File indexing completed on 2024-12-29 03:29:28

 /*
 * 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_PULLEY_JOINT_H
 #define B2_PULLEY_JOINT_H
 
 #include <Box2D/Dynamics/Joints/b2Joint.h>
 
 const float32 b2_minPulleyLength = 2.0f;
 
 /// Pulley joint definition. This requires two ground anchors,
 /// two dynamic body anchor points, 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;
         lengthB = 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,
                     float32 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.
     float32 lengthA;
 
     /// The a reference length for the segment attached to bodyB.
     float32 lengthB;
 
     /// The pulley ratio, used to simulate a block-and-tackle.
     float32 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.
 /// Warning: the pulley joint can get a bit squirrelly by itself. They often
 /// work better when combined with prismatic joints. You should also cover the
 /// the anchor points with static shapes to prevent one side from going to
 /// zero length.
 class b2PulleyJoint : public b2Joint
 {
 public:
     b2Vec2 GetAnchorA() const;
     b2Vec2 GetAnchorB() const;
 
     b2Vec2 GetReactionForce(float32 inv_dt) const;
     float32 GetReactionTorque(float32 inv_dt) const;
 
     /// 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 bodyA.
     float32 GetLengthA() const;
 
     /// Get the current length of the segment attached to bodyB.
     float32 GetLengthB() const;
 
     /// Get the pulley ratio.
     float32 GetRatio() const;
 
     /// Get the current length of the segment attached to bodyA.
     float32 GetCurrentLengthA() const;
 
     /// Get the current length of the segment attached to bodyB.
     float32 GetCurrentLengthB() const;
 
     /// Dump joint to dmLog
     void Dump();
 
     /// Implement b2Joint::ShiftOrigin
     void ShiftOrigin(const b2Vec2& newOrigin);
 
 protected:
 
     friend class b2Joint;
     b2PulleyJoint(const b2PulleyJointDef* data);
 
     void InitVelocityConstraints(const b2SolverData& data);
     void SolveVelocityConstraints(const b2SolverData& data);
     bool SolvePositionConstraints(const b2SolverData& data);
 
     b2Vec2 m_groundAnchorA;
     b2Vec2 m_groundAnchorB;
     float32 m_lengthA;
     float32 m_lengthB;
     
     // Solver shared
     b2Vec2 m_localAnchorA;
     b2Vec2 m_localAnchorB;
     float32 m_constant;
     float32 m_ratio;
     float32 m_impulse;
 
     // Solver temp
     int32 m_indexA;
     int32 m_indexB;
     b2Vec2 m_uA;
     b2Vec2 m_uB;
     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;
 };
 
 #endif