source: other-projects/playing-in-the-street/summer-2013/trunk/Playing-in-the-Street-WPF/Content/Web/mrdoob-three.js-4862f5f/src/extras/helpers/DirectionalLightHelper.js

/**
 * @author alteredq / http://alteredqualia.com/
 * @author mrdoob / http://mrdoob.com/
 * @author WestLangley / http://github.com/WestLangley
 */

THREE.DirectionalLightHelper = function ( light, size ) {

    THREE.Object3D.call( this );

    this.light = light;
    this.light.updateMatrixWorld();

    this.matrixWorld = light.matrixWorld;
    this.matrixAutoUpdate = false;

    size = size || 1;
    var geometry = new THREE.PlaneGeometry( size, size );
    var material = new THREE.MeshBasicMaterial( { wireframe: true, fog: false } );
    material.color.copy( this.light.color ).multiplyScalar( this.light.intensity );

    this.lightPlane = new THREE.Mesh( geometry, material );
    this.add( this.lightPlane );

    geometry = new THREE.Geometry();
    geometry.vertices.push( new THREE.Vector3() );
    geometry.vertices.push( new THREE.Vector3() );

    material = new THREE.LineBasicMaterial( { fog: false } );
    material.color.copy( this.light.color ).multiplyScalar( this.light.intensity );

    this.targetLine = new THREE.Line( geometry, material );
    this.add( this.targetLine );

    this.update();

};

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

THREE.DirectionalLightHelper.prototype.dispose = function () {
    
    this.lightPlane.geometry.dispose();
    this.lightPlane.material.dispose();
    this.targetLine.geometry.dispose();
    this.targetLine.material.dispose();
};

THREE.DirectionalLightHelper.prototype.update = function () {

    var v1 = new THREE.Vector3();
    var v2 = new THREE.Vector3();
    var v3 = new THREE.Vector3();

    return function () {

        v1.setFromMatrixPosition( this.light.matrixWorld );
        v2.setFromMatrixPosition( this.light.target.matrixWorld );
        v3.subVectors( v2, v1 );

        this.lightPlane.lookAt( v3 );
        this.lightPlane.material.color.copy( this.light.color ).multiplyScalar( this.light.intensity );

        this.targetLine.geometry.vertices[ 1 ].copy( v3 );
        this.targetLine.geometry.verticesNeedUpdate = true;
        this.targetLine.material.color.copy( this.lightPlane.material.color );

    }

}();