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/*
* Copyright (c) 2006-2007 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_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 bodyA's origin.
b2Vec2 localAnchorA;
/// The local anchor point relative to bodyB's origin.
b2Vec2 localAnchorB;
/// The natural length between the anchor points.
float32 length;
/// The mass-spring-damper frequency in Hertz. A value of 0
/// disables softness.
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 override;
b2Vec2 GetAnchorB() const override;
/// Get the reaction force given the inverse time step.
/// Unit is N.
b2Vec2 GetReactionForce(float32 inv_dt) const override;
/// Get the reaction torque given the inverse time step.
/// Unit is N*m. This is always zero for a distance joint.
float32 GetReactionTorque(float32 inv_dt) const override;
/// 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; }
/// 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;
/// Dump joint to dmLog
void Dump() override;
protected:
friend class b2Joint;
b2DistanceJoint(const b2DistanceJointDef* data);
void InitVelocityConstraints(const b2SolverData& data) override;
void SolveVelocityConstraints(const b2SolverData& data) override;
bool SolvePositionConstraints(const b2SolverData& data) override;
float32 m_frequencyHz;
float32 m_dampingRatio;
float32 m_bias;
// Solver shared
b2Vec2 m_localAnchorA;
b2Vec2 m_localAnchorB;
float32 m_gamma;
float32 m_impulse;
float32 m_length;
// Solver temp
int32 m_indexA;
int32 m_indexB;
b2Vec2 m_u;
b2Vec2 m_rA;
b2Vec2 m_rB;
b2Vec2 m_localCenterA;
b2Vec2 m_localCenterB;
float32 m_invMassA;
float32 m_invMassB;
float32 m_invIA;
float32 m_invIB;
float32 m_mass;
};
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
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