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// CLASS CONSTRUCTOR
/**
* A distance joint constrains two points on two bodies to
* remain at a fixed distance from each other. You can view this
* as a massless, rigid rod.
*
* @class b2DistanceJoint
* @constructor
* @extends {b2Joint}
* @param {B2DistanceJointDef} distanceJointDef
* @module Joints
*/
function b2DistanceJoint( distanceJointDef ) {
/**
* Invokes parent class constructor function reference.
*/
this.constructor( distanceJointDef );
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////////////////////////////////////////////////////////////////////////////////////////////////////
// property DECLARATIONS
/**
* @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_localAnchorA
* @type {b2Vec2}
*/
this.m_localAnchorA = new b2Vec2;
/**
* @public
* @property m_localAnchorB
* @type {b2Vec2}
*/
this.m_localAnchorB = new b2Vec2;
/**
*
* @public
* @property m_u
* @type {b2Vec2}
*/
this.m_u = new b2Vec2;
/**
*
* @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_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;
// property INITIALISATIONS
this.m_localAnchorA.copy( distanceJointDef.localAnchorA );
this.m_localAnchorB.copy( distanceJointDef.localAnchorB );
/**
*
* @public
* @property m_length
* @type {float}
*/
this.m_length = distanceJointDef.length;
/**
*
* @public
* @property m_frequencyHz
* @type {float}
*/
this.m_frequencyHz = distanceJointDef.frequencyHz;
/**
*
* @public
* @property m_dampingRatio
* @type {float}
*/
this.m_dampingRatio = distanceJointDef.dampingRatio;
/**
*
* @public
* @property m_impulse
* @type {number}
* @default 0.0
*/
this.m_impulse = 0.0;
/**
*
* @public
* @property m_gamma
* @type {number}
* @default 0.0
*/
this.m_gamma = 0.0;
/**
*
* @public
* @property m_bias
* @type {float}
* @default 0.0
*/
this.m_bias = 0.0;
/**
*
* @public
* @property m_indexA
* @type {float}
* @default 0.0
*/
this.m_indexA = 0.0;
/**
*
* @public
* @property m_indexB
* @type {float}
* @default 0.0
*/
this.m_indexB = 0.0;
/**
* @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;
/**
* @public
* @property m_mass
* @type {float}
* @default 0.0
*/
this.m_mass = 0.0;
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////////////////////////////////////////////////////////////////////////////////////////////////////
} b2DistanceJoint.prototype = p = new b2Joint(); Box2D.b2DistanceJoint = b2DistanceJoint;
// STATIC CLASS PROPERTIES
/**
* Object pool for memory management.
*/
b2DistanceJoint._B2VEC2_POOL0 = new b2Vec2;
b2DistanceJoint._B2VEC2_POOL1 = new b2Vec2;
b2DistanceJoint._B2VEC2_POOL2 = new b2Vec2;
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////////////////////////////////////////////////////////////////////////////////////////////////////
// INSTANCE METHODS
/**
* @public
* @method getAnchorA
* @param {b2Vec2|Object=} [out=b2Vec2] reusable object
* @return {b2Vec2|Object} out
*/
p.getAnchorA = function ( out ) {
out = out || b2DistanceJoint._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 || b2DistanceJoint._B2VEC2_POOL0;
return this.m_bodyB.getWorldPoint( this.m_localAnchorB, out );
};
/**
* 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 || b2DistanceJoint._B2VEC2_POOL0;
return out.copy( this.m_localAnchorA );
};
/**
* The local anchor point relative to bodyA's origin.
*
* @public
* @method getLocalAnchorB
* @param {b2Vec2|Object=} [out=b2Vec2] reusable object
* @return {b2Vec2|Object} out
*/
p.getLocalAnchorB = function ( out ) {
out = out || b2DistanceJoint._B2VEC2_POOL0;
return out.copy( this.m_localAnchorA );
};
/**
* 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 || b2DistanceJoint._B2VEC2_POOL0;
return out.set( invDeltaTime * this.m_impulse * this.m_u.x, invDeltaTime * this.m_impulse * this.m_u.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 0.0;
};
/**
* @public
* @method getLength
* @return {float}
*/
p.getLength = function () {
return this.m_length;
};
/**
* @public
* @method setLength
* @return {void}
*/
p.setLength = function ( length ) {
length = length || 0;
this.m_length = length;
};
/**
* Get frequency in Hz.
