spline(n)Tk Spline - An additional smoothing method for canvas items spline(n)



______________________________________________________________________________

NAME
       spline, - additional smoothing method for canvas items.

SYNOPSIS
            package require Tkspline
            ...
            .c create line ... -smooth spline ...
            .c create polygon ... -smooth spline ...
_________________________________________________________________

INTRODUCTION
       The new option value: -smooth spline provides an additional smoothing
       method to line and polygon canvas items.


       Spline smoothing will revert to the builtin smoothing method unless the
       number of points is 3n+1, where n is the number of spline segments.
       (Normally in polygons this means 3n points because the last point of
       the spline is understood to be the same as the first in order to close
       the polygon).


       In line and polygon items, the curves generated with the standard
       -smooth true option have the following properties:

       -  the curve is always tangential to a straight line between
          consecutive points.

       -  the curve is only guaranteed to intersect the first and last points
          of lines.

       -  the curve is not guaranteed to intersect any points of polygons.


       With -smooth spline (and the right number of coordinates) the curves
       generated have the following different properties:

       -  the curve is guaranteed to intersect the first point, and every
          third point after that.

       -  each segment of the curve shares endpoints with the adjacent
          segments, but is otherwise independant of them.

       -  the curve is guaranteed to be tangential to a line between n and n+1
          at point n, and also to a line between n+2 and n+3 at point n+3.

       -  the curve is not guaranteed to be smooth at the junctions between
          segments unless the shared point and the points either side of it
          are on a straight line.


       These alternative properties are useful to some path planning
       algorithms.


CREDITS
       The underlying Bezier code is in John Ousterhout's original canvas
       widget, this extension just provides an alternate interface to it.
       The hooks into the canvas are provided by Jan Nijtmans in his "dash"
       patch.


KEYWORDS
       spline, line, polygon, bezier, canvas, widget


AUTHOR
       John Ellson, ellson@graphviz.org



Tk                                    8.0                            spline(n)
