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

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

THREE.VertexNormalsHelper = function ( object, size, hex, linewidth ) {

    this.object = object;

    this.size = ( size !== undefined ) ? size : 1;

    var color = ( hex !== undefined ) ? hex : 0xff0000;

    var width = ( linewidth !== undefined ) ? linewidth : 1;

    var geometry = new THREE.Geometry();

    var vertices = object.geometry.vertices;

    var faces = object.geometry.faces;

    for ( var i = 0, l = faces.length; i < l; i ++ ) {

        var face = faces[ i ];

        for ( var j = 0, jl = face.vertexNormals.length; j < jl; j ++ ) {

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

        }

    }

    THREE.Line.call( this, geometry, new THREE.LineBasicMaterial( { color: color, linewidth: width } ), THREE.LinePieces );

    this.matrixAutoUpdate = false;

    this.normalMatrix = new THREE.Matrix3();

    this.update();

};

THREE.VertexNormalsHelper.prototype = Object.create( THREE.Line.prototype );

THREE.VertexNormalsHelper.prototype.update = ( function ( object ) {

    var v1 = new THREE.Vector3();

    return function( object ) {

        var keys = [ 'a', 'b', 'c', 'd' ];

        this.object.updateMatrixWorld( true );

        this.normalMatrix.getNormalMatrix( this.object.matrixWorld );

        var vertices = this.geometry.vertices;

        var verts = this.object.geometry.vertices;

        var faces = this.object.geometry.faces;

        var worldMatrix = this.object.matrixWorld;

        var idx = 0;

        for ( var i = 0, l = faces.length; i < l; i ++ ) {

            var face = faces[ i ];

            for ( var j = 0, jl = face.vertexNormals.length; j < jl; j ++ ) {

                var vertexId = face[ keys[ j ] ];
                var vertex = verts[ vertexId ];

                var normal = face.vertexNormals[ j ];

                vertices[ idx ].copy( vertex ).applyMatrix4( worldMatrix );

                v1.copy( normal ).applyMatrix3( this.normalMatrix ).normalize().multiplyScalar( this.size );

                v1.add( vertices[ idx ] );
                idx = idx + 1;

                vertices[ idx ].copy( v1 );
                idx = idx + 1;

            }

        }

        this.geometry.verticesNeedUpdate = true;

        return this;

    }

}());