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 23 ///see for discussion of static island optimizations by Vroonsh here: http://code.google.com/p/bullet/issues/detail?id=406 24 #define STATIC_SIMULATION_ISLAND_OPTIMIZATION 1 25 26 struct btElement 27 { 28 int m_id; 29 int m_sz; 30 }; 31 32 ///UnionFind calculates connected subsets 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 btUnionFind(); 42 ~btUnionFind(); 43 44 //this is a special operation, destroying the content of btUnionFind. 45 //it sorts the elements, based on island id, in order to make it easy to iterate over islands 46 void sortIslands(); 47 48 void reset(int N); 49 getNumElements()50 SIMD_FORCE_INLINE int getNumElements() const 51 { 52 return int(m_elements.size()); 53 } isRoot(int x)54 SIMD_FORCE_INLINE bool isRoot(int x) const 55 { 56 return (x == m_elements[x].m_id); 57 } 58 getElement(int index)59 btElement& getElement(int index) 60 { 61 return m_elements[index]; 62 } getElement(int index)63 const btElement& getElement(int index) const 64 { 65 return m_elements[index]; 66 } 67 68 void allocate(int N); 69 void Free(); 70 find(int p,int q)71 int find(int p, int q) 72 { 73 return (find(p) == find(q)); 74 } 75 unite(int p,int q)76 void unite(int p, int q) 77 { 78 int i = find(p), j = find(q); 79 if (i == j) 80 return; 81 82 #ifndef USE_PATH_COMPRESSION 83 //weighted quick union, this keeps the 'trees' balanced, and keeps performance of unite O( log(n) ) 84 if (m_elements[i].m_sz < m_elements[j].m_sz) 85 { 86 m_elements[i].m_id = j; 87 m_elements[j].m_sz += m_elements[i].m_sz; 88 } 89 else 90 { 91 m_elements[j].m_id = i; 92 m_elements[i].m_sz += m_elements[j].m_sz; 93 } 94 #else 95 m_elements[i].m_id = j; 96 m_elements[j].m_sz += m_elements[i].m_sz; 97 #endif //USE_PATH_COMPRESSION 98 } 99 find(int x)100 int find(int x) 101 { 102 //btAssert(x < m_N); 103 //btAssert(x >= 0); 104 105 while (x != m_elements[x].m_id) 106 { 107 //not really a reason not to use path compression, and it flattens the trees/improves find performance dramatically 108 109 #ifdef USE_PATH_COMPRESSION 110 const btElement* elementPtr = &m_elements[m_elements[x].m_id]; 111 m_elements[x].m_id = elementPtr->m_id; 112 x = elementPtr->m_id; 113 #else // 114 x = m_elements[x].m_id; 115 #endif 116 //btAssert(x < m_N); 117 //btAssert(x >= 0); 118 } 119 return x; 120 } 121 }; 122 123 #endif //BT_UNION_FIND_H 124