2 Bullet Continuous Collision Detection and Physics Library
3 Copyright (c) 2011 Advanced Micro Devices, Inc. http://bulletphysics.org
5 This software is provided 'as-is', without any express or implied warranty.
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8 including commercial applications, and to alter it and redistribute it freely,
9 subject to the following restrictions:
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16 #ifndef GRAHAM_SCAN_2D_CONVEX_HULL_H
17 #define GRAHAM_SCAN_2D_CONVEX_HULL_H
19 #include "btVector3.h"
20 #include "btAlignedObjectArray.h"
22 struct GrahamVector3 : public btVector3
24 GrahamVector3(const btVector3& org, int orgIndex)
33 struct btAngleCompareFunc
36 btAngleCompareFunc(const btVector3& anchor)
40 bool operator()(const GrahamVector3& a, const GrahamVector3& b) const
42 if (a.m_angle != b.m_angle)
43 return a.m_angle < b.m_angle;
46 btScalar al = (a - m_anchor).length2();
47 btScalar bl = (b - m_anchor).length2();
52 return a.m_orgIndex < b.m_orgIndex;
58 inline void GrahamScanConvexHull2D(btAlignedObjectArray<GrahamVector3>& originalPoints, btAlignedObjectArray<GrahamVector3>& hull, const btVector3& normalAxis)
60 btVector3 axis0, axis1;
61 btPlaneSpace1(normalAxis, axis0, axis1);
63 if (originalPoints.size() <= 1)
65 for (int i = 0; i < originalPoints.size(); i++)
66 hull.push_back(originalPoints[0]);
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++)
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);
78 originalPoints.swap(0, i);
82 //also precompute angles
83 originalPoints[0].m_angle = -1e30f;
84 for (int i = 1; i < originalPoints.size(); i++)
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)
91 originalPoints[i].m_angle = 0.0f;
95 originalPoints[i].m_angle = btAtan2Fast(ar1, ar0);
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);
104 for (i = 0; i < 2; i++)
105 hull.push_back(originalPoints[i]);
107 //step 3: keep all 'convex' points and discard concave points (using back tracking)
108 for (; i != originalPoints.size(); i++)
110 bool isConvex = false;
111 while (!isConvex && hull.size() > 1)
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;
119 hull.push_back(originalPoints[i]);
122 if (hull.size() == 1)
124 hull.push_back(originalPoints[i]);
129 #endif //GRAHAM_SCAN_2D_CONVEX_HULL_H