+#else // quadratic error: *much* faster!
+
+ /* convert control point representation to
+ d*x^3 + c*x^2 + b*x + a */
+
+ /* FIXME: we need to do this for the subspline between [start,end],
+ not [0,1] */
+ dx= s->end.x - s->control2.x*3 + s->control1.x*3 - s->start.x;
+ dy= s->end.y - s->control2.y*3 + s->control1.y*3 - s->start.y;
+
+ /* use the integral over (f(x)-g(x))^2 between 0 and 1
+ to measure the approximation quality.
+ (it boils down to const*d^2)
+ */
+ recurse = (dx*dx + dy*dy > quality2);
+#endif