[JavaScript知识库]vue+canvas实现手写签字画板

vue+canvas实现手写签字画板

效果

预览

体验地址

用途

• 涂鸦画板
• 签名板

实现

使用canvas，通过监听鼠标动作来进行绘图。
关键代码如下：

drawing(event){
    if(!this.penClick) return;//鼠标按下状态
	const canvas = document.getElementById('canvas'); //获取canvas标签
	const ctx = canvas.getContext("2d");//创建 contextconst canvas = document.getElementById('canvas');  对象
    const stopAxisX = event.pageX;//当前鼠标x坐标
    const stopAxisY = event.pageY;//当前鼠标y坐标
	const left = document.getElementById('leftMenu');//可忽略
	const lw = left && left.offsetWidth ? (left.offsetWidth || 0) / 2 : 0;
    ctx.beginPath();//是 Canvas 2D API 通过清空子路径列表开始一个新路径的方法。 当你想创建一个新的路径时，调用此方法。
	const wsaW = window.screen.availWidth;
	const cl = canvas.offsetLeft;
	const ct = canvas.offsetTop;
    ctx.moveTo(this.startAxisX-cl,this.startAxisY - ct);//moveTo(x,y) 定义线条开始坐标
    ctx.lineTo(stopAxisX-cl,stopAxisY - ct	);//lineTo(x,y) 定义线条结束坐标
    ctx.strokeStyle = this.penColor;
    ctx.lineWidth = this.penWidth;
    ctx.lineCap = "round";
    ctx.stroke();// stroke() 方法来绘制线条
    this.startAxisX = stopAxisX;
    this.startAxisY = stopAxisY;
}

代码

JCanvasBroad.vue

<template>
	<div id="canvas-broad">
	    <canvas id="canvas" :width="width" :height="height">浏览器不支持canvas<!-- 如果不支持会显示这段文字 --></canvas>
	    <j-tab-bar v-if="toolsTabList"
				:tabList="tabList"
				:showTab="showTab">
			<template v-slot:back-ground-color>
				<div class="section">
				    <span class="info">设置背景颜色：</span>
					<input class="btn input-color" type="color" v-model="brackGroudColor" />
				</div>
			</template>
			<template v-slot:pen-color>
				<div class="section">
				    <span class="info">选择画笔颜色：</span>
					<input class="btn input-color" type="color" v-model="penColor" />
				</div>
			</template>
			<template v-slot:eraser>
				<div class="section">
				    <span class="info">选择橡皮擦：</span>
				    <button class="btn colorBtn" :style="'background-color:' + brackGroudColor + ';'" @click='setPenColor();'>{{brackGroudColor}}</button>
				</div>
				<div class="section">
					<button class="btn" @click="setBackGround()">清空画布</button>
				</div>
			</template>
			<template v-slot:pen-size>
				<div class="section">
					<span class="info">选择画笔大小：</span>
					<progress :value="progressValue" 
							style="cursor: pointer;"
							id="progress"
							max="1" 
							:title="progressValue * 100 +'%'"
							@click="setPenWidth">
					</progress>
					<span style="margin-left: 0.3125rem;">{{20 * progressValue}}px</span>
				</div>
			</template>
			<template v-slot:export>
				<div class="section">
					<span class="info">输出画板内容到下面的图片：</span>
					<button class="btn" @click="createImage();">EXPORT</button>
				</div>
				<img id="image_png">
			</template>
		</j-tab-bar>
		<template v-if="!toolsTabList">
			<div class="section">
				<button class="btn" @click="setBackGround()">清空画布</button>
			</div>
			<div class="section">
				<span class="info">选择画笔颜色：</span>
				<input class="input-color" type="color" v-model="penColor" />
			</div>
			<div class="section">
				<span class="info">设置背景颜色：</span>
				<input class="input-color" type="color" v-model="brackGroudColor" />
			</div>
			<div class="section">
				<span class="info">选择橡皮擦：</span>
				<button class="btn colorBtn" :style="'background-color:' + brackGroudColor + ';'" @click='setPenColor();'>{{brackGroudColor}}</button>
			</div>
			<div class="section">
				<span class="info">选择画笔大小：</span>
				<progress :value="progressValue" 
						style="cursor: pointer;"
						id="progress"
						max="1" 
						:title="progressValue * 100 +'%'"
						@click="setPenWidth">
				</progress>
				<span style="margin-left: 0.3125rem;">{{20 * progressValue}}px</span>
			</div>
			<div class="section">
				<span class="info">输出画板内容到下面的图片：</span>
				<button class="btn" @click="createImage();">EXPORT</button>
			</div>
			<img id="image_png">
		</template>
	</div>
</template>

