1*48508Sbostic /*- 2*48508Sbostic * Copyright (c) 1980 The Regents of the University of California. 3*48508Sbostic * All rights reserved. 4*48508Sbostic * 5*48508Sbostic * %sccs.include.proprietary.c% 619974Sdist */ 719974Sdist 815484Sralph #ifndef lint 9*48508Sbostic static char sccsid[] = "@(#)arc.c 5.2 (Berkeley) 04/22/91"; 10*48508Sbostic #endif /* not lint */ 1115484Sralph 1215484Sralph #include "gigi.h" 1315484Sralph 1415484Sralph /* 1515484Sralph * gigi requires knowing the anlge of arc. To do this, the triangle formula 1615484Sralph * c^2 = a^2 + b^2 - 2*a*b*cos(angle) 1715484Sralph * is used where "a" and "b" are the radius of the circle and "c" is the 1815484Sralph * distance between the beginning point and the end point. 1915484Sralph * 2015484Sralph * This gives us "angle" or angle - 180. To find out which, draw a line from 2115484Sralph * beg to center. This splits the plane in half. All points on one side of the 2215484Sralph * plane will have the same sign when plugged into the equation for the line. 2315484Sralph * Pick a point on the "right side" of the line (see program below). If "end" 2415484Sralph * has the same sign as this point does, then they are both on the same side 2515484Sralph * of the line and so angle is < 180. Otherwise, angle > 180. 2615484Sralph */ 2715484Sralph 2815484Sralph #define side(x,y) (a*(x)+b*(y)+c > 0.0 ? 1 : -1) 2915484Sralph 3015484Sralph arc(xcent,ycent,xbeg,ybeg,xend,yend) 3115484Sralph int xcent,ycent,xbeg,ybeg,xend,yend; 3215484Sralph { 3315484Sralph double radius2, c2; 3415484Sralph double a,b,c; 3515484Sralph int angle; 3615484Sralph 3715484Sralph /* Probably should check that this is really a circular arc. */ 3815484Sralph radius2 = (xcent-xbeg)*(xcent-xbeg) + (ycent-ybeg)*(ycent-ybeg); 3915484Sralph c2 = (xend-xbeg)*(xend-xbeg) + (yend-ybeg)*(yend-ybeg); 4015484Sralph angle = (int) ( 180.0/PI * acos(1.0 - c2/(2.0*radius2)) + 0.5 ); 4115484Sralph 4215484Sralph a = (double) (ycent - ybeg); 4315484Sralph b = (double) (xcent - xbeg); 4415484Sralph c = (double) (ycent*xbeg - xcent*ybeg); 4515484Sralph if (side(xbeg + (ycent-ybeg), ybeg - (xcent-xbeg)) != side(xend,yend)) 4615484Sralph angle += 180; 4715484Sralph 4815484Sralph move(xcent, ycent); 4915484Sralph printf("C(A%d c)[%d,%d]", angle, xbeg, ybeg); 5015484Sralph } 51