/* * Copyright (c) 2006-2007 Erin Catto http://www.gphysics.com * * This software is provided 'as-is', without any express or implied * warranty. In no event will the authors be held liable for any damages * arising from the use of this software. * Permission is granted to anyone to use this software for any purpose, * including commercial applications, and to alter it and redistribute it * freely, subject to the following restrictions: * 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. * 2. Altered source versions must be plainly marked as such, and must not be * misrepresented as being the original software. * 3. This notice may not be removed or altered from any source distribution. */ #ifndef B2_DISTANCE_JOINT_H #define B2_DISTANCE_JOINT_H #include <Box2D/Dynamics/Joints/b2Joint.h> /// Distance joint definition. This requires defining an /// anchor point on both bodies and the non-zero length of the /// distance joint. The definition uses local anchor points /// so that the initial configuration can violate the constraint /// slightly. This helps when saving and loading a game. /// @warning Do not use a zero or short length. struct b2DistanceJointDef : public b2JointDef { b2DistanceJointDef() { type = e_distanceJoint; localAnchorA.Set(0.0f, 0.0f); localAnchorB.Set(0.0f, 0.0f); length = 1.0f; frequencyHz = 0.0f; dampingRatio = 0.0f; } /// Initialize the bodies, anchors, and length using the world /// anchors. void Initialize(b2Body* bodyA, b2Body* bodyB, const b2Vec2& anchorA, const b2Vec2& anchorB); /// The local anchor point relative to body1's origin. b2Vec2 localAnchorA; /// The local anchor point relative to body2's origin. b2Vec2 localAnchorB; /// The natural length between the anchor points. float32 length; /// The mass-spring-damper frequency in Hertz. float32 frequencyHz; /// The damping ratio. 0 = no damping, 1 = critical damping. float32 dampingRatio; }; /// A distance joint constrains two points on two bodies /// to remain at a fixed distance from each other. You can view /// this as a massless, rigid rod. class b2DistanceJoint : public b2Joint { public: b2Vec2 GetAnchorA() const; b2Vec2 GetAnchorB() const; b2Vec2 GetReactionForce(float32 inv_dt) const; float32 GetReactionTorque(float32 inv_dt) const; /// Set/get the natural length. /// Manipulating the length can lead to non-physical behavior when the frequency is zero. void SetLength(float32 length); float32 GetLength() const; // Set/get frequency in Hz. void SetFrequency(float32 hz); float32 GetFrequency() const; // Set/get damping ratio. void SetDampingRatio(float32 ratio); float32 GetDampingRatio() const; protected: friend class b2Joint; b2DistanceJoint(const b2DistanceJointDef* data); void InitVelocityConstraints(const b2TimeStep& step); void SolveVelocityConstraints(const b2TimeStep& step); bool SolvePositionConstraints(float32 baumgarte); b2Vec2 m_localAnchor1; b2Vec2 m_localAnchor2; b2Vec2 m_u; float32 m_frequencyHz; float32 m_dampingRatio; float32 m_gamma; float32 m_bias; float32 m_impulse; float32 m_mass; float32 m_length; }; inline void b2DistanceJoint::SetLength(float32 length) { m_length = length; } inline float32 b2DistanceJoint::GetLength() const { return m_length; } inline void b2DistanceJoint::SetFrequency(float32 hz) { m_frequencyHz = hz; } inline float32 b2DistanceJoint::GetFrequency() const { return m_frequencyHz; } inline void b2DistanceJoint::SetDampingRatio(float32 ratio) { m_dampingRatio = ratio; } inline float32 b2DistanceJoint::GetDampingRatio() const { return m_dampingRatio; } #endif