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1 | /*- |
2 | * Copyright (c) 1980 The Regents of the University of California. | |
3 | * All rights reserved. | |
4 | * | |
5 | * %sccs.include.proprietary.c% | |
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6 | */ |
7 | ||
c122db03 | 8 | #ifndef lint |
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9 | static char sccsid[] = "@(#)arc.c 5.2 (Berkeley) %G%"; |
10 | #endif /* not lint */ | |
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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 | } |