/* * Copyright (c) 1980 Regents of the University of California. * All rights reserved. The Berkeley software License Agreement * specifies the terms and conditions for redistribution. */ #ifndef lint static char sccsid[] = "@(#)arc.c 5.1 (Berkeley) 5/7/85"; #endif not lint #include "gigi.h" /* * gigi requires knowing the anlge of arc. To do this, the triangle formula * c^2 = a^2 + b^2 - 2*a*b*cos(angle) * is used where "a" and "b" are the radius of the circle and "c" is the * distance between the beginning point and the end point. * * This gives us "angle" or angle - 180. To find out which, draw a line from * beg to center. This splits the plane in half. All points on one side of the * plane will have the same sign when plugged into the equation for the line. * Pick a point on the "right side" of the line (see program below). If "end" * has the same sign as this point does, then they are both on the same side * of the line and so angle is < 180. Otherwise, angle > 180. */ #define side(x,y) (a*(x)+b*(y)+c > 0.0 ? 1 : -1) arc(xcent,ycent,xbeg,ybeg,xend,yend) int xcent,ycent,xbeg,ybeg,xend,yend; { double radius2, c2; double a,b,c; int angle; /* Probably should check that this is really a circular arc. */ radius2 = (xcent-xbeg)*(xcent-xbeg) + (ycent-ybeg)*(ycent-ybeg); c2 = (xend-xbeg)*(xend-xbeg) + (yend-ybeg)*(yend-ybeg); angle = (int) ( 180.0/PI * acos(1.0 - c2/(2.0*radius2)) + 0.5 ); a = (double) (ycent - ybeg); b = (double) (xcent - xbeg); c = (double) (ycent*xbeg - xcent*ybeg); if (side(xbeg + (ycent-ybeg), ybeg - (xcent-xbeg)) != side(xend,yend)) angle += 180; move(xcent, ycent); printf("C(A%d c)[%d,%d]", angle, xbeg, ybeg); }