b2RevoluteJoint.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_REVOLUTE_JOINT_H
- #define B2_REVOLUTE_JOINT_H
- #include <Box2D/Dynamics/Joints/b2Joint.h>
- /// Revolute joint definition. This requires defining an
- /// anchor point where the bodies are joined. The definition
- /// uses local anchor points so that the initial configuration
- /// can violate the constraint slightly. You also need to
- /// specify the initial relative angle for joint limits. This
- /// helps when saving and loading a game.
- /// The local anchor points are measured from the body's origin
- /// rather than the center of mass because:
- /// 1. you might not know where the center of mass will be.
- /// 2. if you add/remove shapes from a body and recompute the mass,
- /// the joints will be broken.
- struct b2RevoluteJointDef : public b2JointDef
- {
- b2RevoluteJointDef()
- {
- type = e_revoluteJoint;
- localAnchorA.Set(0.0f, 0.0f);
- localAnchorB.Set(0.0f, 0.0f);
- referenceAngle = 0.0f;
- lowerAngle = 0.0f;
- upperAngle = 0.0f;
- maxMotorTorque = 0.0f;
- motorSpeed = 0.0f;
- enableLimit = false;
- enableMotor = false;
- }
- /// Initialize the bodies, anchors, and reference angle using a world
- /// anchor point.
- void Initialize(b2Body* bodyA, b2Body* bodyB, const b2Vec2& anchor);
- /// The local anchor point relative to body1's origin.
- b2Vec2 localAnchorA;
- /// The local anchor point relative to body2's origin.
- b2Vec2 localAnchorB;
- /// The body2 angle minus body1 angle in the reference state (radians).
- float32 referenceAngle;
- /// A flag to enable joint limits.
- bool enableLimit;
- /// The lower angle for the joint limit (radians).
- float32 lowerAngle;
- /// The upper angle for the joint limit (radians).
- float32 upperAngle;
- /// A flag to enable the joint motor.
- bool enableMotor;
- /// The desired motor speed. Usually in radians per second.
- float32 motorSpeed;
- /// The maximum motor torque used to achieve the desired motor speed.
- /// Usually in N-m.
- float32 maxMotorTorque;
- };
- /// A revolute joint constrains two bodies to share a common point while they
- /// are free to rotate about the point. The relative rotation about the shared
- /// point is the joint angle. You can limit the relative rotation with
- /// a joint limit that specifies a lower and upper angle. You can use a motor
- /// to drive the relative rotation about the shared point. A maximum motor torque
- /// is provided so that infinite forces are not generated.
- class b2RevoluteJoint : public b2Joint
- {
- public:
- b2Vec2 GetAnchorA() const;
- b2Vec2 GetAnchorB() const;
- b2Vec2 GetReactionForce(float32 inv_dt) const;
- float32 GetReactionTorque(float32 inv_dt) const;
- /// Get the current joint angle in radians.
- float32 GetJointAngle() const;
- /// Get the current joint angle speed in radians per second.
- float32 GetJointSpeed() const;
- /// Is the joint limit enabled?
- bool IsLimitEnabled() const;
- /// Enable/disable the joint limit.
- void EnableLimit(bool flag);
- /// Get the lower joint limit in radians.
- float32 GetLowerLimit() const;
- /// Get the upper joint limit in radians.
- float32 GetUpperLimit() const;
- /// Set the joint limits in radians.
- void SetLimits(float32 lower, float32 upper);
- /// Is the joint motor enabled?
- bool IsMotorEnabled() const;
- /// Enable/disable the joint motor.
- void EnableMotor(bool flag);
- /// Set the motor speed in radians per second.
- void SetMotorSpeed(float32 speed);
- /// Get the motor speed in radians per second.
- float32 GetMotorSpeed() const;
- /// Set the maximum motor torque, usually in N-m.
- void SetMaxMotorTorque(float32 torque);
- /// Get the current motor torque, usually in N-m.
- float32 GetMotorTorque() const;
- protected:
-
- friend class b2Joint;
- friend class b2GearJoint;
- b2RevoluteJoint(const b2RevoluteJointDef* def);
- void InitVelocityConstraints(const b2TimeStep& step);
- void SolveVelocityConstraints(const b2TimeStep& step);
- bool SolvePositionConstraints(float32 baumgarte);
- b2Vec2 m_localAnchor1; // relative
- b2Vec2 m_localAnchor2;
- b2Vec3 m_impulse;
- float32 m_motorImpulse;
- b2Mat33 m_mass; // effective mass for point-to-point constraint.
- float32 m_motorMass; // effective mass for motor/limit angular constraint.
-
- bool m_enableMotor;
- float32 m_maxMotorTorque;
- float32 m_motorSpeed;
- bool m_enableLimit;
- float32 m_referenceAngle;
- float32 m_lowerAngle;
- float32 m_upperAngle;
- b2LimitState m_limitState;
- };
- inline float32 b2RevoluteJoint::GetMotorSpeed() const
- {
- return m_motorSpeed;
- }
- #endif