CameraX PreviewView 显示全部但仅记录一个区域

Question

我想要做的是在我的上方显示一个矩形PreviewView，并且仅记录该矩形内部的区域，即使 PreviewView 显示整个相机也是如此。

我只想将白色矩形内的内容保存到文件中，但我希望预览显示所有内容：

活动.xml：

 <androidx.constraintlayout.widget.ConstraintLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.camera.view.PreviewView
        android:id="@+id/textureView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <View
        android:id="@+id/crop"
        android:layout_width="350dp"
        android:layout_height="100dp"
        android:layout_gravity="center"
        android:background="@drawable/background_drawable"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

活动.kt

  private fun startCamera() {
    val cameraProviderFuture = ProcessCameraProvider.getInstance(this)
    cameraProviderFuture.addListener({
        cameraProvider = cameraProviderFuture.get()

        // The display information
        val metrics = DisplayMetrics().also { textureView.display.getRealMetrics(it) }
        // The ratio for the output image and preview
        val aspectRatio = aspectRatio(metrics.widthPixels, metrics.heightPixels)
        // The display rotation
        val rotation = textureView.display.rotation

        val localCameraProvider = cameraProvider
            ?: throw IllegalStateException("Camera initialization failed.")

        // The Configuration of camera preview
        preview = Preview.Builder()
            .setTargetAspectRatio(aspectRatio) // set the camera aspect ratio
            .setTargetRotation(rotation) // set the camera rotation
            .build()

        // The Configuration of video capture
        videoCapture = VideoCapture.Builder().build()

        localCameraProvider.unbindAll() // unbind the use-cases before rebinding them

        try {
            // Bind all use cases to the camera with lifecycle
            camera = localCameraProvider.bindToLifecycle(
                this, // current lifecycle owner
                lensFacing, // either front or back facing
                preview, // camera preview use case
                videoCapture, // video capture use case
            )

            // Attach the viewfinder's surface provider to preview use case
            preview?.setSurfaceProvider(textureView.surfaceProvider)
        } catch (e: Exception) {
            Log.e(tag, "Failed to bind use cases", e)
        }
    }, ContextCompat.getMainExecutor(this))
}

我已经尝试过 ViewPort，但这也改变了预览，这不是我的最终目标，我想记录白色矩形所在的确切 X，Y，但似乎我无法在视口上指定它？

 val viewPort =  ViewPort.Builder(Rational(width, height), rotation).build()
        val useCaseGroup = UseCaseGroup.Builder()
            .addUseCase(preview!!) //your preview
            .addUseCase(videoCapture!!)
            .setViewPort(viewPort)
            .build()

关于 CameraX 的文档太混乱了，从 1.0.0 到 1.1.0 有很多重大变化，我真的很难在这里找到我要找的东西。

如果我不设置 ViewPort，则记录整个相机效果很好，只是记录我正在努力处理的区域。

谢谢。