I want to implement a custom camera. There is a rectangular frame in the middle of the camera preview interface, and the other parts are translucent. Then I want to get the picture in the rectangular frame. Can anyone give me some advice? Similar to the effect below. 
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
Recommended for reference
zxing
Its QR code scanning interface has an effect similar to what you need