微信小程序实现身份证取景框拍摄

<view class="camera_box">
 <camera class="camera" wx:if="{{!show}}" device-position="back" flash="off" binderror="error">
 <cover-view class="id_m">
  <cover-image class="img" src="//img.jbzj.com/file_images/article/202009/202099172501721.png"></cover-image>
 </cover-view>
 </camera>
 <image class="camera_img" src="{{src}}" wx:if="{{show}}"></image>
 <view class="action">
 <button class="takeBtn" type="primary" bindtap="takePhoto" wx:if="{{!show}}"></button>
 <button class="saveImg" type="primary" bindtap="saveImg" wx:if="{{show}}"></button>
 <button class="cancelBtn" wx:if="{{show}}" type="primary" bindtap="cancelBtn"></button>
 </view>
</view>

.camera_box {
 height: 100vh; width: 100vw;
 position: relative;
}
.camera {
 height: 85vh; width: 100vw;
 z-index: 1;
}
.id_m {
 height: 85vh; width: 100vw;
 z-index: 999;
 background: rgba(0, 0, 0, 0.1);
 display: flex;
 position: absolute;
}
.id_m .img {
 width: 550rpx;
 height: 900rpx;
 display: block;
 position: absolute;
 left: 0; right: 0; margin: auto auto;
 top: 0; bottom: 0;
}
.id_m .tips_txt {
 transform:rotate(90deg);
}
.camera_box .action {
 height: 15vh;
 position: relative;
 display: flex;
 justify-content: space-around;
 align-items: center;
} 
.camera_box .takeBtn {
 height: 120rpx; width: 120rpx; border-radius: 50%;
 font-size: 24rpx;
 background: url('https://cache.yisu.com/upload/information/20200909/112/4082.png') no-repeat center;
 background-size: contain;
 border: none;
}
.camera_box .cancelBtn {
 font-size: 24rpx;
 height: 120rpx; width: 120rpx; border-radius: 50%;
 background: url('https://cache.yisu.com/upload/information/20200909/112/4083.png') no-repeat center;
 background-size: contain;
 border: none;
}
.camera_box .saveImg {
 background: url('https://cache.yisu.com/upload/information/20200909/112/4084.png') no-repeat center;
 font-size: 24rpx;
 height: 120rpx; width: 120rpx; border-radius: 50%;
 background-size: contain;
 border: none;
}
.camera_box .takeBtn::after {
 border: none;
}

.camera_img {
 height: 85vh; width: 100%;
}

Page({

 /**
 * 页面的初始数据
 */
 data: {
 src: '',
 show: false
 },
 cancelBtn () {
 this.setData({show: false})
 },
 saveImg () {
 wx.showModal({
  title: '图片地址',
  content: this.data.src,
 })
 },
 takePhoto() {
 const ctx = wx.createCameraContext()
 const listener = ctx.onCameraFrame((frame) => {
  console.log(frame)
 })
 ctx.takePhoto({
  quality: 'high',
  success: (res) => {
  console.log(res)
  this.setData({
   src: res.tempImagePath,
   show: true
  })
  listener.stop({
   success: (res) => {
   console.log(res)
   },
   fail: (err) =>{
   console.log(err)
   }
  })
  },
  fail: (err) => {
  console.log(err)
  }
 })
 },
 error(e) {
 console.log(e.detail)
 },
 /**
 * 生命周期函数--监听页面加载
 */
 onLoad: function (options) {
 
 },

 /**
 * 生命周期函数--监听页面初次渲染完成
 */
 onReady: function () {
 
 },

 /**
 * 生命周期函数--监听页面显示
 */
 onShow: function () {
 
 },

 /**
 * 生命周期函数--监听页面隐藏
 */
 onHide: function () {
 
 },

 /**
 * 生命周期函数--监听页面卸载
 */
 onUnload: function () {
 
 },

 /**
 * 页面相关事件处理函数--监听用户下拉动作
 */
 onPullDownRefresh: function () {
 
 },

 /**
 * 页面上拉触底事件的处理函数
 */
 onReachBottom: function () {
 
 },

 /**
 * 用户点击右上角分享
 */
 onShareAppMessage: function () {
 
 }
})