ref: 63f9a4fda36f916e543c8f3ea117b31c194a4db7
dir: /sys/src/cmd/plot/libplot/spline.c/
/*
Produce spline (uniform knots, second order)
from guiding points
*/
#include "mplot.h"
void splin(int mode, int num[], double *ff[]){
int i, *np, n;
double xa, ya, xc, yc, *xp, *yp, *xp0, *yp0, *xpe, *ype;
double **fp;
np = num;
fp = ff;
while((n = *np++)){
xp = *fp++;
yp = xp + 1;
xp0 = xp;
yp0 = yp;
xpe = xp0 + 2 * (n - 1);
ype = yp0 + 2 * (n - 1);
if (n < 3) {
plotline(*xp, *yp, *(xp + 2), *(yp + 2));
continue;
}
if (mode == 4) { /*closed curve*/
xa = 0.5 * (*xpe + *(xpe - 2));
xc = 0.5 * (*xpe + *xp0);
ya = 0.5 * (*ype + *(ype - 2));
yc = 0.5 * (*ype + *yp0);
parabola(xa, ya, xc, yc, *xpe, *ype);
xa = 0.5 * (*xpe + *xp0);
xc = 0.5 * (*(xp0 + 2) + *xp0);
ya = 0.5 * (*ype + *yp0);
yc = 0.5 * (*(yp0 + 2) + *yp0);
parabola(xa, ya, xc, yc, *xp0, *yp0);
}
else { /*open curve with multiple endpoints*/
if (mode % 2) /*odd mode makes first point double*/
plotline(*xp0,*yp0,0.5*(*xp0+*(xp0+2)),0.5*(*yp0+*(yp0+2)));
}
xp += 2;
yp += 2;
for (i = 1; i < (n - 1); i++, xp += 2, yp += 2) {
xa = 0.5 * (*(xp - 2) + *xp);
xc = 0.5 * ( *xp + *(xp + 2));
ya = 0.5 * (*(yp - 2) + *yp);
yc = 0.5 * ( *yp + *(yp + 2));
parabola(xa, ya, xc, yc, *xp, *yp);
}
if(mode >= 2 && mode != 4)
plotline(0.5*(*(xpe-2)+*xpe),0.5*(*(ype-2)+*ype),*xpe,*ype);
}
}