Android 使用CameraX实现预览/拍照/录制视频/图片分析/对焦/缩放/切换摄像头等操作

1. CameraX架构

看官方文档 CameraX架构
有如下这一段话

使用CameraX，借助名为"用例"的抽象概念与设备的相机进行交互。

• 预览 : 接受用于显示预览的Surface，例如PreviewView
• 图片分析 : 为分析 (例如机器学习) 提供CPU可访问的缓冲区
• 图片拍摄 : 拍摄并保存图片
• 视频拍摄 : 通过VideoCapture拍摄视频和音频

不同用例可以组合使用，也可以同时处于活跃状态。
例如，应用中可以加入预览用例，以便让用户查看进入相机视野的画面
加入图片分析用例，以确定照片里的人物是否在微笑
还可以加入图片拍摄用例，以便在人物微笑时拍摄照片

第一次看的时候，一脸懵逼，“用例”，是个什么鬼玩意。

后来，研究了一下，知道"用例"的英文原文叫做Use Case，CameraX中的每一项操作，对应着一种UseCase

• 预览 : Preview.java
• 图片分析 : ImageAnalysis.java
• 图片拍摄 : ImageCapture.java
• 视频拍摄 : VideoCapture.java

可以看到，这几个类都是继承自UseCase.java类的

public final class Preview extends UseCase {
	//...
}
public final class ImageAnalysis extends UseCase {
	//...
}
public final class ImageCapture extends UseCase {
	//...
}
public final class VideoCapture extends UseCase {
	//...
}

接下来让我们来尝试使用一下。

2. 前置操作

首先，我们需要新建一个项目，然后引入依赖

// CameraX core library using the camera2 implementation
def camerax_version = "1.2.0-alpha02" //1.2.0-alpha02
// The following line is optional, as the core library is included indirectly by camera-camera2
implementation "androidx.camera:camera-core:${camerax_version}"
implementation "androidx.camera:camera-camera2:${camerax_version}"
// If you want to additionally use the CameraX Lifecycle library
implementation "androidx.camera:camera-lifecycle:${camerax_version}"
// If you want to additionally use the CameraX VideoCapture library
implementation "androidx.camera:camera-video:${camerax_version}"
// If you want to additionally use the CameraX View class
implementation "androidx.camera:camera-view:${camerax_version}"
// If you want to additionally add CameraX ML Kit Vision Integration
implementation "androidx.camera:camera-mlkit-vision:${camerax_version}"
// If you want to additionally use the CameraX Extensions library
implementation "androidx.camera:camera-extensions:${camerax_version}"

在AndroidManifest.xml里添加权限

<uses-permission android:name="android.permission.CAMERA" />

<uses-feature android:name="android.hardware.camera.any" />

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

<uses-permission android:name="android.permission.RECORD_AUDIO" />

别忘了申请权限

ActivityCompat.requestPermissions(
        this, arrayOf(
            Manifest.permission.CAMERA,
            Manifest.permission.WRITE_EXTERNAL_STORAGE,
            Manifest.permission.READ_EXTERNAL_STORAGE,
            Manifest.permission.RECORD_AUDIO
        ), 123
    )

3. 预览 : Preview.java

首先修改activity_main.xml

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/camera_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/black">

    <androidx.camera.view.PreviewView
        android:id="@+id/previewView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

androidx.constraintlayout.widget.ConstraintLayout>

修改MainActivity.kt

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    private lateinit var cameraProvider: ProcessCameraProvider
    private var preview: Preview? = null
    private var camera: Camera? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        //TODO 省略了权限申请，具体看文章中 "前置操作" 部分

        setUpCamera(binding.previewView)
    }

    private fun setUpCamera(previewView: PreviewView) {
        val cameraProviderFuture: ListenableFuture<ProcessCameraProvider> =
            ProcessCameraProvider.getInstance(this)
        cameraProviderFuture.addListener({
            try {
                cameraProvider = cameraProviderFuture.get()
                bindPreview(cameraProvider, previewView)
            } catch (e: Exception) {
                e.printStackTrace()
            }
        }, ContextCompat.getMainExecutor(this))
    }

    private fun bindPreview(
        cameraProvider: ProcessCameraProvider,
        previewView: PreviewView
    ) {
	    //解除所有绑定，防止CameraProvider重复绑定到Lifecycle发生异常
        cameraProvider.unbindAll()
        preview = Preview.Builder().build()
        camera = cameraProvider.bindToLifecycle(
            this,
            CameraSelector.DEFAULT_BACK_CAMERA, preview
        )
        preview?.setSurfaceProvider(previewView.surfaceProvider)
    }
}