<script>
	import JTabBar from '../../pagesTools/JTabBar.vue';
	export default{
		name:'JCanvasBroad',
		props:{
			height:{
				type:Number,
				default:-1
			},
			width:{
				type:Number,
				default:-1
			},
			defaultPenColor:{
				type:String,
				default:'#000000'
			},
			defaultPenSize:{
				type:Number,
				default:4
			},
			defaultBackGroundColor:{
				type:String,
				default:"#ffffff"
			},
			toolsTabList:{
				type:Boolean,
				default:false
			}
		},
		components:{
			JTabBar
		},
		watch:{
			brackGroudColor:{
				handler(newVal,oldVal){
					this.setBackGround();
				}
			}
		},
		data() {
			return{
				penColor:"#000000",
				penWidth:4,
				penClick:false,
				startAxisX:0,
				startAxisY:0,
				brackGroudColor:"#ffffff",
				progressValue:0.2,
				tabList:[{
					label:'背景颜色',
					id:'back-ground-color'
				},{
					label:'画笔颜色',
					id:'pen-color'
				},{
					label:'橡皮擦',
					id:'eraser'
				},{
					label:'画笔大小',
					id:'pen-size'
				},{
					label:'导出图片',
					id:'export'
				}],
				showTab:0
			}
		},
		created(){
			
		},
		mounted() {
			this.init();
		},
		methods:{
			//页面初始化
			init(){
				let height = this.height;
				let width = this.width;
				if(width == -1){
					const cbw = document.getElementById('canvas-broad');
					width = cbw.offsetWidth * 0.9;
					height = cbw.offsetHeight * 0.6;
					this.width = width;
					this.height = height;
				}
				this.penColor = this.defaultPenColor;
				this.brackGroudColor = this.defaultBackGroundColor;
				this.penWidth = this.defaultPenSize;
				
				let canvas = document.getElementById('canvas'); //获取canvas标签
				let ctx = canvas.getContext("2d");//创建 context 对象
				ctx.fillStyle = this.brackGroudColor;//画布背景色
				ctx.fillRect(0,0,width,height);//在画布上绘制 width * height 的矩形，从左上角开始 (0,0)
				canvas.addEventListener("mousemove",this.drawing); //鼠标移动事件
				canvas.addEventListener("mousedown",this.penDown); //鼠标按下事件
				canvas.addEventListener("mouseup",this.penUp); //鼠标弹起事件
			},
			getWidthSelect(width){
				if(width == this.penWidth){
					return "btn bg penBtn fw"
				}
				return "btn bg penBtn"
			},
			getColorSelect(color){
				if(color == this.penColor){
					return 'btn colorBtn fw'
				}
				return 'btn colorBtn';
			},
			setBackGround(){
				const canvas = document.getElementById('canvas'); //获取canvas标签
				const ctx = canvas.getContext("2d");//创建 context 对象
				ctx.fillStyle = this.brackGroudColor;//画布背景色
				ctx.fillRect(0,0,this.width,this.height);//在画布上绘制 600x300 的矩形，从左上角开始 (0,0)
			},
			setPenWidth(event){
				const progress = document.getElementById('progress');
				this.progressValue = (event.pageX - progress.offsetLeft) / progress.offsetWidth;
				this.penWidth = 20 * this.progressValue;
			},
			//设置画笔颜色
			setPenColor(color = ''){
				if(color == '') this.penColor = this.brackGroudColor;
			    else this.penColor = color;
			},
			penDown(event){
			    this.penClick = true;
			    this.startAxisX = event.pageX;
			    this.startAxisY = event.pageY;
			},
			penUp(){
			    this.penClick = false;
			},
			drawing(event){
			    if(!this.penClick) return;
				const canvas = document.getElementById('canvas'); //获取canvas标签
				const ctx = canvas.getContext("2d");//创建 contextconst canvas = document.getElementById('canvas');  对象
			    const stopAxisX = event.pageX;
			    const stopAxisY = event.pageY;
				const left = document.getElementById('leftMenu');
				const lw = left && left.offsetWidth ? (left.offsetWidth || 0) / 2 : 0;
			    ctx.beginPath();
				const wsaW = window.screen.availWidth;
				const cl = canvas.offsetLeft;
				const ct = canvas.offsetTop;
			    ctx.moveTo(this.startAxisX-cl,this.startAxisY - ct);//moveTo(x,y) 定义线条开始坐标
			    ctx.lineTo(stopAxisX-cl,stopAxisY - ct	);//lineTo(x,y) 定义线条结束坐标
			    ctx.strokeStyle = this.penColor;
			    ctx.lineWidth = this.penWidth;
			    ctx.lineCap = "round";
			    ctx.stroke();// stroke() 方法来绘制线条
			    this.startAxisX = stopAxisX;
			    this.startAxisY = stopAxisY;
			},
			createImage() {
				const canvas = document.getElementById('canvas'); //获取canvas标签
			    const img_png_src = canvas.toDataURL("image/png"); //将画板保存为图片格式的函数
			    document.getElementById("image_png").src = img_png_src;
			}
		}
	}
</script>

