tkspline(Tk Spline - An additional smoothing method for canvas itemtkspline(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 consecu‐
tive 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 seg‐
ments, 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 algo‐
rithms.
CREDITS
The underlying Bezier code is in John Ousterhout's original canvas wid‐
get, 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(n)
