three.js/src/objects/LOD.js

/**
 * @author mikael emtinger / http://gomo.se/
 * @author alteredq / http://alteredqualia.com/
 * @author mrdoob / http://mrdoob.com/
 */

THREE.LOD = function () {

	THREE.Object3D.call( this );

	this.LODs = [];

};


THREE.LOD.prototype = Object.create( THREE.Object3D.prototype );

THREE.LOD.prototype.addLevel = function ( object3D, visibleAtDistance ) {

	if ( visibleAtDistance === undefined ) {

		visibleAtDistance = 0;

	}

	visibleAtDistance = Math.abs( visibleAtDistance );

	for ( var l = 0; l < this.LODs.length; l ++ ) {

		if ( visibleAtDistance < this.LODs[ l ].visibleAtDistance ) {

			break;

		}

	}

	this.LODs.splice( l, 0, { visibleAtDistance: visibleAtDistance, object3D: object3D } );
	this.add( object3D );

};

THREE.LOD.prototype.update = function ( camera ) {

	if ( this.LODs.length > 1 ) {

		camera.matrixWorldInverse.getInverse( camera.matrixWorld );

		var inverse  = camera.matrixWorldInverse;
		var distance = -( inverse.elements[2] * this.matrixWorld.elements[12] + inverse.elements[6] * this.matrixWorld.elements[13] + inverse.elements[10] * this.matrixWorld.elements[14] + inverse.elements[14] );

		this.LODs[ 0 ].object3D.visible = true;

		for ( var l = 1; l < this.LODs.length; l ++ ) {

			if( distance >= this.LODs[ l ].visibleAtDistance ) {

				this.LODs[ l - 1 ].object3D.visible = false;
				this.LODs[ l     ].object3D.visible = true;

			} else {

				break;

			}

		}

		for( ; l < this.LODs.length; l ++ ) {

			this.LODs[ l ].object3D.visible = false;

		}

	}

};