Declaration:

parameter_vertex <name> ( <scalar>, <scalar>, <tangent type>, (<scalar>, <scalar>), <tangent type>, (<scalar>, <scalar>) )

In version 7, pv is a shorter keyword name for parameter_vertex that can be used interchangeably.

Reference:

<name>

Literal:

parameter_vertex ( <scalar>, <scalar>,

	<tangent type>, ( <scalar>, <scalar> ),

	<tangent type>, ( <scalar>, <scalar> ) )

Purpose:

This allows you to define in and out tangents at a keyframe point on a two-dimensional parameter curve. A parameter_vertex may be specified as a literal or as a variable. If specified as a variable, it must have a name. A collection of these form a two-dimensional parameter curve which can be used for animation of a scalar. All components of a parameter_vertex are given by position, not by keyword. They are interpreted as:

	keyframe time, keyframe value, in tangent type, (in tangent x, y), out tangent type, (out tangent x, y)

The first and second parameters specify the value for the parameter curve at a point in time. If the in/out tangent type is TAN_FIXED then the in/out tangent x, y values specify the direction of a tangent vector which represents the slope of the parameter curve as it enters/leaves the given keyframe. Varying the direction of the tangent vector can be used to control the shape of the curve before/after the keyframe.

In order to have a continuous animation, the tangent in vector and the tangent out vector at a parameter_vertex should both point in a “forwards” direction. Discontinuities can be introduced by making them point in different directions.

When in/out tangent types other than TAN_FIXED are chosen the tangent x, y values are ignored and the specified tangent type is used to determine the shape of the curve before/after the keyframe.

Example:

parameter_vertex ( 1, 0, TAN_FIXED, (-1,-1), TAN_LINEAR, (1,1) );