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// CLASS CONSTRUCTOR
/**
* Friction joint. This is used for top-down friction. It
* provides 2D translational friction and angular friction.
*
* @class b2FrictionJoint
* @constructor
* @param {b2FrictionJointDef} frictionJointDef
* @extends {b2Joint}
* @module Joints
*/
//TODO: test b2FrictionJoint. Ported but not yet tested.
function b2FrictionJoint( frictionJointDef ) {
/**
* Invokes parent class constructor function reference.
*/
this.constructor( frictionJointDef );
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////////////////////////////////////////////////////////////////////////////////////////////////////
// property DECLARATIONS
/**
* @public
* @property m_localAnchorA
* @type {b2Vec2}
*/
this.m_localAnchorA = new b2Vec2;
/**
* @public
* @property m_localAnchorB
* @type {b2Vec2}
*/
this.m_localAnchorB = new b2Vec2;
/**
* @public
* @property m_linearImpulse
* @type {b2Vec2}
*/
this.m_linearImpulse = new b2Vec2;
/**
*
* @public
* @property m_linearMass
* @type {b2Mat22}
*/
this.m_linearMass = new b2Mat22;
/**
* @public
* @property m_rA
* @type {b2Vec2}
*/
this.m_rA = new b2Vec2;
/**
* @public
* @property m_rB
* @type {b2Vec2}
*/
this.m_rB = new b2Vec2;
/**
* @public
* @property m_localCenterA
* @type {b2Vec2}
*/
this.m_localCenterA = new b2Vec2;
/**
* @public
* @property m_localCenterB
* @type {b2Vec2}
*/
this.m_localCenterB = new b2Vec2;
/**
* @public
* @property m_qA
* @type {b2Rot}
*/
this.m_qA = new b2Rot;
/**
* @public
* @property m_qB
* @type {b2Rot}
*/
this.m_qB = new b2Rot;
/**
* @public
* @property m_lalcA
* @type {b2Vec2}
*/
this.m_lalcA = new b2Vec2;
/**
* @public
* @property m_lalcB
* @type {b2Vec2}
*/
this.m_lalcB = new b2Vec2;
/**
* @public
* @property m_K
* @type {b2Mat22}
*/
this.m_K = new b2Mat22;
// property INITIALISATIONS
this.m_localAnchorA.copy( frictionJointDef.localAnchorA );
this.m_localAnchorB.copy( frictionJointDef.localAnchorB );
this.m_linearMass.setZero();
this.m_linearImpulse.setZero();
/**
* @public
* @property m_maxForce
* @type {float}
*/
this.m_maxForce = frictionJointDef.maxForce;
/**
* @public
* @property m_maxTorque
* @type {float}
*/
this.m_maxTorque = frictionJointDef.maxTorque;
/**
*
* @public
* @property m_angularMass
* @type {number}
* @default 0
*/
this.m_angularMass = 0.0;
/**
* @public
* @property m_angularImpulse
* @type {float}
* @default 0.0
*/
this.m_angularImpulse = 0.0;
// Solver temp
/**
* @public
* @property m_indexA
* @type {int}
* @default 0
*/
this.m_indexA = 0;
/**
* @public
* @property m_indexB
* @type {int}
* @default 0
*/
this.m_indexB = 0;
/**
* @public
* @property m_invMassA
* @type {float}
* @default 0.0
*/
this.m_invMassA = 0.0;
/**
* @public
* @property m_invMassB
* @type {float}
* @default 0.0
*/
this.m_invMassB = 0.0;
/**
* @public
* @property m_invIA
* @type {float}
* @default 0.0
*/
this.m_invIA = 0.0;
/**
* @public
* @property m_invIB
* @type {float}
* @default 0.0
*/
this.m_invIB = 0.0;
////////////////////////////////////////////////////////////////////////////////////////////////////
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////////////////////////////////////////////////////////////////////////////////////////////////////
} b2FrictionJoint.prototype = p = new b2Joint(); Box2D.b2FrictionJoint = b2FrictionJoint;
// STATIC CLASS PROPERTIES
/**
* Object pool for memory management.
