uni-app 使用web-view引入本地html，用 canvas制作涂鸦功能

uni-app canvas 技术

uni-app 使用web-view引入本地html，用 canvas制作涂鸦功能

2019-04-02 12:17 4201 更新于 2019-04-02 12:18

之前用[canvas接口](https://uniapp.dcloud.net.cn/api/canvas/CanvasContext?id=canvascontextarc "canvas接口")实现了功能，但是打包成app后，发现，在app里使用，会卡顿，不流畅等问题

然后用[web-view组件](https://uniapp.dcloud.net.cn/component/web-view?id=web-view "web-view组件")加载本地html页面，用js 重写，在app上的效果还可以，html源码如下
```
<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8" />
		<meta name="viewport" content="width=device-width, initial-scale=1">
		<title>画室</title>
		<style type="text/css">
			body{
				margin: 0px;
				padding: 0px;
			}
			.page-head{
				padding: 10px;
			}
			.segmented-control{
				border:1px solid #0076FF;
				border-radius: 5px;
				display: flex;
				justify-content: center;
				width: 75%;
				font-size: 13px;
				border-radius: 4px;
				box-sizing: border-box;
				margin: 0 auto;
				overflow: hidden;
			}
			.segmented-control .control-item{
				flex: 1;
				text-align: center;
				line-height: 28px;
				border-right: 1px solid #0076FF;
			}
			.segmented-control .bottom{
				background: #007AFF;
				color: #fff;
			}
			.colors-area{
				padding-bottom: 10px;
				white-space:nowrap;
				overflow-x:auto;
				overflow-y:hidden;
			}
			.colors-area .color-item{
				display: inline-block;
				margin: 0px 5px;
				border-radius: 25px;
				width: 25px;
				height: 25px;
				border: 1px solid #999;
			}
			.imgs-area{
				padding-bottom: 10px;
				white-space:nowrap;
				overflow-x:auto;
				overflow-y:hidden;
				display: flex;
				flex-direction: row;
			}
			.img-item{
				margin: 5px;
				padding: 5px 10px;
				background: #FE390E;
				text-align: center;
				color:#fff;
				font-weight: 400;
				font-size: 14px;
				border-radius: 5px;
			}
			#myCanvas{
				/* width: 300px; */
				border-top: 1px solid #eee;
				border-bottom: 1px solid #eee;
			}
			.btn-area{
				margin: 5px auto;
				margin-top: 10px;
				display: flex;
				flex-direction: row;
			}
			.btn-item{
				color: #fff;
				text-align: center;
				width: 50%;
			}
			.btn-item span{
				padding: 5px 0px;
				border-radius: 30px;
				font-size: 16px;
				width: 100px;
			}
			.m-btn{
				display: inline-block;
				background: #FFCD00;
				box-shadow: 0px 2px 5px #999;
			}
			/* .btn-submit{
				display: inline-block;
				background: #FFCD00;
			}
			.btn-cancel{
				display: inline-block;
				background: #FFCD00;
			} */
			/* 弹窗 */
			.dialog-area{
				display: none;
			}
			.dialog-area .uni-mask {
				position: fixed;
				z-index: 999;
				top: 0;
				right: 0;
				left: 0;
				bottom: 0;
				background: rgba(0,0,0,.6);
			}
			.dialog-area .uni-modal {
				position: fixed;
				z-index: 999;
				width: 80%;
				max-width: 300px;
				top: 50%;
				left: 50%;
				-webkit-transform: translate(-50%,-50%);
				transform: translate(-50%,-50%);
				background-color: #fff;
				text-align: center;
				border-radius: 3px;
				overflow: hidden;
			}
			.dialog-area .uni-modal__title {
				font-weight: 400;
				font-size: 18px;
				word-wrap: break-word;
				word-break: break-all;
				overflow: hidden;
				text-overflow: ellipsis;
				display: -webkit-box;
				-webkit-line-clamp: 2;
				-webkit-box-orient: vertical;
			}
			.dialog-area .uni-modal__bd {
				padding: 1.3em 1.6em 1.3em;
				min-height: 40px;
				font-size: 15px;
				line-height: 1.4;
				word-wrap: break-word;
				word-break: break-all;
				color: #999;
				max-height: 400px;
				overflow-y: auto;
			}
			.dialog-area .uni-modal__hd {