*
* @public
* @method getFrequency
* @return {float}
*/
p.getFrequency = function () {
return this.m_frequencyHz;
};
/**
* Set frequency in Hz.
*
* @public
* @method setFrequency
* @param {float} hz
* @return {void}
*/
p.setFrequency = function ( hz ) {
hz = hz || 0.0;
this.m_frequencyHz = hz;
};
/**
* Get damping ratio.
*
* @public
* @method getDampingRatio
* @return {float}
*/
p.getDampingRatio = function () {
return this.m_dampingRatio;
};
/**
* Set damping ratio.
*
* @public
* @method setDampingRatio
* @return {float}
*/
p.setDampingRatio = function ( ratio ) {
ratio = ratio || 0;
this.m_dampingRatio = ratio;
};
/**
* @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;
// var qA = new b2Rot(aA), qB = new b2Rot(aB);
var qA = this.m_qA.setAngle( aA ), qB = this.m_qB.setAngle( aB );
// m_rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
b2Vec2.subtract( this.m_localAnchorA, this.m_localCenterA, this.m_lalcA );
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 );
b2Rot.timesV2( qB, this.m_lalcB, this.m_rB );
// m_u = cB + m_rB - cA - m_rA;
this.m_u.x = cB.x + this.m_rB.x - cA.x - this.m_rA.x;
this.m_u.y = cB.y + this.m_rB.y - cA.y - this.m_rA.y;
// Handle singularity.
var length = this.m_u.length();
if ( length > b2Settings.b2_linearSlop ) {
this.m_u.times( 1 / length );
}
else {
this.m_u.setZero();
}
// float32 crAu = b2Cross(m_rA, m_u);
var crAu = b2Vec2.cross( this.m_rA, this.m_u );
// float32 crBu = b2Cross(m_rB, m_u);
var crBu = b2Vec2.cross( this.m_rB, this.m_u );
// float32 invMass = m_invMassA + m_invIA * crAu * crAu + m_invMassB + m_invIB * crBu * crBu;
var invMass = this.m_invMassA + this.m_invIA * crAu * crAu + this.m_invMassB + this.m_invIB * crBu * crBu;
// Compute the effective mass matrix.
this.m_mass = invMass !== 0 ? 1 / invMass : 0;
if ( this.m_frequencyHz > 0 ) {
var C = length - this.m_length;
// Frequency
var omega = 2 * Math.PI * this.m_frequencyHz;
// Damping coefficient
var d = 2 * this.m_mass * this.m_dampingRatio * omega;
// Spring stiffness
var k = this.m_mass * omega * omega;
// magic formulas
/*float32*/var h = data.step.dt;
this.m_gamma = h * (d + h * k);
this.m_gamma = this.m_gamma !== 0 ? 1 / this.m_gamma : 0;
this.m_bias = C * h * k * this.m_gamma;
invMass += this.m_gamma;
this.m_mass = invMass !== 0 ? 1 / invMass : 0;
}
else {
this.m_gamma = 0;
this.m_bias = 0;
}
if ( data.step.warmStarting ) {
// Scale the impulse to support a variable time step.
