Bullet Collision Detection & Physics Library: gim_box_set.cpp Source File

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gim_box_set.cpp
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1
2/*
3-----------------------------------------------------------------------------
4This source file is part of GIMPACT Library.
5
6For the latest info, see http://gimpact.sourceforge.net/
7
8Copyright (c) 2006 Francisco Leon Najera. C.C. 80087371.
9email: projectileman@yahoo.com
10
11 This library is free software; you can redistribute it and/or
12 modify it under the terms of EITHER:
13 (1) The GNU Lesser General Public License as published by the Free
14 Software Foundation; either version 2.1 of the License, or (at
15 your option) any later version. The text of the GNU Lesser
16 General Public License is included with this library in the
17 file GIMPACT-LICENSE-LGPL.TXT.
18 (2) The BSD-style license that is included with this library in
19 the file GIMPACT-LICENSE-BSD.TXT.
20 (3) The zlib/libpng license that is included with this library in
21 the file GIMPACT-LICENSE-ZLIB.TXT.
22
23 This library is distributed in the hope that it will be useful,
24 but WITHOUT ANY WARRANTY; without even the implied warranty of
25 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the files
26 GIMPACT-LICENSE-LGPL.TXT, GIMPACT-LICENSE-ZLIB.TXT and GIMPACT-LICENSE-BSD.TXT for more details.
27
28-----------------------------------------------------------------------------
29*/
30
31#include "gim_box_set.h"
32
33 GUINT GIM_BOX_TREE::_calc_splitting_axis(
34 gim_array<GIM_AABB_DATA>& primitive_boxes, GUINT startIndex, GUINT endIndex)
35{
36 GUINT i;
37
38 btVector3 means(btScalar(0.), btScalar(0.), btScalar(0.));
39 btVector3 variance(btScalar(0.), btScalar(0.), btScalar(0.));
40 GUINT numIndices = endIndex - startIndex;
41
42 for (i = startIndex; i < endIndex; i++)
43 {
44 btVector3 center = btScalar(0.5) * (primitive_boxes[i].m_bound.m_max +
45 primitive_boxes[i].m_bound.m_min);
46 means += center;
47 }
48 means *= (btScalar(1.) / (btScalar)numIndices);
49
50 for (i = startIndex; i < endIndex; i++)
51 {
52 btVector3 center = btScalar(0.5) * (primitive_boxes[i].m_bound.m_max +
53 primitive_boxes[i].m_bound.m_min);
54 btVector3 diff2 = center - means;
55 diff2 = diff2 * diff2;
56 variance += diff2;
57 }
58 variance *= (btScalar(1.) / ((btScalar)numIndices - 1));
59
60 return variance.maxAxis();
61}
62
63 GUINT GIM_BOX_TREE::_sort_and_calc_splitting_index(
64 gim_array<GIM_AABB_DATA>& primitive_boxes, GUINT startIndex,
65 GUINT endIndex, GUINT splitAxis)
66{
67 GUINT i;
68 GUINT splitIndex = startIndex;
69 GUINT numIndices = endIndex - startIndex;
70
71 // average of centers
72 btScalar splitValue = 0.0f;
73 for (i = startIndex; i < endIndex; i++)
74 {
75 splitValue += 0.5f * (primitive_boxes[i].m_bound.m_max[splitAxis] +
76 primitive_boxes[i].m_bound.m_min[splitAxis]);
77 }
78 splitValue /= (btScalar)numIndices;
79
80 //sort leafNodes so all values larger then splitValue comes first, and smaller values start from 'splitIndex'.
81 for (i = startIndex; i < endIndex; i++)
82 {
83 btScalar center = 0.5f * (primitive_boxes[i].m_bound.m_max[splitAxis] +
84 primitive_boxes[i].m_bound.m_min[splitAxis]);
85 if (center > splitValue)
86 {
87 //swap
88 primitive_boxes.swap(i, splitIndex);
89 splitIndex++;
90 }
91 }
92
93 //if the splitIndex causes unbalanced trees, fix this by using the center in between startIndex and endIndex
94 //otherwise the tree-building might fail due to stack-overflows in certain cases.
