CenterStage Object Class:  Arrows
Subclass of:  Polyhedron

The Arrows class allows you to specify arrows by giving the two
endpoints of each arrow.  You can create lists of vertices, with
optional names to use as a reference when creating the arrows, or you
can simply give arrows as pairs of points.  You can specify colors and
other characteristics on an arrow-by-arrow basis, or for groups of arrows.

The Arrows class supports the the standard directives, plus the following:

    Vertices {vertex list}

	This specifies a list of vertices that you can use to define
	your arrows.  Its format is the same as that used in the
	Polyhedron class


    Arrows {arrow list}

	The arrow list uses the same format as the Faces list
	of the Polyhedron class, except that the "faces" are only
	allowed to contain two points.  These points specify the
	positions of the tips and tails of the arrows to be displayed.

        The arrow list can specify arrow attributes using the "<-"
	symbol, just as in the Polyhedron Faces list.  Arrow support
	all the polhedron attributes except vcolors, plus the following:

	    head {r w}	where {r and w} are as in ArrowHead below.

	    relative	means the arrow head measurements are relative
			to the legth of the arrow.

	    absolute	means the arrow head measurements are absolute
			rather than relative to the length of the arrow.


    ArrowHead r w [-solid | -outline] [-relative | -absolute]

	This directive specifies the size for the arrowheads, where r
	is the lingth along the shaft of the arrow and w is the
	distance away from the shaft on either side.  If -relative is
	specified (the default), then these measurements are relative
	to the total length of the arrow (e.g., ArrowHead .1 .02 means
	the head is 1/10th of the length of the arrow and extends
	2/100ths of the length on either side of the arrow).  If
	-absolute is specified, then the measurements are not relative
	to the length of the arrow but rather represent absolute sizes
	(all the arrowheads will be the same size).  The -solid and
	-outline options determine wether the arrow head is shown as a
	solid triangle or as an outlined triangle.

    ArrowScale scale

	Specifies a scaling factor by which all the arrows will be
	scaled.  This is most useful for subclasses of the Arrow class
	where the arrow data is generated by the class itself; it
	provides a means of globally scaling all the arrows.


    ArrowMaxLen len [-keep]

	Arrows that are longer than this length are either shortened
	to this length (if -keep is present) or removed (if -keep is
	not specified).  If ArrowMaxLen is not specified, then arrows
	can be arbitrarily long.