歌手详情页：下拉方大歌手图片

1.缩放图片；

  // 背景图片的缩放
          let scale = 1
          const percent = Math.abs(newY/this.imageHeight)//这么计算，图片的高度相当于增加了newY;
          if(newY > 0){//向下拉的时候
            scale = 1 + percent
          }
          this.$refs.bgImage.style['transform'] = `scale(${scale})`
          this.$refs.bgImage.style['webkittransform']  = `scale(${scale})`
        }

注意：将北京图片的transfomr-origin:top;