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Annotation of 43BSD/usr.lib/libplot/hp2648/arc.c, revision 1.1.1.1

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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