this.m_impulse *= data.step.dtRatio;
// b2Vec2 P = m_impulse * m_u;
var P = b2Vec2.numTimes( this.m_impulse, this.m_u, b2DistanceJoint._B2VEC2_POOL0 );
// vA -= m_invMassA * P;
vA.minusEqualsMul( this.m_invMassA, P );
// wA -= m_invIA * b2Cross(m_rA, P);
wA -= this.m_invIA * b2Vec2.cross( this.m_rA, P );
// vB += m_invMassB * P;
vB.plusEqualsMul( this.m_invMassB, P );
// wB += m_invIB * b2Cross(m_rB, P);
wB += this.m_invIB * b2Vec2.cross( this.m_rB, P );
}
else {
this.m_impulse = 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;
// b2Vec2 vpA = vA + b2Cross(wA, m_rA);
var vpA = b2Vec2.vPlusCrossFV( vA, wA, this.m_rA, b2DistanceJoint._B2VEC2_POOL0 );
// b2Vec2 vpB = vB + b2Cross(wB, m_rB);
var vpB = b2Vec2.vPlusCrossFV( vB, wB, this.m_rB, b2DistanceJoint._B2VEC2_POOL1 );
// float32 Cdot = b2Dot(m_u, vpB - vpA);
var Cdot = b2Vec2.dot( this.m_u, b2Vec2.subtract( vpB, vpA, b2Vec2.POOL0 ) );
var impulse = (-this.m_mass * (Cdot + this.m_bias + this.m_gamma * this.m_impulse));
this.m_impulse += impulse;
// b2Vec2 P = impulse * m_u;
var P = b2Vec2.numTimes( impulse, this.m_u, b2DistanceJoint._B2VEC2_POOL2 );
// vA -= m_invMassA * P;
vA.minusEqualsMul( this.m_invMassA, P );
// wA -= m_invIA * b2Cross(m_rA, P);
wA -= this.m_invIA * b2Vec2.cross( this.m_rA, P );
// vB += m_invMassB * P;
vB.plusEqualsMul( this.m_invMassB, P );
// wB += m_invIB * b2Cross(m_rB, P);
wB += this.m_invIB * b2Vec2.cross( this.m_rB, P );
// 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 solvePositionConstraints
* @param {b2SolverData} data
* @return {void}
*/
// Implement b2Joint.solvePositionConstraints
p.solvePositionConstraints = function ( data ) {
if ( this.m_frequencyHz > 0 ) {
// There is no position correction for soft distance constraints.
return true;
}
/*b2Vec2&*/var cA = data.positions[this.m_indexA].c;
/*float32*/var aA = data.positions[this.m_indexA].a;
/*b2Vec2&*/var cB = data.positions[this.m_indexB].c;
/*float32*/var aB = data.positions[this.m_indexB].a;
// var qA = new b2Rot(aA), qB = new b2Rot(aB);
var qA = this.m_qA.setAngle( aA ), qB = this.m_qB.setAngle( aB );
// b2Vec2 rA = b2Mul(qA, m_localAnchorA - m_localCenterA);
var rA = b2Rot.timesV2( this.m_qA, this.m_lalcA, this.m_rA ); // use m_rA
// b2Vec2 rB = b2Mul(qB, m_localAnchorB - m_localCenterB);
var rB = b2Rot.timesV2( this.m_qB, this.m_lalcB, this.m_rB ); // use m_rB
// b2Vec2 u = cB + rB - cA - rA;
var u = this.m_u; // use m_u
u.x = cB.x + rB.x - cA.x - rA.x;
u.y = cB.y + rB.y - cA.y - rA.y;
// float32 length = u.norm();
var length = this.m_u.norm();
// float32 C = length - m_length;
var C = length - this.m_length;
C = b2Math.clamp( C, (-b2Settings.b2_maxLinearCorrection), b2Settings.b2_maxLinearCorrection );
var impulse = (-this.m_mass * C);
// b2Vec2 P = impulse * u;
var P = b2Vec2.numTimes( impulse, u, b2DistanceJoint._B2VEC2_POOL0 );
// cA -= m_invMassA * P;
cA.minusEqualsMul( this.m_invMassA, P );
// aA -= m_invIA * b2Cross(rA, P);
aA -= this.m_invIA * b2Vec2.cross( rA, P );
// cB += m_invMassB * P;
cB.plusEqualsMul( this.m_invMassB, P );
// aB += m_invIB * b2Cross(rB, P);
aB += this.m_invIB * b2Vec2.cross( rB, P );
// data.positions[this.m_indexA].c = cA;
data.positions[this.m_indexA].a = aA;
// data.positions[this.m_indexB].c = cB;
data.positions[this.m_indexB].a = aB;
return Math.abs( C ) < b2Settings.b2_linearSlop;
};
