dali-physics/third-party/bullet3/src/LinearMath/btGrahamScan2dConvexHull.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 GRAHAM_SCAN_2D_CONVEX_HULL_H
  17 #define GRAHAM_SCAN_2D_CONVEX_HULL_H
  18
  19 #include "btVector3.h"
  20 #include "btAlignedObjectArray.h"
  21
  22 struct GrahamVector3 : public btVector3
  23 {
  24         GrahamVector3(const btVector3& org, int orgIndex)
  25                 : btVector3(org),
  26                   m_orgIndex(orgIndex)
  27         {
  28         }
  29         btScalar m_angle;
  30         int m_orgIndex;
  31 };
  32
  33 struct btAngleCompareFunc
  34 {
  35         btVector3 m_anchor;
  36         btAngleCompareFunc(const btVector3& anchor)
  37                 : m_anchor(anchor)
  38         {
  39         }
  40         bool operator()(const GrahamVector3& a, const GrahamVector3& b) const
  41         {
  42                 if (a.m_angle != b.m_angle)
  43                         return a.m_angle < b.m_angle;
  44                 else
  45                 {
  46                         btScalar al = (a - m_anchor).length2();
  47                         btScalar 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 GrahamScanConvexHull2D(btAlignedObjectArray<GrahamVector3>& originalPoints, btAlignedObjectArray<GrahamVector3>& hull, const btVector3& normalAxis)
  59 {
  60         btVector3 axis0, axis1;
  61         btPlaneSpace1(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 btVector3& left = originalPoints[i];
  73                 //              const btVector3& right = originalPoints[0];
  74                 btScalar projL = originalPoints[i].dot(axis0);
  75                 btScalar 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                 btVector3 ar = originalPoints[i] - originalPoints[0];
  87                 btScalar ar1 = axis1.dot(ar);
  88                 btScalar ar0 = axis0.dot(ar);
  89                 if (ar1 * ar1 + ar0 * ar0 < FLT_EPSILON)
  90                 {
  91                         originalPoints[i].m_angle = 0.0f;
  92                 }
  93                 else
  94                 {
  95                         originalPoints[i].m_angle = btAtan2Fast(ar1, ar0);
  96                 }
  97         }
  98
  99         //step 2: sort all points, based on 'angle' with this anchor
 100         btAngleCompareFunc comp(originalPoints[0]);
 101         originalPoints.quickSortInternal(comp, 1, originalPoints.size() - 1);
 102
 103         int i;
 104         for (i = 0; i < 2; i++)
 105                 hull.push_back(originalPoints[i]);
 106
 107         //step 3: keep all 'convex' points and discard concave points (using back tracking)
 108         for (; i != originalPoints.size(); i++)
 109         {
 110                 bool isConvex = false;
 111                 while (!isConvex && hull.size() > 1)
 112                 {
 113                         btVector3& a = hull[hull.size() - 2];
 114                         btVector3& b = hull[hull.size() - 1];
 115                         isConvex = btCross(a - b, a - originalPoints[i]).dot(normalAxis) > 0;
 116                         if (!isConvex)
 117                                 hull.pop_back();
 118                         else
 119                                 hull.push_back(originalPoints[i]);
 120                 }
 121
 122                 if (hull.size() == 1)
 123                 {
 124                         hull.push_back(originalPoints[i]);
 125                 }
 126         }
 127 }
 128
 129 #endif  //GRAHAM_SCAN_2D_CONVEX_HULL_H