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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