2 Bullet Continuous Collision Detection and Physics Library
3 Copyright (c) 2011 Advanced Micro Devices, Inc. http://bulletphysics.org
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16 #ifndef B3_GRAHAM_SCAN_2D_CONVEX_HULL_H
17 #define B3_GRAHAM_SCAN_2D_CONVEX_HULL_H
19 #include "Bullet3Common/b3Vector3.h"
20 #include "Bullet3Common/b3AlignedObjectArray.h"
22 struct b3GrahamVector3 : public b3Vector3
24 b3GrahamVector3(const b3Vector3& org, int orgIndex)
33 struct b3AngleCompareFunc
36 b3AngleCompareFunc(const b3Vector3& anchor)
40 bool operator()(const b3GrahamVector3& a, const b3GrahamVector3& b) const
42 if (a.m_angle != b.m_angle)
43 return a.m_angle < b.m_angle;
46 b3Scalar al = (a - m_anchor).length2();
47 b3Scalar bl = (b - m_anchor).length2();
52 return a.m_orgIndex < b.m_orgIndex;
58 inline void b3GrahamScanConvexHull2D(b3AlignedObjectArray<b3GrahamVector3>& originalPoints, b3AlignedObjectArray<b3GrahamVector3>& hull, const b3Vector3& normalAxis)
60 b3Vector3 axis0, axis1;
61 b3PlaneSpace1(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 b3Vector3& left = originalPoints[i];
73 // const b3Vector3& right = originalPoints[0];
74 b3Scalar projL = originalPoints[i].dot(axis0);
75 b3Scalar 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 b3Vector3 xvec = axis0;
87 b3Vector3 ar = originalPoints[i] - originalPoints[0];
88 originalPoints[i].m_angle = b3Cross(xvec, ar).dot(normalAxis) / ar.length();
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);
96 for (i = 0; i < 2; i++)
97 hull.push_back(originalPoints[i]);
99 //step 3: keep all 'convex' points and discard concave points (using back tracking)
100 for (; i != originalPoints.size(); i++)
102 bool isConvex = false;
103 while (!isConvex && hull.size() > 1)
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;
111 hull.push_back(originalPoints[i]);
116 #endif //B3_GRAHAM_SCAN_2D_CONVEX_HULL_H