微信小程序绘制canvas图片

1.效果图

2.注意事项

1.https网址图片需要预先下载到本地用wx.downloadFile方法2.wx.downloadFile需要在微信公众号后台配置域名才能获取图片，如图：

3.代码

1.wxml

canvas.wxml<cover-view bindtap='savePic'><canvas style="width:100%;height:{{contentHeight}}px" canvas-id="myCanvas" bindlongpress="savePic"> </canvas></cover-view><button bindtap='savePic' class="buttonStyle">预览并发送</button>

2.js代码

1.图片需要先下载到本地，并保存本地图片路径，包括头像，头像图片的域名同样要在后台配置，不然发布线上获取不到。

canvas.jsvar util = require('../../utils/md5.js');var tool = require('../../utils/base64tool.js')var app = new getApp();//canvas.jsPage({data: {windowWidth: 0, //屏幕宽度windowHeight: 0,//屏幕高度contentHeight: 0,//内容高度thinkList: [], //文字超出换行处理lineHeight: 30, //固定值contentTitle: "我的昵称", //我的昵称canvasUrl: "", //canvasurlqrCode: "", //小程序码https图片路径goodsInfoImg: "", //海报图片specText: "京东社交电商合作伙伴", //京东社交电商合作伙伴userIcon:""//微信头像},onLoad: function (options) {let that = this;that.getQr();// 查看是否授权wx.getSetting({success(res) {if (res.authSetting['scope.userInfo']) {// 已经授权，可以直接调用 getUserInfo 获取头像昵称wx.getUserInfo({success(resInfo) {that.setData({ contentTitle: resInfo.userInfo.nickName})wx.downloadFile({url: resInfo.userInfo.avatarUrl,success(downloadRes) {if (downloadRes.statusCode === 200) {that.setData({userIcon: downloadRes.tempFilePath})}}})}})} else {that.setData({userIcon: '/img/noperson.png'})}}})//获取设备信息高度。计算出其他的高度等wx.getSystemInfo({success: function (res) {that.setData({windowWidth: res.windowWidth,windowHeight: res.windowHeight,normalPageX:res.windowWidth * 0.045, //左边文本图片X轴位置boxWidth: res.windowWidth * 0.91, //分享图片box宽度boxheight: res.windowHeight, //分享图片box高度boxPageY: res.windowWidth * 0.2, //boxY轴位置imgWidth: res.windowWidth * 0.91, //海报图片宽度imgHeight: res.windowHeight * 0.82, //海报图片高度imgPageY: res.windowWidth * 0, //海报图片Y轴位置userIconWidth: res.windowWidth * 0.162,//头像图片宽度userIconHeight: res.windowWidth * 0.162,//头像图片高度userIconPageY: res.windowHeight * 0.82 + 15,//头像Y轴位置codeWidth: res.windowWidth * 0.25, //小程序码图片宽度codeHeight: res.windowWidth * 0.25, //小程序码图片高度codePageY: res.windowHeight * 0.80, //小程序码Y轴位置avatarPageY: res.windowHeight * 0.82 + 15, //头像Y轴位置titlePageY: res.windowHeight * 0.82 + 25, //微信昵称Y轴位置specPageY: res.windowHeight * 0.82 + 42, //京东社交Y轴位置});}});//网络图片转为本地图片，直接显示网络图片的话真机不显示// that.getTempFile("cloud://luer-f3ipn.6c75-luer-f3ipn-1301025398/6684e5652d611c27b5895a6911e51b7.png");that.getTempFile(app.globeData.shareCodeImg); },//获取小程序码getQr: function () {var that = this;var phone = wx.getStorageSync('phone');var apiKey = 's!sluer!@￥%GFYLCL#*WLMinPro!!;';var time = Date.parse(new Date());var sign = util.hexMD5(apiKey + time);apiKey = util.hexMD5(apiKey);var url = app.globeData.host + 'minPro/getShareMinCode?sign=' + sign + '&apiKey=' + apiKey + '&time=' + time + '&phone=' + phone;that.setData({qrCode: url})},//临时图片路径getTempFile: function (url) {wx.showLoading({});let that = this;wx.cloud.downloadFile({fileID: url,success: function (res) {console.log("res.tempFilePath===>", res.tempFilePath)that.setData({goodsInfoImg: res.tempFilePath});//继续生成商品的小程序码that.downloadSkuQrCode(that.data.qrCode);},fail: function (err) { }});},getData: function () {let that = this;let i = 0;let lineNum = 1;let thinkStr = "";let thinkList = [];for (let item of that.data.contentTitle) {if (item === "\n") {thinkList.push(thinkStr);thinkList.push("a");i = 0;thinkStr = "";lineNum += 1;} else if (i === 21) {thinkList.push(thinkStr);i = 1;thinkStr = item;lineNum += 1;} else {thinkStr += item;i += 1;}}thinkList.push(thinkStr);that.setData({thinkList: thinkList});that.createNewImg(lineNum);},//画矩形，也是整块画布的大小，宽度是屏幕宽度，高度根据内容多少来动态设置。