微信小程序实现手指触摸画板

<!--pages/shouxieban/shouxieban.wxml-->
<view class="container">
 <view>手写板（请在下方区域手写内容）</view>
 <canvas style="width: {{canvasw}}px; height: {{canvash}}px" class="canvas" id="canvas" canvas-id="canvas" disable-scroll="true" bindtouchstart="canvasStart" bindtouchmove="canvasMove" bindtouchend="canvasEnd" touchcancel="canvasEnd" binderror="canvasIdErrorCallback"></canvas>
 <view class='btns canvaspd'>
 <button bindtap="cleardraw">清除画板</button>
 <button bindtap="setSign">确定</button>
 </view>
 <image src='{{canvasimgsrc}}'></image> 
</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
// pages/shouxieban/shouxieban.js
Page({
 /**
 * 页面的初始数据
 */
 data: {
 //canvas宽高
 canvasw: 0,
 canvash: 0,
 //canvas生成的图片路径
 canvasimgsrc: ""
 },
 //画布初始化执行
 startCanvas: function () {
 var that = this;
 //创建canvas
 this.initCanvas();
 //获取系统信息
 wx.getSystemInfo({
  success: function (res) {
  canvasw = res.windowWidth - 0;//设备宽度
  canvash = canvasw;
  that.setData({ 'canvasw': canvasw });
  that.setData({ 'canvash': canvash });
  }
 });
 
 },
 //初始化函数
 initCanvas: function () {
 // 使用 wx.createContext 获取绘图上下文 context
 context = wx.createCanvasContext('canvas');
 context.beginPath()
 context.setStrokeStyle('#000000');
 context.setLineWidth(4);
 context.setLineCap('round');
 context.setLineJoin('round');
 },
 //事件监听
 canvasIdErrorCallback: function (e) {
 console.error(e.detail.errMsg)
 },
 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 () {
 //清除画布
 arrx = [];
 arry = [];
 arrz = [];
 context.clearRect(0, 0, canvasw, canvash);
 context.draw(true);
 },
 //提交签名内容
 setSign: function () {
 var that = this;
 if (arrx.length == 0) {
  wx.showModal({
  title: '提示',
  content: '签名内容不能为空！',
  showCancel: false
  });
  return false;
 };
 console.log("不是空的，canvas即将生成图片")
 //生成图片
 wx.canvasToTempFilePath({
  canvasId: 'canvas',
  success: function (res) {
  console.log("canvas可以生成图片")
  console.log(res.tempFilePath, 'canvas图片地址');
  that.setData({ canvasimgsrc: res.tempFilePath })
  //code 比如上传操作
 
  },
  fail: function () {
  console.log("canvas不可以生成图片")
  wx.showModal({
   title: '提示',
   content: '微信当前版本不支持，请更新到最新版本！',
   showCancel: false
  });
  },
  complete: function () {
 
  }
 })
 
 },
 /**
 * 生命周期函数--监听页面加载
 */
 onLoad: function (options) {
 //画布初始化执行
 this.startCanvas();
 
 }
})

/* pages/shouxieban/shouxieban.wxss */
/*手写板 */
page{
 background: #f6f6f6;
 padding: 5px auto
}
canvas{
 border: 1px solid #d0d0d0;
 margin: 5rpx;
 background: #f2f2f2
}