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
area(Real A[2],Real B[2],Real C[2])43 Real 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 */
pointLeftLine(Real A[2],Real B[2],Real P[2])64 Int 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 */
pointLeft2Lines(Real A[2],Real B[2],Real C[2],Real P[2])78 Int 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