記錄學習內容。看網路上大大們的文章和影片，做些紀錄。
以下內容還不太懂。

來閱讀這篇大大的程式，先來查看不懂的地方 。還沒實作:
CameraView/Sources/CameraView/CameraView.swift

1

private struct PreviewHolder: UIViewRepresentable

    private var delegate: CameraViewDelegate?
    private var cameraType: AVCaptureDevice.DeviceType
    private var cameraPosition: AVCaptureDevice.Position
    private var view: PreviewView

CameraViewDelegate 是一個作者寫的介面:

//
//  CameraViewDelegate.swift
//  
//
//  Created by Brett Fazio on 3/21/20.
//
import Foundation

public protocol CameraViewDelegate {
    func cameraAccessGranted()
    func cameraAccessDenied()
    func noCameraDetected()
    func cameraSessionStarted()
}

cameraAccessGranted() --- >相機權限允許
cameraAccessDenied() ---- > 相機權限否定
noCameraDetected() --- > 手機沒相機
cameraSessionStarted() --- >還不確定，大概是相機開始

接著來看

2 AVCaptureDevice.DeviceType

builtInTripleCamera (三鏡頭)

A device that consists of three cameras of fixed focal length, one ultrawide angle(超廣角?), one wide angle(廣角?), and one telephoto(長焦?)

三鏡頭參考:
小丰子3C俱樂部

angle(超廣角?), one wide angle(廣角?), and one telephoto(長焦?) 的意思應該是指
[廣角RGB+超廣角RGB+望遠Tele]

3

作者寫的這段:

private class PreviewView: UIView, AVCapturePhotoCaptureDelegate {

裡面有處理權限:
requestAccess(for:completionHandler:)
Day 22: 再次向使用者請求開啟功能的權限。

有AVCaptureSession()的設定:

有 input 、 output設定:

Input 是指這個(相機的前後鏡、幾個鏡頭、video就是錄影或拍照):

let videoDevice = AVCaptureDevice.default(cameraType,
                                                  for: .video, position: cameraPosition)

output設定指的是AVCapturePhotoOutput() ，用來判斷輸出的圖片有甚麼功能，像是高解析度、LivePhoto:

        photoOutput!.isHighResolutionCaptureEnabled = true
        photoOutput!.isLivePhotoCaptureEnabled = photoOutput!.isLivePhotoCaptureSupported

開始相機，應該就是指:
captureSession?.startRunning()
https://developer.apple.com/documentation/avfoundation/avcapturesession

You invoke startRunning() to start the flow of data from the inputs to the outputs, and invoke stopRunning() to stop the flow.

func capturePhoto() 裡的內容:

AVCapturePhotoSettings

AVCapturePhotoSettings 代表一些 拍照時的設定 ，
像是要不要開閃光、設定圖片類型(jpeg、hevc):

閃光:

var flashMode: AVCaptureDevice.FlashMode
A setting for whether to fire the flash when capturing photos.

圖片類型:

https://developer.apple.com/documentation/avfoundation/avvideocodectype

沒有png?

static let jpeg: AVVideoCodecType
The JPEG video codec.

static let hevc: AVVideoCodecType
The HEVC video codec.

什麼是HEVC ?
[Windows] 如何在Windows10安裝免費模組讀取iPhone的HEIC格式的影片及圖片？

蘋果的 照片-- >.HEIF（高效率影像檔案格式）
影片-- >.HEVC（高效率視訊編碼），亦稱為 H.265

接著來看 func photoOutput 裡的內容 :

跟這個有關:
previewCGImageRepresentation
https://developer.apple.com/documentation/avfoundation/avcapturephoto/2873945-previewcgimagerepresentation?language=objc
先跳過。

didMoveToSuperview()

https://developer.apple.com/documentation/uikit/uiview/1622433-didmovetosuperview

Any

24-Any & AnyObject types | is typeCheck operator | as? as! type conversion(casting)operator| Swift
https://www.youtube.com/watch?v=ZryV2Dj2XSA&ab_channel=Appleapps

錄音

iOS App 實作(12)錄音功能(AVAudioRecorder)
https://ithelp.ithome.com.tw/articles/10195621

Voice Recorder App In SwiftUI – #1 Implementing The Audio Recorder
https://blckbirds.com/post/voice-recorder-app-in-swiftui-1/

Audio Visualization in Swift Using Metal and Accelerate (Part 1)
https://betterprogramming.pub/audio-visualization-in-swift-using-metal-accelerate-part-1-390965c095d7