*/
b2FrictionJoint._B2VEC2_POOL0 = new b2Vec2;
b2FrictionJoint._B2VEC2_POOL1 = new b2Vec2;
b2FrictionJoint._B2VEC2_POOL2 = new b2Vec2;
////////////////////////////////////////////////////////////////////////////////////////////////////
// //
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////////////////////////////////////////////////////////////////////////////////////////////////////
// INSTANCE METHODS
/**
* @public
* @override
* @method solvePositionConstraints
* @param {b2SolverData} data
* @return {void}
*/
// Implement b2Joint.solvePositionConstraints
p.solvePositionConstraints = function ( data ) {
return true;
};
/**
* @public
* @method getAnchorA
* @param {b2Vec2|Object=} [out=b2Vec2] reusable object
* @return {b2Vec2|Object} out
*/
p.getAnchorA = function ( out ) {
out = out || b2FrictionJoint._B2VEC2_POOL0;
return this.m_bodyA.getWorldPoint( this.m_localAnchorA, out );
};
/**
* @public
* @method getAnchorB
* @param {b2Vec2|Object=} [out=b2Vec2] reusable object
* @return {b2Vec2|Object} out
*/
p.getAnchorB = function ( out ) {
out = out || b2FrictionJoint._B2VEC2_POOL0;
return this.m_bodyB.getWorldPoint( this.m_localAnchorB, out );
};
/**
* Get the reaction force given the inverse time step.
* Unit is N.
*
* @public
* @method getReactionForce
* @param {float} invDeltaTime
* @param {b2Vec2|Object=} [out=b2Vec2] reusable object
* @return {b2Vec2|Object} out
*/
p.getReactionForce = function ( invDeltaTime, out ) {
out = out || b2FrictionJoint._B2VEC2_POOL0;
return out.set( invDeltaTime * this.m_linearImpulse.x, invDeltaTime * this.m_linearImpulse.y );
};
/**
* Get the reaction torque given the inverse time step.
* Unit is N*m. This is always zero for a distance joint.
*
* @public
* @method getReactionTorque
* @param {float} invDeltaTime
* @return {float}
*/
p.getReactionTorque = function ( invDeltaTime ) {
return invDeltaTime * this.m_angularImpulse;
};
/**
* The local anchor point relative to bodyA's origin.
*
* @public
* @method getLocalAnchorA
* @param {b2Vec2|Object=} [out=b2Vec2] reusable object
* @return {b2Vec2|Object} out
*/
p.getLocalAnchorA = function ( out ) {
out = out || b2FrictionJoint._B2VEC2_POOL0;
return out.copy( this.m_localAnchorA );
};
/**
* The local anchor point relative to bodyB's origin.
*
* @public
* @method getLocalAnchorB
* @param {b2Vec2|Object=} [out=b2Vec2] reusable object
* @return {b2Vec2|Object} out
*/
p.getLocalAnchorB = function ( out ) {
out = out || b2FrictionJoint._B2VEC2_POOL0;
return out.copy( this.m_localAnchorB );
};
/**
* Set the maximum friction force in N.
*
* @public
* @method setMaxForce
* @param {float} force
* @return {void}
*/
p.setMaxForce = function ( force ) {
this.m_maxForce = force;
};
/**
* Get the maximum friction force in N.
*
* @public
* @method getMaxForce
* @return {float}
*/
p.getMaxForce = function () {
return this.m_maxForce;
};
/**
* Set the maximum friction torque in N*m.
*
* @public
* @method setMaxTorque
* @param {float} torque
* @return {void}
*/
p.setMaxTorque = function ( torque ) {
this.m_maxTorque = torque;
};
/**
* Get the maximum friction torque in N*m.