				padding: 1em 1.6em .3em;
			}
			.dialog-area .uni-modal__ft {
				position: relative;
				line-height: 48px;
				font-size: 18px;
				display: -webkit-box;
				display: -webkit-flex;
				display: flex;
				border-top: 1px solid #eee;
			}
			.dialog-area .uni-modal__btn {
				display: block;
				-webkit-box-flex: 1;
				-webkit-flex: 1;
				flex: 1;
				text-decoration: none;
				-webkit-tap-highlight-color: rgba(0,0,0,0);
				position: relative;
			}
			.dialog-area .uni-modal__ft {
				position: relative;
				line-height: 48px;
				font-size: 18px;
			}
			.dialog-area .uni-modal__btn_default {
				border-right: 1px solid #eee;
			}
		</style>
		
		<script type="text/javascript" src="https://js.cdn.aliyun.dcloud.net.cn/dev/uni-app/uni.webview.1.5.0.js"></script>
		<script type="text/javascript" src="jquery.min.js"></script>
	</head>
	<body>
		<div class="page-head">
			<div class="segmented-control">
				<div class="control-item bottom">涂鸦</div>
				<div class="control-item">素描</div>
				<div class="control-item" style="border-right: 0px;">填色</div>
			</div>
		</div>
		
		<div class="colors-area">
			
		</div>
		
		<div class="imgs-area">
			
		</div>
		
		<div class="canvas-area">
			<canvas id="myCanvas" height="300"></canvas>
		</div>
		
		<div class="btn-area">
			<div class="btn-item"><span class="m-btn btn-cancel" onclick="cancel()">撤销</span></div>
			<div class="btn-item"><span class="m-btn btn-submit" id="submitDo" >发布作品</span></div>
		</div>
		<div class="dialog-area" id="dialog_area">
			<div class="uni-mask"></div>
			<div class="uni-modal">
				<div class="uni-modal__hd">
					<strong class="uni-modal__title">提示</strong>
				</div>
				<div class="uni-modal__bd">确认发布吗？</div>
				<div class="uni-modal__ft">
					<div class="uni-modal__btn uni-modal__btn_default" style="color: rgb(0, 0, 0);" onclick="submitCancel()">取消</div>
					<div class="uni-modal__btn uni-modal__btn_primary" style="color: rgb(0, 122, 255);" onclick="submitDo()">确定</div>
				</div>
			</div>
		</div>
	</body>
<script type="text/javascript">
	$('.control-item').on("tap click",function(){
		$('.control-item').siblings().removeClass('bottom');
		$(this).addClass('bottom');
	});
	//颜色-start
	var colors = [
		'#ffffff','#000000','#FF4081',
		'#FF9800','#3F51B5','#3FFB6F',
		'#EA20D8','#F5C965','#1131E4',
		'#FFFAE8','#76D6E8','#41A863',
		'#F029C4','#F05229','#B4F029',
		];
	var html = '';
	for(var k in colors){
		html += '<div class="color-item" onclick="setColor(\''+colors[k]+'\')" style="background: '+colors[k]+';"></div>';
	}
	$('.colors-area').html(html);
	//颜色-end
	//图片 -start
	var imgs = [
		{name:'老虎',url:'http://img.jam00.com/FrtvnogQn4qFIl3dWkLtBZeftZ2N'},
		{name:'皮卡丘',url:'http://img.jam00.com/20150410H0059_kKVyt.jpeg'},
		{name:'鳄鱼',url:'http://img.jam00.com/Flfbw9juhNuqvlBGMzlf2-ORaKaL'},
		{name:'古典建筑',url:'http://img.jam00.com/FoMQ4QOY7mraQkXEGrdqdKB2MKuN'},
		{name:'猴子',url:'http://img.jam00.com/20150410H0059_kKVyt.jpeg'},
		{name:'狮子',url:'http://img.jam00.com/20150410H0059_kKVyt.jpeg'},
		{name:'斑马',url:'http://img.jam00.com/20150410H0059_kKVyt.jpeg'},
		{name:'犀牛',url:'http://img.jam00.com/20150410H0059_kKVyt.jpeg'},
		{name:'大象',url:'http://img.jam00.com/20150410H0059_kKVyt.jpeg'},
		{name:'火烈鸟',url:'http://img.jam00.com/20150410H0059_kKVyt.jpeg'},
		{name:'高达',url:'http://img.jam00.com/20150410H0059_kKVyt.jpeg'},
		{name:'机器猫',url:'http://img.jam00.com/20150410H0059_kKVyt.jpeg'},
		{name:'哈士奇',url:'http://img.jam00.com/FoMQ4QOY7mraQkXEGrdqdKB2MKuN'},
		{name:'天使',url:'http://img.jam00.com/20150410H0059_kKVyt.jpeg'},
