HTML5 Canvas 超炫酷烟花绽放动画教程

这是一个很酷的HTML5 Canvas动画，它将模拟的是我们现实生活中烟花绽放的动画特效，效果非常逼真，但是毕竟是电脑模拟，带女朋友看就算了，效果还是差了点，呵呵。这个HTML5 Canvas动画有一点比较出色，就是其性能，Chrome上基本没有卡的感觉，就算你放出很多烟花也一样。

你可以在这里看在线演示

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:;
}

canvas {
    cursor: crosshair;
    display: block;
    position: relative;
    z-index:;
}

canvas:active {
    cursor: crosshair;
}

#skyline {
    background: url(skyline.png) repeat-x 50% 0;
    bottom:;
    height: 135px;
    left:;
    position: absolute;
    width: 100%;
    z-index:;
}

#mountains1 {
    background: url(mountains1.png) repeat-x 40% 0;
    bottom:;
    height: 200px;
    left:;
    position: absolute;
    width: 100%;
    z-index:;
}

#mountains2 {
    background: url(mountains2.png) repeat-x 30% 0;
    bottom:;
    height: 250px;
    left:;
    position: absolute;
    width: 100%;
    z-index:;
}

#gui {
    right:;
    position: fixed;
    top:;
    z-index:;
}

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。源代码下载>>