微信小程序 canvas签名、绘图

效果图：

image.png
image.png

canvas.wxml

<canvas class="canvas" id="canvas" canvas-id="canvas" disable-scroll="true" bindtouchstart="canvasStart" bindtouchmove="canvasMove" bindtouchend="canvasEnd" touchcancel="canvasEnd" binderror="canvasIdErrorCallback"></canvas>

<button type="default" bindtap="cleardraw">清除画布</button>
<button type="default" bindtap="getimg">导出图片</button>

canvas.wxss

.canvas {
  width: 100%;
  min-height: 400rpx;
  border: 1rpx solid #000;  //突出canvas画布范围
  box-sizing: border-box;
}

canvas.js

// canvas 全局配置
var context = null;// 使用 wx.createContext 获取绘图上下文 context
var isButtonDown = false;
var arrx = [];
var arry = [];
var arrz = [];
var canvasw = 0;
var canvash = 0;
//获取系统信息
wx.getSystemInfo({
  success: function (res) {
    canvasw = res.windowWidth;//设备宽度
    // canvash = res.windowWidth * 7 / 15;
    canvash = res.windowHeight
  }
});
//注册页面
Page({
  canvasIdErrorCallback: function (e) {
    console.error(e.detail.errMsg)
  },
//开始
  canvasStart: function (event) {
    isButtonDown = true;
    arrz.push(0);
    arrx.push(event.changedTouches[0].x);
    arry.push(event.changedTouches[0].y);
    //context.moveTo(event.changedTouches[0].x, event.changedTouches[0].y);

  },
//过程
  canvasMove: function (event) {
    if (isButtonDown) {
      arrz.push(1);
      arrx.push(event.changedTouches[0].x);
      arry.push(event.changedTouches[0].y);
      // context.lineTo(event.changedTouches[0].x, event.changedTouches[0].y);
      // context.stroke();
      // context.draw()

    };

    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;
  },
  cleardraw: function () {
    //清除画布
    arrx = [];
    arry = [];
    arrz = [];
    context.clearRect(0, 0, canvasw, canvash);
    context.draw(true);
  },
  //导出图片
  getimg: function () {
    if (arrx.length == 0) {
      wx.showModal({
        title: '提示',
        content: '签名内容不能为空！',
        showCancel: false
      });
      return false;
    };
    //生成图片
    wx.canvasToTempFilePath({
      canvasId: 'canvas',
      success: function (res) {
        console.log(res.tempFilePath);
        //存入服务器
        wx.uploadFile({
          url: 'a.php', //接口地址
          filePath: res.tempFilePath,
          name: 'file',
          formData: {                                 //HTTP 请求中其他额外的 form data 
            'user': 'test'
          },
          success: function (res) {
            console.log(res);
          },
          fail: function (res) {
            console.log(res);
          },
          complete: function (res) {
          }
        });
      }
    })

  },
  /**
   * 页面的初始数据
   */
  data: {
    src: ""
  },
  /**
   * 生命周期函数--监听页面加载
   */
  onLoad: function (options) {
    // 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');
  }
})