I've been working with Spline2D and BezierCurve2D in Toxiclibs. To draw them, I compute the vertices with a certain resolution and then draw them as a series of vertices, or as a Polygon with ToxiclibsSupport, as it's done in the examples.
The problem is that, with variable segment lengths, either I found the resolution to be too small (I see the angles) or too high (the stroke is not smooth). That's especially noticeable if you have to export to a PDF vector file, where instead of having a nice bezier with control points you end up with a series of straight lines.
I haven't looked at the Processing implementation, but I wonder if there's any way to render this curves smoothly, like ellipse(), arc() or curveVertex() do in Processing.
