ref: c7d9da8f5a41b833946027c802e0e8d7dd014b22
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); } }