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。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。