canvas实例--签字

var canvas=document.querySelector('#test');
if(canvas.getContext){
    var ctx=canvas.getContext("2d");}
canvas.onmousedown=function (ev) {
ev=ev||event;
if(canvas.setCapture){
    canvas.setCapture();}
ctx.save();  //在栈里添加黑色
ctx.strokeStyle='pink';   //将样式改成粉色
    // ctx.lineWidth=10;
ctx.beginPath();  ctx.moveTo(ev.clientX-canvas.offsetLeft,ev.clientY-canvas.offsetLeft);
    //鼠标移动时发生
document.onmousemove=function (ev) {
    ev=ev||event;
ctx.lineTo(ev.clientX-canvas.offsetLeft,ev.clientY-canvas.offsetLeft);
    ctx.stroke();
    ctx.restore();};
document.onmouseup=function () {
document.onmousemove=document.onmouseup=null;
if(document.releaseCapture){
    document.releaseCapture();}};
// ctx.restore();
return false;}