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