threex/src/threex.particles/examples/js/threex.textureutils.js

Game Extensions for three.js http://www.threejsgames.com/extensions/

var THREEx	= THREEx	|| {}

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THREEx.TextureUtils	= {};

/**
 * set the alpha channel of a texture based on its luminance. 
 * very usefull to generate alpha channel from image which doesnt have one (like .jpg files)
 *
 * @param {THREE.texture} texture the texture to modify
 * @param {function} computeAlpha function(p, i) which returns the alpha
 * @param {number} power the value by which the luminance will be powered	 
*/
THREEx.TextureUtils.generateAlpha	= function(texture, computeAlpha){
	// sanity check
	console.assert( texture instanceof THREE.Texture );
	// create a canvas
	var image	= texture.image;
	var canvas	= document.createElement('canvas');
	canvas.width	= image.width;
	canvas.height	= image.height;	
	var ctx		= canvas.getContext('2d');
	// draw the image in it
	ctx.drawImage(image, 0, 0);
	
	// create an alpha channel based on color luminance
	var imgData	= ctx.getImageData(0, 0, canvas.width, canvas.height);
	var p		= imgData.data;
	for(var i = 0, y = 0; y < canvas.height; y++){
		for(var x = 0; x < canvas.width; x++, i += 4){
			// compute alpha pixel value
			var alpha	= computeAlpha(p, i);
			// set the alpha in the imageData 
			p[i+3]		= alpha;
		}
	}
	// put the generated image in the canvas
	ctx.putImageData(imgData, 0, 0);
	// update the texture object itself
	texture.image		= canvas;
	texture.needsUpdate	= true;		
}

/**
 * set the alpha channel of a texture based on its luminance. 
 * very usefull to generate alpha channel from image which doesnt have one (like .jpg files)
 * TODO Find a better name. shorter one
 *
 * @param {THREE.texture} texture the texture to modify
 * @param {number} multiplier the value by which the luminance will be multiplied
 * @param {number} power the value by which the luminance will be powered	 
*/
THREEx.TextureUtils.generateAlphaFromLuminance	= function(texture, multiplier, power){
	// handle parameters polymorphism
	multiplier	= multiplier !== undefined ? multiplier	: 1;
	power		= power !== undefined ? power : 1;
	// forward to THREEx.TextureUtils.setAlphaFromLuminance
	THREEx.TextureUtils.generateAlpha(texture, function(p, i){
		// compute luminance
		var luminance	= (0.2126*p[i+0]) + (0.7152*p[i+1]) + (0.0722*p[i+2]);
		// increase contrast of the luminance based on 'power'
		// TODO experiment with normal tween funciton
		var alpha	= Math.pow(luminance/255, power)*255;
		// set the luminance after mutiplying it
		alpha		*= multiplier;
		return alpha;
	});
}

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/**
 * Load multiple images 
 * 
 * @param {array.<string>} urls the urls to load
 * @param {function(Array.<Image>, Array.<string>)} onLoad the function 
 *        called when all the images are loaded
*/
THREEx.TextureUtils.loadImages	= function(urls, onLoad){
	// handle parameter polymorphism
	if( typeof(urls) === 'string' )	urls	= [urls];
	// init images
	var images	= new Array(urls.length);
	// load all the images and convert them
	var flow	= Flow();
	urls.forEach(function(url, idx){
		flow.par(function(next){
			var image	= new Image;
			// TODO what if the images isnt properly loaded
			image.onload	= function(){
				images[idx]	= image;
				next();
			};
			image.src	= url;
		});
	});

	// build the function which is run once all is loaded
	flow.seq(function(){
		//console.log("all flow completed")
		// notify the caller
		onLoad(images, urls);
	});
	
	return;
	
	/**
	 * Flow control - from https://github.com/jeromeetienne/gowiththeflow.js
	*/
	function Flow(){
		var self, stack = [], timerId = setTimeout(function(){ timerId = null; self._next(); }, 0);
		return self = {
			destroy	: function(){ timerId && clearTimeout(timerId);	},
			par	: function(callback, isSeq){
				if(isSeq || !(stack[stack.length-1] instanceof Array)) stack.push([]);
				stack[stack.length-1].push(callback);
				return self;
			},seq	: function(callback){ return self.par(callback, true);	},
			_next	: function(err, result){
				var errors = [], results = [], callbacks = stack.shift() || [], nbReturn = callbacks.length, isSeq = nbReturn == 1;
				callbacks && callbacks.forEach(function(fct, index){
					fct(function(error, result){
						errors[index]	= error;
						results[index]	= result;		
						if(--nbReturn == 0)	self._next(isSeq?errors[0]:errors, isSeq?results[0]:results)
					}, err, result)
				})
			}
		}
	};

};

/**
 * Build a canvas spritesheet based on opts
*/
THREEx.TextureUtils.buildTiledSpriteSheet	= function(opts){
	var images	= opts.images	|| console.assert(false);
	var spriteW	= opts.spriteW	|| console.assert(false);
	var spriteH	= opts.spriteH	|| console.assert(false);
	var nSpriteX	= opts.nSpriteX	|| 1;
	var nSpriteY	= opts.nSpriteY	|| (images.length / nSpriteX);
	
	var canvasW	= opts.canvasW	|| (spriteW * nSpriteX);
	var canvasH	= opts.canvasH	|| (spriteH * nSpriteY);

	// create the canvas
	var canvas	= document.createElement('canvas');
	canvas.width	= canvasW;
	canvas.height	= canvasH;
	var ctx		= canvas.getContext('2d');

	// draw each images in the canvas
	images.forEach(function(image, idx){
		var destX	= spriteW * (idx % nSpriteX);
		var destY	= spriteH * Math.floor(idx / nSpriteX);
		ctx.drawImage(image, 
			0, 0, image.width, image.height,
			destX, destY, spriteW, spriteH);
	});

	// return the resulting canvas
	return canvas;
}