File indexing completed on 2025-08-03 03:49:59

 /*
 * 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_PULLEY_JOINT_H
 #define B2_PULLEY_JOINT_H
 
 #include <Box2D/Dynamics/Joints/b2Joint.h>
 
 const qreal b2_minPulleyLength = 2.0f;
 
 /// Pulley joint definition. This requires two ground anchors,
 /// two dynamic body anchor points, max lengths for each side,
 /// and a pulley ratio.
 struct b2PulleyJointDef : public b2JointDef
 {
     b2PulleyJointDef()
     {
         type = e_pulleyJoint;
         groundAnchorA.Set(-1.0f, 1.0f);
         groundAnchorB.Set(1.0f, 1.0f);
         localAnchorA.Set(-1.0f, 0.0f);
         localAnchorB.Set(1.0f, 0.0f);
         lengthA = 0.0f;
         maxLengthA = 0.0f;
         lengthB = 0.0f;
         maxLengthB = 0.0f;
         ratio = 1.0f;
         collideConnected = true;
     }
 
     /// Initialize the bodies, anchors, lengths, max lengths, and ratio using the world anchors.
     void Initialize(b2Body* bodyA, b2Body* bodyB,
                     const b2Vec2& groundAnchorA, const b2Vec2& groundAnchorB,
                     const b2Vec2& anchorA, const b2Vec2& anchorB,
                     qreal ratio);
 
     /// The first ground anchor in world coordinates. This point never moves.
     b2Vec2 groundAnchorA;
 
     /// The second ground anchor in world coordinates. This point never moves.
     b2Vec2 groundAnchorB;
 
     /// The local anchor point relative to bodyA's origin.
     b2Vec2 localAnchorA;
 
     /// The local anchor point relative to bodyB's origin.
     b2Vec2 localAnchorB;
 
     /// The a reference length for the segment attached to bodyA.
     qreal lengthA;
 
     /// The maximum length of the segment attached to bodyA.
     qreal maxLengthA;
 
     /// The a reference length for the segment attached to bodyB.
     qreal lengthB;
 
     /// The maximum length of the segment attached to bodyB.
     qreal maxLengthB;
 
     /// The pulley ratio, used to simulate a block-and-tackle.
     qreal ratio;
 };
 
 /// The pulley joint is connected to two bodies and two fixed ground points.
 /// The pulley supports a ratio such that:
 /// length1 + ratio * length2 <= constant
 /// Yes, the force transmitted is scaled by the ratio.
 /// The pulley also enforces a maximum length limit on both sides. This is
 /// useful to prevent one side of the pulley hitting the top.
 class b2PulleyJoint : public b2Joint
 {
 public:
     b2Vec2 GetAnchorA() const override;
     b2Vec2 GetAnchorB() const override;
 
     b2Vec2 GetReactionForce(qreal inv_dt) const override;
     qreal GetReactionTorque(qreal inv_dt) const override;
 
     /// Get the first ground anchor.
     b2Vec2 GetGroundAnchorA() const;
 
     /// Get the second ground anchor.
     b2Vec2 GetGroundAnchorB() const;
 
     /// Get the current length of the segment attached to body1.
     qreal GetLength1() const;
 
     /// Get the current length of the segment attached to body2.
     qreal GetLength2() const;
 
     /// Get the pulley ratio.
     qreal GetRatio() const;
 
 protected:
 
     friend class b2Joint;
     b2PulleyJoint(const b2PulleyJointDef* data);
 
     void InitVelocityConstraints(const b2TimeStep& step) override;
     void SolveVelocityConstraints(const b2TimeStep& step) override;
     bool SolvePositionConstraints(qreal baumgarte) override;
 
     b2Vec2 m_groundAnchor1;
     b2Vec2 m_groundAnchor2;
     b2Vec2 m_localAnchor1;
     b2Vec2 m_localAnchor2;
 
     b2Vec2 m_u1;
     b2Vec2 m_u2;
     
     qreal m_constant;
     qreal m_ratio;
     
     qreal m_maxLength1;
     qreal m_maxLength2;
 
     // Effective masses
     qreal m_pulleyMass;
     qreal m_limitMass1;
     qreal m_limitMass2;
 
     // Impulses for accumulation/warm starting.
     qreal m_impulse;
     qreal m_limitImpulse1;
     qreal m_limitImpulse2;
 
     b2LimitState m_state;
     b2LimitState m_limitState1;
     b2LimitState m_limitState2;
 };
 
 #endif