TYPE: VOP
TITLE: Parameter VOP

This operator creates a parameter to appear in the signature of the VEX function
defined by the VOP network (VOPNET) and in the interface of any OP type that
uses the VOPNET. 

By providing VEX parameters, it becomes possible to customize the operation of
the VOPNET for each instance of the operator using the VOPNET.  For example, if
a Surface VOPNET is used in a surface shader for a variety of colored balloons,
the balloon color should be defined by a Parameter VOP.  This way there may be
100 individually colored balloons, with a single VOP network defining the
surface shader (i.e. the SHOP) for all of them.

Parameters:
    Parameter Type  - Specifies the VEX data type of the new parameter. It can
              also specify how the parameter should be represented in an OP
              dialog. For example, a VEX vector can be viewed as 3 float values
              or as a color value.
    Parameter Name  - The name of the new parameter, both in the VEX function
              declaration, the definition of any OP type that uses the VOPNET,
              and the VOP tile's output. If a parameter by this name already 
              exists, this operator will reference it and will disable most of
              of its own fields, such as the Parameter Type and Parameter Label.
    Parameter Label - The label that appears in the dialog of the OP type that
              uses the VOPNET, and in the baloon help over the VOP tile output.
    Use Input Value If Parameter Not Bound - If true, the VEX function parameter
              is checked to see if it is bound to an attribute in the current
              VEX context (e.g. point color). If not bound, the input value is
              is assigned to the VEX parameter. In a Surface VOP context, a VEX
              parameter is bound if the geometry being shaded has an attribute
              with the VEX parameter name.
    Export Parameter - Specifies whether the new parameter can be exported to
              other contexts (written to as well as read from). If true, this
              operator gets an input. The value wired into this input is then
              assigned to the exported parameter. In a Surface network, exported
              parameters can be used to create deep rasters. In SOP and POP
              networks, the exported parameters create new geometry attributes.
    Provide Menu of Choices - If the parameter type is String or Integer, check
              this toggle to provide a menu of choices instead of a string entry
              field or an integer slider.
    Menu Choices    - A list of pairs of strings. The first string in each pair
              is the parameter value if that menu item is chosen. The second
              string is the label that appears in the dialog for that menu item.
    Default Values  - Depending on the parameter type selected, it represents 
              the default value of the parameter in the VEX function and in the
              OP type that uses this VOP network.

Inputs:
    Unbound or Export Value - The value assigned to the new parameter if the
              "Export Parameter" toggle is checked or if the parameter is not
              bound when "Use Input Value If Parameter Not Bound" is checked.

Outputs:
    Output Parameter   - The value of this VEX function parameter.
    Is Parameter Bound - True is the new parameter is bound to an attribute.

See also: Constant, Global Variables(global), Output Variables(output),
          Shading Layer Parameter(shadinglayer)
