在微信小程序项目中，开发模块涉及到手写签名功能，微信小程序canvas闪亮登场

前言

微信小程序canvas实现签名功能

核心内容简介：

（1）签名实现，开始，移动，结束

（2）重写

（3）完成

（4）上传

一、微信小程序canvas实现签名功能

效果演示：

（1）签名实现

（2）重写

（3）完成

完成后将图片展示在相应的位置

（4）根据业务需求，可以将图片上传到后台，在需要的地方展示

二、上代码

1.全部演示

wxml

<!--pages/canvas-test/canvas-test.wxml--><view class="handCenter"> <canvas class="handWriting" disable-scroll="true" bindtouchstart="uploadScaleStart" bindtouchmove="uploadScaleMove" bindtouchend="uploadScaleEnd" bindtap="mouseDown" canvas-id="handWriting"> </canvas></view><view class="handBtn"> <button catchtap="retDraw" class="delBtn">重写</button> <button catchtap="subCanvas" class="subBtn">完成</button> </view><view class="preview"> <image wx:if="{{tmpPath}}" style="width:100%;height:100%;" src="{{tmpPath}}"></image></view>

js

const app = getApp()const api = require('../../utils/request.js'); //相对路径const apiEev = require('../../config/config');Page({ data: { canvasName: 'handWriting', ctx: '', canvasWidth: 0, canvasHeight: 0, transparent: 1, // 透明度 selectColor: 'black', lineColor: '#1A1A1A', // 颜色 lineSize: 1.5, // 笔记倍数 lineMin: 0.5, // 最小笔画半径 lineMax: 4, // 最大笔画半径 pressure: 1, // 默认压力 smoothness: 60, //顺滑度，用60的距离来计算速度 currentPoint: {}, currentLine: [], // 当前线条 firstTouch: true, // 第一次触发 radius: 1, //画圆的半径 cutArea: { top: 0, right: 0, bottom: 0, left: 0 }, //裁剪区域 bethelPoint: [], //保存所有线条 生成的贝塞尔点； lastPoint: 0, chirography: [], //笔迹 currentChirography: {}, //当前笔迹 linePrack: [], //划线轨迹 , 生成线条的实际点 tmpPath:'' }, // 笔迹开始 uploadScaleStart (e) { if (e.type != 'touchstart') return false; let ctx = this.data.ctx; ctx.setFillStyle(this.data.lineColor); // 初始线条设置颜色 ctx.setGlobalAlpha(this.data.transparent); // 设置半透明 let currentPoint = { x: e.touches[0].x, y: e.touches[0].y } let currentLine = this.data.currentLine; currentLine.unshift({ time: new Date().getTime(), dis: 0, x: currentPoint.x, y: currentPoint.y }) this.setData({ currentPoint, // currentLine }) if (this.data.firstTouch) { this.setData({ cutArea: { top: currentPoint.y, right: currentPoint.x, bottom: currentPoint.y, left: currentPoint.x }, firstTouch: false }) } this.pointToLine(currentLine); }, // 笔迹移动 uploadScaleMove (e) { if (e.type != 'touchmove') return false; if (e.cancelable) { // 判断默认行为是否已经被禁用 if (!e.defaultPrevented) { e.preventDefault(); } } let point = { x: e.touches[0].x, y: e.touches[0].y } //测试裁剪 if (point.y < this.data.cutArea.top) { this.data.cutArea.top = point.y; } if (point.y < 0) this.data.cutArea.top = 0; if (point.x > this.data.cutArea.right) { this.data.cutArea.right = point.x; } if (this.data.canvasWidth - point.x <= 0) { this.data.cutArea.right = this.data.canvasWidth; } if (point.y > this.data.cutArea.bottom) { this.data.cutArea.bottom = point.y; } if (this.data.canvasHeight - point.y <= 0) { this.data.cutArea.bottom = this.data.canvasHeight; } if (point.x < this.data.cutArea.left) { this.data.cutArea.left = point.x; } if (point.x < 0) this.data.cutArea.left = 0; this.setData({ lastPoint: this.data.currentPoint, currentPoint: point }) let currentLine = this.data.currentLine currentLine.unshift({ time: new Date().getTime(), dis: this.distance(this.data.currentPoint, this.data.lastPoint), x: point.x, y: point.y }) // this.setData({ // currentLine // }) this.pointToLine(currentLine); }, // 笔迹结束 uploadScaleEnd (e) { if (e.type != 'touchend') return 0; let point = { x: e.changedTouches[0].x, y: e.changedTouches[0].y } this.setData({ lastPoint: this.data.currentPoint, currentPoint: