Mathmatical Expressions For Dummies.pdf

Tutorial • “Expressions for Dummies”

“Expressions for Dummies”

Expressions is the kind of topic that makes many animators

say “That’s way too complicated for me!” However,

expressions can be surprisingly easy to understand, once you

get your feet wet. The best way to understand how to use

expressions is to apply some and see what they do ... so let’s

go!

Tutorial • “Expressions for Dummies”

Jumping into Expressions

To understand expressions better, try the following simple

exercises. Once you’re comfortable with the process and the

expression editor, you can go on to more complicated

expressions and setups.

Setting Up a Constant Expression

1. Get a primitive sphere (or something equally as exciting).

2. Select the sphere and press Ctrl+k (this opens the sphere’s

Local Transform property editor).

3. Right-click on the animation icon (green box) of the local

Position Y parameter and choose Set Expression .

4. In the expression editor, enter the value of 5 in the

expression pane and click the Apply button, but keep the

expression editor open to take a peek at what you just

did:

- At the top of the expression editor is the parameter

(sphere.kine.local.posy) that you’ve set to be equal

to 5.

- Notice that the Position Y animation icon has the

letter “C” in it to indicate that it’s a constant

expression (where the value is a number).

- An Expression page is added to the Local Transform

property editor so that you can easily edit this

expression later, including adding comments.

Tutorial • “Expressions for Dummies”

Congratulations, you’ve just set the simplest kind of

expression known to humankind! The sphere is now fixed at

5 units on its Y axis. You won’t be able to translate it

anywhere else in this direction, but you can still move it in X

and Z.

Trying It Another Way

Here’s another way of creating a constant expression:

1. Get yet another sphere and set its Translation Y value to

2. Again, press Ctrl+k, right-click on the Position Y

parameter’s animation icon, and choose Set Expression .

Notice the expression editor opens with the value of 5

already in it. You’ve just created a constant expression the

same as in the first exercise.

Creating a Simple Equivalency Expression

You can also easily create simple A = B expressions between

parameters:

1. Open a new scene and get a sphere and a null.

2. Translate the null in X a little to offset it from the origin

and the sphere.

3. Select the sphere and press Ctrl+k to open its Local

Transform property editor. Lock this property editor to

keep it open (click its keyhole icon).

4. Select the null and press Ctrl+k to open a Local Transform

property editor for it.

Tutorial • “Expressions for Dummies”

5. Drag and drop the animation icon for the null’s Position X

parameter to the sphere’s Position X parameter in the

other property editor.

- The expression editor opens with the affected

parameter, sphere.kine.local.posx. Its expression

below is null.kine.local.posx, meaning that the

sphere takes its Position X value from the null’s

Position X value.

- The sphere’s animation icon for the Position X

parameter now has an equal sign (=) in it to indicate

the expression.

If there would have been animation on the

animation icon being dragged, the animation

would have simply been copied to the other

parameter, but no expression would have been

set.

6. Test the expression by translating the null in X: the sphere

should follow in X.

7. Close the expression editor and the two property editors

to keep the scene uncluttered.

One More Time

Here’s another way to create an equivalency expression:

1. Select the sphere, press Ctrl+k, right-click on the

animation icon for Position Y, and choose Set

Expression .

Tutorial • “Expressions for Dummies”

2. In the expression editor, type null.kine.local.posx in the

white expression pane below and click the Apply button.

Now as the null is translated in X, the sphere moves

diagonally, getting both its X and Y Position values from the

null’s Position X value.

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