I’ve been meaning to give Spiro curves a try for a while. By now, I’m fairly confident with Bezier curves, but I’m always interested in finding other ways to do things, and Spiro curves have a very different quality to them. As we all know, Bezier splines are especially nightmarish when drawing curves that don’t have an even radius — think of a slightly bowed vertical stem leading into a much tighter serif bracket. The problem is Beziers only allow control of the slope of a curve, without balancing the curvature. So extra points and handles are required to create smoothly connecting curves. With spiro curves, on the other hand, as points are moved, the equation instantly rebalances to maintain a smoothly changing curvature, even when the curves have a significant change in radius from one point to the next. There are no control handles to worry about, making it easier to quickly adjust letterforms.
I used Raph Levien’s Spiro tools on FontForge. FontForge was a complete nuisance to install, and doesn’t feel very natural yet, but my first adventures with spiro curves seem quite promising, and it would be hugely interesting if FontLab could add support for this alternative way of drawing in the future.
The best thing about Spiro on FontForge is when the equation can’t be solved and the curve pops into loopy madness! I’m looking forward to seeing the more sensible results of this little experiment.