95 //unbalanced1 is unsafe: it can cause stack overflows
96 //bool unbalanced1 = ((splitIndex==startIndex) || (splitIndex == (endIndex-1)));
97
98 //unbalanced2 should work too: always use center (perfect balanced trees)
99 //bool unbalanced2 = true;
100
101 //this should be safe too:
102 GUINT rangeBalancedIndices = numIndices / 3;
103 bool unbalanced = ((splitIndex <= (startIndex + rangeBalancedIndices)) || (splitIndex >= (endIndex - 1 - rangeBalancedIndices)));
104
105 if (unbalanced)
106 {
107 splitIndex = startIndex + (numIndices >> 1);
108 }
109
110 btAssert(!((splitIndex == startIndex) || (splitIndex == (endIndex))));
111
112 return splitIndex;
113}
114
115 void GIM_BOX_TREE::_build_sub_tree(gim_array<GIM_AABB_DATA>& primitive_boxes, GUINT startIndex, GUINT endIndex)
116{
117 GUINT current_index = m_num_nodes++;
118
119 btAssert((endIndex - startIndex) > 0);
120
121 if ((endIndex - startIndex) == 1) //we got a leaf
122 {
123 m_node_array[current_index].m_left = 0;
124 m_node_array[current_index].m_right = 0;
125 m_node_array[current_index].m_escapeIndex = 0;
126
127 m_node_array[current_index].m_bound = primitive_boxes[startIndex].m_bound;
128 m_node_array[current_index].m_data = primitive_boxes[startIndex].m_data;
129 return;
130 }
131
132 //configure inner node
133
134 GUINT splitIndex;
135
136 //calc this node bounding box
137 m_node_array[current_index].m_bound.invalidate();
138 for (splitIndex = startIndex; splitIndex < endIndex; splitIndex++)
139 {
140 m_node_array[current_index].m_bound.merge(primitive_boxes[splitIndex].m_bound);
141 }
142
143 //calculate Best Splitting Axis and where to split it. Sort the incoming 'leafNodes' array within range 'startIndex/endIndex'.
144
145 //split axis
146 splitIndex = _calc_splitting_axis(primitive_boxes, startIndex, endIndex);
147
148 splitIndex = _sort_and_calc_splitting_index(
149 primitive_boxes, startIndex, endIndex, splitIndex);
150
151 //configure this inner node : the left node index
152 m_node_array[current_index].m_left = m_num_nodes;
153 //build left child tree
154 _build_sub_tree(primitive_boxes, startIndex, splitIndex);
155
156 //configure this inner node : the right node index
157 m_node_array[current_index].m_right = m_num_nodes;
158
159 //build right child tree
160 _build_sub_tree(primitive_boxes, splitIndex, endIndex);
161
162 //configure this inner node : the escape index
163 m_node_array[current_index].m_escapeIndex = m_num_nodes - current_index;
164}
165
167 void GIM_BOX_TREE::build_tree(
168 gim_array<GIM_AABB_DATA>& primitive_boxes)
169{
170 // initialize node count to 0
171 m_num_nodes = 0;
172 // allocate nodes
173 m_node_array.resize(primitive_boxes.size() * 2);
174
175 _build_sub_tree(primitive_boxes, 0, primitive_boxes.size());
176}
btScalar
float btScalar
The btScalar type abstracts floating point numbers, to easily switch between double and single floati...
Definition: btScalar.h:314
btAssert
#define btAssert(x)
Definition: btScalar.h:153
GIM_BOX_TREE::_calc_splitting_axis
GUINT _calc_splitting_axis(gim_array< GIM_AABB_DATA > &primitive_boxes, GUINT startIndex, GUINT endIndex)
Definition: gim_box_set.cpp:33
GIM_BOX_TREE::m_node_array
gim_array< GIM_BOX_TREE_NODE > m_node_array
Definition: gim_box_set.h:111
GIM_BOX_TREE::_sort_and_calc_splitting_index
GUINT _sort_and_calc_splitting_index(gim_array< GIM_AABB_DATA > &primitive_boxes, GUINT startIndex, GUINT endIndex, GUINT splitAxis)
Definition: gim_box_set.cpp:63
GIM_BOX_TREE::m_num_nodes
GUINT m_num_nodes
Definition: gim_box_set.h:110
GIM_BOX_TREE::_build_sub_tree
void _build_sub_tree(gim_array< GIM_AABB_DATA > &primitive_boxes, GUINT startIndex, GUINT endIndex)
Definition: gim_box_set.cpp:115
GIM_BOX_TREE::build_tree
void build_tree(gim_array< GIM_AABB_DATA > &primitive_boxes)
prototype functions for box tree management
Definition: gim_box_set.cpp:167
btVector3
btVector3 can be used to represent 3D points and vectors.
Definition: btVector3.h:82
btVector3::maxAxis
int maxAxis() const
Return the axis with the largest value Note return values are 0,1,2 for x, y, or z.
Definition: btVector3.h:477
gim_array
Very simple array container with fast access and simd memory.
Definition: gim_array.h:43
gim_array::size
GUINT size() const
Definition: gim_array.h:143
gim_array::swap
void swap(GUINT i, GUINT j)
Definition: gim_array.h:208
gim_array::resize
void resize(GUINT size, bool call_constructor=true, const T &fillData=T())
Definition: gim_array.h:287
gim_array::m_data
T * m_data
properties
Definition: gim_array.h:47
gim_box_set.h
GUINT
#define GUINT
Definition: gim_math.h:40