I searched this site and I read that in general it is not possible to calculate offset of a Bezier curve.
But is it possible to calculate the offset in some special cases? Obviously, if the Bezier looks like straight line, it is possible - but what about other special cases?
I'm asking because this article claims that it is possible to always exactly calculate the offset iff the bezier has "at most one directional change in its curvature".
Is it true?
And more importantly, the article claims that the rule for deciding whether it is possible or not is "as long as the lines perpendicular to the start and end of the curve do not intersect the curve, and the angle the two lines is no greater than 90°".
Why 90°? Why no intersection with the original curve? Does it work for Beziers of any degree?