最近做了个播放页面，标题和一个iframe;需要对这个iframe可以进行网页涂鸦。
网页涂鸦肯定是canvas了。网上找了个差不多的，实验下来问题很多，干脆自己一步步修改，学习。
效果：
本项目没有引入其他的任何工具库，复制代码可以直接运行，下面贴出代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>小小英语-阅读</title>
<meta name="viewport" content="width=device-width,height=device-height,initial-scale=1.0,maximum-scale=1.0,user-scalable=no">
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-status-bar-style" content="black">
<meta name="format-detection" content="telephone=no">
<meta name="description" content="数千册优质分级阅读绘本">
<style>
*{
padding:0;margin:0;
}
li{
list-style-type:none;
}
html,body{
height:100%;
}
.content-page{
min-width:1500px;
min-height: 100%;
background:#f6f6f6;
}
#page{
position:relative;
width:1200px;
margin:0 auto;
border-top:1px solid rgba(0,0,0,0)
}
h3{
position: relative;
margin:40px 0;
color:#ff8e5d;
font-size:30px;
text-align:center;
}
.back{
position:absolute;
left:0;
top:50%;
transform:translate(0,-50%);
font-family:PingFang-SC-Regular;
font-size:20px;
padding-left:20px;
background:url(‘../assets/images/icon_back-red.png‘) no-repeat;
background-size:20px 20px;
}
#content-iframe{
width:100%;
background: #ccc;
min-height: 800px;
border:none;
}
#canvas{
position:absolute;
left:0;
top:0;
z-index:100;
cursor:default;
top:120px;
left:50%;
transform:translate(-50%,0);
display: none;/*canvas刚进来是隐藏的，需要选颜色激活*/
}
.right-bar{
width:100px;
position: absolute;
right:-120px;
top:120px;
color:#000;
z-index:1;
}
.word{
font-size:24px;
font-family:FredokaOne-Regular;
color:rgba(255,142,93,1);
text-align:center;
}
.right-bar>span{
display: block;
width:90px;
height:40px;
color:#fff;
font-size:16px;
padding:0;
line-height: 40px;
border:none;
background: #FF8E5D;
margin:18px auto;
text-align: center;
cursor: pointer;
}
.btn-active{background:#ED723D !important}
#color{
padding-left:8px;
margin-top:10px;
}
#color>i{
position:relative;
display:inline-block;
width:34px;
height:34px;
border-radius: 50%;
margin-right:8px;
margin-bottom:5px;
border:none;
cursor: pointer;
z-index:50;
}
.color-active{
position:absolute;
top:50%;
left:50%;
transform:translate(-50%,-50%);
display: block;
border: 1px solid #FF8E5D;
border-radius: 50%;
width:40px;
height:40px;
z-index:40;
display: none;
}
.i1{
background:#DF4BFF;
}
.i2{
background:#9CCB68;
}
.i3{
background:#3DC1FF;
}
.i4{
background:#FFD338;
}
.i5{
background:#FF6262;
}
.i6{
background: #000000;
}
</style>
</head>
<body>
<div class="content-page">
<div id="page">
<h3>
标题
<p class="back" @click="goBack()">
返回上一级
</p>
</h3>
<iframe id="content-iframe" :src="iframeUrl">
</iframe>
<div class="right-bar">
<div class="word">color</div>
<div id="color">
<i class="i1"><span class="color-active"></span></i>
<i class="i2"><span class="color-active"></span></i>
<i class="i3"><span class="color-active"></span></i>
<i class="i4"><span class="color-active"></span></i>
<i class="i5"><span class="color-active"></span></i>
<i class="i6"><span class="color-active"></span></i>
</div>
<span id="eraser">橡皮擦</span>
<span id="revocation">撤销</span>
<span id="clear">清除</span>
<span id="hide" class="btn-active">关闭</span>
</div>
</div>
<canvas id="canvas" width="740" height="420">您的<u>浏览器</u>不支持 canvas 标签</canvas>
</div>
<script type="text/javascript">
var paint={
load:function(){
this.x=[];//记录鼠标移动是的X坐标
this.y=[];//记录鼠标移动是的Y坐标
this.clickDrag=[];
this.lock=false;//鼠标移动前，判断鼠标是否按下
this.isEraser=false;
this.storageColor="#f00";
this.eraserRadius=15;//擦除半径值
this.color=["#DF4BFF","#9CCB68","#3DC1FF","#FFD338","#FF6262","#000000"];//画笔颜色
this.$=function(id){return typeof id=="string"?document.getElementById(id):id;};
this.canvas=this.$("canvas");
this.canvas.width=this.$(‘content-iframe‘).offsetWidth;//设定canvas的宽度
this.canvas.height=this.$(‘content-iframe‘).offsetHeight;//设定canvas的高度
if (!this.canvas.getContext) {
alert("您的浏览器不支持 canvas 标签");
return;
}
this.cxt=this.canvas.getContext(‘2d‘);
this.cxt.lineJoin = "round";//context.lineJoin - 指定两条线段的连接方式
this.cxt.lineWidth = 5;//线条的宽度
this.iptClear=this.$("clear");
this.revocation=this.$("revocation");
this.hide = this.$(‘hide‘);
