iOS 开发一个水印相机

引言

随着手机摄影的普及，拍照已经成为人们日常生活中的重要活动之一。然而，简单的拍照功能已经不能满足用户的需求，用户希望能够添加一些个性化的效果在照片上，比如水印效果。本文将介绍如何使用iOS开发一个水印相机，让用户可以在拍照的同时添加水印。

功能需求

• 实时预览相机画面
• 支持拍照和保存照片
• 用户可以选择添加水印的位置和样式
• 水印可以是文字或者图片

技术方案

本文将使用Swift语言和UIKit框架来开发水印相机应用。具体的技术方案如下：

类图

classDiagram
    class CameraViewController {
        + captureButton: UIButton
        + previewView: UIView
        + watermarkLabel: UILabel
        + watermarkImageView: UIImageView
        - position: CGPoint
        - style: WatermarkStyle
        - captureSession: AVCaptureSession
        - stillImageOutput: AVCaptureStillImageOutput
        - previewLayer: AVCaptureVideoPreviewLayer
        - setupCamera()
        - setupPreviewLayer()
        - capturePhoto()
        - applyWatermark()
        - savePhoto(image: UIImage)
    }

状态图

stateDiagram
    [*] --> Idle
    Idle --> Previewing: Start Preview
    Previewing --> Capturing: Capture Button Pressed
    Capturing --> Saving: Photo Captured
    Saving --> Idle: Photo Saved
    Saving --> Capturing: Recapture Button Pressed

代码实现

首先，我们创建一个名为CameraViewController的类来管理相机功能。

import UIKit
import AVFoundation

class CameraViewController: UIViewController {
    
    @IBOutlet weak var captureButton: UIButton!
    @IBOutlet weak var previewView: UIView!
    @IBOutlet weak var watermarkLabel: UILabel!
    @IBOutlet weak var watermarkImageView: UIImageView!
    
    private var position: CGPoint = .zero
    private var style: WatermarkStyle = .text
    
    private var captureSession: AVCaptureSession?
    private var stillImageOutput: AVCaptureStillImageOutput?
    private var previewLayer: AVCaptureVideoPreviewLayer?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupCamera()
        setupPreviewLayer()
    }
    
    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        captureSession?.stopRunning()
    }
    
    private func setupCamera() {
        captureSession = AVCaptureSession()
        captureSession?.sessionPreset = AVCaptureSession.Preset.photo
        
        let devices = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInWideAngleCamera], mediaType: AVMediaType.video, position: .unspecified).devices
        
        let frontCamera = devices.first(where: { $0.position == .front })
        let backCamera = devices.first(where: { $0.position == .back })
        
        guard let captureSession = captureSession else { return }
        
        if let frontCamera = frontCamera {
            do {
                let input = try AVCaptureDeviceInput(device: frontCamera)
                if captureSession.canAddInput(input) {
                    captureSession.addInput(input)
                }
            } catch {
                print(error)
            }
        } else if let backCamera = backCamera {
            do {
                let input = try AVCaptureDeviceInput(device: backCamera)
                if captureSession.canAddInput(input) {
                    captureSession.addInput(input)
                }
            } catch {
                print(error)
            }
        }
        
        stillImageOutput = AVCaptureStillImageOutput()
        if let stillImageOutput = stillImageOutput {
            if captureSession.canAddOutput(stillImageOutput) {
                captureSession.addOutput(stillImageOutput)
            }
        }
        
        captureSession.startRunning()
    }
    
    private func setupPreviewLayer() {
        guard let captureSession = captureSession else { return }
        
        previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        previewLayer?.videoGravity = AVLayerVideoGravity.resizeAspectFill
        previewLayer?.frame = view.bounds
        previewView.layer.insertSublayer(previewLayer!, at: 0)
    }
    
    @IBAction func captureButtonPressed(_ sender: UIButton) {
        capturePhoto()
    }
    
    private func capturePhoto() {
        guard let stillImageOutput = stillImageOutput else { return }
        
        if let videoConnection = stillImageOutput.connection(with: AVMediaType.video) {
            stillImageOutput.captureStillImageAsynchronously(from: videoConnection) { (imageDataSampleBuffer, error) -> Void in
                if let imageData = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(imageDataSampleBuffer!) {
                    if let image = UIImage(data: imageData) {