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 "gigi.h" 13 14 /* 15 * gigi requires knowing the anlge of arc. To do this, the triangle formula 16 * c^2 = a^2 + b^2 - 2*a*b*cos(angle) 17 * is used where "a" and "b" are the radius of the circle and "c" is the 18 * distance between the beginning point and the end point. 19 * 20 * This gives us "angle" or angle - 180. To find out which, draw a line from 21 * beg to center. This splits the plane in half. All points on one side of the 22 * plane will have the same sign when plugged into the equation for the line. 23 * Pick a point on the "right side" of the line (see program below). If "end" 24 * has the same sign as this point does, then they are both on the same side 25 * of the line and so angle is < 180. Otherwise, angle > 180. 26 */ 27 28 #define side(x,y) (a*(x)+b*(y)+c > 0.0 ? 1 : -1) 29 30 arc(xcent,ycent,xbeg,ybeg,xend,yend) 31 int xcent,ycent,xbeg,ybeg,xend,yend; 32 { 33 double radius2, c2; 34 double a,b,c; 35 int angle; 36 37 /* Probably should check that this is really a circular arc. */ 38 radius2 = (xcent-xbeg)*(xcent-xbeg) + (ycent-ybeg)*(ycent-ybeg); 39 c2 = (xend-xbeg)*(xend-xbeg) + (yend-ybeg)*(yend-ybeg); 40 angle = (int) ( 180.0/PI * acos(1.0 - c2/(2.0*radius2)) + 0.5 ); 41 42 a = (double) (ycent - ybeg); 43 b = (double) (xcent - xbeg); 44 c = (double) (ycent*xbeg - xcent*ybeg); 45 if (side(xbeg + (ycent-ybeg), ybeg - (xcent-xbeg)) != side(xend,yend)) 46 angle += 180; 47 48 move(xcent, ycent); 49 printf("C(A%d c)[%d,%d]", angle, xbeg, ybeg); 50 } 51