<style lang="scss" scoped="scoped">
	*{
	    margin: 0;
	    padding: 0;
	}
	#canvas-broad{
	    margin: 0 auto;
	    /*text-align: center;*/
	}
	#canvas{
	    border: 2px solid #ff6700;
	    cursor:crosshair;
	    /*不能用这种方式给canvas设置宽高*/
	    /*width: 600px;*/
	    /*height: 300px;*/
	}
	.btn{
	    width:70px;
	    height: 40px;
	    border-radius: 10px;
	    border: 1px solid #aaa;/*去掉<button>默认边框*/
	    outline:none;/*去掉<button>选中时的默认边框*/
		cursor: pointer;
	}
	.input-color{
	    width:70px;
	    height: 40px;
	    border-radius: 10px;
	    border: 0;/*去掉<button>默认边框*/
	    outline:none;/*去掉<button>选中时的默认边框*/
	}
	#image_png{
	    width: 300px;
	    height: 150px;
	    border:  2px solid #ff6700;
	    display: block;
	    margin: 10px auto;
	 }
	.section{
	    margin-top: 10px;
	}
	.info{
	    color: #f0f;
	    font-size: 14px;
	    line-height: 40px;
	}
	.bg{
	    background: #ff6700;
	}
	.fw{
	    font-weight: 700;
	}
</style>

JTabBar.vue

<template>
	<div class="j-tab-bar">
		<div class="bar-items">
			<div v-for="(item,index) in tabList"
				:key="item.id"
				:class="getBarClass(index,'bar-item')"
				:title="item.label"
				@click="barClick(index)">
				{{item.label}}
			</div>
		</div>
		<div v-for="(item,index) in tabList" 
			:key="item.id"
			>
			<slot v-if="item.id == tabList[showTab].id" 
				:name="item.id">
				
			</slot>
		</div>
	</div>
</template>

<script>
	export default{
		name:"JTabBar",
		props:{
			tabList:{
				type:Array,
				default:[
					{
						label:'tab',
						id:'tab'
					},
					{
						label:'tab1',
						id:'tab1'
					}
				]
			},
			defaultShowTab:{
				type:Number,
				default:0
			}
		},
		data() {
			return{
				showTab:0
			}
		},
		created() {
			this.init();
		},
		methods:{
			init(){
				this.showTab = this.defaultShowTab;
			},
			barClick(index){
				this.showTab = index;
				this.$emit('clickTab',index);
			},
			getBarClass(index,val=''){
				let res = '';
				if(index == this.showTab){
					res += 'active-tab';
				}
				return res + ' ' + val;
			}
		}
	}
</script>

<style lang="scss" scoped="scoped">
	.j-tab-bar{
		.bar-items{
			display: flex;
			flex-direction: row;
			line-height: 2rem;
			.bar-item{
				flex: 1;
				color: black;
				border: 1px solid deepskyblue;
				cursor: pointer;
			}
			.active-tab{
				color: cadetblue;
			}
		}
	}
</style>

npm引入

组件以上传到npm，可以直接install使用

1.安装

npm i @jyeontu/jvuewheel -S

2.引入

//引入组件库
import jvuewheel from '@jyeontu/jvuewheel'
//引入样式
import '@jyeontu/jvuewheel/lib/jvuewhell.css'
Vue.use(jvuewheel);

3.vue中引用组件

<j-canvas-broad class = "canvas-baroad" 
				:toolsTabList = "true">
</j-canvas-broad>

资源地址

组件文档

文档地址：http://120.79.163.94/JYeontuComponents/#/homePage

代码地址

Gitee：https://gitee.com/zheng_yongtao/jyeontu-component-warehouse/tree/master/JYeontuComponentWarehouse

canvas学习

MDN地址：https://developer.mozilla.org/zh-CN/docs/Web/API/CanvasRenderingContext2D