效果图如下：

clock.gif

wxml文件

<view>
  <canvas canvas-id='clock' class='canvas'></canvas>
</view>

wxss文件

.canvas{
  width: 100%;
  height: 100%;
  position: fixed;
}

json文件（可以为空下面设置的是标题）

{
  "navigationBarTitleText": "消息"
}

js文件

Page({
  data: {
    width:0,
    height:0
  },
  onLoad: function () {
    var that = this;
    wx.getSystemInfo({
      success: function(res) {
        that.width = res.windowWidth;
        that.height = res.windowHeight;
      },
    })
  },
  onReady: function () {
    this.canvasClock();
    this.interval = setInterval(this.canvasClock,1000);
  },
  onUnload: function () {
    clearInterval(this.interval)
  },
  onShareAppMessage: function () {
    return {
      title:'转发canvas时钟'
    }
  },
  canvasClock: function(){
    const ctx = wx.createContext();
    const width = this.width;
    const height = this.height;
    const R = width/2-55;
    function reSet(){
      ctx.height = ctx.height;
      ctx.translate(width/2,height/2);
      ctx.save();
    }
    // 圆盘
    function circle(){
      ctx.setLineWidth(2);
      ctx.beginPath();
      ctx.setStrokeStyle('gray');
      ctx.arc(0,0,width/2-30,0,2 * Math.PI,true);
      ctx.closePath();
      ctx.stroke();
      ctx.beginPath();
      ctx.arc(0,0,8,0,2 * Math.PI,true);
      ctx.closePath();
      ctx.stroke();
    }
    // 数字
    function num(){
      ctx.setFontSize(20);
      ctx.setTextBaseline('middle');
      for(let i = 1; i < 13; i++){
        const x = (R - 10) * Math.cos(i * Math.PI / 6 - Math.PI / 2);
        const y = (R - 10) * Math.sin(i * Math.PI / 6 - Math.PI / 2);
        if(i === 11 || i === 12){
          ctx.fillText(i, x-12, y+9);
        }else{
          ctx.fillText(i, x-6, y+9);
        }
      }
    }
    // 刻度 start
    function smallGrid(){
      ctx.setLineWidth(1);
      ctx.rotate(-Math.PI / 2);
      for( let i = 0; i < 60; i++){
        ctx.beginPath();
        ctx.rotate(Math.PI / 30);
        ctx.moveTo(width / 2 - 30, 0);
        ctx.lineTo(width / 2 - 40, 0);
        ctx.stroke();
      }
    }
    function bigGrid() {
      ctx.setLineWidth(5);
      for (let i = 0; i < 12; i++) {
        ctx.beginPath();
        ctx.rotate(Math.PI / 6);
        ctx.moveTo(width / 2 - 30, 0);
        ctx.lineTo(width / 2 - 45, 0);
        ctx.setStrokeStyle('black');
        ctx.stroke();
      }
    }
    // 刻度 end
    // 指针移动方法
    function move(){
      const date = new Date();
      let h = date.getHours();
      h = (h > 12) ? (h - 12) : h;
      const m = date.getMinutes();
      const s = date.getSeconds();
      ctx.save();
      // 时针
      ctx.setLineWidth(7);
      ctx.beginPath();
      ctx.setStrokeStyle('orange');
      ctx.rotate((Math.PI / 6) * (h + m / 60 + s / 3600));
      ctx.moveTo(-20, 0);
      ctx.lineTo(width / 4.5 - 20,0);
      ctx.stroke();
      ctx.restore();
      ctx.save();
      // 分针
      ctx.setLineWidth(5);
      ctx.beginPath();
      ctx.setStrokeStyle('blue');
      ctx.rotate((Math.PI / 30) * (m + s / 60));
      ctx.moveTo(-20, 0);
      ctx.lineTo(width / 3.5 - 20, 0);
      ctx.stroke();
      ctx.restore();
      ctx.save();
      // 秒针
      ctx.setLineWidth(2);
      ctx.beginPath();
      ctx.setStrokeStyle('red');
      ctx.rotate((Math.PI / 30) * s);
      ctx.moveTo(-20, 0);
      ctx.lineTo(width / 3 - 20, 0);
      ctx.stroke();
    }
    function drawClock(){
      reSet();
      circle();
      num();
      smallGrid();
      bigGrid();
      move();
    }
    drawClock();
    wx.drawCanvas({
      canvasId: 'clock',
      actions: ctx.getActions()
    })
  }
})