drawSquare: function (ctx, height) {let that = this;ctx.rect(that.data.windowWidth * 0.045,that.data.boxPageY,that.data.boxWidth,height);ctx.setFillStyle("#fff");ctx.fill();},// 设置文字大小，并填充颜色。drawFont: function (ctx, contentTitle, height) {let that = this;let str = that.data.contentTitle;let firstline;let secondline;//一行显示12个字，超过一行时if (str.length > 11) {//第一行截取前14个字符firstline = str.substring(0, 11);} else {//一行就能显示时候firstline = str;}//填充微信昵称ctx.setFontSize(14);ctx.setFillStyle("#000");ctx.fillText(firstline, that.data.normalPageX + that.data.userIconWidth+20, that.data.titlePageY+10);//填充京东社交合作伙伴if (that.data.specText) {ctx.setFontSize(12);ctx.setFillStyle("#999999");ctx.fillText(that.data.specText,that.data.normalPageX + that.data.userIconWidth+20,that.data.specPageY + 18);}},// 根据文字多少动态计算高度，然后依次画出矩形，文字，横线和小程序码。createNewImg: function (lineNum) {let that = this;let ctx = wx.createCanvasContext("myCanvas");let contentHeight = that.data.boxheight;that.drawSquare(ctx, contentHeight);that.setData({contentHeight: contentHeight});let height = 100;for (let item of that.data.thinkList) {if (item !== "a") {that.drawFont(ctx, item, height);height += that.data.lineHeight;}}//海报图片ctx.drawImage(that.data.goodsInfoImg,that.data.normalPageX,that.data.imgPageY,that.data.imgWidth,that.data.imgHeight);//画圆形ctx.save();ctx.beginPath(); //开始绘制ctx.arc(that.data.userIconWidth / 2 + 28, that.data.userIconWidth / 2 + that.data.userIconPageY, that.data.userIconWidth / 2, 0, Math.PI * 2, false);ctx.clip();//头像ctx.drawImage(that.data.userIcon,that.data.normalPageX+10,that.data.userIconPageY,that.data.userIconWidth,that.data.userIconHeight);ctx.restore();// 填充小程序码ctx.drawImage(that.data.qrCode,that.data.normalPageX + that.data.windowWidth * 0.65,that.data.codePageY,that.data.codeWidth,that.data.codeHeight);// 长按分享给好友ctx.setFillStyle("#333");ctx.font = "normal normal 9px sans-serif";ctx.fillText("长按分享",that.data.normalPageX +that.data.windowWidth * 0.65 +that.data.codeWidth/3,that.data.codePageY + that.data.codeWidth + 10);ctx.draw(); //绘制到canvas},// 保存图片savePic: function () {let that = this;wx.canvasToTempFilePath({x: 0,y: 50,width: that.data.windowWidth * 2,height: that.data.contentHeight * 2,canvasId: "myCanvas",success: function (res) {// util.savePicToAlbum(res.tempFilePath);wx.hideLoading();var tempFilePath = res.tempFilePath;that.setData({canvasUrl: tempFilePath});if (tempFilePath !== "") {wx.hideLoading();wx.previewImage({current: that.data.canvasUrl, // 当前显示图片的http链接urls: [that.data.canvasUrl], // 需要预览的图片http链接列表success: function (_res) {console.log("预览成功啦");}});}}});},//下载小程序码downloadSkuQrCode: function (url) {let that = this;wx.downloadFile({url: url,success: function (res) {that.setData({qrCode: res.tempFilePath});wx.hideLoading();//生成数据that.getData();},fail: function (err) {wx.showToast({title: "下载小程序码失败,稍后重试！",icon: "none",duration: 5000});}});},//点击保存到相册saveShareImg: function () {var that = this;wx.showLoading({title: '正在保存',mask: true,})setTimeout(function () {wx.canvasToTempFilePath({canvasId: 'myCanvas',success: function (res) {wx.hideLoading();var tempFilePath = res.tempFilePath;wx.saveImageToPhotosAlbum({filePath: tempFilePath,success(res) {// utils.aiCardActionRecord(19);wx.showModal({content: '图片已保存到相册，赶紧晒一下吧~',showCancel: false,confirmText: '好的',confirmColor: '#333',success: function (res) {if (res.confirm) { }},fail: function (res) { }})},fail: function (res) {wx.showToast({title: res.errMsg,icon: 'none',duration: 2000})}})}});}, 1000);}});