1*15445Sralph #ifndef lint 2*15445Sralph static char sccsid[] = "@(#)arc.c 4.1 (Berkeley) 11/10/83"; 3*15445Sralph #endif 4*15445Sralph 5*15445Sralph #include "hp2648.h" 6*15445Sralph 7*15445Sralph arc(xcent,ycent,xbeg,ybeg,xend,yend) 8*15445Sralph int xcent,ycent,xbeg,ybeg,xend,yend; 9*15445Sralph { 10*15445Sralph double costheta,sintheta,x,y,xn,r; 11*15445Sralph double x1,y1,x2,y2; 12*15445Sralph int xi,yi,crosspflag,crossp; 13*15445Sralph 14*15445Sralph r = (xcent-xbeg)*(xcent-xbeg)+(ycent-ybeg)*(ycent-ybeg); 15*15445Sralph r = pow(r,0.5); 16*15445Sralph if(r<1){ 17*15445Sralph point(xcent,ycent); 18*15445Sralph return; 19*15445Sralph } 20*15445Sralph sintheta = 1.0/r; 21*15445Sralph costheta = pow(1-sintheta*sintheta,0.5); 22*15445Sralph xi = x = xbeg-xcent; 23*15445Sralph yi = y = ybeg-ycent; 24*15445Sralph x1 = xcent; 25*15445Sralph y1 = ycent; 26*15445Sralph x2 = xend; 27*15445Sralph y2 = yend; 28*15445Sralph crosspflag = 0; 29*15445Sralph do { 30*15445Sralph crossp = cross_product(x1,y1,x2,y2,x,y); 31*15445Sralph if(crossp >0 && crosspflag == 0) crosspflag = 1; 32*15445Sralph point(xcent+xi,ycent+yi); 33*15445Sralph xn = x; 34*15445Sralph xi = x = x*costheta + y*sintheta; 35*15445Sralph yi = y = y*costheta - xn*sintheta; 36*15445Sralph } while( crosspflag == 0 || crossp >0); 37*15445Sralph } 38*15445Sralph 39*15445Sralph cross_product(x1,y1,x2,y2,x3,y3) 40*15445Sralph double x1,x2,x3,y1,y2,y3; 41*15445Sralph { 42*15445Sralph double z,a,b; 43*15445Sralph a = (y3-y2)*(x2-x1); 44*15445Sralph b = (x3-x2)*(y2-y1); 45*15445Sralph z = a-b; 46*15445Sralph if(z<0) return(-1); 47*15445Sralph if(z>0) return(1); 48*15445Sralph return(0); 49*15445Sralph } 50