看下效果

4. 图像分析 : ImageAnalysis.java

图像分析用例ImageAnalysis为应用提供可实时分析的图像数据，我们可以对这些图像执行图像处理、计算机视觉或机器学习推断。

val imageAnalysis = ImageAnalysis.Builder()
    // enable the following line if RGBA output is needed.
    // .setOutputImageFormat(ImageAnalysis.OUTPUT_IMAGE_FORMAT_RGBA_8888)
    .setTargetResolution(Size(1280, 720))
    .setBackpressureStrategy(ImageAnalysis.STRATEGY_KEEP_ONLY_LATEST)
    .build()
imageAnalysis.setAnalyzer(executor, ImageAnalysis.Analyzer { imageProxy ->
    val rotationDegrees = imageProxy.imageInfo.rotationDegrees
    // insert your code here.
    // 在这里处理图片的解析，比如解析成二维码之类的
    ...
    // after done, release the ImageProxy object
    imageProxy.close()
})

在调用cameraProvider.bindToLifecycle()时，进行传入

cameraProvider.bindToLifecycle(
	this, CameraSelector.DEFAULT_BACK_CAMERA, preview, imageAnalysis
)

5. 拍照 : ImageCapture.java

5.1 仅拍照

这里，我们需要先创建一个imageCapture

imageCapture = ImageCapture.Builder()
	.setCaptureMode(ImageCapture.CAPTURE_MODE_MINIMIZE_LATENCY)
	//.setTargetAspectRatio(screenAspectRatio)
	//.setTargetRotation(binding.previewView.display.rotation)
	.build()

然后，在调用cameraProvider.bindToLifecycle()时，进行传入

camera = cameraProvider.bindToLifecycle(
    this,CameraSelector.DEFAULT_BACK_CAMERA, preview, imageCapture
)

增加takePicture()方法进行拍照

//进行拍照
private fun takePicture() {
    imageCapture?.let { imageCapture ->
        val mainExecutor = ContextCompat.getMainExecutor(this)
        imageCapture.takePicture(mainExecutor, object : ImageCapture.OnImageCapturedCallback() {
            override fun onCaptureSuccess(image: ImageProxy) {
                super.onCaptureSuccess(image)
            }

            override fun onError(exception: ImageCaptureException) {
                super.onError(exception)
            }
        })

        // 让画面闪一下，营造拍照的感觉
        // We can only change the foreground Drawable using API level 23+ API
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            // Display flash animation to indicate that photo was captured
            binding.root.postDelayed({
                binding.root.foreground = ColorDrawable(Color.WHITE)
                binding.root.postDelayed(
                    { binding.root.foreground = null }, 50L
                )
            }, 100L)
        }
    }
}

5.2 拍照并保存到本地存储

我们也可以拍照后，保存到本地存储中

/** Helper function used to create a timestamped file */
private fun createFile(baseFolder: File, format: String, extension: String) =
    File(
        baseFolder, SimpleDateFormat(format, Locale.US)
            .format(System.currentTimeMillis()) + extension
    )

/** Use external media if it is available, our app's file directory otherwise */
fun getOutputDirectory(context: Context): File {
    val appContext = context.applicationContext
    val mediaDir = context.externalMediaDirs.firstOrNull()?.let {
        File(it, appContext.resources.getString(R.string.app_name)).apply { mkdirs() }
    }
    return if (mediaDir != null && mediaDir.exists())
        mediaDir else appContext.filesDir
}

companion object {
    private const val FILENAME = "yyyy-MM-dd-HH-mm-ss-SSS"
    private const val PHOTO_EXTENSION = ".jpg"
}

//进行拍照并保存到本地
private fun takePictureSaveToDisk() {
    imageCapture?.let { imageCapture ->

        // Create output file to hold the image
        val photoFile = createFile(getOutputDirectory(this), FILENAME, PHOTO_EXTENSION)
        Log.i(TAG, "photoFile:$photoFile")

        // Setup image capture metadata
        val metadata = ImageCapture.Metadata().apply {

