path.pointAtLength(length [, opt])
Divide the path into two paths at the point that lies
length away from the beginning of the path.
Returns an array with two new paths without modifying the original path. The returned paths are valid; that is, they both start with an appropriate Moveto segment. Additionally, Closepath segments are converted into Lineto segments if necessary. If negative
length is provided, the algorithm starts looking from the end of the path. If
length is higher than path length, the path is divided at the closest visible path endpoint instead. Invisible segments (e.g. Moveto segments) have no length and are therefore skipped by the algorithm. If the path contains no visible segments, the
end point of the last segment is returned. If the path has no segments at all,
null is returned.
One visible segment is identified which contains the point at
length. Finding the desired point is straightforward for linear segments (see
line.pointAtLength() for reference). Finding the desired point in curved segments is more complex, as illustrated by the
opt argument is optional. Two properties may be specified,
opt.segmentSubdivisions, which determine maximum error allowed in
pointAtLength calculations for curved segments (default precision is 3; this corresponds to maximum observed error of 0.1%). The
opt.segmentSubdivisions property is an array of individual segments' subdivision arrays. The
path.getSegmentSubdivisions() function may be used to obtain the
segmentSubdivisions array. The
opt.precision property is still necessary, however; it determines the precision of the point search algorithm in curved segments.