Expression

The FcrvEdit->Expression command in the Motion module lets you use mathematical expressions as an editing tool for any selected function curve.

For a full description of expressions, what they can consist of, and their proper syntax, see the Expressions section of the Animating User's Guide.

There are three ways to use expressions: as a custom constraint, to generate or edit a function curve, or to use with Channels. These methods correspond to the following commands:

• The Expressions->Edit menu cell command for creating a custom constraint (see the Writing and Editing an Expression section of the Animating User's Guide for information on using this command).
• The FcrvEdit->Expression command (this command) for generating or modifying a function curve (see the Editing Function Curves section of the Animating User's Guide for information on using this command).
• The Expressions button in the Channel->Connection Setup dialogue box for use with Channels (see the Using Expressions with Channels section of the Animating User's Guide for information on using this command).

Procedure

1. Select an animated element. This can be an object, a light, a camera, etc. - anything with a function curve. This is called the "affected element."
2. Choose the FcrvSelect command and the appropriate command relating to the type of function curve you want to modify.
3. Choose the FcrvEdit->Expression command.
   
   The Expression Editor dialogue box appears.
   
   For a description of all the parameters in this dialogue box, see Parameters on page 625.
   
   There are many possibilities for using the options in this dialogue box, but the following example shows some of the basic steps for editing a function curve.
   
   
4. The element and its function curve selected in the scene appears in the Affected Element text box. This cannot be changed.
5. Now create your expression. If there is a predefined expression you want to use, click Select and choose that expression from the browser that appears.
   
   To create an expression from scratch, follow these steps:

• If you want to create an expression that doesn't relate to any other element in the scene, skip steps 6 and 7.
• If you want to reference the values or animation of other elements, select the element and then do steps 6 and 7.

6. Click in the Expression text box and then click the Scn Element button. The Select Element browser appears in which you can choose any element from the scene.
7. Add the scene element's function curve that is used to affect the element's function curve. Click at the end of the element's name (after the period) and then click the Fcurve button. Select one of the possible function curves from the Function Curves dialogue box that appears.
8. At this point, you may add an operator and some numeric values to this expression, such as + 3. You could also use the predefined math Functions such as cosine, logarithm, or conditional, or Variables such as current frame, first frame, or a random value.
   
   If a segment of the expression needs to be repeated, you can define it in the Local Variables text boxes. This lets you keep the main expression simpler. To refer to a local variable, use the corresponding letter (A, B, C, or D) in the main expression.
   
   
9. Click Validate to make sure you have a valid expression.
10. If you want to save the expression to a file, click Save and specify a name for it in the Save Expression dialogue box that appears.
11. Click Ok to apply this expression to your affected element, or click Cancel to exit without saving any changes.

Last updated 02-apr-1998