Box2D  2.4.0
A 2D physics engine for games
b2_rope.h
1 // MIT License
2 
3 // Copyright (c) 2019 Erin Catto
4 
5 // Permission is hereby granted, free of charge, to any person obtaining a copy
6 // of this software and associated documentation files (the "Software"), to deal
7 // in the Software without restriction, including without limitation the rights
8 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
9 // copies of the Software, and to permit persons to whom the Software is
10 // furnished to do so, subject to the following conditions:
11 
12 // The above copyright notice and this permission notice shall be included in all
13 // copies or substantial portions of the Software.
14 
15 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
18 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
20 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
21 // SOFTWARE.
22 
23 #ifndef B2_ROPE_H
24 #define B2_ROPE_H
25 
26 #include "b2_api.h"
27 #include "b2_math.h"
28 
29 class b2Draw;
30 struct b2RopeStretch;
31 struct b2RopeBend;
32 
33 enum b2StretchingModel
34 {
35  b2_pbdStretchingModel,
36  b2_xpbdStretchingModel
37 };
38 
39 enum b2BendingModel
40 {
41  b2_springAngleBendingModel = 0,
42  b2_pbdAngleBendingModel,
43  b2_xpbdAngleBendingModel,
44  b2_pbdDistanceBendingModel,
45  b2_pbdHeightBendingModel
46 };
47 
49 struct B2_API b2RopeTuning
50 {
51  b2RopeTuning()
52  {
53  stretchingModel = b2_pbdStretchingModel;
54  bendingModel = b2_pbdAngleBendingModel;
55  damping = 0.0f;
56  stretchStiffness = 1.0f;
57  bendStiffness = 0.5f;
58  bendHertz = 1.0f;
59  bendDamping = 0.0f;
60  isometric = false;
61  fixedEffectiveMass = false;
62  warmStart = false;
63  }
64 
65  b2StretchingModel stretchingModel;
66  b2BendingModel bendingModel;
67  float damping;
68  float stretchStiffness;
69  float stretchHertz;
70  float stretchDamping;
71  float bendStiffness;
72  float bendHertz;
73  float bendDamping;
74  bool isometric;
75  bool fixedEffectiveMass;
76  bool warmStart;
77 };
78 
80 struct B2_API b2RopeDef
81 {
82  b2RopeDef()
83  {
84  position.SetZero();
85  vertices = nullptr;
86  count = 0;
87  masses = nullptr;
88  gravity.SetZero();
89  }
90 
91  b2Vec2 position;
92  b2Vec2* vertices;
93  int32 count;
94  float* masses;
95  b2Vec2 gravity;
96  b2RopeTuning tuning;
97 };
98 
100 class B2_API b2Rope
101 {
102 public:
103  b2Rope();
104  ~b2Rope();
105 
107  void Create(const b2RopeDef& def);
108 
110  void SetTuning(const b2RopeTuning& tuning);
111 
113  void Step(float timeStep, int32 iterations, const b2Vec2& position);
114 
116  void Reset(const b2Vec2& position);
117 
119  void Draw(b2Draw* draw) const;
120 
121 private:
122 
123  void SolveStretch_PBD();
124  void SolveStretch_XPBD(float dt);
125  void SolveBend_PBD_Angle();
126  void SolveBend_XPBD_Angle(float dt);
127  void SolveBend_PBD_Distance();
128  void SolveBend_PBD_Height();
129  void ApplyBendForces(float dt);
130 
131  b2Vec2 m_position;
132 
133  int32 m_count;
134  int32 m_stretchCount;
135  int32 m_bendCount;
136 
137  b2RopeStretch* m_stretchConstraints;
138  b2RopeBend* m_bendConstraints;
139 
140  b2Vec2* m_bindPositions;
141  b2Vec2* m_ps;
142  b2Vec2* m_p0s;
143  b2Vec2* m_vs;
144 
145  float* m_invMasses;
146  b2Vec2 m_gravity;
147 
148  b2RopeTuning m_tuning;
149 };
150 
151 #endif
b2Vec2
A 2D column vector.
Definition: b2_math.h:42
b2RopeDef
Definition: b2_rope.h:81
b2Draw
Definition: b2_draw.h:49
b2RopeTuning
Definition: b2_rope.h:50
b2Rope
Definition: b2_rope.h:101