1 /*-
2 * Copyright (c) 1980, 1993
3 * The Regents of the University of California. All rights reserved.
4 *
5 * %sccs.include.proprietary.c%
6 */
7
8 #ifndef lint
9 static char sccsid[] = "@(#)arc.c 8.1 (Berkeley) 06/04/93";
10 #endif /* not lint */
11
12 #include "hp2648.h"
13
arc(xcent,ycent,xbeg,ybeg,xend,yend)14 arc(xcent,ycent,xbeg,ybeg,xend,yend)
15 int xcent,ycent,xbeg,ybeg,xend,yend;
16 {
17 double costheta,sintheta,x,y,xn,r;
18 double x1,y1,x2,y2;
19 int xi,yi,crosspflag,crossp;
20
21 r = (xcent-xbeg)*(xcent-xbeg)+(ycent-ybeg)*(ycent-ybeg);
22 r = pow(r,0.5);
23 if(r<1){
24 point(xcent,ycent);
25 return;
26 }
27 sintheta = 1.0/r;
28 costheta = pow(1-sintheta*sintheta,0.5);
29 xi = x = xbeg-xcent;
30 yi = y = ybeg-ycent;
31 x1 = xcent;
32 y1 = ycent;
33 x2 = xend;
34 y2 = yend;
35 crosspflag = 0;
36 do {
37 crossp = cross_product(x1,y1,x2,y2,x,y);
38 if(crossp >0 && crosspflag == 0) crosspflag = 1;
39 point(xcent+xi,ycent+yi);
40 xn = x;
41 xi = x = x*costheta + y*sintheta;
42 yi = y = y*costheta - xn*sintheta;
43 } while( crosspflag == 0 || crossp >0);
44 }
45
cross_product(x1,y1,x2,y2,x3,y3)46 cross_product(x1,y1,x2,y2,x3,y3)
47 double x1,x2,x3,y1,y2,y3;
48 {
49 double z,a,b;
50 a = (y3-y2)*(x2-x1);
51 b = (x3-x2)*(y2-y1);
52 z = a-b;
53 if(z<0) return(-1);
54 if(z>0) return(1);
55 return(0);
56 }
57