Bullet Collision Detection & Physics Library
btGrahamScan2dConvexHull.h
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1/*
2Bullet Continuous Collision Detection and Physics Library
3Copyright (c) 2011 Advanced Micro Devices, Inc. http://bulletphysics.org
4
5This software is provided 'as-is', without any express or implied warranty.
6In no event will the authors be held liable for any damages arising from the use of this software.
7Permission is granted to anyone to use this software for any purpose,
8including commercial applications, and to alter it and redistribute it freely,
9subject to the following restrictions:
10
111. 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.
122. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
133. This notice may not be removed or altered from any source distribution.
14*/
15
16
17#ifndef GRAHAM_SCAN_2D_CONVEX_HULL_H
18#define GRAHAM_SCAN_2D_CONVEX_HULL_H
19
20
21#include "btVector3.h"
23
24struct GrahamVector3 : public btVector3
25{
26 GrahamVector3(const btVector3& org, int orgIndex)
27 :btVector3(org),
28 m_orgIndex(orgIndex)
29 {
30 }
33};
34
35
39 : m_anchor(anchor)
40 {
41 }
42 bool operator()(const GrahamVector3& a, const GrahamVector3& b) const {
43 if (a.m_angle != b.m_angle)
44 return a.m_angle < b.m_angle;
45 else
46 {
47 btScalar al = (a-m_anchor).length2();
48 btScalar bl = (b-m_anchor).length2();
49 if (al != bl)
50 return al < bl;
51 else
52 {
53 return a.m_orgIndex < b.m_orgIndex;
54 }
55 }
56 }
57};
58
60{
61 btVector3 axis0,axis1;
62 btPlaneSpace1(normalAxis,axis0,axis1);
63
64
65 if (originalPoints.size()<=1)
66 {
67 for (int i=0;i<originalPoints.size();i++)
68 hull.push_back(originalPoints[0]);
69 return;
70 }
71 //step1 : find anchor point with smallest projection on axis0 and move it to first location
72 for (int i=0;i<originalPoints.size();i++)
73 {
74// const btVector3& left = originalPoints[i];
75// const btVector3& right = originalPoints[0];
76 btScalar projL = originalPoints[i].dot(axis0);
77 btScalar projR = originalPoints[0].dot(axis0);
78 if (projL < projR)
79 {
80 originalPoints.swap(0,i);
81 }
82 }
83
84 //also precompute angles
85 originalPoints[0].m_angle = -1e30f;
86 for (int i=1;i<originalPoints.size();i++)
87 {
88 btVector3 ar = originalPoints[i]-originalPoints[0];
89 btScalar ar1 = axis1.dot(ar);
90 btScalar ar0 = axis0.dot(ar);
91 if( ar1*ar1+ar0*ar0 < FLT_EPSILON )
92 {
93 originalPoints[i].m_angle = 0.0f;
94 }
95 else
96 {
97 originalPoints[i].m_angle = btAtan2Fast(ar1, ar0);
98 }
99 }
100
101 //step 2: sort all points, based on 'angle' with this anchor
102 btAngleCompareFunc comp(originalPoints[0]);
103 originalPoints.quickSortInternal(comp,1,originalPoints.size()-1);
104
105 int i;
106 for (i = 0; i<2; i++)
107 hull.push_back(originalPoints[i]);
108
109 //step 3: keep all 'convex' points and discard concave points (using back tracking)
110 for (; i != originalPoints.size(); i++)
111 {
112 bool isConvex = false;
113 while (!isConvex&& hull.size()>1) {
114 btVector3& a = hull[hull.size()-2];
115 btVector3& b = hull[hull.size()-1];
116 isConvex = btCross(a-b,a-originalPoints[i]).dot(normalAxis)> 0;
117 if (!isConvex)
118 hull.pop_back();
119 else
120 hull.push_back(originalPoints[i]);
121 }
122
123 if( hull.size() == 1 )
124 {
125 hull.push_back( originalPoints[i] );
126 }
127 }
128}
129
130#endif //GRAHAM_SCAN_2D_CONVEX_HULL_H
void GrahamScanConvexHull2D(btAlignedObjectArray< GrahamVector3 > &originalPoints, btAlignedObjectArray< GrahamVector3 > &hull, const btVector3 &normalAxis)
float btScalar
The btScalar type abstracts floating point numbers, to easily switch between double and single floati...
Definition: btScalar.h:292
btScalar btAtan2Fast(btScalar y, btScalar x)
Definition: btScalar.h:531
void btPlaneSpace1(const T &n, T &p, T &q)
Definition: btVector3.h:1283
btVector3 btCross(const btVector3 &v1, const btVector3 &v2)
Return the cross product of two vectors.
Definition: btVector3.h:931
The btAlignedObjectArray template class uses a subset of the stl::vector interface for its methods It...
int size() const
return the number of elements in the array
void swap(int index0, int index1)
void push_back(const T &_Val)
void quickSortInternal(const L &CompareFunc, int lo, int hi)
btVector3 can be used to represent 3D points and vectors.
Definition: btVector3.h:84
btScalar dot(const btVector3 &v) const
Return the dot product.
Definition: btVector3.h:235
GrahamVector3(const btVector3 &org, int orgIndex)
bool operator()(const GrahamVector3 &a, const GrahamVector3 &b) const
btAngleCompareFunc(const btVector3 &anchor)