/* * Copyright (c) 2006-2011 Erin Catto http://www.box2d.org * * 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_WHEEL_JOINT_H #define B2_WHEEL_JOINT_H #include <Box2D/Dynamics/Joints/b2Joint.h> /// Wheel joint definition. This requires defining a line of /// motion using an axis and an anchor point. The definition uses local /// anchor points and a local axis so that the initial configuration /// can violate the constraint slightly. The joint translation is zero /// when the local anchor points coincide in world space. Using local /// anchors and a local axis helps when saving and loading a game. struct b2WheelJointDef : public b2JointDef { b2WheelJointDef() { type = e_wheelJoint; localAnchorA.SetZero(); localAnchorB.SetZero(); localAxisA.Set(1.0f, 0.0f); enableMotor = false; maxMotorTorque = 0.0f; motorSpeed = 0.0f; frequencyHz = 2.0f; dampingRatio = 0.7f; } /// Initialize the bodies, anchors, axis, and reference angle using the world /// anchor and world axis. void Initialize(b2Body* bodyA, b2Body* bodyB, const b2Vec2& anchor, const b2Vec2& axis); /// The local anchor point relative to bodyA's origin. b2Vec2 localAnchorA; /// The local anchor point relative to bodyB's origin. b2Vec2 localAnchorB; /// The local translation axis in bodyA. b2Vec2 localAxisA; /// Enable/disable the joint motor. bool enableMotor; /// The maximum motor torque, usually in N-m. float32 maxMotorTorque; /// The desired motor speed in radians per second. float32 motorSpeed; /// Suspension frequency, zero indicates no suspension float32 frequencyHz; /// Suspension damping ratio, one indicates critical damping float32 dampingRatio; }; /// A wheel joint. This joint provides two degrees of freedom: translation /// along an axis fixed in bodyA and rotation in the plane. You can use a /// joint limit to restrict the range of motion and a joint motor to drive /// the rotation or to model rotational friction. /// This joint is designed for vehicle suspensions. class b2WheelJoint : public b2Joint { public: void GetDefinition(b2WheelJointDef* def) const; b2Vec2 GetAnchorA() const; b2Vec2 GetAnchorB() const; b2Vec2 GetReactionForce(float32 inv_dt) const; float32 GetReactionTorque(float32 inv_dt) const; /// The local anchor point relative to bodyA's origin. const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; } /// The local anchor point relative to bodyB's origin. const b2Vec2& GetLocalAnchorB() const { return m_localAnchorB; } /// The local joint axis relative to bodyA. const b2Vec2& GetLocalAxisA() const { return m_localXAxisA; } /// Get the current joint translation, usually in meters. float32 GetJointTranslation() const; /// Get the current joint translation speed, usually in meters per second. float32 GetJointSpeed() const; /// Is the joint motor enabled? bool IsMotorEnabled() const; /// Enable/disable the joint motor. void EnableMotor(bool flag); /// Set the motor speed, usually in radians per second. void SetMotorSpeed(float32 speed); /// Get the motor speed, usually in radians per second. float32 GetMotorSpeed() const; /// Set/Get the maximum motor force, usually in N-m. void SetMaxMotorTorque(float32 torque); float32 GetMaxMotorTorque() const; /// Get the current motor torque given the inverse time step, usually in N-m. float32 GetMotorTorque(float32 inv_dt) const; /// Set/Get the spring frequency in hertz. Setting the frequency to zero disables the spring. void SetSpringFrequencyHz(float32 hz); float32 GetSpringFrequencyHz() const; /// Set/Get the spring damping ratio void SetSpringDampingRatio(float32 ratio); float32 GetSpringDampingRatio() const; /// Dump to b2Log void Dump(); protected: friend class b2Joint; b2WheelJoint(const b2WheelJointDef* def); void InitVelocityConstraints(const b2SolverData& data); void SolveVelocityConstraints(const b2SolverData& data); bool SolvePositionConstraints(const b2SolverData& data); float32 m_frequencyHz; float32 m_dampingRatio; // Solver shared b2Vec2 m_localAnchorA; b2Vec2 m_localAnchorB; b2Vec2 m_localXAxisA; b2Vec2 m_localYAxisA; float32 m_impulse; float32 m_motorImpulse; float32 m_springImpulse; float32 m_maxMotorTorque; float32 m_motorSpeed; bool m_enableMotor; // Solver temp int32 m_indexA; int32 m_indexB; b2Vec2 m_localCenterA; b2Vec2 m_localCenterB; float32 m_invMassA; float32 m_invMassB; float32 m_invIA; float32 m_invIB; b2Vec2 m_ax, m_ay; float32 m_sAx, m_sBx; float32 m_sAy, m_sBy; float32 m_mass; float32 m_motorMass; float32 m_springMass; float32 m_bias; float32 m_gamma; }; inline float32 b2WheelJoint::GetMotorSpeed() const { return m_motorSpeed; } inline float32 b2WheelJoint::GetMaxMotorTorque() const { return m_maxMotorTorque; } inline void b2WheelJoint::SetSpringFrequencyHz(float32 hz) { m_frequencyHz = hz; } inline float32 b2WheelJoint::GetSpringFrequencyHz() const { return m_frequencyHz; } inline void b2WheelJoint::SetSpringDampingRatio(float32 ratio) { m_dampingRatio = ratio; } inline float32 b2WheelJoint::GetSpringDampingRatio() const { return m_dampingRatio; } #endif