170 lines
4.5 KiB
C++
170 lines
4.5 KiB
C++
/*
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* Copyright (c) 2006-2007 Erin Catto http://www.box2d.org
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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*/
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#ifndef B2_DISTANCE_JOINT_H
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#define B2_DISTANCE_JOINT_H
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#include "Box2D/Dynamics/Joints/b2Joint.h"
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/// Distance joint definition. This requires defining an
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/// anchor point on both bodies and the non-zero length of the
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/// distance joint. The definition uses local anchor points
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/// so that the initial configuration can violate the constraint
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/// slightly. This helps when saving and loading a game.
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/// @warning Do not use a zero or short length.
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struct b2DistanceJointDef : public b2JointDef
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{
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b2DistanceJointDef()
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{
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type = e_distanceJoint;
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localAnchorA.Set(0.0f, 0.0f);
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localAnchorB.Set(0.0f, 0.0f);
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length = 1.0f;
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frequencyHz = 0.0f;
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dampingRatio = 0.0f;
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}
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/// Initialize the bodies, anchors, and length using the world
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/// anchors.
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void Initialize(b2Body* bodyA, b2Body* bodyB,
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const b2Vec2& anchorA, const b2Vec2& anchorB);
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/// The local anchor point relative to bodyA's origin.
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b2Vec2 localAnchorA;
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/// The local anchor point relative to bodyB's origin.
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b2Vec2 localAnchorB;
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/// The natural length between the anchor points.
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float32 length;
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/// The mass-spring-damper frequency in Hertz. A value of 0
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/// disables softness.
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float32 frequencyHz;
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/// The damping ratio. 0 = no damping, 1 = critical damping.
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float32 dampingRatio;
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};
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/// A distance joint constrains two points on two bodies
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/// to remain at a fixed distance from each other. You can view
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/// this as a massless, rigid rod.
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class b2DistanceJoint : public b2Joint
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{
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public:
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b2Vec2 GetAnchorA() const override;
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b2Vec2 GetAnchorB() const override;
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/// Get the reaction force given the inverse time step.
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/// Unit is N.
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b2Vec2 GetReactionForce(float32 inv_dt) const override;
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/// Get the reaction torque given the inverse time step.
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/// Unit is N*m. This is always zero for a distance joint.
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float32 GetReactionTorque(float32 inv_dt) const override;
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/// The local anchor point relative to bodyA's origin.
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const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; }
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/// The local anchor point relative to bodyB's origin.
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const b2Vec2& GetLocalAnchorB() const { return m_localAnchorB; }
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/// Set/get the natural length.
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/// Manipulating the length can lead to non-physical behavior when the frequency is zero.
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void SetLength(float32 length);
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float32 GetLength() const;
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/// Set/get frequency in Hz.
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void SetFrequency(float32 hz);
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float32 GetFrequency() const;
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/// Set/get damping ratio.
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void SetDampingRatio(float32 ratio);
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float32 GetDampingRatio() const;
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/// Dump joint to dmLog
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void Dump() override;
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protected:
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friend class b2Joint;
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b2DistanceJoint(const b2DistanceJointDef* data);
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void InitVelocityConstraints(const b2SolverData& data) override;
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void SolveVelocityConstraints(const b2SolverData& data) override;
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bool SolvePositionConstraints(const b2SolverData& data) override;
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float32 m_frequencyHz;
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float32 m_dampingRatio;
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float32 m_bias;
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// Solver shared
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b2Vec2 m_localAnchorA;
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b2Vec2 m_localAnchorB;
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float32 m_gamma;
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float32 m_impulse;
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float32 m_length;
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// Solver temp
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int32 m_indexA;
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int32 m_indexB;
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b2Vec2 m_u;
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b2Vec2 m_rA;
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b2Vec2 m_rB;
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b2Vec2 m_localCenterA;
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b2Vec2 m_localCenterB;
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float32 m_invMassA;
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float32 m_invMassB;
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float32 m_invIA;
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float32 m_invIB;
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float32 m_mass;
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};
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inline void b2DistanceJoint::SetLength(float32 length)
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{
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m_length = length;
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}
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inline float32 b2DistanceJoint::GetLength() const
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{
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return m_length;
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}
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inline void b2DistanceJoint::SetFrequency(float32 hz)
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{
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m_frequencyHz = hz;
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}
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inline float32 b2DistanceJoint::GetFrequency() const
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{
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return m_frequencyHz;
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}
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inline void b2DistanceJoint::SetDampingRatio(float32 ratio)
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{
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m_dampingRatio = ratio;
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}
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inline float32 b2DistanceJoint::GetDampingRatio() const
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{
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return m_dampingRatio;
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}
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#endif
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