//绘制点
function drawPoints(m,n){
      //创建临时存储碎片
    var frag = document.createDocumentFragment();
    //创建span
        var oSpan = document.createElement('span');
    

        //oSpan元素相关操作
        //To do...
        oSpan.style.cssText = "position:absolute;border:1px solid red; width:1rem;height:1rem;background-color:red;boeder-radius:50%;";
        oSpan.style.left = m/15+ "rem";
        oSpan.style.right = n/15 + "rem";


        //将oSpan追加到临时碎片文档
        frag.appendChild(oSpan);

        //追加到Body
        document.body.appendChild(frag);
    
    }