text: var dustObj = function(){
      this.x = [];
      this.y = [];
      this.amp = [];
      this.pics = [];
      this.NO = [];
      this.alpha = [];
  }
  dustObj.prototype.num = 30;
      
  dustObj.prototype.init = function(){
  
      for(var i=0;i<this.num;i++){
          this.x[i] = Math.random()*canWidth;
          this.y[i] = Math.random()*canHeigh;
          this.amp[i] = 20 + Math.random()*50;
          this.NO[i] = Math.floor(Math.random()*7);//归一（0，7）
      }
      this.alpha = 0;
  
  
      for(var i=0;i<7;i++){
          this.pics[i] = new Image();
          this.pics[i].src = "./src/dust"+i+".png";
      }
  }
  dustObj.prototype.draw = function(){
      //console.log(this.pics);
      this.alpha += deltaTime * 0.0008;
      var l = Math.sin(this.alpha);
      for(var i=0;i<this.num;i++){
          var no = this.NO[i];
          ctx1.drawImage(this.pics[no],this.x[i]+this.amp[i]*l,this.y[i]);
      }
  }
  