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 "hp7221.h" 12 13 /* 14 * 7221 requires knowing the anlge of arc. To do this, the triangle formula 15 * c^2 = a^2 + b^2 - 2*a*b*cos(angle) 16 * is used where "a" and "b" are the radius of the circle and "c" is the 17 * distance between the beginning point and the end point. 18 * 19 * This gives us "angle" or angle - 180. To find out which, draw a line from 20 * beg to center. This splits the plane in half. All points on one side of the 21 * plane will have the same sign when plugged into the equation for the line. 22 * Pick a point on the "right side" of the line (see program below). If "end" 23 * has the same sign as this point does, then they are both on the same side 24 * of the line and so angle is < 180. Otherwise, angle > 180. 25 */ 26 27 #define side(x,y) (a*(x)+b*(y)+c > 0.0 ? 1 : -1) 28 29 arc(xcent,ycent,xbeg,ybeg,xend,yend) 30 int xcent,ycent,xbeg,ybeg,xend,yend; 31 { 32 double radius2, c2; 33 double a,b,c; 34 int angle; 35 36 /* Probably should check that this is really a circular arc. */ 37 radius2 = (xcent-xbeg)*(xcent-xbeg) + (ycent-ybeg)*(ycent-ybeg); 38 c2 = (xend-xbeg)*(xend-xbeg) + (yend-ybeg)*(yend-ybeg); 39 angle = (int) ( 180.0/PI * acos(1.0 - c2/(2.0*radius2)) + 0.5 ); 40 41 a = (double) (ycent - ybeg); 42 b = (double) (xcent - xbeg); 43 c = (double) (ycent*xbeg - xcent*ybeg); 44 if (side(xbeg + (ycent-ybeg), ybeg - (xcent-xbeg)) != side(xend,yend)) 45 angle += 180; 46 47 move(xcent, ycent); 48 /* Not quite implemented... 49 printf("C(A%d c)[%d,%d]", angle, xbeg, ybeg); 50 */ 51 } 52