dll/opengl/glu32/src/libnurbs/nurbtess/polyUtil.cc

   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 }