## Expression

Object Hierarchy | Related C++ Class: Expression

### Inheritance

SIObject

ProjectItem

Operator

Expression

### Introduced

v2.0

### Description

An Expression object is a kind of Operator representing an animation source on a parameter which you can create with Parameter.AddExpression. Expressions in Softimage allow you to control animatable parameters through a mathematical formula, which may include references to the value of other parameters. This formula is stored as the value of the "Definition" Parameter, and it can be changed via the Object Model as shown in the example below.
If a Parameter's value is driven by an Expression then the Expression can be retrieved via the Parameter.Source property.
Since the expression object is kind of operator, you can use the Operator.InputPorts property to access the parameters from which the expression is reading. Access to port groups is also provided (since this is a kind of operator); however, the expression doesn't define port groups but will pretend it has one for easy access through the SDK (see Operator.GetNumPortGroups for more details).
For more details, see "Expression Reference" in the Softimage User?s Guide.

### Methods

AddCustomOp | AddICEAttribute | AddScriptedOp | AddScriptedOpFromFile
AnimatedParameters2 | BelongsTo | Connect | ConnectToGroup
Copy | Disconnect | DisconnectGroup | EvaluateAt
GetICEAttributeFromName | GetInputValue | GetNumInstancesInGroup | GetNumPortGroups
GetNumPortsInGroup | GetPort2 | GetPort3 | GetPortAt
IsA | IsAnimated2 | IsClassOf | IsEqualTo
IsKindOf | IsLocked | IsSelected | LockOwners
PortAt | RemoveICEAttribute | SetAsSelected | SetCapabilityFlag
SetLock | SupportsBranchGroup | TaggedParameters | UnSetLock

### Properties

Application | BranchFlag | Capabilities | Categories
EvaluationID | Families | FullName | Help
HierarchicalEvaluationID | ICEAttributes | InputPorts | IsConnected
LockLevel | LockMasters | LockType | Model
Mute | Name | NestedObjects | ObjectID
Origin | OriginPath | OutputPorts | Owners
PPGLayout | Parameters | Parent | Parent3DObject
Port | PortGroups | Selected | Type

### Examples

#### JScript Example

    // This example illustrates how to apply an expression and access it.
    NewScene( null, false );
    var oNull = ActiveSceneRoot.AddNull();
    var oAnotherNull = ActiveSceneRoot.AddNull("AnotherNull");
    strExpr = oAnotherNull.posy.FullName + " + 2";
    var oExpr = oNull.posx.AddExpression(strExpr);
    //You can access the parameter to which an expression is connected by using the output port.
    Application.LogMessage("Parameter owner of the expression " + oExpr.OutputPorts(0).Target2.FullName);
    //You can access the parameter which are used inside an expression by using the input ports of
    //the expression operator.
    var oInputPorts = oExpr.InputPorts
    for(i = 0; i < oInputPorts.Count; i++)
    {
            Application.LogMessage("Parameter client of the expression " + oInputPorts(i).Target2.FullName);
    }
    // Formula that defines the expression is available as a Parameter value
    oDefinitionParam = oExpr.Parameters( "Definition" )
    Application.LogMessage( "Expression definition :" + oDefinitionParam.Value) ;
    // Expression can be changed
    strNewExpr = oAnotherNull .posy.FullName + " - " + oAnotherNull .posx.FullName ;
    oDefinitionParam.Value = strNewExpr ;
    Application.LogMessage( "New expression definition : " + oDefinitionParam.Value ) ;
    // Show the new expression formula in action
    oAnotherNull.posy = 10 ;
    oAnotherNull.posx = 4 ;
    // Value should be 10 - 4 = 6
    Application.LogMessage( "With new expression posx is " + oNull.posx.value ) ;
    // Remove the expression
    oNull.posx.Disconnect() ;
    //INFO : Parameter owner of the expression null.kine.local.posx
    //INFO : Parameter client of the expression AnotherNull.kine.local.posy
    //INFO : Expression definition :AnotherNull.kine.local.posy + 2
    //INFO : New expression definition : AnotherNull.kine.local.posy - AnotherNull.kine.local.posx
    //INFO : With new expression posx is 6

### See Also

Parameter.Source Parameter.AddExpression Parameter.Value AddExpr SetExpr