b2PulleyJoint.h
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上传日期:2022-01-07
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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 <Box2D/Dynamics/Joints/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;
- 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,
- 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 maximum length of the segment attached to bodyA.
- float32 maxLengthA;
- /// The a reference length for the segment attached to bodyB.
- float32 lengthB;
- /// The maximum length of the segment attached to bodyB.
- float32 maxLengthB;
- /// 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 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 body1.
- float32 GetLength1() const;
- /// Get the current length of the segment attached to body2.
- float32 GetLength2() const;
- /// Get the pulley ratio.
- float32 GetRatio() const;
- protected:
- friend class b2Joint;
- b2PulleyJoint(const b2PulleyJointDef* data);
- void InitVelocityConstraints(const b2TimeStep& step);
- void SolveVelocityConstraints(const b2TimeStep& step);
- bool SolvePositionConstraints(float32 baumgarte);
- 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_impulse;
- float32 m_limitImpulse1;
- float32 m_limitImpulse2;
- b2LimitState m_state;
- b2LimitState m_limitState1;
- b2LimitState m_limitState2;
- };
- #endif