NAME

       spline, - additional smoothing method for canvas items.

SYNOPSIS

            package require Tkspline
            ...
            .c create line ... -smooth spline ...
            .c create polygon ... -smooth spline ...
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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 independent 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                                         tkspline(3tk)