dali-physics/third-party/bullet3/src/Bullet3Geometry/b3GrahamScan2dConvexHull.h

   1 /*
   2 Bullet Continuous Collision Detection and Physics Library
   3 Copyright (c) 2011 Advanced Micro Devices, Inc.  http://bulletphysics.org
   4
   5 This software is provided 'as-is', without any express or implied warranty.
   6 In no event will the authors be held liable for any damages arising from the use of this software.
   7 Permission is granted to anyone to use this software for any purpose,
   8 including commercial applications, and to alter it and redistribute it freely,
   9 subject to the following restrictions:
  10
  11 1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
  12 2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
  13 3. This notice may not be removed or altered from any source distribution.
  14 */
  15
  16 #ifndef B3_GRAHAM_SCAN_2D_CONVEX_HULL_H
  17 #define B3_GRAHAM_SCAN_2D_CONVEX_HULL_H
  18
  19 #include "Bullet3Common/b3Vector3.h"
  20 #include "Bullet3Common/b3AlignedObjectArray.h"
  21
  22 struct b3GrahamVector3 : public b3Vector3
  23 {
  24         b3GrahamVector3(const b3Vector3& org, int orgIndex)
  25                 : b3Vector3(org),
  26                   m_orgIndex(orgIndex)
  27         {
  28         }
  29         b3Scalar m_angle;
  30         int m_orgIndex;
  31 };
  32
  33 struct b3AngleCompareFunc
  34 {
  35         b3Vector3 m_anchor;
  36         b3AngleCompareFunc(const b3Vector3& anchor)
  37                 : m_anchor(anchor)
  38         {
  39         }
  40         bool operator()(const b3GrahamVector3& a, const b3GrahamVector3& b) const
  41         {
  42                 if (a.m_angle != b.m_angle)
  43                         return a.m_angle < b.m_angle;
  44                 else
  45                 {
  46                         b3Scalar al = (a - m_anchor).length2();
  47                         b3Scalar bl = (b - m_anchor).length2();
  48                         if (al != bl)
  49                                 return al < bl;
  50                         else
  51                         {
  52                                 return a.m_orgIndex < b.m_orgIndex;
  53                         }
  54                 }
  55         }
  56 };
  57
  58 inline void b3GrahamScanConvexHull2D(b3AlignedObjectArray<b3GrahamVector3>& originalPoints, b3AlignedObjectArray<b3GrahamVector3>& hull, const b3Vector3& normalAxis)
  59 {
  60         b3Vector3 axis0, axis1;
  61         b3PlaneSpace1(normalAxis, axis0, axis1);
  62
  63         if (originalPoints.size() <= 1)
  64         {
  65                 for (int i = 0; i < originalPoints.size(); i++)
  66                         hull.push_back(originalPoints[0]);
  67                 return;
  68         }
  69         //step1 : find anchor point with smallest projection on axis0 and move it to first location
  70         for (int i = 0; i < originalPoints.size(); i++)
  71         {
  72                 //              const b3Vector3& left = originalPoints[i];
  73                 //              const b3Vector3& right = originalPoints[0];
  74                 b3Scalar projL = originalPoints[i].dot(axis0);
  75                 b3Scalar projR = originalPoints[0].dot(axis0);
  76                 if (projL < projR)
  77                 {
  78                         originalPoints.swap(0, i);
  79                 }
  80         }
  81
  82         //also precompute angles
  83         originalPoints[0].m_angle = -1e30f;
  84         for (int i = 1; i < originalPoints.size(); i++)
  85         {
  86                 b3Vector3 xvec = axis0;
  87                 b3Vector3 ar = originalPoints[i] - originalPoints[0];
  88                 originalPoints[i].m_angle = b3Cross(xvec, ar).dot(normalAxis) / ar.length();
  89         }
  90
  91         //step 2: sort all points, based on 'angle' with this anchor
  92         b3AngleCompareFunc comp(originalPoints[0]);
  93         originalPoints.quickSortInternal(comp, 1, originalPoints.size() - 1);
  94
  95         int i;
  96         for (i = 0; i < 2; i++)
  97                 hull.push_back(originalPoints[i]);
  98
  99         //step 3: keep all 'convex' points and discard concave points (using back tracking)
 100         for (; i != originalPoints.size(); i++)
 101         {
 102                 bool isConvex = false;
 103                 while (!isConvex && hull.size() > 1)
 104                 {
 105                         b3Vector3& a = hull[hull.size() - 2];
 106                         b3Vector3& b = hull[hull.size() - 1];
 107                         isConvex = b3Cross(a - b, a - originalPoints[i]).dot(normalAxis) > 0;
 108                         if (!isConvex)
 109                                 hull.pop_back();
 110                         else
 111                                 hull.push_back(originalPoints[i]);
 112                 }
 113         }
 114 }
 115
 116 #endif  //B3_GRAHAM_SCAN_2D_CONVEX_HULL_H