three.js/src/core/Spline.js

/**
 * Spline from Tween.js, slightly optimized
 * http://sole.github.com/tween.js/examples/05_spline.html
 *
 * @author mrdoob / http://mrdoob.com/
 */
 
THREE.Spline = function () {

	var c = [], v3 = { x: 0, y: 0, z: 0 },
	point, intPoint, weight, w2, w3,
	pa, pb, pc, pd;

	this.get2DPoint = function ( points, k ) {

		point = ( points.length - 1 ) * k;
		intPoint = Math.floor( point );
		weight = point - intPoint;

		c[ 0 ] = intPoint == 0 ? intPoint : intPoint - 1;
		c[ 1 ] = intPoint;
		c[ 2 ] = intPoint > points.length - 2 ? intPoint : intPoint + 1;
		c[ 3 ] = intPoint > points.length - 3 ? intPoint : intPoint + 2;

		pa = points[ c[ 0 ] ];
		pb = points[ c[ 1 ] ];
		pc = points[ c[ 2 ] ];
		pd = points[ c[ 3 ] ];

		w2 = weight * weight;
		w3 = weight * w2;
		
		v3.x = interpolate( pa.x, pb.x, pc.x, pd.x, weight, w2, w3 );
		v3.y = interpolate( pa.y, pb.y, pc.y, pd.y, weight, w2, w3 );
		v3.z = interpolate( pa.z, pb.z, pc.z, pd.z, weight, w2, w3 );
		
		return v3;

	}

	// Catmull-Rom

	function interpolate( p0, p1, p2, p3, t, t2, t3 ) {

		var v0 = ( p2 - p0 ) * 0.5,
			v1 = ( p3 - p1 ) * 0.5;

		return ( 2 * ( p1 - p2 ) + v0 + v1 ) * t3 + ( - 3 * ( p1 - p2 ) - 2 * v0 - v1 ) * t2 + v0 * t + p1;

	}

};