*
* @public
* @method getMaxTorque
* @return {float}
*/
p.getMaxTorque = function () {
return this.m_maxTorque;
};
/**
* @public
* @override
* @method initVelocityConstraints
* @param {b2SolverData} data
* @return {void}
*/
// Implement b2Joint.initVelocityConstraints
p.initVelocityConstraints = function ( data ) {
this.m_indexA = this.m_bodyA.m_islandIndex;
this.m_indexB = this.m_bodyB.m_islandIndex;
this.m_localCenterA.copy( this.m_bodyA.m_sweep.localCenter );
this.m_localCenterB.copy( this.m_bodyB.m_sweep.localCenter );
this.m_invMassA = this.m_bodyA.m_invMass;
this.m_invMassB = this.m_bodyB.m_invMass;
this.m_invIA = this.m_bodyA.m_invI;
this.m_invIB = this.m_bodyB.m_invI;
// /*b2Vec2&*/ var cA = data.positions[this.m_indexA].c;
/**float32*/var aA = data.positions[this.m_indexA].a;
/**b2Vec2&*/var vA = data.velocities[this.m_indexA].v;
/**float32*/var wA = data.velocities[this.m_indexA].w;
// /*b2Vec2&*/ var cB = data.positions[this.m_indexB].c;
/**float32*/var aB = data.positions[this.m_indexB].a;
/**b2Vec2&*/var vB = data.velocities[this.m_indexB].v;
/**float32*/var wB = data.velocities[this.m_indexB].w;
// /*b2Rot*/ var qA = new b2Rot(aA), /*b2Rot*/ qB = new b2Rot(aB);
var qA = this.m_qA.setAngle( aA ), qB = this.m_qB.setAngle( aB );
// Compute the effective mass matrix.
// m_rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
b2Vec2.subtract( this.m_localAnchorA, this.m_localCenterA, this.m_lalcA );
var rA = b2Rot.timesV2( qA, this.m_lalcA, this.m_rA );
// m_rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
b2Vec2.subtract( this.m_localAnchorB, this.m_localCenterB, this.m_lalcB );
var rB = b2Rot.timesV2( qB, this.m_lalcB, this.m_rB );
// J = [-I -r1_skew I r2_skew]
// [ 0 -1 0 1]
// r_skew = [-ry; rx]
// Matlab
// K = [ mA+r1y^2*iA+mB+r2y^2*iB, -r1y*iA*r1x-r2y*iB*r2x, -r1y*iA-r2y*iB]
// [ -r1y*iA*r1x-r2y*iB*r2x, mA+r1x^2*iA+mB+r2x^2*iB, r1x*iA+r2x*iB]
// [ -r1y*iA-r2y*iB, r1x*iA+r2x*iB, iA+iB]
/*float32*/var mA = this.m_invMassA, mB = this.m_invMassB;
/*float32*/var iA = this.m_invIA, iB = this.m_invIB;
/*b2Mat22*/var K = this.m_K; //new b2Mat22();
K.ex.x = mA + mB + iA * rA.y * rA.y + iB * rB.y * rB.y;
K.ex.y = -iA * rA.x * rA.y - iB * rB.x * rB.y;
K.ey.x = K.ex.y;
K.ey.y = mA + mB + iA * rA.x * rA.x + iB * rB.x * rB.x;
K.getInverse( this.m_linearMass );
this.m_angularMass = iA + iB;
if ( this.m_angularMass > 0 ) {
this.m_angularMass = 1 / this.m_angularMass;
}
if ( data.step.warmStarting ) {
// Scale impulses to support a variable time step.
