// XXXX.wxml
<view class="signName">
 <canvas class="canvas" id="canvas" canvas-id="canvas" disable-scroll="true" bindtouchstart="canvasStart"
  bindtouchmove="canvasMove" bindtouchend="canvasEnd" touchcancel="canvasEnd"
  binderror="canvasIdErrorCallback"></canvas>
 </view>
 <view class="CList flex">
 <view class="flex_item marginR20" >
  <view class="saveBtn" bindtap="uploadImg">上传签名</view>
 </view>
 <view class="flex_item">
  <view class="clearBtn" bindtap="cleardraw">清除签名</view>
</view> 

var context = null;// 使用 wx.createContext 获取绘图上下文 context
var isButtonDown = false;//是否在绘制中
var arrx = [];//动作横坐标
var arry = [];//动作纵坐标
var arrz = [];//总做状态，标识按下到抬起的一个组合
var canvasw = 0;//画布宽度
var canvash = 0;//画布高度
Page({

 data: {
 },
 
 onLoad: function () {
  this.startCanvas();
 },
 /**
 * 以下 - 手写签名 / 上传签名
 */
 startCanvas: function () {//画布初始化执行
 var that = this;
 //获取系统信息
 wx.getSystemInfo({
  success: function (res) {
  canvasw = res.windowWidth;
  canvash = res.windowHeight;
  that.setData({ canvasw: canvasw });
  that.setData({ canvash: canvash });
  }
 }); 
 this.initCanvas();
 this.cleardraw(); 
 },
 //初始化函数
 initCanvas: function () {
 context = wx.createCanvasContext('canvas');
 context.beginPath()
 context.fillStyle = 'rgba(255, 255, 255, 0)';
 context.setStrokeStyle('#000000');
 context.setLineWidth(4);
 context.setLineCap('round');
 context.setLineJoin('round');
 },
 canvasStart: function (event) {
 isButtonDown = true;
 arrz.push(0);
 arrx.push(event.changedTouches[0].x);
 arry.push(event.changedTouches[0].y);
 },
 canvasMove: function (event) {
 if (isButtonDown) {
  arrz.push(1);
  arrx.push(event.changedTouches[0].x);
  arry.push(event.changedTouches[0].y);
 }
 for (var i = 0; i < arrx.length; i++) {
  if (arrz[i] == 0) {
  context.moveTo(arrx[i], arry[i])
  } else {
  context.lineTo(arrx[i], arry[i])
  }
 }
 context.clearRect(0, 0, canvasw, canvash);
 context.setStrokeStyle('#000000');
 context.setLineWidth(4);
 context.setLineCap('round');
 context.setLineJoin('round');
 context.stroke();
 context.draw(false);
 },
 canvasEnd: function (event) {
 isButtonDown = false;
 },
 //清除画布
 cleardraw: function () {
 arrx = [];
 arry = [];
 arrz = [];
 context.clearRect(0, 0, canvasw, canvash);
 context.draw(true);
 },
 uploadImg(){
 var that = this
 //生成图片
 wx.canvasToTempFilePath({
  canvasId: 'canvas',
  //设置输出图片的宽高
  // destWidth:150, 
  // destHeight:150,
  // fileType:'jpg',
  quality:1.0,
  success: function (res) {
  console.log(res)
  // canvas图片地址 res.tempFilePath
  },
  fail: function () {
  wx.showModal({
   title: '提示',
   content: 'canvas生成图片失败。微信当前版本不支持，请更新到最新版本！',
   showCancel: false
  });
  },
  complete: function () {}
 })
 },
})