		{name:'藏羚羊',url:'http://img.jam00.com/20150410H0059_kKVyt.jpeg'},
		{name:'熊猫',url:'http://img.jam00.com/20150410H0059_kKVyt.jpeg'},
		];
	var html = '';
	for(var k in imgs){
		html += '<div class="img-item" onclick="setImg(\''+imgs[k]['url']+'\')" >'+imgs[k]['name']+'</div>';
	}
	$('.imgs-area').html(html);
	//图片 -end
	
	//绘图
	var lastX, lastY;
	var mousePressed = false;//是否点击了鼠标
	var canvas = document.getElementById('myCanvas');
	canvas.setAttribute("width",document.body.clientWidth);//设置样式不起作用
	var ctx = canvas.getContext("2d");
	//设置白色背景
	ctx.fillStyle = "#fff";
	ctx.fillRect(0, 0, canvas.width, canvas.height);
	//默认画笔颜色
	ctx.strokeStyle = '#000';
	//默认画笔宽度
	ctx.lineWidth = '1';
	//线条圆润 ,结束线帽
	ctx.lineJoin = "round";
	ctx.lineCap = "round";

$('#myCanvas').on('touchstart',function (e) {
		saveCanvasData();
		mousePressed = true;
		Draw(e.originalEvent.touches[0].clientX,e.originalEvent.touches[0].clientY,false);
    });
	$('#myCanvas').on('touchmove',function (e) {
		if (mousePressed) {
			Draw(e.originalEvent.touches[0].clientX,e.originalEvent.touches[0].clientY,true);
		}
    });
	$('#myCanvas').on('touchend',function (e) {
	    
	});
	$('#myCanvas').on('mouseup',function (e) {
        mousePressed = false;
    });
	$('#myCanvas').on('mouseleave',function (e) {
        mousePressed = false;
    });
	//绘图
	function Draw(x, y, isDown) {
		y = y - 142;
		if (isDown) {
			ctx.beginPath();
			ctx.moveTo(lastX, lastY);
			ctx.lineTo(x, y);
			ctx.closePath();
			ctx.stroke();
		}
		lastX = x; lastY = y;
	}
	//设置颜色
	function setColor(color){
		ctx.strokeStyle = color;
	}
	
	//载入图像
	function setImg(url){
		saveCanvasData();
		var img = new Image();
		img.src = url;
		img.crossOrigin = "Anonymous";
		//防止图片未加载完成,而没有操作
		img.onload = function(){
			ctx.drawImage(img,0,0,ctx.canvas.clientWidth,ctx.canvas.clientHeight);
		}
	}
	var imgData = [];//每步图像数据,用于撤销
	function saveCanvasData(){
		imgData.push(ctx.getImageData(0,0,ctx.canvas.clientWidth,ctx.canvas.clientHeight));
	}
	function getCanvasData(){
		if(imgData.length == 0){
			return false
		}
		tmpImgData = imgData.pop();
		ctx.putImageData(tmpImgData,0,0)
	}
	//撤销功能
	function cancel(){
		getCanvasData();
	}
	
	//绘图结束
	function showConfirm(){
		$('#dialog_area').show();
	}
	function submitCancel(){
		$('#dialog_area').hide();
	}
	function submitDo(){
		var base64Data = canvas.toDataURL('image/jpeg', 1);
		$('#dialog_area').hide();
		var sid = getQueryString('id');
		//向 app 发送消息
		uni.postMessage({  
			data: {  
				imgData: base64Data ,
				id:sid
			}
		});  
		uni.redirectTo({
			url: '/pages/index/studio?type=share'
		});
	}
	document.addEventListener('UniAppJSBridgeReady', function() {
		//发布作品
		document.getElementById('submitDo').addEventListener('click',function(e){
			showConfirm();
		})
		
	});
	var title = unescape(getQueryString('title'));
	$(document).attr('title',title);
	function getQueryString(name) { 
        var reg = new RegExp("(^|&)" + name + "=([^&]*)(&|$)", "i"); 
        var r = window.location.search.substr(1).match(reg); 
        if (r != null) return unescape(r[2]); 
        return null; 
    } 
</script>
</html>
```
我用了`jquery`，其实可以不使用的，你们随意

注意几点

1、加载图片时，使用如下代码，防止未加载完成时，canvas执行载入图片
```
img.onload = function(){
	...
}
```
2、将canvas背景设置为白色，防止获取图像数据时（canvas.toDataURL），是透明背景
```
ctx.fillStyle = "#fff";
```
最后来张效果图

![](https://blog.jam00.com/uploads/article/201904/02/121839vhn9oqonl3kcnk1h.jpg)

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uni-app 使用web-view引入本地html，用 canvas制作涂鸦功能