added another method for spline-approximation error-estimation.

diff --git a/lib/drawer.c b/lib/drawer.c
index 3ff0299..1b4f7e9 100644 (file)
--- a/lib/drawer.c
+++ b/lib/drawer.c
@@ -168,6 +168,7 @@ static int approximate3(const struct cspline*s, struct qspline*q, int size, doub
        char left = 0,recurse=0;
        int t;
        int probes = 15;
+       double dx,dy;
 
        /* create simple approximation: a qspline which run's through the
           qspline point at 0.5 */
@@ -202,8 +203,9 @@ static int approximate3(const struct cspline*s, struct qspline*q, int size, doub
            test.control.y += test.end.y;
        }
 
+#define PROBES
+#ifdef PROBES
        /* measure the spline's accurancy, by taking a number of probes */
-
        for(t=0;t<probes;t++) {
            struct SPLINEPOINT qr1,qr2,cr1,cr2;
            double pos = 0.5/(probes*2)*(t*2+1);
@@ -230,6 +232,19 @@ static int approximate3(const struct cspline*s, struct qspline*q, int size, doub
                recurse=1;break;
            }
        }
+#else // quadratic error: *much* faster!
+
+       /* convert control point representation to 
+          d*x^3 + c*x^2 + b*x + a */
+       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
 
        if(recurse && istep>1 && size-level > num) {
            istep >>= 1;