微信小程序用canvas画图并分享

<canvas style='width:{{canvasWidth}}px;height:{{canvasHeight}}px' canvas-id='myCanvas'></canvas>
<button open-type='share'>分享</button>

var ctx = "" // 用于获取canvas
var leftMargin = "" //文字距离左边边距
var Margin = "" //文字距离右边边距
Page({

 /
  页面的初始数据
 /
 data: {
 title: '人人车司机',
 salary: '500-8000元/月',
 rtype: '日结',
 rmoney: '20元',
 canvasWidth: '', // canvas宽度
 canvasHeight: '', // canvas高度
 imagePath: '' // 分享的图片路径
 },

 /
  生命周期函数--监听页面加载
 /
 onLoad: function (options) {
 var that = this
 var sysInfo = wx.getSystemInfo({
  suess: function (res) {
  that.setData({
   //设置宽高为屏幕宽，高为屏幕高的80%，因为文档比例为5:4
   canvasWidth: res.windowWidth,
   canvasHeight: res.windowWidth  0.8
  })
  leftMargin = res.windowWidth
  Margin = res.windowWidth  0.8
  },
 })
 },

 /
  生命周期函数--监听页面初次渲染完成
 /
 onReady: function () {
 ctx = wx.createCanvasContext('myCanvas')
 this.addImage()
 this.tempFilePath()
 
 },
 //画背景图
 addImage: function () {
 var context = wx.createContext();
 var that = this;
 var path = "/images/share.jpg";
 //将模板图片绘制到canvas,在开发工具中drawImage()函数有问题，不显示图片
 //不知道是什么原因，手机环境能正常显示
 ctx.drawImage(path, 0, 0, this.data.canvasWidth, this.data.canvasHeight);
 this.addTitle()
 this.addRtype()
 this.addRmoney()
 this.addSalary()
 ctx.draw()
 },
 //画标题
 addTitle: function (){
 var str = this.data.title
 ctx.font = 'normal bold 20px sans-serif';
 ctx.setTextAlign('center'); // 文字居中
 ctx.setFillStyle("#222222");
 ctx.fillText(str, this.data.canvasWidth/2,65)
 },
 // 画返费方式
 addRtype: function () {
 var str = this.data.rtype
 ctx.setFontSize(16)
 ctx.setFillStyle("#ff4200");
 ctx.setTextAlign('left');
 ctx.fillText(str, leftMargin  0.35, Margin  0.4)
 },
 // 画返费金额
 addRmoney: function () {
 var str = this.data.rmoney
 ctx.setFontSize(16)
 ctx.setFillStyle("#222");
 ctx.setTextAlign('left');
 ctx.fillText(str, leftMargin  0.35, Margin  0.5)
 },
 // 画薪资
 addSalary: function () {
 var str = this.data.salary
 ctx.setFontSize(16)
 ctx.setFillStyle("#222");
 ctx.setTextAlign('left');
 ctx.fillText(str, leftMargin  0.35, Margin  0.61)
 },
 /
  用户点击右上角分享
 /
 onShareAppMessage: function (res) {
 // return eventHandler接收到的分享参数
 return {
  title: this.data.title,
  path: '/pages/test/test',
  imageUrl: this.data.imagePath
 };
 },
 //导出图片
 tempFilePath: function(){
 let that = this;
 wx.canvasToTempFilePath({
  canvasId: 'myCanvas',
  suess: function suess(res) {
  wx.saveFile({
   tempFilePath: res.tempFilePath,
   suess: function suess(res) {
   that.setData({
    imagePath: res.savedFilePath
   });
   }
  });
  }
 });
 },

 /
  生命周期函数--监听页面显示
 /
 onShow: function () {

 },

 /
  生命周期函数--监听页面隐藏
 /
 onHide: function () {

 },

 /
  生命周期函数--监听页面卸载
 /
 onUnload: function () {

 },

 /
  页面相关事件处理函数--监听用户下拉动作
 /
 onPullDownRefresh: function () {

 },

 /
  页面上拉触底事件的处理函数
 /
 onReachBottom: function () {

 }


})