参考自：https://www.jb51.net/article/145086.htm

step1：创建随机验证码绘制组件 RandomCode.vue

该组件实现：
1、生成随机颜色
2、绘制背景、文字、干扰线、干扰点
3、验证码样式

绘制实现：通过监听 identifyCode 数据变化，调用绘制方法 drawPic()

drawPic() 为核心代码

<template>
	<!-- 自定义一个绘制随机验证码的组件，其本质是使用canvas绘制 -->
	<div class="s-canvas">
		<canvas id="s-canvas" :width="contentWidth" :height="contentHeight"></canvas>
	</div>
</template>

<script>
	export default {
		name: 'SIdentify',
		props: {
			identifyCode: {
				type: String,
				default: '1234'
			},
			fontSizeMin: {
				type: Number,
				default: 16
			},
			fontSizeMax: {
				type: Number,
				default: 40
			},
			backgroundColorMin: {
				type: Number,
				default: 180
			},
			backgroundColorMax: {
				type: Number,
				default: 240
			},
			colorMin: {
				type: Number,
				default: 50
			},
			colorMax: {
				type: Number,
				default: 160
			},
			lineColorMin: {
				type: Number,
				default: 40
			},
			lineColorMax: {
				type: Number,
				default: 180
			},
			dotColorMin: {
				type: Number,
				default: 0
			},
			dotColorMax: {
				type: Number,
				default: 255
			},
			contentWidth: {
				type: Number,
				default: 112
			},
			contentHeight: {
				type: Number,
				default: 38
			}
		},
		methods: {
			// 生成一个随机数
			randomNum(min, max) {
				return Math.floor(Math.random() * (max - min) + min)
			},
			// 生成一个随机的颜色
			randomColor(min, max) {
				var r = this.randomNum(min, max)
				var g = this.randomNum(min, max)
				var b = this.randomNum(min, max)
				return 'rgb(' + r + ',' + g + ',' + b + ')'
			},
			drawPic() {
				var canvas = document.getElementById('s-canvas')
				var ctx = canvas.getContext('2d')
				ctx.textBaseline = 'bottom'
				// 绘制背景
				ctx.fillStyle = this.randomColor(
					this.backgroundColorMin,
					this.backgroundColorMax
				)
				ctx.fillRect(0, 0, this.contentWidth, this.contentHeight)
				// 绘制文字
				for (let i = 0; i < this.identifyCode.length; i++) {
					this.drawText(ctx, this.identifyCode[i], i)
				}
				this.drawLine(ctx)
				this.drawDot(ctx)
			},
			drawText(ctx, txt, i) {
				ctx.fillStyle = this.randomColor(this.colorMin, this.colorMax)
				ctx.font =
					this.randomNum(this.fontSizeMin, this.fontSizeMax) + 'px SimHei'
				var x = (i + 1) * (this.contentWidth / (this.identifyCode.length + 1))
				var y = this.randomNum(this.fontSizeMax, this.contentHeight - 5)
				var deg = this.randomNum(-45, 45)
				// 修改坐标原点和旋转角度
				ctx.translate(x, y)
				ctx.rotate(deg * Math.PI / 180)
				ctx.fillText(txt, 0, 0)
				// 恢复坐标原点和旋转角度
				ctx.rotate(-deg * Math.PI / 180)
				ctx.translate(-x, -y)
			},
			drawLine(ctx) {
				// 绘制干扰线
				for (let i = 0; i < 8; i++) {
					ctx.strokeStyle = this.randomColor(
						this.lineColorMin,
						this.lineColorMax
					)
					ctx.beginPath()
					ctx.moveTo(
						this.randomNum(0, this.contentWidth),
						this.randomNum(0, this.contentHeight)
					)
					ctx.lineTo(
						this.randomNum(0, this.contentWidth),
						this.randomNum(0, this.contentHeight)
					)
					ctx.stroke()
				}
			},
			drawDot(ctx) {
				// 绘制干扰点
				for (let i = 0; i < 100; i++) {
					ctx.fillStyle = this.randomColor(0, 255)
					ctx.beginPath()
					ctx.arc(
						this.randomNum(0, this.contentWidth),
						this.randomNum(0, this.contentHeight),
						1,
						0,
						2 * Math.PI
					)
					ctx.fill()
				}
			}
		},
		// 监听--watch中包含immediate属性和deep属性。immediate属性：immediate:true，首次绑定的时候执行watch中的方法；immediate:false，当数据发生变化时执行watch中的方法（首次绑定时不执行）
		watch: {
			identifyCode: {
			    handler() {
			      this.drawPic()
			    },
			    immediate: false
			  }
		},
		// mounted 完成挂载：在这发起后端请求，拿回数据，配合路由钩子做一些事情
		mounted() {
			this.drawPic()
		}
	}
</script>

<style>
</style>

step2：创建随机验证码生成组件 RandomCodeProduce.vue

该组件实现：
1、验证码背景和样式：调用验证码绘制组件，使用其中的绘制方法
2、生成随机数（四位）
3、刷新验证码、校验验证码

<template>
	<div class="randomcodeuse">
		<el-form class="login-form" status-icon :rules="loginRules" ref="loginForm" :model="loginForm" label-width="0">
			<!-- 随机验证码 输入框 -->
			<el-form-item prop="verifycode">
				<el-input v-model="loginForm.verifycode" placeholder="请输入验证码" class="identifyinput"></el-input>
			</el-form-item>
			<!-- 随机验证码 -->
			<el-form-item>
				<div class="identifybox">
					<div @click="refreshCode">
						<s-identify :identifyCode="identifyCode"></s-identify>
					</div>
					<!-- 刷新验证码 -->
					<el-button @click="refreshCode" type='text' class="textbtn">看不清，换一张</el-button>
				</div>
			</el-form-item>
		</el-form>
	</div>
</template>

<script>
	import SIdentify from './RandomCode.vue'
	export default {
		name: 'userlogin',
		data() {
			// 自定义验证规则：验证码验证规则
			const validateVerifycode = (rule, value, callback) => {
				if (value === '') {
					callback(new Error('请输入验证码'))
				} else if (value !== this.identifyCode) {
					console.log('validateVerifycode:', value)
					callback(new Error('验证码不正确'))
				} else {
					callback()
				}
			}
			return {
				loginForm: {
					verifycode: ''
				},
				identifyCodes: '1234567890',
				identifyCode: '',
				loginRules: { 
					verifycode: [
						{ required: true, trigger: 'blur', validator: validateVerifycode },
					]
				}
			}
		},
		components: {
			// 注册绘制随机验证码的组件
			SIdentify
		},
		created() {},
		mounted() {
			// 验证码初始化
			this.identifyCode = ''
			this.makeCode(this.identifyCodes, 4)
		},
		computed: {},
		methods: {
			// 生成随机数
			randomNum(min, max) {
				return Math.floor(Math.random() * (max - min) + min)
			},
			// 切换验证码
			refreshCode() {
				this.identifyCode = ''
				this.makeCode(this.identifyCodes, 4)
			},
			// 生成四位随机验证码
			makeCode(o, l) {
				for (let i = 0; i < l; i++) {
					this.identifyCode += this.identifyCodes[this.randomNum(0, this.identifyCodes.length)]
				}
				console.log(this.identifyCode)
			}
		}
	}
</script>

<style scoped>
	.randomcodeuse{
		width: 60%;
		margin: auto;
		display: flex;
		align-items: center;
	}
	.identifybox {
		display: flex;
		justify-content: space-between;
		margin-top: 7px;
	}
	.iconstyle {
		color: #409EFF;
	}
</style>

效果图