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// MIT License
// Copyright (c) 2019 Erin Catto
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
#ifndef B2_REVOLUTE_JOINT_H
#define B2_REVOLUTE_JOINT_H
#include "b2_api.h"
#include "b2_joint.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 B2_API 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 bodyA's origin.
b2Vec2 localAnchorA;
/// The local anchor point relative to bodyB's origin.
b2Vec2 localAnchorB;
/// The bodyB angle minus bodyA angle in the reference state (radians).
float referenceAngle;
/// A flag to enable joint limits.
bool enableLimit;
/// The lower angle for the joint limit (radians).
float lowerAngle;
/// The upper angle for the joint limit (radians).
float upperAngle;
/// A flag to enable the joint motor.
bool enableMotor;
/// The desired motor speed. Usually in radians per second.
float motorSpeed;
/// The maximum motor torque used to achieve the desired motor speed.
/// Usually in N-m.
float 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 B2_API b2RevoluteJoint : public b2Joint
{
public:
b2Vec2 GetAnchorA() const override;
b2Vec2 GetAnchorB() const override;
/// The local anchor point relative to bodyA's origin.
const b2Vec2& GetLocalAnchorA() const { return m_localAnchorA; }
/// The local anchor point relative to bodyB's origin.
const b2Vec2& GetLocalAnchorB() const { return m_localAnchorB; }
/// Get the reference angle.
float GetReferenceAngle() const { return m_referenceAngle; }
/// Get the current joint angle in radians.
float GetJointAngle() const;
/// Get the current joint angle speed in radians per second.
float 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.
float GetLowerLimit() const;
/// Get the upper joint limit in radians.
float GetUpperLimit() const;
/// Set the joint limits in radians.
void SetLimits(float lower, float 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(float speed);
/// Get the motor speed in radians per second.
float GetMotorSpeed() const;
/// Set the maximum motor torque, usually in N-m.
void SetMaxMotorTorque(float torque);
float GetMaxMotorTorque() const { return m_maxMotorTorque; }
/// Get the reaction force given the inverse time step.
/// Unit is N.
b2Vec2 GetReactionForce(float inv_dt) const override;
/// Get the reaction torque due to the joint limit given the inverse time step.
/// Unit is N*m.
float GetReactionTorque(float inv_dt) const override;
/// Get the current motor torque given the inverse time step.
/// Unit is N*m.
float GetMotorTorque(float inv_dt) const;
/// Dump to b2Log.
void Dump() override;
///
void Draw(b2Draw* draw) const override;
protected:
friend class b2Joint;
friend class b2GearJoint;
b2RevoluteJoint(const b2RevoluteJointDef* def);
void InitVelocityConstraints(const b2SolverData& data) override;
void SolveVelocityConstraints(const b2SolverData& data) override;
bool SolvePositionConstraints(const b2SolverData& data) override;
// Solver shared
b2Vec2 m_localAnchorA;
b2Vec2 m_localAnchorB;
b2Vec2 m_impulse;
float m_motorImpulse;
float m_lowerImpulse;
float m_upperImpulse;
bool m_enableMotor;
float m_maxMotorTorque;
float m_motorSpeed;
bool m_enableLimit;
float m_referenceAngle;
float m_lowerAngle;
float m_upperAngle;
// Solver temp
int32 m_indexA;
int32 m_indexB;
b2Vec2 m_rA;
b2Vec2 m_rB;
b2Vec2 m_localCenterA;
b2Vec2 m_localCenterB;
float m_invMassA;
float m_invMassB;
float m_invIA;
float m_invIB;
b2Mat22 m_K;
float m_angle;
float m_axialMass;
};
inline float b2RevoluteJoint::GetMotorSpeed() const
{
return m_motorSpeed;
}
#endif
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