uni.app的画布，签字，canvas

<template>
	<view class="canvas-wrapper">
        //这里是画布的位置
		<canvas class="mycanvas" canvas-id="mycanvas" @touchstart="touchstart" @touchmove="touchmove"
			@touchend="touchend"></canvas>
        //下方按钮，完成和清空
		<view class="footer">
			<view class="left" @click="finish">完成</view>
			<view class="right" @click="clear">清除</view>
		</view>
	</view>
</template>

<script>
	var x = 20;
	var y = 20;
	export default {
		
		data() {
			return {
				ctx: '', //绘图图像
				points: [] //路径点集合 
			}
		},

		mounted() {
            //这里主要，必须要在mounted里进行获取，再其它位置获取的话可能那不到mycanvas
			this.ctx = uni.createCanvasContext("mycanvas", this); //创建绘图对象
			//设置画笔样式
			this.ctx.lineWidth = 4;
			this.ctx.lineCap = "round"
			this.ctx.lineJoin = "round"
		},
		methods: {
			//触摸开始，获取到起点
			touchstart: function(e) {
				let startX = e.changedTouches[0].x;
				let startY = e.changedTouches[0].y;
				let startPoint = {
					X: startX,
					Y: startY
				};

				/* **************************************************
					#由于uni对canvas的实现有所不同，这里需要把起点存起来
				 * **************************************************/
				this.points.push(startPoint);

				//每次触摸开始，开启新的路径
				this.ctx.beginPath();
			},

			//触摸移动，获取到路径点
			touchmove: function(e) {
				let moveX = e.changedTouches[0].x;
				let moveY = e.changedTouches[0].y;
				let movePoint = {
					X: moveX,
					Y: moveY
				};
				this.points.push(movePoint); //存点
				let len = this.points.length;
				if (len >= 2) {
					this.draw(); //绘制路径
				}

			},

			// 触摸结束，将未绘制的点清空防止对后续路径产生干扰
			touchend: function() {
				this.points = [];
			},

			/* ***********************************************
			#   绘制笔迹
			#	1.为保证笔迹实时显示，必须在移动的同时绘制笔迹
			#	2.为保证笔迹连续，每次从路径集合中区两个点作为起点（moveTo）和终点(lineTo)
			#	3.将上一次的终点作为下一次绘制的起点（即清除第一个点）
			************************************************ */
			draw: function() {
				let point1 = this.points[0]
				let point2 = this.points[1]
				this.points.shift()
				this.ctx.moveTo(point1.X, point1.Y)
				this.ctx.lineTo(point2.X, point2.Y)
				this.ctx.stroke()
				this.ctx.draw(true)
			},

			//清空画布
			clear: function() {
				let that = this;
				uni.getSystemInfo({
					success: function(res) {
						let canvasw = res.windowWidth;
						let canvash = res.windowHeight;
						that.ctx.clearRect(0, 0, canvasw, canvash);
						that.ctx.draw(true);
					},
				})
			},

			//完成绘画并保存到本地
			finish: function() {
				uni.canvasToTempFilePath({
					canvasId: 'mycanvas',
					success: function(res) {
						let path = res.tempFilePath;
						console.log(this.index);
					}
				})
			}
		},
	}
</script>

<style>
	.mycanvas {
		width: 95%;
		height: 380rpx;
		margin: auto;
		background-color: #fff;
		display: block;
		margin-top: 50%;
	}

	.footer {
		font-size: 16px;
		height: 150upx;
		display: flex;
		justify-content: space-around;
		align-items: center;
	}

	.left,
	.right {
		line-height: 60upx;
		width: 100upx;
		text-align: center;
		color: white;
		border-radius: 5upx;
		z-index: 1;
	}

	.left {
		background: #007AFF;
		margin-right: 100rpx;
	}

	.right {
		background: #f05d6f;
	}
</style>