* 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) 5/7/85";
* 9*: #endif not lint
* 10*:
* 11*: #include "gigi.h"
* 12*:
* 13*: /*
* 14*: * gigi 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*: printf("C(A%d c)[%d,%d]", angle, xbeg, ybeg);
* 49*: }

#### Defined functions

arc
defined in line

29;

*never used*
#### Defined variables

sccsid
defined in line

8;

*never used*
#### Defined macros

side
defined in line

27; used 2 times