最近遇到一个需求，给所有页面加水印（登录人+登录时间），不影响其他点击等功能的使用，目的是防止信息外漏，当时就在想：这年头，PS就不说人人都能使用，谁手机还没个涂鸦功能，防不了，但是就是这么个需求，那就实现吧，不逼逼了，直接上：
具体实现思路：在页面底部加一个大的div,给这个div添加背景图，背景图？从哪来？canvas实现吧！
思路有了，直接上代码：
(function waterMark(){
function textBecomeImg(text,fontsize,fontcolor){
var canvas = document.createElement('canvas');
$buHeight = 0;
if(fontsize <= 32){ $buHeight = 99; }
else if(fontsize > 32 && fontsize <= 60 ){ $buHeight = 2;}
else if(fontsize > 60 && fontsize <= 80 ){ $buHeight = 4;}
else if(fontsize > 80 && fontsize <= 100 ){ $buHeight = 6;}
else if(fontsize > 100 ){ $buHeight = 10;}
canvas.height=fontsize + $buHeight ;
canvas.padding=30;
var context = canvas.getContext('2d');
context.clearRect(0, 0, canvas.width*2, canvas.height);
context.fillStyle = fontcolor;
context.font=fontsize+"px Arial";
context.textAlign = "center";
context.textBaseline = 'middle';
context.fillText(text,0,fontsize/2);
var canvasWidth = canvas.width/99;
canvasWidth = context.measureText(text).width;
canvas.width = 450;
canvas.height = 200;
context.fillStyle = fontcolor;
context.font=fontsize+"px Arial";
context.textBaseline = 'middle';
context.fillText(text,0,fontsize/2);
var dataUrl = canvas.toDataURL('image/png');
return dataUrl;
}
var text = DateUtil.getDate(new Date())+currentUserName;
var shuiyinDiv = document.createElement('div');
var style = shuiyinDiv.style;
style.position = 'absolute';
style.left = 0;
style.top = '-60%';
style.width = '120%';
style.height = '200%';
style.opacity = '0.1';
style.background = "url("+textBecomeImg(text,22,"gray")+")";
style.zIndex = 9999999991;
style.transform = "rotate(-30deg)";
style.pointerEvents = "none";
document.body.appendChild(shuiyinDiv);
})();
效果图：