point }) let currentLine = this.data.currentLine currentLine.unshift({ time: new Date().getTime(), dis: this.distance(this.data.currentPoint, this.data.lastPoint), x: point.x, y: point.y }) // this.setData({ // currentLine // }) if (currentLine.length > 2) { var info = (currentLine[0].time - currentLine[currentLine.length - 1].time) / currentLine.length; //$("#info").text(info.toFixed(2)); } //一笔结束，保存笔迹的坐标点，清空，当前笔迹 //增加判断是否在手写区域； this.pointToLine(currentLine); var currentChirography = { lineSize: this.data.lineSize, lineColor: this.data.lineColor }; var chirography = this.data.chirography chirography.unshift(currentChirography); this.setData({ chirography }) var linePrack = this.data.linePrack linePrack.unshift(this.data.currentLine); this.setData({ linePrack, currentLine: [] }) }, onLoad () { let canvasName = this.data.canvasName let ctx = wx.createCanvasContext(canvasName) this.setData({ ctx: ctx }) var query = wx.createSelectorQuery(); query.select('.handCenter').boundingClientRect(rect => { this.setData({ canvasWidth: rect.width, canvasHeight: rect.height }) }).exec(); }, subCanvas(){ // 新增我的 let that = this let ctx = this.data.ctx; ctx.draw(true,setTimeout(function(){ //我的新增定时器及回调 wx.canvasToTempFilePath({ x: 0, y: 0, width: 375, height: 152, canvasId: 'handWriting', fileType: 'png', success: function(res) { that.setData({ tmpPath:res.tempFilePath }) console.log(that.data.tmpPath,'看下是个啥玩意') that.upImgs(that.data.tmpPath,0) } }, ctx) },1000)) },// 新增将保存的图片路径上传到文件服务器upImgs: function (imgurl, index) { console.log(imgurl,'看下路径是多少') var that = this; wx.uploadFile({ url: apiEev.api + 'xxxx',//后台上传路径 filePath: imgurl, name: 'file', header: { 'content-type': 'multipart/form-data' }, formData: null, success: function (res) { console.log(res) //接口返回网络路径 var data = JSON.parse(res.data) console.log(data,'看下data是个啥') if (data.code == "success") { console.log('成功') } } })}, retDraw () { this.data.ctx.clearRect(0, 0, 700, 730) this.data.ctx.draw() this.setData({ tmpPath:'' }) }, //画两点之间的线条；参数为:line，会绘制最近的开始的两个点； pointToLine (line) { this.calcBethelLine(line); return; }, //计算插值的方式； calcBethelLine (line) { if (line.length <= 1) { line[0].r = this.data.radius; return; } let x0, x1, x2, y0, y1, y2, r0, r1, r2, len, lastRadius, dis = 0, time = 0, curveValue = 0.5; if (line.length <= 2) { x0 = line[1].x y0 = line[1].y x2 = line[1].x + (line[0].x - line[1].x) * curveValue; y2 = line[1].y + (line[0].y - line[1].y) * curveValue; //x2 = line[1].x; //y2 = line[1].y; x1 = x0 + (x2 - x0) * curveValue; y1 = y0 + (y2 - y0) * curveValue;; } else { x0 = line[2].x + (line[1].x - line[2].x) * curveValue; y0 = line[2].y + (line[1].y - line[2].y) * curveValue; x1 = line[1].x; y1 = line[1].y; x2 = x1 + (line[0].x - x1) * curveValue; y2 = y1 + (line[0].y - y1) * curveValue; } //从计算公式看，三个点分别是(x0,y0),(x1,y1),(x2,y2) ；(x1,y1)这个是控制点，控制点不会落在曲线上；实际上，这个点还会手写获取的实际点，却落在曲线上 len = this.distance({ x: x2, y: y2 }, { x: x0, y: y0 }); lastRadius = this.data.radius; for (let n = 0; n < line.length - 1; n++) { dis += line[n].dis; time += line[n].time - line[n + 1].time; if (dis > this.data.smoothness) break; } this.setData({ radius: Math.min(time / len * this.data.pressure + this.data.lineMin, this.data.lineMax) * this.data.lineSize }); line[0].r = this.data.radius; //计算笔迹半径； if (line.length <= 2) { r0 = (lastRadius + this.data.radius) / 2; r1 = r0; r2 = r1; //return; } else { r0 = (line[2].r + line[1].r) / 2; r1 = line[1].r; r2 = (line[1].r + line[0].r) / 2; } let n = 5; let point = []; for (let i = 0; i < n; i++) { let t = i / (n - 1); let x = (1 - t) * (1 - t) * x0 + 2 * t * (1 - t) * x1 + t * t * x2; let y = (1 - t) * (1 - t) * y0 + 2 * t * (1 - t) * y1 + t * t * y2; let r = lastRadius + (this.data.radius - lastRadius) / n * i; point.push({ x: x, y: y, r: r }); if (point.length == 3) { let a = this.ctaCalc(point[0].x, point[0].y, point[0].r, point[1].x, point[1].y, point[1].r, point[2].x, point[2].y, point[2].r); a[0].color = this.data.lineColor; // let bethelPoint = this.data.bethelPoint; // console.log(a) // console.log(this.data.bethelPoint) // bethelPoint = bethelPoint.push(a); this.bethelDraw(a, 1); point = [{ x: x, y: y, r: r }]; } } this.setData({ currentLine: line }) }, //求两点之间距离 distance (a, b) { let x = b.x - a.x; let y = b.y - a.y; return Math.sqrt(x * x + y * y); }, ctaCalc (x0, y0, r0, x1, y1, r1, x2, y2, r2) { let a = [], vx01, vy01, norm, n_x0, n_y0, vx21, vy21, n_x2, n_y2; vx01 = x1 - x0; vy01 = y1 - y0; norm = Math.sqrt(vx01 * vx01 + vy01 * vy01 + 0.0001) * 2; vx01 = vx01 / norm * r0; vy01 = vy01 / norm * r0; n_x0 = vy01; n_y0 = -vx01; vx21 = x1 - x2; vy21 = y1 - y2; norm = Math.sqrt(vx21 * vx21 + vy21 * vy21 + 0.0001) * 2; vx21 = vx21 / norm * r2; vy21 = vy21 / norm * r2; n_x2 = -vy21; n_y2 = vx21; a.push({ mx: x0 + n_x0, my: y0 + n_y0, color: "#1A1A1A" }); a.push({ c1x: x1 + n_x0, c1y: y1 + n_y0, c2x: x1 + n_x2, c2y: y1 + n_y2, ex: x2 + n_x2, ey: y2 + n_y2 }); a.push({ c1x: x2 + n_x2 - vx21, c1y: y2 + n_y2 - vy21, c2x: x2 - n_x2 - vx21, c2y: y2 - n_y2 - vy21, ex: x2 - n_x2, ey: y2 - n_y2 }); a.push({ c1x: x1 - n_x2, c1y: y1 - n_y2, c2x: x1 - n_x0, c2y: y1 - n_y0, ex: x0 - n_x0, ey: y0 - n_y0 }); a.push({ c1x: x0 - n_x0 - vx01, c1y: y0 - n_y0 - vy01, c2x: x0 + n_x0 - vx01, c2y: y0 + n_y0 - vy01, ex: x0 + n_x0, ey: y0 + n_y0 }); a[0].mx = a[0].mx.toFixed(1); a[0].mx = parseFloat(a[0].mx); a[0].my = a[0].my.toFixed(1); a[0].my = parseFloat(a[0].my); for (let i = 1; i < a.length; i++) { a[i].c1x = a[i].c1x.toFixed(1); a[i].c1x = parseFloat(a[i].c1x); a[i].c1y = a[i].c1y.toFixed(1); a[i].c1y = parseFloat(a[i].c1y); a[i].c2x = a[i].c2x.toFixed(1); a[i].c2x = parseFloat(a[i].c2x); a[i].c2y = a[i].c2y.toFixed(1); a[i].c2y = parseFloat(a[i].c2y); a[i].ex = a[i].ex.toFixed(1); a[i].ex = parseFloat(a[i].ex); a[i].ey = a[i].ey.toFixed(1); a[i].ey = parseFloat(a[i].ey); } return a; }, bethelDraw (point, is_fill, color) { // 新增我的 let that = this let ctx = this.data.ctx; ctx.beginPath(); ctx.moveTo(point[0].mx, point[0].my); if (undefined != color) { ctx.setFillStyle(color); ctx.setStrokeStyle(color); } else { ctx.setFillStyle(point[0].color); ctx.setStrokeStyle(point[0].color); } for (let i = 1; i < point.length; i++) { ctx.bezierCurveTo(point[i].c1x, point[i].c1y, point[i].c2x, point[i].c2y, point[i].ex, point[i].ey); } ctx.stroke(); if (undefined != is_fill) { ctx.fill(); //填充图形 ( 后绘制的图形会覆盖前面的图形, 绘制时注意先后顺序 ) } ctx.draw(true) }, selectColorEvent (event) { console.log(event) var color = event.currentTarget.dataset.colorValue; var colorSelected = event.currentTarget.dataset.color; this.setData({ selectColor: colorSelected, lineColor: color }) }}).canvasId { position: absolute; left: 50%; top: 0; transform: translate(-50%); z-index: 1; border: 2px dashed #ccc; border-radius: 8px; margin-bottom: 66px;}.handCenter { border: 1px solid red;}.handWriting { width: 100%;}.preview { width: 375px; height: 152px;}

