HTML5の超クールなパーティクルエフェクトのプログレスバーグラフィックコードの詳細紹介

/*========================================================*/  
/* Light Loader
/*========================================================*/
var lightLoader = function(c, cw, ch){

	var _this = this;
	this.c = c;
	this.ctx = c.getContext('2d');
	this.cw = cw;
	this.ch = ch;			

	this.loaded = 0;
	this.loaderSpeed = .6;
	this.loaderHeight = 10;
	this.loaderWidth = 310;				
	this.loader = {
		x: (this.cw/2) - (this.loaderWidth/2),
		y: (this.ch/2) - (this.loaderHeight/2)
	};
	this.particles = [];
	this.particleLift = 180;
	this.hueStart = 0
	this.hueEnd = 120;
	this.hue = 0;
	this.gravity = .15;
	this.particleRate = 4;	

	/*========================================================*/	
	/* Initialize
	/*========================================================*/
	this.init = function(){
		this.loop();
	};

	/*========================================================*/	
	/* Utility Functions
	/*========================================================*/				
	this.rand = function(rMi, rMa){return ~~((Math.random()*(rMa-rMi+1))+rMi);};
	this.hitTest = function(x1, y1, w1, h1, x2, y2, w2, h2){return !(x1 + w1 < x2 || x2 + w2 < x1 || y1 + h1 < y2 || y2 + h2 < y1);};

	/*========================================================*/	
	/* Update Loader
	/*========================================================*/
	this.updateLoader = function(){
		if(this.loaded < 100){
			this.loaded += this.loaderSpeed;
		} else {
			this.loaded = 0;
		}
	};

	/*========================================================*/	
	/* Render Loader
	/*========================================================*/
	this.renderLoader = function(){
		this.ctx.fillStyle = &#39;#000&#39;;
		this.ctx.fillRect(this.loader.x, this.loader.y, this.loaderWidth, this.loaderHeight);

		this.hue = this.hueStart + (this.loaded/100)*(this.hueEnd - this.hueStart);

		var newWidth = (this.loaded/100)*this.loaderWidth;
		this.ctx.fillStyle = &#39;hsla(&#39;+this.hue+&#39;, 100%, 40%, 1)&#39;;
		this.ctx.fillRect(this.loader.x, this.loader.y, newWidth, this.loaderHeight);

		this.ctx.fillStyle = &#39;#222&#39;;
		this.ctx.fillRect(this.loader.x, this.loader.y, newWidth, this.loaderHeight/2);
	};	

	/*========================================================*/	
	/* Particles
	/*========================================================*/
	this.Particle = function(){					
		this.x = _this.loader.x + ((_this.loaded/100)*_this.loaderWidth) - _this.rand(0, 1);
		this.y = _this.ch/2 + _this.rand(0,_this.loaderHeight)-_this.loaderHeight/2;
		this.vx = (_this.rand(0,4)-2)/100;
		this.vy = (_this.rand(0,_this.particleLift)-_this.particleLift*2)/100;
		this.width = _this.rand(1,4)/2;
		this.height = _this.rand(1,4)/2;
		this.hue = _this.hue;
	};

	this.Particle.prototype.update = function(i){
		this.vx += (_this.rand(0,6)-3)/100; 
		this.vy += _this.gravity;
		this.x += this.vx;
		this.y += this.vy;

		if(this.y > _this.ch){
			_this.particles.splice(i, 1);
		}					
	};

	this.Particle.prototype.render = function(){
		_this.ctx.fillStyle = &#39;hsla(&#39;+this.hue+&#39;, 100%, &#39;+_this.rand(50,70)+&#39;%, &#39;+_this.rand(20,100)/100+&#39;)&#39;;
		_this.ctx.fillRect(this.x, this.y, this.width, this.height);
	};

	this.createParticles = function(){
		var i = this.particleRate;
		while(i--){
			this.particles.push(new this.Particle());
		};
	};

	this.updateParticles = function(){					
		var i = this.particles.length;						
		while(i--){
			var p = this.particles[i];
			p.update(i);											
		};						
	};

	this.renderParticles = function(){
		var i = this.particles.length;						
		while(i--){
			var p = this.particles[i];
			p.render();											
		};					
	};

	/*========================================================*/	
	/* Clear Canvas
	/*========================================================*/
	this.clearCanvas = function(){
		this.ctx.globalCompositeOperation = &#39;source-over&#39;;
		this.ctx.clearRect(0,0,this.cw,this.ch);					
		this.ctx.globalCompositeOperation = &#39;lighter&#39;;
	};

	/*========================================================*/	
	/* Animation Loop
	/*========================================================*/
	this.loop = function(){
		var loopIt = function(){
			requestAnimationFrame(loopIt, _this.c);
			_this.clearCanvas();

			_this.createParticles();

			_this.updateLoader();
			_this.updateParticles();

			_this.renderLoader();
			_this.renderParticles();

		};
		loopIt();					
	};

};

/*========================================================*/	
/* Check Canvas Support
/*========================================================*/
var isCanvasSupported = function(){
	var elem = document.createElement(&#39;canvas&#39;);
	return !!(elem.getContext && elem.getContext(&#39;2d&#39;));
};

/*========================================================*/	
/* Setup requestAnimationFrame
/*========================================================*/
var setupRAF = function(){
	var lastTime = 0;
	var vendors = [&#39;ms&#39;, &#39;moz&#39;, &#39;webkit&#39;, &#39;o&#39;];
	for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x){
		window.requestAnimationFrame = window[vendors[x]+&#39;RequestAnimationFrame&#39;];
		window.cancelAnimationFrame = window[vendors[x]+&#39;CancelAnimationFrame&#39;] || window[vendors[x]+&#39;CancelRequestAnimationFrame&#39;];
	};

	if(!window.requestAnimationFrame){
		window.requestAnimationFrame = function(callback, element){
			var currTime = new Date().getTime();
			var timeToCall = Math.max(0, 16 - (currTime - lastTime));
			var id = window.setTimeout(function() { callback(currTime + timeToCall); }, timeToCall);
			lastTime = currTime + timeToCall;
			return id;
		};
	};

	if (!window.cancelAnimationFrame){
		window.cancelAnimationFrame = function(id){
			clearTimeout(id);
		};
	};
};			

/*========================================================*/	
/* Define Canvas and Initialize
/*========================================================*/
if(isCanvasSupported){
  var c = document.createElement(&#39;canvas&#39;);
  c.width = 400;
  c.height = 100;			
  var cw = c.width;
  var ch = c.height;	
  document.body.appendChild(c);	
  var cl = new lightLoader(c, cw, ch);				

  setupRAF();
  cl.init();
}