Bullet Collision Detection & Physics Library: btGrahamScan2dConvexHull.h Source File

Bullet Collision Detection & Physics Library

btGrahamScan2dConvexHull.h
Go to the documentation of this file.
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
17 #ifndef GRAHAM_SCAN_2D_CONVEX_HULL_H
18 #define GRAHAM_SCAN_2D_CONVEX_HULL_H
19
20
21 #include "btVector3.h"
22 #include "btAlignedObjectArray.h"
23
24 struct GrahamVector3 : public btVector3
25 {
26 GrahamVector3(const btVector3& org, int orgIndex)
27 :btVector3(org),
28 m_orgIndex(orgIndex)
29 {
30 }
31 btScalar m_angle;
32 int m_orgIndex;
33 };
34
35
36 struct btAngleCompareFunc {
37 btVector3 m_anchor;
38 btAngleCompareFunc(const btVector3& anchor)
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
59 inline void GrahamScanConvexHull2D(btAlignedObjectArray<GrahamVector3>& originalPoints, btAlignedObjectArray<GrahamVector3>& hull, const btVector3& normalAxis)
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
btAlignedObjectArray::push_back
void push_back(const T &_Val)
Definition: btAlignedObjectArray.h:274
btAlignedObjectArray
The btAlignedObjectArray template class uses a subset of the stl::vector interface for its methods It...
Definition: btAlignedObjectArray.h:53
btVector3.h
btPlaneSpace1
void btPlaneSpace1(const T &n, T &p, T &q)
Definition: btVector3.h:1283
GrahamVector3::m_orgIndex
int m_orgIndex
Definition: btGrahamScan2dConvexHull.h:32
btAngleCompareFunc::operator()
bool operator()(const GrahamVector3 &a, const GrahamVector3 &b) const
Definition: btGrahamScan2dConvexHull.h:42
btAlignedObjectArray::swap
void swap(int index0, int index1)
Definition: btAlignedObjectArray.h:405
btCross
btVector3 btCross(const btVector3 &v1, const btVector3 &v2)
Return the cross product of two vectors.
Definition: btVector3.h:931
btVector3::dot
btScalar dot(const btVector3 &v) const
Return the dot product.
Definition: btVector3.h:235
btAtan2Fast
btScalar btAtan2Fast(btScalar y, btScalar x)
Definition: btScalar.h:531
btAngleCompareFunc
Definition: btGrahamScan2dConvexHull.h:36
btAlignedObjectArray::pop_back
void pop_back()
Definition: btAlignedObjectArray.h:199
btVector3
btVector3 can be used to represent 3D points and vectors.
Definition: btVector3.h:83
btAlignedObjectArray::size
int size() const
return the number of elements in the array
Definition: btAlignedObjectArray.h:155
btAngleCompareFunc::m_anchor
btVector3 m_anchor
Definition: btGrahamScan2dConvexHull.h:37
GrahamVector3::m_angle
btScalar m_angle
Definition: btGrahamScan2dConvexHull.h:31
GrahamVector3
Definition: btGrahamScan2dConvexHull.h:24
btAngleCompareFunc::btAngleCompareFunc
btAngleCompareFunc(const btVector3 &anchor)
Definition: btGrahamScan2dConvexHull.h:38
GrahamScanConvexHull2D
void GrahamScanConvexHull2D(btAlignedObjectArray< GrahamVector3 > &originalPoints, btAlignedObjectArray< GrahamVector3 > &hull, const btVector3 &normalAxis)
Definition: btGrahamScan2dConvexHull.h:59
btAlignedObjectArray.h
GrahamVector3::GrahamVector3
GrahamVector3(const btVector3 &org, int orgIndex)
Definition: btGrahamScan2dConvexHull.h:26
btAlignedObjectArray::quickSortInternal
void quickSortInternal(const L &CompareFunc, int lo, int hi)
Definition: btAlignedObjectArray.h:333
btScalar
float btScalar
The btScalar type abstracts floating point numbers, to easily switch between double and single floati...
Definition: btScalar.h:292