three.js/src/extras/ImageUtils.js

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

THREE.ImageUtils = {

	crossOrigin: '',

	loadTexture: function ( path, mapping, callback ) {

		var image = new Image(), texture = new THREE.Texture( image, mapping );

		image.onload = function () { texture.needsUpdate = true; if ( callback ) callback( this ); };
		image.crossOrigin = this.crossOrigin;
		image.src = path;

		return texture;

	},

	loadTextureCube: function ( array, mapping, callback ) {

		var i, l, images = [], texture = new THREE.Texture( images, mapping );

		images.loadCount = 0;

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

			images[ i ] = new Image();
			images[ i ].onload = function () {

				images.loadCount += 1;
				if ( images.loadCount === 6 ) texture.needsUpdate = true;
				if ( callback ) callback( this );

			};

			images[ i ].crossOrigin = '';
			images[ i ].src = array[ i ];

		}

		return texture;

	},

	getNormalMap: function ( image, depth ) {

		// Adapted from http://www.paulbrunt.co.uk/lab/heightnormal/

		var cross = function ( a, b ) {

			return [ a[ 1 ] * b[ 2 ] - a[ 2 ] * b[ 1 ], a[ 2 ] * b[ 0 ] - a[ 0 ] * b[ 2 ], a[ 0 ] * b[ 1 ] - a[ 1 ] * b[ 0 ] ];

		}

		var subtract = function ( a, b ) {

			return [ a[ 0 ] - b[ 0 ], a[ 1 ] - b[ 1 ], a[ 2 ] - b[ 2 ] ];

		}

		var normalize = function ( a ) {

			var l = Math.sqrt( a[ 0 ] * a[ 0 ] + a[ 1 ] * a[ 1 ] + a[ 2 ] * a[ 2 ] );
			return [ a[ 0 ] / l, a[ 1 ] / l, a[ 2 ] / l ];

		}

		var depth = depth | 1;
		var width = image.width;
		var height = image.height;

		var canvas = document.createElement( 'canvas' );
		canvas.width = width;
		canvas.height = height;

		var context = canvas.getContext( '2d' );
		context.drawImage( image, 0, 0 );

		var data = context.getImageData( 0, 0, width, height ).data;
		var imageData = context.createImageData( width, height );
		var output = imageData.data;

		for ( var x = 0; x < width; x ++ ) {

			for ( var y = 1; y < height; y ++ ) {

				var ly = y - 1 < 0 ? height - 1 : y - 1;
				var uy = ( y + 1 ) % height;
				var lx = x - 1 < 0 ? width - 1 : x - 1;
				var ux = ( x + 1 ) % width;

				var points = [];
				var origin = [ 0, 0, data[ ( y * width + x ) * 4 ] / 255 * depth ];
				points.push( [ - 1, 0, data[ ( y * width + lx ) * 4 ] / 255 * depth ] );
				points.push( [ - 1, - 1, data[ ( ly * width + lx ) * 4 ] / 255 * depth ] );
				points.push( [ 0, - 1, data[ ( ly * width + x ) * 4 ] / 255 * depth ] );
				points.push( [  1, - 1, data[ ( ly * width + ux ) * 4 ] / 255 * depth ] );
				points.push( [ 1, 0, data[ ( y * width + ux ) * 4 ] / 255 * depth ] );
				points.push( [ 1, 1, data[ ( uy * width + ux ) * 4 ] / 255 * depth ] );
				points.push( [ 0, 1, data[ ( uy * width + x ) * 4 ] / 255 * depth ] );
				points.push( [ - 1, 1, data[ ( uy * width + lx ) * 4 ] / 255 * depth ] );

				var normals = [];
				var num_points = points.length;

				for ( var i = 0; i < num_points; i ++ ) {

					var v1 = points[ i ];
					var v2 = points[ ( i + 1 ) % num_points ];
					v1 = subtract( v1, origin );
					v2 = subtract( v2, origin );
					normals.push( normalize( cross( v1, v2 ) ) );

				}

				var normal = [ 0, 0, 0 ];

				for ( var i = 0; i < normals.length; i ++ ) {

					normal[ 0 ] += normals[ i ][ 0 ];
					normal[ 1 ] += normals[ i ][ 1 ];
					normal[ 2 ] += normals[ i ][ 2 ];

				}

				normal[ 0 ] /= normals.length;
				normal[ 1 ] /= normals.length;
				normal[ 2 ] /= normals.length;

				var idx = ( y * width + x ) * 4;

				output[ idx ] = ( ( normal[ 0 ] + 1.0 ) / 2.0 * 255 ) | 0;
				output[ idx + 1 ] = ( ( normal[ 1 ] + 1.0 / 2.0 ) * 255 ) | 0;
				output[ idx + 2 ] = ( normal[ 2 ] * 255 ) | 0;
				output[ idx + 3 ] = 255;

			}

		}

		context.putImageData( imageData, 0, 0 );

		return canvas;

	}

};