this.eraser = this.$(‘eraser‘);
this.colorSpan = this.$(‘color‘).getElementsByTagName(‘span‘);//颜色的外框的span集合
this.imgArr = [];//保存每个状态,撤销的时候用到
this.touch =("createTouch" in document);//判定是否为手持设备
this.StartEvent = this.touch ? "touchstart" : "mousedown";//支持触摸式使用相应的事件替代
this.MoveEvent = this.touch ? "touchmove" : "mousemove";
this.EndEvent = this.touch ? "touchend" : "mouseup";
this.bind();
},
bind:function(){
var t=this;
this.hide.onclick = function(){
t.canvas.style.display = ‘none‘;
t.eraser.className = "";
t.hide.className = ‘btn-active‘
t.hideColorSpan();
}
/*清除画布*/
this.iptClear.onclick=function(){
t.cxt.clearRect(0, 0, t.canvas.width, t.canvas.height-1);
};
/*鼠标按下事件，记录鼠标位置，并绘制，解锁lock，打开mousemove事件*/
this.canvas[‘on‘+t.StartEvent]=function(e){
// debugger;
t.imgArr.push(t.cxt.getImageData(0, 0,t.canvas.width,t.canvas.height));
var touch=t.touch ? e.touches[0] : e;
var box = t.canvas.getBoundingClientRect();
var _x = (touch.clientX - box.left) * t.canvas.width / box.width
var _y = (touch.clientY - box.top) * t.canvas.height / box.height
if(t.isEraser){
t.resetEraser(_x,_y,touch);
}else{
t.movePoint(_x,_y);//记录鼠标位置
t.drawPoint();//绘制路线
}
t.lock=true;
};
/*鼠标移动事件*/
this.canvas[‘on‘+t.MoveEvent]=function(e){
// console.log(t.touch);
var touch=t.touch ? e.touches[0] : e;
//var touch = e;
if(t.lock){
var touch=t.touch ? e.touches[0] : e;
var box = t.canvas.getBoundingClientRect();
var _x = (touch.clientX - box.left) * t.canvas.width / box.width
var _y = (touch.clientY - box.top) * t.canvas.height / box.height
if(t.isEraser){
t.resetEraser(_x,_y,touch);
}
else{
t.movePoint(_x,_y,true);//记录鼠标位置
t.drawPoint();//绘制路线
}
}
};
this.canvas[‘on‘+t.EndEvent]=function(e){
/*重置数据*/
t.lock=false;
t.x=[];
t.y=[];
t.clickDrag=[];
clearInterval(t.Timer);
t.Timer=null;
};
this.revocation.onclick=function(){
if(t.imgArr.length>0){
t.cxt.putImageData(t.imgArr[t.imgArr.length-1], 0, 0);
t.imgArr.pop();
}
};
this.changeColor();
/*橡皮擦*/
this.$("eraser").onclick=function(e){
if(t.hide.className ===‘‘){
t.hideColorSpan();//这里是
t.isEraser=true;
t.eraser.className = ‘btn-active‘;
}
};
},
movePoint:function(x,y,dragging){
// debugger;
/*将鼠标坐标添加到各自对应的数组里*/
this.x.push(x);
this.y.push(y);
this.clickDrag.push(y);
},
drawPoint:function(x,y,radius){
for(var i=0; i < this.x.length; i++){
this.cxt.beginPath();//context.beginPath() , 准备绘制一条路径
if(this.clickDrag[i] && i){//当是拖动而且i!=0时，从上一个点开始画线。
this.cxt.moveTo(this.x[i-1], this.y[i-1]);//context.moveTo(x, y) , 新开一个路径，并指定路径的起点
}else{
this.cxt.moveTo(this.x[i]-1, this.y[i]);
}
this.cxt.lineTo(this.x[i], this.y[i]);//context.lineTo(x, y) , 将当前点与指定的点用一条笔直的路径连接起来
this.cxt.closePath();//context.closePath() , 如果当前路径是打开的则关闭它
this.cxt.stroke();//context.stroke() , 绘制当前路径
}
},
preventDefault:function(e){
/*阻止默认*/
var touch=this.touch ? e.touches[0] : e;
if(this.touch)touch.preventDefault();
else window.event.returnValue = false;
},
changeColor:function(){
/*为按钮添加事件*/
var t=this,iptNum=this.$("color").getElementsByTagName("i");
for(let i=0,l=iptNum.length;i<l;i++){//这里要么用let,要么用闭包
iptNum[i].index=i;
iptNum[i].onclick=function(){
t.hideColorSpan();//隐藏所有颜色的选中
t.colorSpan[i].style.display = ‘block‘//选中点击的颜色
t.canvas.style.display = ‘block‘;
// debugger;
t.cxt.save();
t.cxt.strokeStyle = t.color[this.index];
t.storageColor=t.color[this.index];
t.$("hide").className = ‘‘;
t.$("eraser").className = ‘‘;//清除橡皮擦选中状态
t.cxt.strokeStyle = t.storageColor;
t.isEraser=false;
}
}
},
resetEraser:function(_x,_y,touch){
var t=this;
//this.cxt.lineWidth = 30;
/*source-over 默认,相交部分由后绘制图形的填充(颜色,渐变,纹理)覆盖,全部浏览器通过*/
t.cxt.globalCompositeOperation = "destination-out";
t.cxt.beginPath();
t.cxt.arc(_x, _y, t.eraserRadius, 0, Math.PI * 2);
t.cxt.strokeStyle = "rgba(250,250,250,0)";
t.cxt.fill();
t.cxt.globalCompositeOperation = "source-over"
},
hideColorSpan:function(){//隐藏颜色的选中状态
for(var i =0,length = this.colorSpan.length;i<length;i++){
this.colorSpan[i].style.display = ‘none‘
}
}
};
paint.load();
</script>
</body>
</html>
原文：http://www.cnblogs.com/xiaochongchong/p/7833777.html