tspline.c - plan9port - [fork] Plan 9 from user space
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       tspline.c (1351B)
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            1 /*
            2 Produce spline (uniform knots, second order)
            3 from guiding points
            4 */
            5 #include "mplot.h"
            6 void splin(int mode, int num[], double *ff[]){
            7         int        i,  *np, n;
            8         double        xa, ya, xc, yc, *xp, *yp, *xp0, *yp0, *xpe, *ype;
            9         double **fp;
           10         np = num;
           11         fp = ff;
           12         while((n = *np++)){
           13                 xp = *fp++;
           14                 yp = xp + 1;
           15                 xp0 = xp;
           16                 yp0 = yp;
           17                 xpe = xp0 + 2 * (n - 1);
           18                 ype = yp0 + 2 * (n - 1);
           19                 if (n < 3) {
           20                         plotline(*xp, *yp, *(xp + 2), *(yp + 2));
           21                         continue;
           22                 }
           23                 if (mode == 4) {        /*closed curve*/
           24                         xa = 0.5 * (*xpe + *(xpe - 2));
           25                         xc = 0.5 * (*xpe + *xp0);
           26                         ya = 0.5 * (*ype + *(ype - 2));
           27                         yc = 0.5 * (*ype + *yp0);
           28                         parabola(xa, ya, xc, yc, *xpe, *ype);
           29                         xa = 0.5 * (*xpe + *xp0);
           30                         xc = 0.5 * (*(xp0 + 2) + *xp0);
           31                         ya = 0.5 * (*ype + *yp0);
           32                         yc = 0.5 * (*(yp0 + 2) + *yp0);
           33                         parabola(xa, ya, xc, yc, *xp0, *yp0);
           34                 }
           35                 else {        /*open curve with multiple endpoints*/
           36                         if (mode % 2) /*odd mode makes first point double*/
           37                                 plotline(*xp0,*yp0,0.5*(*xp0+*(xp0+2)),0.5*(*yp0+*(yp0+2)));
           38                 }
           39                 xp += 2;
           40                 yp += 2;
           41                 for (i = 1; i < (n - 1); i++, xp += 2, yp += 2) {
           42                         xa = 0.5 * (*(xp - 2) + *xp);
           43                         xc = 0.5 * ( *xp + *(xp + 2));
           44                         ya = 0.5 * (*(yp - 2) + *yp);
           45                         yc = 0.5 * ( *yp + *(yp + 2));
           46                         parabola(xa, ya, xc, yc, *xp, *yp);
           47                 }
           48                 if(mode >= 2 && mode != 4)
           49                         plotline(0.5*(*(xpe-2)+*xpe),0.5*(*(ype-2)+*ype),*xpe,*ype);
           50         }
           51 }