js画线

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<body>

    <div id="main">

    </div>

    <div id="fd" style="filter:alpha(opacity=100);opacity:1;position: absolute;text-align: center; z-index:9999; width: 100px; height: 78px; left: 155px; top: 177px; border-right: #0099ff 1px solid; border-top: #0099ff 1px solid; border-left: #0099ff 1px solid; border-bottom: #0099ff 1px solid;">

        拖动的div

    </div>

    <script language="javascript">

   //----------------鼠标拖动-------------------

   var od = document.getElementById("fd");

    var dx,dy,mx,my,mouseD;

    var odrag;

    var isIE = document.all ? true : false;

    document.onmousedown = function(e){

        var e = e ? e : event;

        if(e.button == (document.all ? 1 : 0))

        {

            mouseD = true;

        }

    }

    document.onmouseup = function(){

        mouseD = false;

        odrag = "";

        if(isIE)

        {

            od.releaseCapture();

            od.filters.alpha.opacity = 100;

        }

        else

        {

            window.releaseEvents(od.MOUSEMOVE);

            od.style.opacity = 1;

        }

    }

    od.onmousedown = function(e){

        odrag = this;

        var e = e ? e : event;

        if(e.button == (document.all ? 1 : 0))

        {

            mx = e.clientX;

            my = e.clientY;

            od.style.left = od.offsetLeft + "px";

            od.style.top = od.offsetTop + "px";

            if(isIE)

            {

                od.setCapture();

                od.filters.alpha.opacity = 50;

            }

            else

            {

                window.captureEvents(Event.MOUSEMOVE);

                od.style.opacity = 0.5;

            }

        }

    }

    document.onmousemove = function(e){

        var e = e ? e : event;

        if(mouseD==true && odrag)

        {

            var mrx = e.clientX - mx;

            var mry = e.clientY - my;

            var result=parseInt(od.style.left) +mrx;

            od.style.left = parseInt(od.style.left) +mrx + "px";

            od.style.top = parseInt(od.style.top) + mry + "px";

            mx = e.clientX;

            my = e.clientY;

         var html="";

         var x=od.style.left;

         var y=od.style.top;

         var lineHtml=drawLine(0,0,parseInt(x),parseInt(y),"red");

         document.getElementById("main").innerHTML=lineHtml;

        }

    }

    function drawLine(x0, y0, x1, y1, color) {

        var rs = "";

        if (y0 == y1)  //画横线

        {

            if (x0 > x1) {

                var t = x0;

                x0 = x1;

                x1 = t;

            }

            rs = "<span style='top:" + y0 + ";left:" + x0 + ";position:absolute;font-size:1px;background-color:" + color + ";height:1; width:" + Math.abs(x1 - x0) + "'></span>";

        }

        else if (x0 == x1)  //画竖线

        {

            if (y0 > y1) {

                var t = y0;

                y0 = y1;

                y1 = t;

            }

            rs = "<span style='top:" + y0 + ";left:" + x0 + ";position:absolute;font-size:1px;background-color:" + color + ";width:1;height:" + Math.abs(y1 - y0) + "'></span>";

        }

        else {

            var lx = x1 - x0;

            var ly = y1 - y0;

            var l = Math.sqrt(lx * lx + ly * ly);

            rs = new Array();

            for (var i = 0; i < l; i += 1) {

                var p = i / l;

                var px = parseInt(x0 + lx * p);

                var py = parseInt(y0 + ly * p);

                rs[rs.length] = "<span style='top:" + py + ";left:" + px + ";height:1;width:1;position:absolute;font-size:1px;background-color:" + color + "'></span>";

            }

            rs = rs.join("");

        }

        return rs;

    }

    </script>

</body>