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) 05/07/85"; 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 } 56