/**
 * Hilbert Curve: Generates 2D-Coordinates in a very fast way.
 *
 * @author Dylan Grafmyre
 *
 * Based on work by:
 * @author Thomas Diewald
 * @link http://www.openprocessing.org/sketch/15493
 *
 * @param center     Center of Hilbert curve.
 * @param size       Total width of Hilbert curve.
 * @param iterations Number of subdivisions.
 * @param v0         Corner index -X, -Z.
 * @param v1         Corner index -X, +Z.
 * @param v2         Corner index +X, +Z.
 * @param v3         Corner index +X, -Z.
 */
function hilbert2D (center, size, iterations, v0, v1, v2, v3) {
	// Default Vars
	var center     = undefined !== center ? center : new THREE.Vector3(0, 0, 0),
		size       = undefined !== size ? size : 10,
		half       = size / 2,
		iterations = undefined !== iterations ? iterations : 1,
		v0 = undefined !== v0 ? v0 : 0,
		v1 = undefined !== v1 ? v1 : 1,
		v2 = undefined !== v2 ? v2 : 2,
		v3 = undefined !== v3 ? v3 : 3
	;

	var vec_s = [
		new THREE.Vector3( center.x - half, center.y, center.z - half ),
		new THREE.Vector3( center.x - half, center.y, center.z + half ),
		new THREE.Vector3( center.x + half, center.y, center.z + half ),
		new THREE.Vector3( center.x + half, center.y, center.z - half )
	];

	var vec = [
		vec_s[ v0 ],
		vec_s[ v1 ],
		vec_s[ v2 ],
		vec_s[ v3 ]
	];

	// Recurse iterations
	if (0 <= -- iterations) {
		var tmp = [];

		Array.prototype.push.apply( tmp, hilbert2D ( vec[ 0 ], half, iterations, v0, v3, v2, v1 ) );
		Array.prototype.push.apply( tmp, hilbert2D ( vec[ 1 ], half, iterations, v0, v1, v2, v3 ) );
		Array.prototype.push.apply( tmp, hilbert2D ( vec[ 2 ], half, iterations, v0, v1, v2, v3 ) );
		Array.prototype.push.apply( tmp, hilbert2D ( vec[ 3 ], half, iterations, v2, v1, v0, v3 ) );

		// Return recursive call
		return tmp;
	}

	// Return complete Hilbert Curve.
	return vec;
}