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

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btUnionFind.h
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1 /*
2 Bullet Continuous Collision Detection and Physics Library
3 Copyright (c) 2003-2006 Erwin Coumans http://continuousphysics.com/Bullet/
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 BT_UNION_FIND_H
17 #define BT_UNION_FIND_H
18
19 #include "LinearMath/btAlignedObjectArray.h"
20
21 #define USE_PATH_COMPRESSION 1
22
24 #define STATIC_SIMULATION_ISLAND_OPTIMIZATION 1
25
26 struct btElement
27 {
28 int m_id;
29 int m_sz;
30 };
31
33 // Implements weighted Quick Union with path compression
34 // optimization: could use short ints instead of ints (halving memory, would limit the number of rigid bodies to 64k, sounds reasonable)
35 class btUnionFind
36 {
37 private:
38 btAlignedObjectArray<btElement> m_elements;
39
40 public:
41
42 btUnionFind();
43 ~btUnionFind();
44
45
46 //this is a special operation, destroying the content of btUnionFind.
47 //it sorts the elements, based on island id, in order to make it easy to iterate over islands
48 void sortIslands();
49
50 void reset(int N);
51
52 SIMD_FORCE_INLINE int getNumElements() const
53 {
54 return int(m_elements.size());
55 }
56 SIMD_FORCE_INLINE bool isRoot(int x) const
57 {
58 return (x == m_elements[x].m_id);
59 }
60
61 btElement& getElement(int index)
62 {
63 return m_elements[index];
64 }
65 const btElement& getElement(int index) const
66 {
67 return m_elements[index];
68 }
69
70 void allocate(int N);
71 void Free();
72
73
74
75
76 int find(int p, int q)
77 {
78 return (find(p) == find(q));
79 }
80
81 void unite(int p, int q)
82 {
83 int i = find(p), j = find(q);
84 if (i == j)
85 return;
86
87 #ifndef USE_PATH_COMPRESSION
88 //weighted quick union, this keeps the 'trees' balanced, and keeps performance of unite O( log(n) )
89 if (m_elements[i].m_sz < m_elements[j].m_sz)
90 {
91 m_elements[i].m_id = j; m_elements[j].m_sz += m_elements[i].m_sz;
92 }
93 else
94 {
95 m_elements[j].m_id = i; m_elements[i].m_sz += m_elements[j].m_sz;
96 }
97 #else
98 m_elements[i].m_id = j; m_elements[j].m_sz += m_elements[i].m_sz;
99 #endif //USE_PATH_COMPRESSION
100 }
101
102 int find(int x)
103 {
104 //btAssert(x < m_N);
105 //btAssert(x >= 0);
106
107 while (x != m_elements[x].m_id)
108 {
109 //not really a reason not to use path compression, and it flattens the trees/improves find performance dramatically
110
111 #ifdef USE_PATH_COMPRESSION
112 const btElement* elementPtr = &m_elements[m_elements[x].m_id];
113 m_elements[x].m_id = elementPtr->m_id;
114 x = elementPtr->m_id;
115 #else//
116 x = m_elements[x].m_id;
117 #endif
118 //btAssert(x < m_N);
119 //btAssert(x >= 0);
120
121 }
122 return x;
123 }
124
125
126 };
127
128
129 #endif //BT_UNION_FIND_H
btUnionFind::find
int find(int p, int q)
Definition: btUnionFind.h:76
btAlignedObjectArray< btElement >
btUnionFind::getElement
btElement & getElement(int index)
Definition: btUnionFind.h:61
btElement::m_sz
int m_sz
Definition: btUnionFind.h:29
SIMD_FORCE_INLINE
#define SIMD_FORCE_INLINE
Definition: btScalar.h:63
btUnionFind
UnionFind calculates connected subsets.
Definition: btUnionFind.h:35
btUnionFind::find
int find(int x)
Definition: btUnionFind.h:102
btAlignedObjectArray::size
int size() const
return the number of elements in the array
Definition: btAlignedObjectArray.h:155
btElement::m_id
int m_id
Definition: btUnionFind.h:28
btAlignedObjectArray.h
btUnionFind::getNumElements
int getNumElements() const
Definition: btUnionFind.h:52
btUnionFind::getElement
const btElement & getElement(int index) const
Definition: btUnionFind.h:65
btUnionFind::unite
void unite(int p, int q)
Definition: btUnionFind.h:81
btUnionFind::isRoot
bool isRoot(int x) const
Definition: btUnionFind.h:56
btUnionFind::m_elements
btAlignedObjectArray< btElement > m_elements
Definition: btUnionFind.h:38
btElement
Definition: btUnionFind.h:26