前言

CameraX 基于 Camera2 构建而成，并且 CameraX 提供了在 Camera2 实现中读取甚至写入属性的方式。如需了解完整详情，请参阅互操作性软件包。

那么该如何使用呢

注意：在 CameraX 中，设置底层 Camera2 属性会被标记为“实验性”，因为 Google 希望开发者能了解其使用情况。您设置的值会替换 CameraX 所设置的任何值。我们建议您仅在绝对必要时执行此操作，也建议在您这一端进行其他测试。

Camera2CameraInfo

使用 Camera2CameraInfo 读取底层 CameraCharacteristics

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val c2ci = Camera2CameraInfo.from(cameraInfo)
c2ci.apply {
    // 获取设备支持的硬件级别
    val level = getCameraCharacteristic(CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL) ?: INFO_SUPPORTED_HARDWARE_LEVEL_LIMITED
}

Camera2CameraControl

使用 Camera2CameraControl，它让您可以在底层 CaptureRequest 上设置属性，例如自动AWB模式。

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val c2cc = Camera2CameraControl.from(cameraControl)
c2cc.captureRequestOptions = CaptureRequestOptions.Builder()
    .setCaptureRequestOption(CaptureRequest.CONTROL_AWB_MODE, CaptureRequest.CONTROL_AWB_MODE_OFF)
    .setCaptureRequestOption(CaptureRequest.COLOR_CORRECTION_MODE, CaptureRequest.COLOR_CORRECTION_MODE_TRANSFORM_MATRIX)
    .setCaptureRequestOption(CaptureRequest.COLOR_CORRECTION_GAINS, ColorTemperatureConverter.colorTemperature(2000))
    .build()

Camera2Interop.Extender

使用 Camera2Interop.Extender 扩展 CameraX UseCase。这样您就可以在 CaptureRequest 上设置属性，就像使用 Camera2CameraControl 一样。它还提供了一些额外的控件，例如设置数据流用例以根据您的使用场景优化相机。

以下代码示例使用数据流用例来优化视频通话。使用 Camera2CameraInfo 可提取视频通话流用例是否可用。然后，使用 Camera2Interop.Extender 设置底层数据流用例。

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// Set underlying Camera2 stream use case to optimize for video calls.

val videoCallStreamId =
    CameraMetadata.SCALER_AVAILABLE_STREAM_USE_CASES_VIDEO_CALL.toLong()

// Check available CameraInfos to find the first one that supports
// the video call stream use case.
val frontCameraInfo = cameraProvider.getAvailableCameraInfos()
    .first { cameraInfo ->
        val isVideoCallStreamingSupported = Camera2CameraInfo.from(cameraInfo)
            .getCameraCharacteristic(
                CameraCharacteristics.SCALER_AVAILABLE_STREAM_USE_CASES
            )?.contains(videoCallStreamId)
        val isFrontFacing = (cameraInfo.getLensFacing() ==
                             CameraSelector.LENS_FACING_FRONT)
        (isVideoCallStreamingSupported == true) && isFrontFacing
    }

val cameraSelector = frontCameraInfo.cameraSelector

// Start with a Preview Builder.
val previewBuilder = Preview.Builder()
    .setTargetAspectRatio(screenAspectRatio)
    .setTargetRotation(rotation)

// Use Camera2Interop.Extender to set the video call stream use case.
Camera2Interop.Extender(previewBuilder).setStreamUseCase(videoCallStreamId)

// Bind the Preview UseCase and the corresponding CameraSelector.
val preview = previewBuilder.build()
camera = cameraProvider.bindToLifecycle(this, cameraSelector, preview)
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// Set underlying Camera2 stream use case to optimize for video calls.

Long videoCallStreamId =
    CameraMetadata.SCALER_AVAILABLE_STREAM_USE_CASES_VIDEO_CALL.toLong();

// Check available CameraInfos to find the first one that supports
// the video call stream use case.
List<CameraInfo> cameraInfos = cameraProvider.getAvailableCameraInfos();
CameraInfo frontCameraInfo = null;
for (cameraInfo in cameraInfos) {
    Long[] availableStreamUseCases = Camera2CameraInfo.from(cameraInfo)
        .getCameraCharacteristic(
            CameraCharacteristics.SCALER_AVAILABLE_STREAM_USE_CASES
        );
    boolean isVideoCallStreamingSupported = Arrays.List(availableStreamUseCases)
                .contains(videoCallStreamId);
    boolean isFrontFacing = (cameraInfo.getLensFacing() ==
                             CameraSelector.LENS_FACING_FRONT);

    if (isVideoCallStreamingSupported && isFrontFacing) {
        frontCameraInfo = cameraInfo;
    }
}

if (frontCameraInfo == null) {
    // Handle case where video call streaming is not supported.
}

CameraSelector cameraSelector = frontCameraInfo.getCameraSelector();

// Start with a Preview Builder.
Preview.Builder previewBuilder = Preview.Builder()
    .setTargetAspectRatio(screenAspectRatio)
    .setTargetRotation(rotation);

// Use Camera2Interop.Extender to set the video call stream use case.
Camera2Interop.Extender(previewBuilder).setStreamUseCase(videoCallStreamId);

// Bind the Preview UseCase and the corresponding CameraSelector.
Preview preview = previewBuilder.build()
Camera camera = cameraProvider.bindToLifecycle(this, cameraSelector, preview)

参考

Android CameraX 架构