You cannot directly use more than one animation source (for example, keys and an expression) on the same parameter. To combine animation sources, see Expressions and Other Animation.
Expressions are mathematical formulas that you can use to control any parameter that can be animated, such as translation, rotation, scaling, material, or texture. You can create almost any connection you like between parameters, from simple “A = B” relationships to very complex ones using predefined variables, standard math functions, random number generators, and more. However you use expressions, you will find that they are very powerful because they allow you to animate precisely, right down to the parameter level.
If you’re a novice to math, there are some basic expressions you can perform without having to understand math functions well. In fact, many common expressions contain little or no math—some of them just make one parameter equal to another to create a constraint. In this case, all you have to know are the names of the objects and their appropriate parameters. To get started with expressions, try out the exercises in Jumping into Expressions.
Once you’re more experienced using the mathematical features in Softimage, you can create all sorts of custom setups, like character rigs, animation control systems, and simulations. In fact, a knowledge of expressions is often the key to setting up complex character setups in a simple and more direct way than you could using other methods, such as constraints.
An expression is a string of characters that may include object and parameter names, mathematical operators, and tokens representing functions or constants. For example, to constrain object A’s Y rotation to object B’s X translation, you would set an expression on A.kine.local.roty consisting of the string B.kine.local.posx.
Once there is an expression on a parameter, you can no longer manipulate that parameter interactively. For example, if you apply an expression on an object’s local X position, you can no longer use the Translate tool to move the object in X.
|
You cannot directly use more than one animation source (for example, keys and an expression) on the same parameter. To combine animation sources, see Expressions and Other Animation. |
Viewing Expression Information
You can identify the objects that have expressions on their parameters in the 3D views and in the schematic view. As well, you can use an expression query to get information the expressions on an object’s parameters.
Viewing in a 3D View
To see expression information in a 3D view
• Click the eye icon on the viewport’s menu bar and make sure that Relations is on:
- If the selected object has parameters with expressions on its transformations, the label Expr is displayed in white.
- If the selected object has parameters with expressions that involve other objects, those objects are linked to the selected object by dotted white lines.
You can click the dotted line to see a list of expressions that involve the linked object. You can also click one of the expressions in the list to open it in the expression editor.
Viewing in the Schematic View
To see expression information in the schematic view
• If an object has parameters with expressions on its transformations, the letter E is displayed above it.
• If Show > Expression Links is on, an object with an expression is linked to objects whose parameters are involved by solid green arrows labelled Expr.
You can select these arrows by clicking and dragging slightly—a list of expressions appear. Click an expression in the list to open it in the expression editor.
Animation Icon
A parameter’s animation icon changes from its default green box to any of the conditions shown below on the left to indicate expressions of different types (see The Animation Icon for more information):
• 
With a letter C, the parameter has an expression that is a constant value.
• 
With an = sign, the parameter has an expression that makes the parameter equal to another one (links them).
• 
With an arrow, the parameter has any type of expression on it other than a constant value or an “equal” link.
You can use a special expression query in the spreadsheet to show the expressions associated with each parameter of a selected object. This query makes it easy to get an overview of expressions on the parameters, as well as activating/deactivating an expression.
To select the query
1. Select one or more objects that have expressions.
2. Open a spreadsheet (press Alt+3) and choose Query > Expressions.
For more information, see The Spreadsheet [ Interface and Tools ].
Selecting Objects with Expressions
When you have a crowded scene, it’s sometimes difficult to select only the objects you want. To make it easier to select only objects that are animated with expressions, you can use a special expressions filter from the Filters menu on the Select panel.
To use the selection filters
1. In the Select panel of the main command panel, click the little arrow button to open the Filters menu.
2. Select the Obj w Expression filter.
Autodesk Softimage v.7.5