            // Mirror image when using the front camera
            isReversedHorizontal = lensFacing == CameraSelector.LENS_FACING_FRONT
        }

        // Create output options object which contains file + metadata
        val outputOptions = ImageCapture.OutputFileOptions.Builder(photoFile)
            .setMetadata(metadata)
            .build()

        // Setup image capture listener which is triggered after photo has been taken
        imageCapture.takePicture(
            outputOptions,
            ContextCompat.getMainExecutor(this),
            object : ImageCapture.OnImageSavedCallback {
                override fun onError(exc: ImageCaptureException) {
                    Log.e(TAG, "Photo capture failed: ${exc.message}", exc)
                }

                override fun onImageSaved(output: ImageCapture.OutputFileResults) {
                    val savedUri = output.savedUri ?: Uri.fromFile(photoFile)
                    Log.d(TAG, "Photo capture succeeded: $savedUri")

                    // Implicit broadcasts will be ignored for devices running API level >= 24
                    // so if you only target API level 24+ you can remove this statement
                    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.N) {
                        application.sendBroadcast(
                            Intent(android.hardware.Camera.ACTION_NEW_PICTURE, savedUri)
                        )
                    }

                    // If the folder selected is an external media directory, this is
                    // unnecessary but otherwise other apps will not be able to access our
                    // images unless we scan them using [MediaScannerConnection]
                    val mimeType = MimeTypeMap.getSingleton()
                        .getMimeTypeFromExtension(savedUri.toFile().extension)
                    MediaScannerConnection.scanFile(
                        application,
                        arrayOf(savedUri.toFile().absolutePath),
                        arrayOf(mimeType)
                    ) { _, uri ->
                        Log.d(TAG, "Image capture scanned into media store: $uri")
                    }
                }
            })

 		// 让画面闪一下，营造拍照的感觉
        // We can only change the foreground Drawable using API level 23+ API
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            // Display flash animation to indicate that photo was captured
            binding.root.postDelayed({
                binding.root.foreground = ColorDrawable(Color.WHITE)
                binding.root.postDelayed(
                    { binding.root.foreground = null }, 50L
                )
            }, 100L)
        }
    }
}

然后，我们可以在相册里找到这张图片了，图片的真实位置位于/storage/emulated/0/Android/media/你的包名/项目名/中。

6. 视频录制 : VideoCapture.java

视频录制用的是VideoCapture

videoCapture = VideoCapture.Builder()
	//.setTargetRotation(previewView.getDisplay().getRotation())
	.setVideoFrameRate(25)
	.setBitRate(3 * 1024 * 1024)
	.build()

在调用cameraProvider.bindToLifecycle()时，进行传入。

camera = cameraProvider.bindToLifecycle(
    this,CameraSelector.DEFAULT_BACK_CAMERA, preview, videoCapture 
)

需要注意的是，videoCapture无法和imageAnalysis、imageCapture一起使用。
如果同一个页面中这几个功能融合在一起，则需要通过标志位来进行判断。

if (isVideo) {
    mCamera = cameraProvider.bindToLifecycle(this, cameraSelector,
            preview, videoCapture);
} else {
    mCamera = cameraProvider.bindToLifecycle(this, cameraSelector,
            preview, imageCapture, imageAnalysis);
}

开始录制

private val RECORDED_FILE_NAME = "recorded_video"
private val RECORDED_FILE_NAME_END = "video/mp4"

@SuppressLint("RestrictedApi")
private fun startRecording() {
	//TODO 这里省略了RECORD_AUDIO、PERMISSION_GRANTED权限的判断
	
    val contentValues = ContentValues()
    contentValues.put(
        MediaStore.MediaColumns.DISPLAY_NAME,
        RECORDED_FILE_NAME + "_" + System.currentTimeMillis()
    )
    contentValues.put(MediaStore.MediaColumns.MIME_TYPE, RECORDED_FILE_NAME_END)

    val outputFileOptions = VideoCapture.OutputFileOptions.Builder(
        getContentResolver(),
        MediaStore.Video.Media.EXTERNAL_CONTENT_URI, contentValues
    ).build()
    videoCapture.startRecording(
        outputFileOptions,
        ContextCompat.getMainExecutor(this),
        object : VideoCapture.OnVideoSavedCallback {
            override fun onVideoSaved(outputFileResults: VideoCapture.OutputFileResults) {
                Log.i(TAG, "视频保存成功:${outputFileResults.savedUri}")
            }

            override fun onError(
                videoCaptureError: Int,
                message: String,
                cause: Throwable?
            ) {
                Log.i(TAG, "当出现异常 cause:$cause")
            }
        }
    )
}

