看了一个烟花的html作品

最近老大想把项目改成响应式，一直在学习没时间更新博客。今天看到一个原生的js烟花项目，感觉很好，把记下来，以后把妹用。

[run]<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8"/>
<meta name="viewport" content="width=device-width"/>
<title>烟花</title>
<style type="text/css">
body{
    background-color: black;
    margin: 0;
}
#canvas{
    cursor: pointer;
}
</style>
</head>
<body>
<canvas id="canvas"></canvas>
<script type="text/javascript">
    window.requestAnimFrame = (function () {
      return window.requestAnimFrame ||
             window.webkitRequestAnimationFrame ||
             window.mozRequestAnimationFrame ||
             window.oRequestAnimationFrame ||
             window.msRequestAnimationFrame ||
             function(callback){
                window.setTimeout(callback,1000 / 60);
             };
    })();
    Function.prototype.extend = function (oContext, bIsStatic) {
        var oThis = (typeof bIsStatic != 'undefined' && bIsStatic)? this: this.prototype;
        for ( var prop in oContext) {
            oThis[prop] = oContext[prop];
        }
    }
    var opt = {
      canvas : document.getElementById('canvas'),
      ctx: document.getElementById('canvas').getContext('2d'),
      w: window.innerWidth,
      h: window.innerHeight,
      fireworks: [],//烟花
      grains: [],//粒子
      x: 0,
      y: 0,
      mousedown: false,
      hue: 0,//色调
      totalLimite: 5,
      limite: 0,
      totalTime: 80,
      time: 0
    };
    opt.canvas.width = opt.w;
    opt.canvas.height = opt.h;
    function random(min,max){
      return Math.random()*(max-min)+min;
    }
    function calcuDis(x1,y1,x2,y2){
      return Math.sqrt(Math.pow(x1-x2,2)+Math.sqrt(y1-y2,2));
    }
    function Firework( x1, y1, x2, y2 ) {
      this.x = this.x1 = x1;
      this.y = this.y1 = y1;
      this.x2 = x2;
      this.y2 = y2;
      this.target = calcuDis( x1, y1, x2, y2 );
      this.distance = 0;
      this.position = [];
      for(var i = 2; i >= 0; i--) {
        this.position.push( [ this.x, this.y ] );
      }
      this.angle = Math.atan2( y2 - y1, x2 - x1 );
      this.speed = 2;
      this.acceleration = 1.05;//加速度
      this.lightness = random( 50, 70 );
      this.targetRadius = 1;
    }
    Firework.extend({
        update: function(index) {
            this.position.pop();
            this.position.unshift( [ this.x, this.y ] );
            if( this.targetRadius < 8 ) {
              this.targetRadius += 0.3;
            } else {
              this.targetRadius = 1;
            }
            this.speed *= this.acceleration;
            var x = Math.cos( this.angle ) * this.speed,
                y = Math.sin( this.angle ) * this.speed;
            this.distance = calcuDis( this.x1, this.y1, this.x + x, this.y + y );
            if( this.distance >= this.target ) {
              for(var i = 50; i >= 0; i--) {
                opt.grains.push( new Grain( this.x2, this.y2 ) );
              }
              opt.fireworks.splice( index, 1 );
            } else {
              this.x += x;
              this.y += y;
            }
        },
        draw: function() {
            opt.ctx.beginPath();
            opt.ctx.moveTo( this.position[ this.position.length - 1][ 0 ], this.position[ this.position.length - 1][ 1 ] );
            opt.ctx.lineTo( this.x, this.y );
            opt.ctx.strokeStyle = 'hsl(' + opt.hue + ', 100%, ' + this.lightness + '%)';
            opt.ctx.stroke();
            opt.ctx.closePath();
            opt.ctx.beginPath();
            opt.ctx.arc( this.x2, this.y2, this.targetRadius, 0, Math.PI * 2 );
            opt.ctx.stroke();
            opt.ctx.closePath();
        }
    });
    function Grain( x, y ) {
      this.x = x;
      this.y = y;
      this.position = [];
      for(var i = 4; i >= 0; i--) {
        this.position.push( [ this.x, this.y ] );
      }
      this.angle = random( 0, Math.PI * 2 );
      this.speed = random( 1, 10 );
      this.friction = 0.95;
      this.gravity = 1;
      this.hue = random( opt.hue - 10, opt.hue + 10 );
      this.lightness = random( 50, 80 );
      this.alpha = 1;
      this.decay = random( 0.01, 0.03 );
    }
    Grain.extend({
        update: function(index) {
            this.position.pop();
            this.position.unshift( [ this.x, this.y ] );
            this.speed *= this.friction;
            this.x += Math.cos( this.angle ) * this.speed;
            this.y += Math.sin( this.angle ) * this.speed + this.gravity;
            this.alpha -= this.decay;
            if( this.alpha <= this.decay ) {
              opt.grains.splice( index, 1 );
            }
        },
        draw: function() {
            opt.ctx.beginPath();
            opt.ctx.moveTo( this.position[ this.position.length - 1 ][ 0 ], this.position[ this.position.length - 1 ][ 1 ] );
            opt.ctx.lineTo( this.x, this.y );
            opt.ctx.strokeStyle = 'hsla(' + this.hue + ', 100%, ' + this.lightness + '%, ' + this.alpha + ')';
            opt.ctx.stroke();
            opt.ctx.closePath();
        }
    });
    function loop(){
      opt.ctx.globalCompositeOperation = 'destination-out';
      opt.ctx.fillStyle = 'rgba(0, 0, 0, 0.5)';
      opt.ctx.fillRect( 0, 0, opt.w, opt.h );
      opt.ctx.globalCompositeOperation = 'lighter';
      opt.hue += 0.5;
      var i = opt.fireworks.length;
      while( i-- ) {
        opt.fireworks[ i ].draw();
        opt.fireworks[ i ].update( i );
      }
      i = opt.grains.length;
      while( i-- ) {
        opt.grains[ i ].draw();
        opt.grains[ i ].update( i );
      }
      if( opt.time >= opt.totalTime ) {
        if( !opt.mousedown ) {
          opt.fireworks.push( new Firework( opt.w / 2, opt.h, random( 0, opt.w ), random( 0, opt.h / 2 ) ) );
          opt.time= 0;
        }
      } else {
        opt.time++;
      }
      if( opt.limite >= opt.totalLimite ) {
        if( opt.mousedown ) {
          opt.fireworks.push( new Firework( opt.w / 2, opt.h, opt.x, opt.y ) );
          opt.limite = 0;
        }
      } else {
        opt.limite++;
      }
      requestAnimFrame(loop);
    }
    opt.canvas.onmousemove = function(e){
      opt.x = e.pageX - opt.canvas.offsetLeft;
      opt.y = e.pageY - opt.canvas.offsetTop;
    }
    opt.canvas.onmousedown = function(e){
      opt.mousedown = true;
    }
    opt.canvas.onmouseup = function(e){
      opt.mousedown = false;
    }
    window.onload= function(){
      loop();
    };
</script>
</body>
</html>