three.js/src/extras/curves/SplineCurve.js

/**************************************************************
 *	Spline curve
 **************************************************************/

THREE.SplineCurve = function ( points /* array of Vector2 */ ) {

	this.points = ( points == undefined ) ? [] : points;

};

THREE.SplineCurve.prototype = Object.create( THREE.Curve.prototype );
THREE.SplineCurve.prototype.constructor = THREE.SplineCurve;

THREE.SplineCurve.prototype.getPoint = function ( t ) {

	var points = this.points;
	var point = ( points.length - 1 ) * t;

	var intPoint = Math.floor( point );
	var weight = point - intPoint;

	var point0 = points[ intPoint == 0 ? intPoint : intPoint - 1 ]
	var point1 = points[ intPoint ]
	var point2 = points[ intPoint > points.length - 2 ? points.length - 1 : intPoint + 1 ]
	var point3 = points[ intPoint > points.length - 3 ? points.length - 1 : intPoint + 2 ]

	var vector = new THREE.Vector2();

	vector.x = THREE.Curve.Utils.interpolate( point0.x, point1.x, point2.x, point3.x, weight );
	vector.y = THREE.Curve.Utils.interpolate( point0.y, point1.y, point2.y, point3.y, weight );

	return vector;

};