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<h1 class="file-heading">File: src/constraints/LockConstraint.js</h1>
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<pre class="code prettyprint linenums">
var Constraint = require('./Constraint')
, vec2 = require('../math/vec2')
, Equation = require('../equations/Equation');
module.exports = LockConstraint;
/**
* Locks the relative position and rotation between two bodies.
*
* @class LockConstraint
* @constructor
* @author schteppe
* @param {Body} bodyA
* @param {Body} bodyB
* @param {Object} [options]
* @param {Array} [options.localOffsetB] The offset of bodyB in bodyA's frame. If not given the offset is computed from current positions.
* @param {number} [options.localAngleB] The angle of bodyB in bodyA's frame. If not given, the angle is computed from current angles.
* @param {number} [options.maxForce]
* @extends Constraint
*
* @example
* // Locks the relative position and rotation between bodyA and bodyB
* var constraint = new LockConstraint(bodyA, bodyB);
* world.addConstraint(constraint);
*/
function LockConstraint(bodyA, bodyB, options){
options = options || {};
Constraint.call(this,bodyA,bodyB,Constraint.LOCK,options);
var maxForce = ( typeof(options.maxForce)==="undefined" ? Number.MAX_VALUE : options.maxForce );
var localAngleB = options.localAngleB || 0;
// Use 3 equations:
// gx = (xj - xi - l) * xhat = 0
// gy = (xj - xi - l) * yhat = 0
// gr = (xi - xj + r) * that = 0
//
// ...where:
// l is the localOffsetB vector rotated to world in bodyA frame
// r is the same vector but reversed and rotated from bodyB frame
// xhat, yhat are world axis vectors
// that is the tangent of r
//
// For the first two constraints, we get
// G*W = (vj - vi - ldot ) * xhat
// = (vj - vi - wi x l) * xhat
//
// Since (wi x l) * xhat = (l x xhat) * wi, we get
// G*W = [ -1 0 (-l x xhat) 1 0 0] * [vi wi vj wj]
//
// The last constraint gives
// GW = (vi - vj + wj x r) * that
// = [ that 0 -that (r x t) ]
var x = new Equation(bodyA,bodyB,-maxForce,maxForce),
y = new Equation(bodyA,bodyB,-maxForce,maxForce),
rot = new Equation(bodyA,bodyB,-maxForce,maxForce);
var l = vec2.create(),
g = vec2.create(),
that = this;
x.computeGq = function(){
vec2.rotate(l, that.localOffsetB, bodyA.angle);
vec2.sub(g, bodyB.position, bodyA.position);
vec2.sub(g, g, l);
return g[0];
};
y.computeGq = function(){
vec2.rotate(l, that.localOffsetB, bodyA.angle);
vec2.sub(g, bodyB.position, bodyA.position);
vec2.sub(g, g, l);
return g[1];
};
var r = vec2.create(),
t = vec2.create();
rot.computeGq = function(){
vec2.rotate(r, that.localOffsetB, bodyB.angle - that.localAngleB);
vec2.scale(r,r,-1);
vec2.sub(g,bodyA.position,bodyB.position);
vec2.add(g,g,r);
vec2.rotate(t,r,-Math.PI/2);
vec2.normalize(t,t);
return vec2.dot(g,t);
};
/**
* The offset of bodyB in bodyA's frame.
* @property {Array} localOffsetB
*/
this.localOffsetB = vec2.create();
if(options.localOffsetB){
vec2.copy(this.localOffsetB, options.localOffsetB);
} else {
// Construct from current positions
vec2.sub(this.localOffsetB, bodyB.position, bodyA.position);
vec2.rotate(this.localOffsetB, this.localOffsetB, -bodyA.angle);
}
/**
* The offset angle of bodyB in bodyA's frame.
* @property {Number} localAngleB
*/
this.localAngleB = 0;
if(typeof(options.localAngleB) === 'number'){
this.localAngleB = options.localAngleB;
} else {
// Construct
this.localAngleB = bodyB.angle - bodyA.angle;
}
this.equations.push(x, y, rot);
this.setMaxForce(maxForce);
}
LockConstraint.prototype = new Constraint();
LockConstraint.prototype.constructor = LockConstraint;
/**
* Set the maximum force to be applied.
* @method setMaxForce
* @param {Number} force
*/
LockConstraint.prototype.setMaxForce = function(force){
var eqs = this.equations;
for(var i=0; i<this.equations.length; i++){
eqs[i].maxForce = force;
eqs[i].minForce = -force;
}
};
/**
* Get the max force.
* @method getMaxForce
* @return {Number}
*/
LockConstraint.prototype.getMaxForce = function(){
return this.equations[0].maxForce;
};
var l = vec2.create();
var r = vec2.create();
var t = vec2.create();
var xAxis = vec2.fromValues(1,0);
var yAxis = vec2.fromValues(0,1);
LockConstraint.prototype.update = function(){
var x = this.equations[0],
y = this.equations[1],
rot = this.equations[2],
bodyA = this.bodyA,
bodyB = this.bodyB;
vec2.rotate(l,this.localOffsetB,bodyA.angle);
vec2.rotate(r,this.localOffsetB,bodyB.angle - this.localAngleB);
vec2.scale(r,r,-1);
vec2.rotate(t,r,Math.PI/2);
vec2.normalize(t,t);
x.G[0] = -1;
x.G[1] = 0;
x.G[2] = -vec2.crossLength(l,xAxis);
x.G[3] = 1;
y.G[0] = 0;
y.G[1] = -1;
y.G[2] = -vec2.crossLength(l,yAxis);
y.G[4] = 1;
rot.G[0] = -t[0];
rot.G[1] = -t[1];
rot.G[3] = t[0];
rot.G[4] = t[1];
rot.G[5] = vec2.crossLength(r,t);
};
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