微信小程序拍照截取指定区域图片
### 效果图
## 实现步骤
1. 获取拍摄图片（wx.createCameraContext()）
2. canvas绘制拍摄图片（wx.wx.createCanvasContext()）
3. canvas导出指定区域 （wx.canvasToTempFilePath()）
### 话不多少 直接上代码
> wxml
```html
<camera wx:if='{{isShowCamera}}' class="camera-box" devic-position="width" flash="off" style='width:{{windowWidth}}px; height:{{windowHeight}}px;'>
<cover-view class='camerabgImage'>
<cover-view class="active">
<cover-image class="active-image" src="https://oss.mukang.net/blog/2020/12/0716073342969601272.png"></cover-image>
<cover-view class="text">请将VIN码放入框中，点击拍照进行识别</cover-view>
</cover-view>
<cover-view class="btn" bindtap="takePhotoAction">
<cover-view class="button"></cover-view>
</cover-view>
</cover-view>
</camera>
<canvas wx:if='{{isShowImage}}' canvas-id="image-canvas" id="canvas"
style='width:{{windowWidth}}px; height:{{windowHeight}}px;'></canvas>
```
> wxss
```css
.camera-box {
width: 100vw;
height: 100vh
}
.camera-box .camerabgImage {
position: fixed;
top: 0;
left: 0;
right: 0;
bottom: 0
}
.camera-box .camerabgImage .active {
position: absolute;
top: 400rpx;
left: 36rpx;
right: 36rpx
}
.camera-box .camerabgImage .active-image {
display: block;
width: 680rpx;
height: 280rpx
}
.camera-box .camerabgImage .text {
text-align: center;
margin-top: 56rpx;
margin-bottom: 240rpx;
font-size: 28rpx;
font-weight: 400;
color: #D9D9D9;
line-height: 40rpx
}
.camera-box .btn {
position: fixed;
left: 50%;
bottom: 120rpx;
margin-left: -55rpx;
width: 110rpx;
height: 110rpx;
border-radius: 50%;
background: #fff;
border: 6rpx solid#fff;
display: flex;
align-items: center;
justify-content: center;
}
.camera-box .btn .button {
width: 102rpx;
height: 102rpx;
border-radius: 50%;
border: 4rpx solid#000
}
.canvas{
position: absolute;
top: -10000rpx;
left: -10000rpx;
}
```
>js
```javascript
// 创建页面实例对象
Page({
// 页面的初始数据
data: {
isShowCamera: false,
isShowImage: true,
image: '',
windowWidth: '',
windowHeight: ''
},
onLoad() {
/**
* @name: 创建 拍照 获取 可视区域宽高
* @description:
* @version:
* @author: WangJian
* @time: 2021-01-22 10:34:39
*/
this.ctx = wx.createCameraContext()
let {windowWidth, windowHeight} = wx.getSystemInfoSync()
this.setData({windowWidth, windowHeight})
},
onShow: function () {
/**
* @name: 获取摄像头权限
* @description: 授权失败返回上一页
* @version:
* @author: WangJian
* @time: 2021-01-22 10:35:28
*/
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.navigateBack({delta: 1})
}
}
})
} else { //取消
wx.showToast({
title: '授权失败',
icon: 'none',
duration: 1000
})
wx.navigateBack({delta: 1})
}
}
})
}
})
},
/**
* @name: 拍照
* @description: 详细参数可参考官方文档
* @version:
* @author: WangJian
* @time: 2021-01-22 10:36:17
*/
takePhotoAction: function () {
var that = this
that.ctx.takePhoto({
quality: 'high', //高质量
success: (res) => {
that.loadTempImagePath(res.tempImagePath);
},
fail(error) {
console.log(error)
}
})
},
/**
* @name: canvas绘制拍照图片
* @description:
* @version:
* @author: WangJian
* @time: 2021-01-22 10:36:45
*/
loadTempImagePath: function (options) {
var that = this
wx.getSystemInfo({
success: function (res) {
// px与rpx之间转换的公式：px = rpx / 750 * wx.getSystemInfoSync().windowWidth;
var image_x = 36 / 750 * that.data.windowWidth; // x 坐标位置
var image_y = 400 / 750 * that.data.windowWidth; // y 坐标位置
var image_width = 680 / 750 * that.data.windowWidth; // 图片宽度
var image_height = 280 / 750 * that.data.windowWidth; // 图片高度
console.log(image_x, image_y, image_width, image_height)
wx.getImageInfo({
src: options,
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(options, 0, 0, that.data.windowWidth, that.data.windowHeight)
wx.showLoading({
title: '数据处理中...',
icon: 'loading',
duration: 10000
})
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) {
// 生成本地文件路径 可上传服务器
console.log(res.tempFilePath);
that.setData({
image: res.tempFilePath,
})
// 生成base64 图片格式
wx.hideLoading()
console.log(res.tempFilePath);
wx.getFileSystemManager().readFile({
filePath: res.tempFilePath, //图片路径
encoding: 'base64', //编码格式
success: result => { //成功的回调
console.log('data:image/png;base64,' + result.data)
},
fail: function (e) {
wx.hideLoading()
wx.showToast({
title: '出错啦...',
icon: 'loading'
})
}
});
}
})
}, 1000);
}
})
}
})
},
});
```
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微信小程序拍照截取指定区域图片