停止视频录制

videoCapture.stopRecording()

当我们执行停止视频录制之后，就可以在相册里看到多了一个录制的视频了。

介绍了CameraX里一些常用的UseCase，我们接下来来看下CameraX中的其他一些功能。

7. 切换前后摄像头

我们之前使用cameraProvider.bindToLifecycle()的时候，有一个参数是CameraSelector。
CameraX默认给我们提供了前置摄像头和后置摄像头的CameraSelector

public final class CameraSelector {
    @NonNull
    public static final CameraSelector DEFAULT_FRONT_CAMERA =
            new CameraSelector.Builder().requireLensFacing(LENS_FACING_FRONT).build();

    @NonNull
    public static final CameraSelector DEFAULT_BACK_CAMERA =
            new CameraSelector.Builder().requireLensFacing(LENS_FACING_BACK).build();

	//...
}

我们去切换摄像头的时候，就是重新调用一下bindPreview方法，传入新的cameraSelector值就好了

private fun bindPreview(
        cameraProvider: ProcessCameraProvider,
        previewView: PreviewView,
        cameraSelector : CameraSelector
    ) {
        // 解除所有绑定，防止CameraProvider重复绑定到Lifecycle发生异常
        cameraProvider.unbindAll()
        preview = Preview.Builder().build()
        camera = cameraProvider.bindToLifecycle(
            this,
            cameraSelector, preview
        )
        preview?.setSurfaceProvider(previewView.surfaceProvider)
    }

CameraX还为我们提供了判断前置/后置摄像头是否存在的方法

/** Returns true if the device has an available back camera. False otherwise */
private fun hasBackCamera(): Boolean {
    return cameraProvider?.hasCamera(CameraSelector.DEFAULT_BACK_CAMERA) ?: false
}

/** Returns true if the device has an available front camera. False otherwise */
private fun hasFrontCamera(): Boolean {
    return cameraProvider?.hasCamera(CameraSelector.DEFAULT_FRONT_CAMERA) ?: false
}

看下效果

8. 对焦

当点击androidx.camera.view.PreviewView的时候，去调用CameraX的对焦方法startFocusAndMetering()就好了。

在onCreate()中添加如下代码

binding.previewView.setOnTouchListener { view, event ->
    val action = FocusMeteringAction.Builder(
        binding.previewView.getMeteringPointFactory()
            .createPoint(event.getX(), event.getY())
    ).build();
    showTapView(event.x.toInt(), event.y.toInt())
    camera?.getCameraControl()?.startFocusAndMetering(action)
    true
}

增加showTapView()

private fun showTapView(x: Int, y: Int) {
    val popupWindow = PopupWindow(
        ViewGroup.LayoutParams.WRAP_CONTENT,
        ViewGroup.LayoutParams.WRAP_CONTENT
    )
    val imageView = ImageView(this)
    imageView.setImageResource(R.drawable.ic_focus_view)
    popupWindow.contentView = imageView
    popupWindow.showAsDropDown(binding.previewView, x, y)
    binding.previewView.postDelayed({ popupWindow.dismiss() }, 600)
    binding.previewView.playSoundEffect(SoundEffectConstants.CLICK)
}

看下效果

9. 缩放

通过GestureDetector监听缩放事件，然后在回调的时候进行执行如下代码，就可以使用双指放大缩小图像

override fun zoom(delta: Float) {
	val zoomState = camera?.cameraInfo?.zoomState
	zoomState?.value?.let {
		val currentZoomRatio = it.zoomRatio
		camera?.cameraControl?.setZoomRatio(currentZoomRatio * delta)
	}
}

缩放操作具体详见这篇文章 Android使用CameraX实现相机快速实现放大缩小

10. 本文Demo下载

本文的源码Demo详见 : Android CameraX Demo : 实现预览/拍照/录制视频/图片分析/对焦/切换摄像头等操作

推荐阅读 我的另一篇关于Camera的文章 : Android 从零开发一个简易的相机App

参考
Android Developer | CameraX
新技术介绍来了，CameraX 一统江湖？