```   1: /*
2:  * Copyright (c) 1980 Regents of the University of California.
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: {
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
• in line 44(2)
 Last modified: 1985-05-07 Generated: 2016-12-26 Generated by src2html V0.67 page hit count: 698