javascript实现的白板效果(可以直接在网页上写字)

　　<script type="text/javascript">

　　var ball;

　　var mouseX = 100;

　　var mouseY = 100;

　　var angle = 0;

　　var radius = 0;

　　function draw(){

　　ball = document.createElement("span");

　　ball.style.position = "absolute";

　　ball.style.color = "#FF0000";

　　ball.style.zIndex = 999999999;

　　ball.innerHTML = "●";

　　document.body.appendChild(ball);

　　ball.style["left"] = mouseX+ "px";

　　ball.style["top"] = mouseY+ "px";

　　}

　　function MousePos(e)

　　{

　　e = e || window.event;

　　var x,y;

　　if(!document.all){

　　x = e.pageX;

　　y = e.pageY;

　　}

　　else{

　　x = event.clientX + document.documentElement.scrollLeft;

　　y = event.clientY + document.documentElement.scrollTop;

　　}

　　return {x:x,y:y};

　　}

　　function setXY(e)

　　{

　　e = e || window.event;

　　var pos = MousePos(e);

　　mouseX = pos.x;

　　mouseY = pos.y;

　　draw();

　　}

　　window.onload = function(){

　　document.documentElement.onmousemove = function(e){

　　e = e || window.event;

　　setXY(e);

　　};

　　}

　　</script>