// m_linearImpulse *= data.step.dtRatio;
this.m_linearImpulse.times( data.step.dtRatio );
this.m_angularImpulse *= data.step.dtRatio;
// /*b2Vec2*/ var P(m_linearImpulse.x, m_linearImpulse.y);
/*b2Vec2*/
var P = this.m_linearImpulse;
// vA -= mA * P;
vA.minusEqualsMul( mA, P );
// wA -= iA * (b2Cross(m_rA, P) + m_angularImpulse);
wA -= iA * (b2Vec2.cross( this.m_rA, P ) + this.m_angularImpulse);
// vB += mB * P;
vB.plusEqualsMul( mB, P );
// wB += iB * (b2Cross(m_rB, P) + m_angularImpulse);
wB += iB * (b2Vec2.cross( this.m_rB, P ) + this.m_angularImpulse);
}
else {
this.m_linearImpulse.setZero();
this.m_angularImpulse = 0;
}
// data.velocities[this.m_indexA].v = vA;
data.velocities[this.m_indexA].w = wA;
// data.velocities[this.m_indexB].v = vB;
data.velocities[this.m_indexB].w = wB;
};
/**
*
* @public
* @override
* @method solveVelocityConstraints
* @param {b2SolverData} data
* @return {void}
*/
// Implement b2Joint.solveVelocityConstraints
p.solveVelocityConstraints = function ( data ) {
/*b2Vec2&*/var vA = data.velocities[this.m_indexA].v;
/*float32*/var wA = data.velocities[this.m_indexA].w;
/*b2Vec2&*/var vB = data.velocities[this.m_indexB].v;
/*float32*/var wB = data.velocities[this.m_indexB].w;
/*float32*/var mA = this.m_invMassA, mB = this.m_invMassB;
/*float32*/var iA = this.m_invIA, iB = this.m_invIB;
/**float32*/var h = data.step.dt;
// Solve angular friction
{
/**float32*/var Cdot = wB - wA;
/**float32*/var impulse = (-this.m_angularMass * Cdot);
/**float32*/var oldImpulse = this.m_angularImpulse;
/**float32*/var maxImpulse = h * this.m_maxTorque;
this.m_angularImpulse = b2Math.clamp( this.m_angularImpulse + impulse, (-maxImpulse), maxImpulse );
impulse = this.m_angularImpulse - oldImpulse;
wA -= iA * impulse;
wB += iB * impulse;
}
// Solve linear friction
{
// b2Vec2 Cdot = vB + b2Cross(wB, m_rB) - vA - b2Cross(wA, m_rA);
Cdot = b2Vec2.subtract(
b2Vec2.vPlusCrossFV( vB, wB, this.m_rB, b2Vec2.POOL0 ),
b2Vec2.vPlusCrossFV( vA, wA, this.m_rA, b2Vec2.POOL1 ),
b2FrictionJoint._B2VEC2_POOL0 );
// b2Vec2 impulse = -b2Mul(m_linearMass, Cdot);
var impulseV = b2Mat22.timesV2( this.m_linearMass, Cdot, b2FrictionJoint._B2VEC2_POOL1 ).negative();
// b2Vec2 oldImpulse = m_linearImpulse;
var oldImpulseV = b2FrictionJoint._B2VEC2_POOL3.copy( this.m_linearImpulse );
// m_linearImpulse += impulse;
this.m_linearImpulse.plus( impulseV );
maxImpulse = h * this.m_maxForce;
if ( this.m_linearImpulse.lengthSquared() > maxImpulse * maxImpulse ) {
this.m_linearImpulse.norm();
this.m_linearImpulse.times( maxImpulse );
}
// impulse = m_linearImpulse - oldImpulse;
b2Vec2.subtract( this.m_linearImpulse, oldImpulseV, impulseV );
// vA -= mA * impulse;
vA.minusEqualsMul( mA, impulseV );
// wA -= iA * b2Cross(m_rA, impulse);
wA -= iA * b2Vec2.cross( this.m_rA, impulseV );
// vB += mB * impulse;
vB.plusEqualsMul( mB, impulseV );
// wB += iB * b2Cross(m_rB, impulse);
wB += iB * b2Vec2.cross( this.m_rB, impulseV );
}
// data.velocities[this.m_indexA].v = vA;
data.velocities[this.m_indexA].w = wA;
// data.velocities[this.m_indexB].v = vB;
data.velocities[this.m_indexB].w = wB;
};
