微信小程序canvas实现签名功能

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 }
) }
}
    )

/* pages/canvas-test2/canvas-test2.wxss */.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。

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