DIV CSS 佈局教程網

這是一個很酷的Html5 Canvas動畫，它將模擬的是我們現實生活中煙花綻放的動畫特效，效果非常逼真，但是畢竟是電腦模擬，帶女朋友看就算了，效果還是差了點，呵呵。這個 Html5 Canvas動畫有一點比較出色，就是其性能，Chrome上基本沒有卡的感覺，就算你放出很多煙花也一樣。

你可以在這裡看在線演示

下面我們來簡單分析一下實現這款Html5煙花特效的過程及代碼，主要由Html代碼、CSS代碼以及Javascript代碼組成，當然Javascript代碼是最重要的。

Html代碼：

<div id=”gui”></div>
<div id=”canvas-container”>
<div id=”Mountains2″></div>
<div id=”Mountains1″></div>
<div id=”skyline”></div>
</div>

Html的結構非常簡單，即構造了一個canvas容器，我們會利用JS在這個容器中生成一個Canvas對象。看最後的JS代碼你就會知道了。
CSS代碼：


#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代碼沒什麼特別，主要也就定義一下背景色和邊框之類的。

接下來是最重要的Javascript代碼。
Javascript代碼：


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;
        };

    };



這段JS代碼主要是往canvas容器中構造一個Canvas對象，並且對這個canvas對象的外觀以及動畫屬性作了初始化。


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();
            }    
        }
    };



這段JS代碼的功能是實現煙花爆炸後的小顆粒的繪制，從draw方法中可以看出，創建幾個隨機點，煙花顆粒即可在這個范圍的隨機點中散落。


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();
        }                                 
    };

這段JS代碼是創建煙花實例的，我們也可以從draw方法中看出，當我們鼠標點擊畫布中的某點時，煙花發射的目的地就在那個點上。

這款Html5 Canvas煙花效果的核心代碼就是這樣，全部的代碼還請各位下載源代碼研究。源代碼下載>>