小程序使用canvas 2D实现签字效果

效果如下：

请结合小程序官方文档进行解读

wxml：

<view>
  <view>请在下方签字:</view>
  <canvas id="myCanvas"
  type="2d"
  style="border:1px solid #d3d3d3;"
  bindtouchstart="start"
  bindtouchmove="move"
  bindtouchend="end"/>
 <view>
  <button  bind:tap="clearCan">清除</button>
  <button type="submit" bind:tap="submitCan">保存</button>
  <van-image width="100" height="100" model:src="{{canvanImg}}" />
 </view>
</view>

js:

/**
   * 页面的初始数据
*/
data: {
    canvas:null,
    CanvasCote:null,
    canvanImg:"",
},
//触摸开始
start (e) {
    this.data.CanvasCote.beginPath()
    this.data.CanvasCote.moveTo(e.touches[0].x,e.touches[0].y)
},
//触摸移动
move (e) {
    this.data.CanvasCote.lineTo(e.touches[0].x, e.touches[0].y)
    this.data.CanvasCote.stroke()//将上下文绘制到canvas中
},
//触摸结束
end (e) {
    this.data.CanvasCote.closePath()
},
//清除画布内容
clearCan(){
    this.data.CanvasCote.clearRect(0, 0,this.data.canvas.width, this.data.canvas.height)
    this.setData({
        canvanImg:""
    })
},
//点击保存生成图片
submitCan(){
    this.setData({
        canvanImg:this.data.canvas.toDataURL("image/png")
    })
    console.log(this.data.canvas.toDataURL("image/png"))
},

/**
* 生命周期函数--监听页面加载
*/
onLoad: function (options) {
    let that = this;
    //如果在 exec 中获取不到res，这里就写 wx.createSelectorQuery().in(this)
    const query = wx.createSelectorQuery()
    query.select('#myCanvas').node().exec((res) => {
        that.setData({
            canvas: res[0].node,
            CanvasCote: res[0].node.getContext('2d')
        })
        let ctx = that.data.CanvasCote;
        ctx.fillStyle = "#fff"
        ctx.fillRect(0, 0, that.data.canvas.width, that.data.canvas.height);
        ctx.strokeStyle='black'
        ctx.lineCap = 'round'; // 线条末端添加圆形线帽，减少线条的生硬感
        ctx.lineJoin = 'round'; // 线条交汇时为原型边角
        // 利用阴影，消除锯齿
        ctx.shadowBlur = 1;
        ctx.shadowColor = '#000';
    })
},