three.js/examples/js/nodes/utils/VelocityNode.js

/**
 * @author sunag / http://www.sunag.com.br/
 */

THREE.VelocityNode = function ( target, params ) {

	THREE.Vector3Node.call( this );

	this.params = {};

	this.velocity = new THREE.Vector3();

	this.setTarget( target );
	this.setParams( params );

};

THREE.VelocityNode.prototype = Object.create( THREE.Vector3Node.prototype );
THREE.VelocityNode.prototype.constructor = THREE.VelocityNode;
THREE.VelocityNode.prototype.nodeType = "Velocity";

THREE.VelocityNode.prototype.isReadonly = function ( builder ) {

	return false;

};

THREE.VelocityNode.prototype.setParams = function ( params ) {

	switch ( this.params.type ) {

		case "elastic":

			delete this.moment;

			delete this.speed;
			delete this.springVelocity;

			delete this.lastVelocity;

			break;

	}

	this.params = params || {};

	switch ( this.params.type ) {

		case "elastic":

			this.moment = new THREE.Vector3();

			this.speed = new THREE.Vector3();
			this.springVelocity = new THREE.Vector3();

			this.lastVelocity = new THREE.Vector3();

			break;

	}

};

THREE.VelocityNode.prototype.setTarget = function ( target ) {

	if ( this.target ) {

		delete this.position;
		delete this.oldPosition;

	}

	this.target = target;

	if ( target ) {

		this.position = target.getWorldPosition( this.position || new THREE.Vector3() );
		this.oldPosition = this.position.clone();

	}

};

THREE.VelocityNode.prototype.updateFrameVelocity = function ( frame ) {

	if ( this.target ) {

		this.position = this.target.getWorldPosition( this.position || new THREE.Vector3() );
		this.velocity.subVectors( this.position, this.oldPosition );
		this.oldPosition.copy( this.position );

	}

};

THREE.VelocityNode.prototype.updateFrame = function ( frame ) {

	this.updateFrameVelocity( frame );

	switch ( this.params.type ) {

		case "elastic":

			// convert to real scale: 0 at 1 values
			var deltaFps = frame.delta * ( this.params.fps || 60 );

			var spring = Math.pow( this.params.spring, deltaFps ),
				damping = Math.pow( this.params.damping, deltaFps );

			// fix relative frame-rate
			this.velocity.multiplyScalar( Math.exp( - this.params.damping * deltaFps ) );

			// elastic
			this.velocity.add( this.springVelocity );
			this.velocity.add( this.speed.multiplyScalar( damping ).multiplyScalar( 1 - spring ) );

			// speed
			this.speed.subVectors( this.velocity, this.lastVelocity );

			// spring velocity
			this.springVelocity.add( this.speed );
			this.springVelocity.multiplyScalar( spring );

			// moment
			this.moment.add( this.springVelocity );

			// damping
			this.moment.multiplyScalar( damping );

			this.lastVelocity.copy( this.velocity );
			this.value.copy( this.moment );

			break;

		default:

			this.value.copy( this.velocity );

	}

};

THREE.VelocityNode.prototype.toJSON = function ( meta ) {

	var data = this.getJSONNode( meta );

	if ( ! data ) {

		data = this.createJSONNode( meta );

		if ( this.target ) data.target = this.target.uuid;

		// clone params
		data.params = JSON.parse( JSON.stringify( this.params ) );

	}

	return data;

};