56 lines
1.2 KiB
C
56 lines
1.2 KiB
C
/*
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* Copyright (c) 1980 Regents of the University of California.
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* All rights reserved. The Berkeley software License Agreement
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* specifies the terms and conditions for redistribution.
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*/
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#ifndef lint
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static char sccsid[] = "@(#)arc.c 1.1 94/10/31 SMI"; /* from UCB 5.1 5/7/85 */
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#endif not lint
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#include "hp2648.h"
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arc(xcent,ycent,xbeg,ybeg,xend,yend)
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int xcent,ycent,xbeg,ybeg,xend,yend;
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{
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double costheta,sintheta,x,y,xn,r;
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double x1,y1,x2,y2;
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int xi,yi,crosspflag,crossp;
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r = (xcent-xbeg)*(xcent-xbeg)+(ycent-ybeg)*(ycent-ybeg);
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r = pow(r,0.5);
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if(r<1){
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point(xcent,ycent);
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return;
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}
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sintheta = 1.0/r;
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costheta = pow(1-sintheta*sintheta,0.5);
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xi = x = xbeg-xcent;
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yi = y = ybeg-ycent;
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x1 = xcent;
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y1 = ycent;
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x2 = xend;
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y2 = yend;
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crosspflag = 0;
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do {
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crossp = cross_product(x1,y1,x2,y2,x,y);
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if(crossp >0 && crosspflag == 0) crosspflag = 1;
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point(xcent+xi,ycent+yi);
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xn = x;
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xi = x = x*costheta + y*sintheta;
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yi = y = y*costheta - xn*sintheta;
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} while( crosspflag == 0 || crossp >0);
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}
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cross_product(x1,y1,x2,y2,x3,y3)
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double x1,x2,x3,y1,y2,y3;
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{
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double z,a,b;
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a = (y3-y2)*(x2-x1);
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b = (x3-x2)*(y2-y1);
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z = a-b;
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if(z<0) return(-1);
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if(z>0) return(1);
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return(0);
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}
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