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<h1 class="file-heading">File: src/objects/Spring.js</h1>
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<pre class="code prettyprint linenums">
var Vec3 = require('../math/Vec3');
module.exports = Spring;
/**
* A spring, connecting two bodies.
*
* @class Spring
* @constructor
* @param {Body} bodyA
* @param {Body} bodyB
* @param {Object} [options]
* @param {number} [options.restLength] A number > 0. Default: 1
* @param {number} [options.stiffness] A number >= 0. Default: 100
* @param {number} [options.damping] A number >= 0. Default: 1
* @param {Vec3} [options.worldAnchorA] Where to hook the spring to body A, in world coordinates.
* @param {Vec3} [options.worldAnchorB]
* @param {Vec3} [options.localAnchorA] Where to hook the spring to body A, in local body coordinates.
* @param {Vec3} [options.localAnchorB]
*/
function Spring(bodyA,bodyB,options){
options = options || {};
/**
* Rest length of the spring.
* @property restLength
* @type {number}
*/
this.restLength = typeof(options.restLength) === "number" ? options.restLength : 1;
/**
* Stiffness of the spring.
* @property stiffness
* @type {number}
*/
this.stiffness = options.stiffness || 100;
/**
* Damping of the spring.
* @property damping
* @type {number}
*/
this.damping = options.damping || 1;
/**
* First connected body.
* @property bodyA
* @type {Body}
*/
this.bodyA = bodyA;
/**
* Second connected body.
* @property bodyB
* @type {Body}
*/
this.bodyB = bodyB;
/**
* Anchor for bodyA in local bodyA coordinates.
* @property localAnchorA
* @type {Vec3}
*/
this.localAnchorA = new Vec3();
/**
* Anchor for bodyB in local bodyB coordinates.
* @property localAnchorB
* @type {Vec3}
*/
this.localAnchorB = new Vec3();
if(options.localAnchorA){
this.localAnchorA.copy(options.localAnchorA);
}
if(options.localAnchorB){
this.localAnchorB.copy(options.localAnchorB);
}
if(options.worldAnchorA){
this.setWorldAnchorA(options.worldAnchorA);
}
if(options.worldAnchorB){
this.setWorldAnchorB(options.worldAnchorB);
}
}
/**
* Set the anchor point on body A, using world coordinates.
* @method setWorldAnchorA
* @param {Vec3} worldAnchorA
*/
Spring.prototype.setWorldAnchorA = function(worldAnchorA){
this.bodyA.pointToLocalFrame(worldAnchorA,this.localAnchorA);
};
/**
* Set the anchor point on body B, using world coordinates.
* @method setWorldAnchorB
* @param {Vec3} worldAnchorB
*/
Spring.prototype.setWorldAnchorB = function(worldAnchorB){
this.bodyB.pointToLocalFrame(worldAnchorB,this.localAnchorB);
};
/**
* Get the anchor point on body A, in world coordinates.
* @method getWorldAnchorA
* @param {Vec3} result The vector to store the result in.
*/
Spring.prototype.getWorldAnchorA = function(result){
this.bodyA.pointToWorldFrame(this.localAnchorA,result);
};
/**
* Get the anchor point on body B, in world coordinates.
* @method getWorldAnchorB
* @param {Vec3} result The vector to store the result in.
*/
Spring.prototype.getWorldAnchorB = function(result){
this.bodyB.pointToWorldFrame(this.localAnchorB,result);
};
var applyForce_r = new Vec3(),
applyForce_r_unit = new Vec3(),
applyForce_u = new Vec3(),
applyForce_f = new Vec3(),
applyForce_worldAnchorA = new Vec3(),
applyForce_worldAnchorB = new Vec3(),
applyForce_ri = new Vec3(),
applyForce_rj = new Vec3(),
applyForce_ri_x_f = new Vec3(),
applyForce_rj_x_f = new Vec3(),
applyForce_tmp = new Vec3();
/**
* Apply the spring force to the connected bodies.
* @method applyForce
*/
Spring.prototype.applyForce = function(){
var k = this.stiffness,
d = this.damping,
l = this.restLength,
bodyA = this.bodyA,
bodyB = this.bodyB,
r = applyForce_r,
r_unit = applyForce_r_unit,
u = applyForce_u,
f = applyForce_f,
tmp = applyForce_tmp;
var worldAnchorA = applyForce_worldAnchorA,
worldAnchorB = applyForce_worldAnchorB,
ri = applyForce_ri,
rj = applyForce_rj,
ri_x_f = applyForce_ri_x_f,
rj_x_f = applyForce_rj_x_f;
// Get world anchors
this.getWorldAnchorA(worldAnchorA);
this.getWorldAnchorB(worldAnchorB);
// Get offset points
worldAnchorA.vsub(bodyA.position,ri);
worldAnchorB.vsub(bodyB.position,rj);
// Compute distance vector between world anchor points
worldAnchorB.vsub(worldAnchorA,r);
var rlen = r.norm();
r_unit.copy(r);
r_unit.normalize();
// Compute relative velocity of the anchor points, u
bodyB.velocity.vsub(bodyA.velocity,u);
// Add rotational velocity
bodyB.angularVelocity.cross(rj,tmp);
u.vadd(tmp,u);
bodyA.angularVelocity.cross(ri,tmp);
u.vsub(tmp,u);
// F = - k * ( x - L ) - D * ( u )
r_unit.mult(-k*(rlen-l) - d*u.dot(r_unit), f);
// Add forces to bodies
bodyA.force.vsub(f,bodyA.force);
bodyB.force.vadd(f,bodyB.force);
// Angular force
ri.cross(f,ri_x_f);
rj.cross(f,rj_x_f);
bodyA.torque.vsub(ri_x_f,bodyA.torque);
bodyB.torque.vadd(rj_x_f,bodyB.torque);
};
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