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 {
GrahamVector3GrahamVector326 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;
btAngleCompareFuncbtAngleCompareFunc38 btAngleCompareFunc(const btVector3& anchor)
39 : m_anchor(anchor)
40 {
41 }
operatorbtAngleCompareFunc42 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
GrahamScanConvexHull2D(btAlignedObjectArray<GrahamVector3> & originalPoints,btAlignedObjectArray<GrahamVector3> & hull,const btVector3 & normalAxis)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
131