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 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 */ 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 */ 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