微信小程序实现拍照画布指定区域生成图片

最近写识别行驶证功能，点击拍照把指定区域截取，生成图片功能。

系统相机。该组件是原生组件，使用时请注意相关限制。 扫码二维码功能，需升级微信客户端至6.7.3。

微信小程序Camera相机地址

我们看下效果：

1、首先生成一个CanvasContext：

/**
 * 生命周期函数--监听页面加载
 */
 onLoad: function(options) {
 requireJs.adaptionIphoneX(this);

 this.ctx = wx.createCameraContext()

 },

2、相机的 wxml样式

<camera wx:if='{{isShowCamera}}' device - position="width" flash="off" style="width:{{windowWidth}}px; height:{{windowHeight}}px;">

 <cover-view class='camerabgImage-view'>
  <cover-image class='bgImage' src='{{isIphoneX==true?"../../myImage/vehicle/biankuang_x.png":"../../myImage/vehicle/biankuang.png"}}'> </cover-image>

  <cover-view class='cameratop-view1'>中华人民共和国机动车行驶证</cover-view>
  <cover-view class='cameratop-view2'>（行驶证主页）</cover-view>
  <cover-view class='cameracenter-view' style='top:{{isIphoneX==true?"52%":"62%"}}'>请对准左下角发证机关印章</cover-view>

  <!-- 拍照按钮 -->
  <cover-view class='camerabotton-view' style='bottom:{{isIphoneX==true?"75px":"0px"}}'>
  <cover-image class='cancelphoto' src='../../myImage/vehicle/quxiao.png' bindtap='cancelPhotoAction'></cover-image>
  <cover-image class='takephoto' src='../../myImage/vehicle/paizhao.png' bindtap='takePhotoAction'></cover-image>

  <cover-view class='skipphoto' bindtap='skipphotoAction'>{{skipphotoStatus==1?"跳过":""}}
  </cover-view>

  </cover-view>

 </cover-view>

 </camera>

 <canvas wx:if='{{isShowImage}}' canvas-id="image-canvas" style='width:{{windowWidth}}px; height:{{windowHeight}}px;'></canvas>

3、相机的 wxss样式

.camerabgImage-view{
 height: 100%;
 width: 100%;
 position:absolute;
}
.bgImage{
 width: 100%;
 height: 100%;
 position: absolute;
}

.cameratop-view1{
 margin-top: 174rpx;
}
.cameratop-view2{
 margin-top: 220rpx;
}
.cameratop-view1, .cameratop-view2{
 width: 100%;
 display: flex;
 justify-content: center;
 position: absolute;

 font-family: PingFangSC-Medium;
 font-size: 36rpx;
 color: #FFFFFF;
 letter-spacing: 0;
 text-align: center;
}

.cameracenter-view{
 height: 44rpx;
 width: 100%;
 position: absolute;

 font-family: PingFangSC-Medium;
 font-size: 32rpx;
 color: #FFFFFF;
 letter-spacing: 0;
 text-align: center;
}

/* 底部 */
.camerabotton-view{
 height: 200rpx;
 width: 100%;
 position:absolute;

 display: flex;
 justify-content: space-around;
 align-items: center;
}
.cancelphoto{
 width: 50rpx;
 height: 50rpx;
}
.takephoto{
 width: 132rpx;
 height: 132rpx;
}
.skipphoto{
 font-family: PingFangSC-Regular;
 font-size: 32rpx;
 color: #FFFFFF;
 letter-spacing: 0;
 text-align: center;
}

4、js 中访问原生组件 camera  主要针对相机权限处理

微信小程序权限地址

onShow: function() {
 var that = this
 wx.authorize({
  scope: 'scope.camera',
  success: function (res) {
  that.setData({
   isShowCamera: true,
  })
  },
  fail: function (res) {
  console.log("" + res);
  wx.showModal({
   title: '请求授权您的摄像头',
   content: '如需正常使用此小程序功能，请您按确定并在设置页面授权用户信息',
   confirmText: '确定',
   success: res => {
   if (res.confirm) {
    wx.openSetting({
    success: function (res) {
     console.log('成功');
     console.log(res);
     if (res.authSetting['scope.camera']) { //设置允许获取摄像头
     console.log('设置允许获取摄像头')
     wx.showToast({
      title: '授权成功',
      icon: 'success',
      duration: 1000
     })
     that.setData({
      isShowCamera: true,
     })

