这款HTML5烟花动画我们应该比较熟悉，因为之前有分享过类似的HTML5动画了。这个HTML5烟花动画是基于canvas的，可以说是之前分享那款的升级版，它可以控制烟花上升的速度和烟花绽放花朵的大小。由于是在HTML5 Canvas画布上完成，因此也就非常灵活。

下面我们来简单分析一下实现这款HTML5烟花特效的过程及代码，主要由HTML代码、CSS代码以及Javascript代码组成，当然javascript代码是最重要的。

HTML代码：

 
HTML的结构非常简单，即构造了一个canvas容器，我们会利用JS在这个容器中生成一个Canvas对象。看最后的JS代码你就会知道了。

CSS代码：

[css]#canvas-container { background: #000 url(bg.jpg);height: 400px; left: 50%; margin: -200px 0 0 -300px; position: absolute; top: 50%;width: 600px; z-index: 2; }
canvas { cursor: crosshair; display: block; position: relative; z-index: 3; }
canvas:active { cursor: crosshair; }
#skyline { background: url(skyline.png) repeat-x 50% 0; bottom: 0; height: 135px; left: 0; position: absolute; width: 100%; z-index: 1; }
#mountains1 { background: url(mountains1.png) repeat-x 40% 0; bottom: 0; height: 200px; left: 0; position: absolute; width: 100%; z-index: 1; }
#mountains2 { background: url(mountains2.png) repeat-x 30% 0; bottom: 0; height: 250px; left: 0; position: absolute; width: 100%; z-index: 1; }
#gui { right: 0; position: fixed; top: 0; z-index: 3; }[/css]
 
CSS代码没什么特别，主要也就定义一下背景色和边框之类的。
接下来是最重要的Javascript代码。

Javascript代码：

self.init = function(){	
    self.dt = 0;
		self.oldTime = Date.now();
		self.canvas = document.createElement('canvas');				
		self.canvasContainer = $('#canvas-container');
		var canvasContainerDisabled = document.getElementById('canvas-container');
		self.canvas.onselectstart = function() {
			return false;
		};
		self.canvas.width = self.cw = 600;
		self.canvas.height = self.ch = 400;	
		self.particles = [];	
		self.partCount = 30;
		self.fireworks = [];	
		self.mx = self.cw/2;
		self.my = self.ch/2;
		self.currentHue = 170;
		self.partSpeed = 5;
		self.partSpeedVariance = 10;
		self.partWind = 50;
		self.partFriction = 5;
		self.partGravity = 1;
		self.hueMin = 150;
		self.hueMax = 200;
		self.fworkSpeed = 2;
		self.fworkAccel = 4;
		self.hueVariance = 30;
		self.flickerDensity = 20;
		self.showShockwave = false;
		self.showTarget = true;
		self.clearAlpha = 25;
		self.canvasContainer.append(self.canvas);
		self.ctx = self.canvas.getContext('2d');
		self.ctx.lineCap = 'round';
		self.ctx.lineJoin = 'round';
		self.lineWidth = 1;
		self.bindEvents();			
		self.canvasLoop();
		self.canvas.onselectstart = function() {
			return false;
		};
	};

 
这段JS代码主要是往canvas容器中构造一个Canvas对象，并且对这个canvas对象的外观以及动画属性作了初始化。

var Particle = function(x, y, hue){
		this.x = x;
		this.y = y;
		this.coordLast = [
			{x: x, y: y},
			{x: x, y: y},
			{x: x, y: y}
		];
		this.angle = rand(0, 360);
		this.speed = rand(((self.partSpeed - self.partSpeedVariance) <= 0) ? 1 : self.partSpeed - self.partSpeedVariance, (self.partSpeed + self.partSpeedVariance));
		this.friction = 1 - self.partFriction/100;
		this.gravity = self.partGravity/2;
		this.hue = rand(hue-self.hueVariance, hue+self.hueVariance);
		this.brightness = rand(50, 80);
		this.alpha = rand(40,100)/100;
		this.decay = rand(10, 50)/1000;
		this.wind = (rand(0, self.partWind) - (self.partWind/2))/25;
		this.lineWidth = self.lineWidth;
	};
	Particle.prototype.update = function(index){
		var radians = this.angle * Math.PI / 180;
		var vx = Math.cos(radians) * this.speed;
		var vy = Math.sin(radians) * this.speed + this.gravity;
		this.speed *= this.friction;
		this.coordLast[2].x = this.coordLast[1].x;
		this.coordLast[2].y = this.coordLast[1].y;
		this.coordLast[1].x = this.coordLast[0].x;
		this.coordLast[1].y = this.coordLast[0].y;
		this.coordLast[0].x = this.x;
		this.coordLast[0].y = this.y;
		this.x += vx * self.dt;
		this.y += vy * self.dt;
		this.angle += this.wind;				
		this.alpha -= this.decay;
		if(!hitTest(0,0,self.cw,self.ch,this.x-this.radius, this.y-this.radius, this.radius*2, this.radius*2) || this.alpha < .05){					
			self.particles.splice(index, 1);	
		}			
	};
	Particle.prototype.draw = function(){
		var coordRand = (rand(1,3)-1);
		self.ctx.beginPath();								
		self.ctx.moveTo(Math.round(this.coordLast[coordRand].x), Math.round(this.coordLast[coordRand].y));
		self.ctx.lineTo(Math.round(this.x), Math.round(this.y));
		self.ctx.closePath();				
		self.ctx.strokeStyle = 'hsla('+this.hue+', 100%, '+this.brightness+'%, '+this.alpha+')';
		self.ctx.stroke();				
		if(self.flickerDensity > 0){
			var inverseDensity = 50 - self.flickerDensity;					
			if(rand(0, inverseDensity) === inverseDensity){
				self.ctx.beginPath();
				self.ctx.arc(Math.round(this.x), Math.round(this.y), rand(this.lineWidth,this.lineWidth+3)/2, 0, Math.PI*2, false)
				self.ctx.closePath();
				var randAlpha = rand(50,100)/100;
				self.ctx.fillStyle = 'hsla('+this.hue+', 100%, '+this.brightness+'%, '+randAlpha+')';
				self.ctx.fill();
			}	
		}
	};

