File indexing completed on 2025-08-03 03:49:58

 /*
 * 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.
     qreal length;
 
     /// The mass-spring-damper frequency in Hertz.
     qreal frequencyHz;
 
     /// The damping ratio. 0 = no damping, 1 = critical damping.
     qreal 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(qreal 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.
     qreal GetReactionTorque(qreal inv_dt) const override;
 
     /// Set/get the natural length.
     /// Manipulating the length can lead to non-physical behavior when the frequency is zero.
     void SetLength(qreal length);
     qreal GetLength() const;
 
     // Set/get frequency in Hz.
     void SetFrequency(qreal hz);
     qreal GetFrequency() const;
 
     // Set/get damping ratio.
     void SetDampingRatio(qreal ratio);
     qreal GetDampingRatio() const;
 
 protected:
 
     friend class b2Joint;
     b2DistanceJoint(const b2DistanceJointDef* data);
 
     void InitVelocityConstraints(const b2TimeStep& step) override;
     void SolveVelocityConstraints(const b2TimeStep& step) override;
     bool SolvePositionConstraints(qreal baumgarte) override;
 
     b2Vec2 m_localAnchor1;
     b2Vec2 m_localAnchor2;
     b2Vec2 m_u;
     qreal m_frequencyHz;
     qreal m_dampingRatio;
     qreal m_gamma;
     qreal m_bias;
     qreal m_impulse;
     qreal m_mass;
     qreal m_length;
 };
 
 inline void b2DistanceJoint::SetLength(qreal length)
 {
     m_length = length;
 }
 
 inline qreal b2DistanceJoint::GetLength() const
 {
     return m_length;
 }
 
 inline void b2DistanceJoint::SetFrequency(qreal hz)
 {
     m_frequencyHz = hz;
 }
 
 inline qreal b2DistanceJoint::GetFrequency() const
 {
     return m_frequencyHz;
 }
 
 inline void b2DistanceJoint::SetDampingRatio(qreal ratio)
 {
     m_dampingRatio = ratio;
 }
 
 inline qreal b2DistanceJoint::GetDampingRatio() const
 {
     return m_dampingRatio;
 }
 
 #endif