code: function(){
  
      var sprites = this.sprites;
  
      if (Object.keys(sprites).length === 0) {
        Log.debug('no image need merge');
        this.fire('finish:merge', {exit: true});
      } else {
        //拼图
        Api.mergeImages([this.get('file'), sprites], this._finishMerge, this);
      }
    }
docs: 生成sprite图片
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