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Annotation of 43BSDReno/lib/libplot/hp2648/arc.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1980 Regents of the University of California.
        !             3:  * All rights reserved.  The Berkeley software License Agreement
        !             4:  * specifies the terms and conditions for redistribution.
        !             5:  */
        !             6: 
        !             7: #ifndef lint
        !             8: static char sccsid[] = "@(#)arc.c      5.1 (Berkeley) 5/7/85";
        !             9: #endif not lint
        !            10: 
        !            11: #include "hp2648.h"
        !            12: 
        !            13: arc(xcent,ycent,xbeg,ybeg,xend,yend)
        !            14: int xcent,ycent,xbeg,ybeg,xend,yend;
        !            15: {
        !            16:        double costheta,sintheta,x,y,xn,r;
        !            17:        double x1,y1,x2,y2;
        !            18:        int xi,yi,crosspflag,crossp;
        !            19: 
        !            20:        r = (xcent-xbeg)*(xcent-xbeg)+(ycent-ybeg)*(ycent-ybeg);
        !            21:        r = pow(r,0.5);
        !            22:        if(r<1){
        !            23:                point(xcent,ycent);
        !            24:                return;
        !            25:        }
        !            26:        sintheta = 1.0/r;
        !            27:        costheta = pow(1-sintheta*sintheta,0.5);
        !            28:        xi = x = xbeg-xcent;
        !            29:        yi = y = ybeg-ycent;
        !            30:        x1 = xcent;
        !            31:        y1 = ycent;
        !            32:        x2 = xend;
        !            33:        y2 = yend;
        !            34:        crosspflag = 0;
        !            35:        do {
        !            36:                crossp = cross_product(x1,y1,x2,y2,x,y);
        !            37:                if(crossp >0 && crosspflag == 0) crosspflag = 1;
        !            38:                point(xcent+xi,ycent+yi);
        !            39:                xn = x;
        !            40:                xi = x = x*costheta + y*sintheta;
        !            41:                yi = y = y*costheta - xn*sintheta;
        !            42:        } while( crosspflag == 0 || crossp >0);
        !            43: }
        !            44: 
        !            45: cross_product(x1,y1,x2,y2,x3,y3)
        !            46: double x1,x2,x3,y1,y2,y3;
        !            47: {
        !            48:        double z,a,b;
        !            49:        a = (y3-y2)*(x2-x1);
        !            50:        b = (x3-x2)*(y2-y1);
        !            51:        z = a-b;
        !            52:        if(z<0) return(-1);
        !            53:        if(z>0) return(1);
        !            54:        return(0);
        !            55: }

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