curve.tangentAt(ratio [, opt])
Return a line that is tangent to the curve at a point that lies
ratio (normalized length) away from the beginning of the curve.
The function expects
ratio to lie between 0 and 1; values outside the range are constrained to 0 and 1, respectively.
The tangent line starts at the specified point. The direction from
end is the same as the direction of the curve at the specified point.
If the control points of the curve all lie at the same coordinates,
null is returned (it is impossible to determine the slope of a point). The
curve.isDifferentiable() function may be used in advance to determine whether tangents can exist for a given curve.
The function uses the same algorithm as the
The default value for
opt.precision is 3; this corresponds to maximum observed error of 0.1%.
opt.subdivisions property may be specified, directly providing an array of pre-computed curve subdivisions from which to calculate curve length. Use the
curve.getSubdivisions() function to obtain an array of curve subdivisions. The
opt.precision property is still necessary, however; it determines the precision of the point search algorithm.