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[blok] / Box2D / Source / Dynamics / Joints / b2PulleyJoint.h

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+/*
+* 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 "b2Joint.h"
+
+const float32 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;
+               groundAnchor1.Set(-1.0f, 1.0f);
+               groundAnchor2.Set(1.0f, 1.0f);
+               localAnchor1.Set(-1.0f, 0.0f);
+               localAnchor2.Set(1.0f, 0.0f);
+               length1 = 0.0f;
+               maxLength1 = 0.0f;
+               length2 = 0.0f;
+               maxLength2 = 0.0f;
+               ratio = 1.0f;
+               collideConnected = true;
+       }
+
+       /// Initialize the bodies, anchors, lengths, max lengths, and ratio using the world anchors.
+       void Initialize(b2Body* body1, b2Body* body2,
+                                       const b2Vec2& groundAnchor1, const b2Vec2& groundAnchor2,
+                                       const b2Vec2& anchor1, const b2Vec2& anchor2,
+                                       float32 ratio);
+
+       /// The first ground anchor in world coordinates. This point never moves.
+       b2Vec2 groundAnchor1;
+
+       /// The second ground anchor in world coordinates. This point never moves.
+       b2Vec2 groundAnchor2;
+
+       /// The local anchor point relative to body1's origin.
+       b2Vec2 localAnchor1;
+
+       /// The local anchor point relative to body2's origin.
+       b2Vec2 localAnchor2;
+
+       /// The a reference length for the segment attached to body1.
+       float32 length1;
+
+       /// The maximum length of the segment attached to body1.
+       float32 maxLength1;
+
+       /// The a reference length for the segment attached to body2.
+       float32 length2;
+
+       /// The maximum length of the segment attached to body2.
+       float32 maxLength2;
+
+       /// 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.
+/// 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 GetAnchor1() const;
+       b2Vec2 GetAnchor2() const;
+
+       b2Vec2 GetReactionForce() const;
+       float32 GetReactionTorque() const;
+
+       /// Get the first ground anchor.
+       b2Vec2 GetGroundAnchor1() const;
+
+       /// Get the second ground anchor.
+       b2Vec2 GetGroundAnchor2() const;
+
+       /// Get the current length of the segment attached to body1.
+       float32 GetLength1() const;
+
+       /// Get the current length of the segment attached to body2.
+       float32 GetLength2() const;
+
+       /// Get the pulley ratio.
+       float32 GetRatio() const;
+
+       //--------------- Internals Below -------------------
+
+       b2PulleyJoint(const b2PulleyJointDef* data);
+
+       void InitVelocityConstraints(const b2TimeStep& step);
+       void SolveVelocityConstraints(const b2TimeStep& step);
+       bool SolvePositionConstraints();
+
+       b2Body* m_ground;
+       b2Vec2 m_groundAnchor1;
+       b2Vec2 m_groundAnchor2;
+       b2Vec2 m_localAnchor1;
+       b2Vec2 m_localAnchor2;
+
+       b2Vec2 m_u1;
+       b2Vec2 m_u2;
+       
+       float32 m_constant;
+       float32 m_ratio;
+       
+       float32 m_maxLength1;
+       float32 m_maxLength2;
+
+       // Effective masses
+       float32 m_pulleyMass;
+       float32 m_limitMass1;
+       float32 m_limitMass2;
+
+       // Impulses for accumulation/warm starting.
+       float32 m_force;
+       float32 m_limitForce1;
+       float32 m_limitForce2;
+
+       // Position impulses for accumulation.
+       float32 m_positionImpulse;
+       float32 m_limitPositionImpulse1;
+       float32 m_limitPositionImpulse2;
+
+       b2LimitState m_state;
+       b2LimitState m_limitState1;
+       b2LimitState m_limitState2;
+};
+
+#endif