of the many controllers that are available for automating animations.
This controller enables you to define how the object is transformed by means of a mathematical formula or
expression, which you can apply to any of the object’s tracks. It shows up in the controller list, based on the
type of track to which it is assigned, as a Position Expression, Rotation Expression, Scale Expression, Float
Expression, or Point3 Expression controller.

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