2 ** License Applicability. Except to the extent portions of this file are
3 ** made subject to an alternative license as permitted in the SGI Free
4 ** Software License B, Version 1.1 (the "License"), the contents of this
5 ** file are subject only to the provisions of the License. You may not use
6 ** this file except in compliance with the License. You may obtain a copy
7 ** of the License at Silicon Graphics, Inc., attn: Legal Services, 1600
8 ** Amphitheatre Parkway, Mountain View, CA 94043-1351, or at:
10 ** http://oss.sgi.com/projects/FreeB
12 ** Note that, as provided in the License, the Software is distributed on an
13 ** "AS IS" basis, with ALL EXPRESS AND IMPLIED WARRANTIES AND CONDITIONS
14 ** DISCLAIMED, INCLUDING, WITHOUT LIMITATION, ANY IMPLIED WARRANTIES AND
15 ** CONDITIONS OF MERCHANTABILITY, SATISFACTORY QUALITY, FITNESS FOR A
16 ** PARTICULAR PURPOSE, AND NON-INFRINGEMENT.
18 ** Original Code. The Original Code is: OpenGL Sample Implementation,
19 ** Version 1.2.1, released January 26, 2000, developed by Silicon Graphics,
20 ** Inc. The Original Code is Copyright (c) 1991-2000 Silicon Graphics, Inc.
21 ** Copyright in any portions created by third parties is as indicated
22 ** elsewhere herein. All Rights Reserved.
24 ** Additional Notice Provisions: The application programming interfaces
25 ** established by SGI in conjunction with the Original Code are The
26 ** OpenGL(R) Graphics System: A Specification (Version 1.2.1), released
27 ** April 1, 1999; The OpenGL(R) Graphics System Utility Library (Version
28 ** 1.3), released November 4, 1998; and OpenGL(R) Graphics with the X
29 ** Window System(R) (Version 1.3), released October 19, 1998. This software
30 ** was created using the OpenGL(R) version 1.2.1 Sample Implementation
31 ** published by SGI, but has not been independently verified as being
32 ** compliant with the OpenGL(R) version 1.2.1 Specification.
43 Real
area(Real A
[2], Real B
[2], Real C
[2])
52 /* return (B[0]-A[0])*(C[1]-A[1]) - (C[0]-A[0])*(B[1]-A[1]);*/
55 /*given a directed line A->B, and a point P,
56 *determine whether P is to the left of AB.
57 *the line A->B (imagine it has beedn extended both
58 *end to the infinity) divides the plan into two
59 *half planes. When we walk from A to B, one
60 *half is to the left and the other half is to the right.
61 *return 1 if P is to the left.
62 *if P is on AB, 0 is returned.
64 Int
pointLeftLine(Real A
[2], Real B
[2], Real P
[2])
66 if(area(A
, B
, P
) >0) return 1;
70 /*given two directed line: A -> B -> C, and another point P.
71 *determine whether P is to the left hand side of A->B->C.
72 *Think of BA and BC extended as two rays. So that the plane is
73 * divided into two parts. One part is to the left we walk from A
74 *to B and to C, the other part is to the right.
75 * In order for P to be the left, P must be either to the left
78 Int
pointLeft2Lines(Real A
[2], Real B
[2], Real C
[2], Real P
[2])
80 Int C_left_AB
= (area(A
, B
, C
)>0);
81 Int P_left_AB
= (area(A
, B
, P
)>0);
82 Int P_left_BC
= (area(B
, C
, P
)>0);
86 return (P_left_AB
&& P_left_BC
);
89 return (P_left_AB
|| P_left_BC
);