2.重点部分分析

（1）签名基本实现，开始，移动，结束

// 笔迹开始 uploadScaleStart (e) { if (e.type != 'touchstart') return false; let ctx = this.data.ctx; ctx.setFillStyle(this.data.lineColor); // 初始线条设置颜色 ctx.setGlobalAlpha(this.data.transparent); // 设置半透明 let currentPoint = { x: e.touches[0].x, y: e.touches[0].y } let currentLine = this.data.currentLine; currentLine.unshift({ time: new Date().getTime(), dis: 0, x: currentPoint.x, y: currentPoint.y }) this.setData({ currentPoint, // currentLine }) if (this.data.firstTouch) { this.setData({ cutArea: { top: currentPoint.y, right: currentPoint.x, bottom: currentPoint.y, left: currentPoint.x }, firstTouch: false }) } this.pointToLine(currentLine); }, // 笔迹移动 uploadScaleMove (e) { if (e.type != 'touchmove') return false; if (e.cancelable) { // 判断默认行为是否已经被禁用 if (!e.defaultPrevented) { e.preventDefault(); } } let point = { x: e.touches[0].x, y: e.touches[0].y } //测试裁剪 if (point.y < this.data.cutArea.top) { this.data.cutArea.top = point.y; } if (point.y < 0) this.data.cutArea.top = 0; if (point.x > this.data.cutArea.right) { this.data.cutArea.right = point.x; } if (this.data.canvasWidth - point.x <= 0) { this.data.cutArea.right = this.data.canvasWidth; } if (point.y > this.data.cutArea.bottom) { this.data.cutArea.bottom = point.y; } if (this.data.canvasHeight - point.y <= 0) { this.data.cutArea.bottom = this.data.canvasHeight; } if (point.x < this.data.cutArea.left) { this.data.cutArea.left = point.x; } if (point.x < 0) this.data.cutArea.left = 0; this.setData({ lastPoint: this.data.currentPoint, currentPoint: point }) let currentLine = this.data.currentLine currentLine.unshift({ time: new Date().getTime(), dis: this.distance(this.data.currentPoint, this.data.lastPoint), x: point.x, y: point.y }) // this.setData({ // currentLine // }) this.pointToLine(currentLine); }, // 笔迹结束 uploadScaleEnd (e) { if (e.type != 'touchend') return 0; let point = { x: e.changedTouches[0].x, y: e.changedTouches[0].y } this.setData({ lastPoint: this.data.currentPoint, currentPoint: point }) let currentLine = this.data.currentLine currentLine.unshift({ time: new Date().getTime(), dis: this.distance(this.data.currentPoint, this.data.lastPoint), x: point.x, y: point.y }) // this.setData({ // currentLine // }) if (currentLine.length > 2) { var info = (currentLine[0].time - currentLine[currentLine.length - 1].time) / currentLine.length; //$("#info").text(info.toFixed(2)); } //一笔结束，保存笔迹的坐标点，清空，当前笔迹 //增加判断是否在手写区域； this.pointToLine(currentLine); var currentChirography = { lineSize: this.data.lineSize, lineColor: this.data.lineColor }; var chirography = this.data.chirography chirography.unshift(currentChirography); this.setData({ chirography }) var linePrack = this.data.linePrack linePrack.unshift(this.data.currentLine); this.setData({ linePrack, currentLine: [] })},

记得要先在onload中初始化

代码拿走直接用

（2）重新签署

大白话就是清空画布

retDraw () { this.data.ctx.clearRect(0, 0, 700, 730) this.data.ctx.draw() this.setData({ tmpPath:'' })},

（3）签署完成

subCanvas(){ // 新增我的 let that = this let ctx = this.data.ctx; ctx.draw(true,setTimeout(function(){ //我的新增定时器及回调 wx.canvasToTempFilePath({ x: 0, y: 0, width: 375, height: 152, canvasId: 'handWriting', fileType: 'png', success: function(res) { that.setData({ tmpPath:res.tempFilePath }) console.log(that.data.tmpPath,'看下是个啥玩意') that.upImgs(that.data.tmpPath,0) } }, ctx) },1000)) },

里边的回调比较重要哦：

防止拿不到画布内容，可以设置延迟；
wx.canvasToTempFilePath方法获取到画布图片内容；

（4）根据业务需求，可以将图片上传到后台，在需要的地方展示

重点是如何上传到后台

// 新增将保存的图片路径上传到文件服务器upImgs: function (imgurl, index) { console.log(imgurl,'看下路径是多少') var that = this; wx.uploadFile({ url: apiEev.api + 'xxxx',//后台文件上传的路径接口 filePath: imgurl, name: 'file', header: { 'content-type': 'multipart/form-data' }, formData: null, success: function (res) { console.log(res) //接口返回网络路径 var data = JSON.parse(res.data) console.log(data,'看下data是个啥') if (data.code == "success") { console.log('成功') } } })},

总结

微信小程序canvas实现签名功能。

特别提醒：在真机调试和体验版中可能会出现卡顿情况，有条件要发布至预发布中查看是否影响性能。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。