本文作者html5tricks，转载请注明出处
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：
<div id=”gui”></div>
<div id=”canvas-container”>
<div id=”mountains2″></div>
<div id=”mountains1″></div>
<div id=”skyline”></div>
</div>
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：
#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。
不错的效果，赞一个
哪一个代码是可以放大烟花的啊
这个超好用，基本想要什么效果的烟花都可以配置出来
很酷。