 
这段JS代码的功能是实现烟花爆炸后的小颗粒的绘制，从draw方法中可以看出，创建几个随机点，烟花颗粒即可在这个范围的随机点中散落。

var Firework = function(startX, startY, targetX, targetY){
		this.x = startX;
		this.y = startY;
		this.startX = startX;
		this.startY = startY;
		this.hitX = false;
		this.hitY = false;
		this.coordLast = [
			{x: startX, y: startY},
			{x: startX, y: startY},
			{x: startX, y: startY}
		];
		this.targetX = targetX;
		this.targetY = targetY;
		this.speed = self.fworkSpeed;
		this.angle = Math.atan2(targetY - startY, targetX - startX);
		this.shockwaveAngle = Math.atan2(targetY - startY, targetX - startX)+(90*(Math.PI/180));
		this.acceleration = self.fworkAccel/100;
		this.hue = self.currentHue;
		this.brightness = rand(50, 80);
		this.alpha = rand(50,100)/100;
		this.lineWidth = self.lineWidth;
		this.targetRadius = 1;
	};
	Firework.prototype.update = function(index){
		self.ctx.lineWidth = this.lineWidth;
		vx = Math.cos(this.angle) * this.speed,
		vy = Math.sin(this.angle) * this.speed;
		this.speed *= 1 + this.acceleration;				
		this.coordLast[2].x = this.coordLast[1].x;
		this.coordLast[2].y = this.coordLast[1].y;
		this.coordLast[1].x = this.coordLast[0].x;
		this.coordLast[1].y = this.coordLast[0].y;
		this.coordLast[0].x = this.x;
		this.coordLast[0].y = this.y;
		if(self.showTarget){
			if(this.targetRadius < 8){
				this.targetRadius += .25 * self.dt;
			} else {
				this.targetRadius = 1 * self.dt;	
			}
		}
		if(this.startX >= this.targetX){
			if(this.x + vx <= this.targetX){
				this.x = this.targetX;
				this.hitX = true;
			} else {
				this.x += vx * self.dt;
			}
		} else {
			if(this.x + vx >= this.targetX){
				this.x = this.targetX;
				this.hitX = true;
			} else {
				this.x += vx * self.dt;
			}
		}
		if(this.startY >= this.targetY){
			if(this.y + vy <= this.targetY){
				this.y = this.targetY;
				this.hitY = true;
			} else {
				this.y += vy * self.dt;
			}
		} else {
			if(this.y + vy >= this.targetY){
				this.y = this.targetY;
				this.hitY = true;
			} else {
				this.y += vy * self.dt;
			}
		}				
		if(this.hitX && this.hitY){
			var randExplosion = rand(0, 9);
			self.createParticles(this.targetX, this.targetY, this.hue);
			self.fireworks.splice(index, 1);					
		}
	};
	Firework.prototype.draw = function(){
		self.ctx.lineWidth = this.lineWidth;
		var coordRand = (rand(1,3)-1);					
		self.ctx.beginPath();							
		self.ctx.moveTo(Math.round(this.coordLast[coordRand].x), Math.round(this.coordLast[coordRand].y));
		self.ctx.lineTo(Math.round(this.x), Math.round(this.y));
		self.ctx.closePath();
		self.ctx.strokeStyle = 'hsla('+this.hue+', 100%, '+this.brightness+'%, '+this.alpha+')';
		self.ctx.stroke();	
		if(self.showTarget){
			self.ctx.save();
			self.ctx.beginPath();
			self.ctx.arc(Math.round(this.targetX), Math.round(this.targetY), this.targetRadius, 0, Math.PI*2, false)
			self.ctx.closePath();
			self.ctx.lineWidth = 1;
			self.ctx.stroke();
			self.ctx.restore();
		}
		if(self.showShockwave){
			self.ctx.save();
			self.ctx.translate(Math.round(this.x), Math.round(this.y));
			self.ctx.rotate(this.shockwaveAngle);
			self.ctx.beginPath();
			self.ctx.arc(0, 0, 1*(this.speed/5), 0, Math.PI, true);
			self.ctx.strokeStyle = 'hsla('+this.hue+', 100%, '+this.brightness+'%, '+rand(25, 60)/100+')';
			self.ctx.lineWidth = this.lineWidth;
			self.ctx.stroke();
			self.ctx.restore();
		}								 
	};

 
这段JS代码是创建烟花实例的，我们也可以从draw方法中看出，当我们鼠标点击画布中的某点时，烟花发射的目的地就在那个点上。
这款HTML5 Canvas烟花效果的核心代码就是这样，全部的代码还请各位下载源代码研究。
源码下载：html5-canvas-fireworks

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