1/*
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:
9**
10** http://oss.sgi.com/projects/FreeB
11**
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.
17**
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.
23**
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.
33**
34*/
35/*
36*/
37
38#include <stdlib.h>
39#include <stdio.h>
40
41#include "polyUtil.h"
42
43Real area(Real A[2], Real B[2], Real C[2])
44{
45  Real Bx, By, Cx, Cy;
46  Bx = B[0] - A[0];
47  By = B[1] - A[1];
48  Cx = C[0] - A[0];
49  Cy = C[1] - A[1];
50  return Bx*Cy - Cx*By;
51
52/*  return (B[0]-A[0])*(C[1]-A[1]) - (C[0]-A[0])*(B[1]-A[1]);*/
53}
54
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.
63 */
64Int pointLeftLine(Real A[2], Real B[2],  Real P[2])
65{
66  if(area(A, B, P) >0) return 1;
67  else return 0;
68}
69
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
76 *of
77 */
78Int pointLeft2Lines(Real A[2], Real B[2], Real C[2], Real P[2])
79{
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);
83
84  if(C_left_AB)
85    {
86      return (P_left_AB && P_left_BC);
87    }
88  else
89    return  (P_left_AB || P_left_BC);
90}
91