     } else { //不允许
     wx.showToast({
      title: '授权失败',
      icon: 'none',
      duration: 1000
     })
     wx.redirectTo({
      url: 'addCarInfo/addCarInfo',
     })
     }
    }
    })
   } else { //取消
    wx.showToast({
    title: '授权失败',
    icon: 'none',
    duration: 1000
    })
    wx.redirectTo({
    url: 'addCarInfo/addCarInfo',
    })
   }
   }
  })

  }
 })
 },

5、页面初始化数据

/**
 * 页面的初始数据
 */
 data: {
 isShowCamera: false,
 width: 10,
 height: 10,
 src: "",
 image: "",
 skipphotoStatus: "0",// 1跳过 0没有跳过
 isShowImage: false
 },

6、点击拍照 设置照片， 返回拍照图片

/**
 * 拍照
 */
 takePhotoAction: function() {
 var that = this
 that.ctx.takePhoto({
  quality: 'high', //高质量
  success: (res) => {
  this.loadTempImagePath(res.tempImagePath);
  },
 })
 },

7、针对原图片截取尺寸 与 截取后的图片

 loadTempImagePath: function(options) {
 var that = this
 that.path = options
 wx.getSystemInfo({
  success: function(res) {

  // 矩形的位置
  var image_x = 15;
  var image_y = 150;
  var image_width = that.data.width - 2 * 15;
  var image_height = 238;

  wx.getImageInfo({
   src: that.path,
   success: function(res) {
   that.setData({
    isShowImage: true,
   })
   that.canvas = wx.createCanvasContext("image-canvas", that)
   //过渡页面中，图片的路径坐标和大小
   that.canvas.drawImage(that.path, 0, 0, that.data.width, that.data.height)
   wx.showLoading({
    title: '数据处理中...',
    icon: 'loading',
    duration: 10000
   })
   // 这里有一些很神奇的操作,总结就是MD拍出来的照片规格居然不是统一的过渡页面中，对裁剪框的设定
   that.canvas.setStrokeStyle('black')
   that.canvas.strokeRect(image_x, image_y, image_width, image_height)
   that.canvas.draw()
   setTimeout(function() {
    wx.canvasToTempFilePath({ //裁剪对参数
    canvasId: "image-canvas",
    x: image_x, //画布x轴起点
    y: image_y, //画布y轴起点
    width: image_width, //画布宽度
    height: image_height, //画布高度
    destWidth: image_width, //输出图片宽度
    destHeight: image_height, //输出图片高度
    success: function(res) {
     that.setData({
     image: res.tempFilePath,
     })
     //清除画布上在该矩形区域内的内容。
     // that.canvas.clearRect(0, 0, that.data.width, that.data.height)
     // that.canvas.drawImage(res.tempFilePath, image_x, image_y, image_width, image_height)
     // that.canvas.draw()
     wx.hideLoading()

     console.log(res.tempFilePath);
     //在此可进行网络请求
     PublicJS.drivinglicenseUpload(res.tempFilePath, that.uploadFile);
    },
    fail: function(e) {
     wx.hideLoading()
     wx.showToast({
     title: '出错啦...',
     icon: 'loading'
     })
     if (this.data.skipphotoStatus == 1) {
     wx.redirectTo({
      url: 'addCarInfo/addCarInfo',
     })
     } else {
     wx.navigateBack({
      delta: 1
     });
     }
    }
    });
   }, 1000);
   }
  })
  }
 })
 },

// 接口返回结果

uploadFile: function(data) {}

微信小程序Canvas画布地址

1.canvas组件是由客户端创建的原生组件，它的层级是最高的。

2.请勿在scroll-view中使用canvas组件。

3.css动画对canvas组件无效。

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