Camera2使用

随着android9.0的发布，android系统相机换成了Camera2，所以我们也要适配的。

流程示意图

主要类

要枚举，查询和打开可用的摄像头设备，请获取CameraManager实例。

CameraManager manager = (CameraManager) activity.getSystemService(Context.CAMERA_SERVICE);
try {
    if (!mCameraOpenCloseLock.tryAcquire(2500, TimeUnit.MILLISECONDS)) {
        throw new RuntimeException("Time out waiting to lock camera opening.");
    }
    manager.openCamera(mCameraId, mStateCallback, mBackgroundHandler);
} catch (CameraAccessException e) {
    e.printStackTrace();
} catch (InterruptedException e) {
    throw new RuntimeException("Interrupted while trying to lock camera opening.", e);
}

各个CameraDevices提供一组静态属性信息，用于描述硬件设备以及设备的可用设置和输出参数。

private final CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {

    @Override
    public void onOpened(@NonNull CameraDevice cameraDevice) {
        // This method is called when the camera is opened.  We start camera preview here.
        mCameraOpenCloseLock.release();
        mCameraDevice = cameraDevice;
        createCameraPreviewSession();
    }

    @Override
    public void onDisconnected(@NonNull CameraDevice cameraDevice) {
        mCameraOpenCloseLock.release();
        cameraDevice.close();
        mCameraDevice = null;
    }

    @Override
    public void onError(@NonNull CameraDevice cameraDevice, int error) {
        mCameraOpenCloseLock.release();
        cameraDevice.close();
        mCameraDevice = null;
        Activity activity = getActivity();
        if (null != activity) {
            activity.finish();
        }
    }
};

CameraDevices的可用设置和输出参数可通过getCameraCharacteristics（String）获得。

CameraCharacteristics characteristics
        = manager.getCameraCharacteristics(cameraId);
StreamConfigurationMap map = characteristics.get(
        CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
Boolean available = characteristics.get(CameraCharacteristics.FLASH_INFO_AVAILABLE);

要从摄像头设备捕获或流式传输图像，应用程序必须首先使用createCaptureSession（SessionConfiguration）创建一个带有一组输出Surface的摄像头捕获会话，以便与摄像头设备一起使用。

        // Here, we create a CameraCaptureSession for camera preview.
        mCameraDevice.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface()),
                new CameraCaptureSession.StateCallback() {

                    @Override
                    public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
                        // The camera is already closed
                        if (null == mCameraDevice) {
                            return;
                        }

                        // When the session is ready, we start displaying the preview.
                        mCaptureSession = cameraCaptureSession;
                        try {
                            // Auto focus should be continuous for camera preview.
                            mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE,
                                    CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
                            // Flash is automatically enabled when necessary.
                            setAutoFlash(mPreviewRequestBuilder);
                           // mPreviewRequestBuilder.set(CameraRequestApi.getKeyFaceBeautyMode(),1);

                            // Finally, we start displaying the camera preview.
                            mPreviewRequest = mPreviewRequestBuilder.build();
                            mCaptureSession.setRepeatingRequest(mPreviewRequest,
                                    mCaptureCallback, mBackgroundHandler);
                        } catch (CameraAccessException e) {
                            e.printStackTrace();
                        }
                    }
                    @Override
                    public void onConfigureFailed(
                            @NonNull CameraCaptureSession cameraCaptureSession) {
                        showToast("Failed");
                    }
                }, null
        );
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

每个Surface必须预先配置适当的大小和格式（如果适用），以匹配摄像机设备可用的大小和格式。目标Surface可以从各种类中获得，包括SurfaceView，SurfaceTexture via Surface（SurfaceTexture），MediaCodec，MediaRecorder，Allocation和ImageReader。

SurfaceTexture texture = mTextureView.getSurfaceTexture();
assert texture != null;

// We configure the size of default buffer to be the size of camera preview we want.
texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());

// This is the output Surface we need to start preview.
Surface surface = new Surface(texture);

// We set up a CaptureRequest.Builder with the output Surface.
mPreviewRequestBuilder
        = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
mPreviewRequestBuilder.addTarget(surface);

通常，相机预览图像将发送到SurfaceView或TextureView（通过其SurfaceTexture）。可以使用JPEG和RAW_SENSOR格式的ImageReader捕获用于DngCreator的JPEG图像或RAW缓冲区。 RenderScript，OpenGL ES或直接在托管或本机代码中的相机数据的应用驱动处理最好通过分别使用YUV Type，SurfaceTexture和具有YUV_420_888格式的ImageReader进行分配。

mImageReader = ImageReader.newInstance(largest.getWidth(), largest.getHeight(),
        ImageFormat.JPEG, /*maxImages*/2);
mImageReader.setOnImageAvailableListener(
        mOnImageAvailableListener, mBackgroundHandler);
mCameraDevice.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface()),
        new CameraCaptureSession.StateCallback()

// This is the CaptureRequest.Builder that we use to take a picture.
final CaptureRequest.Builder captureBuilder =
        mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
captureBuilder.addTarget(mImageReader.getSurface());

然后，应用程序需要构建一个CaptureRequest，它定义摄像头设备捕获单个图像所需的所有捕获参数。该请求还列出了哪些配置的输出Surface应该用作此捕获的目标。 CameraDevice有一个工厂方法，用于为给定的用例创建请求构建器，该方法针对运行应用程序的Android设备进行了优化。

final CaptureRequest.Builder captureBuilder =
        mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
requestBuilder.set(CaptureRequest.CONTROL_AE_MODE,
        CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);
mCaptureSession.capture(captureBuilder.build(), CaptureCallback, null);

一旦设置了请求，就可以将其传递到活动捕获会话，以进行一次捕获或无休止地重复使用。createCaptureRequest(int templateType)方法创建CaptureRequest.Builder，该方法支持TEMPLATE_PREVIEW（预览）、TEMPLATE_RECORD（拍摄视频）、TEMPLATE_STILL_CAPTURE（拍照）等参数。

调用CaptureRequest.Builder的build()方法即可得到CaptureRequest对象，接下来程序可通过CameraCaptureSession的setRepeatingRequest()方法开始预览，或调用capture()方法拍照。 CaptureRequest.Builder重复请求的优先级低于捕获，因此在配置重复请求时通过capture（）提交的请求将在当前重复（突发）捕获的任何新实例开始捕获之前捕获。

mCaptureSession.capture(mPreviewRequestBuilder.build(), mCaptureCallback,
        mBackgroundHandler);
/**
 * This a callback object for the {@link ImageReader}. "onImageAvailable" will be called when a
 * still image is ready to be saved.
 */
private final ImageReader.OnImageAvailableListener mOnImageAvailableListener
        = new ImageReader.OnImageAvailableListener() {

    @Override
    public void onImageAvailable(ImageReader reader) {
        Log.d(TAG, "onImageAvailable: ");
        mBackgroundHandler.post(new ImageSaver(reader.acquireNextImage(), mFile));
    }
};

处理完请求后，摄像机设备将生成一个TotalCaptureResult对象，该对象包含有关捕获时摄像机设备状态的信息以及使用的最终设置，可以设置重新预览。如果需要舍入或解决相互矛盾的参数，这些可能与请求有所不同。相机设备还将一帧图像数据发送到请求中包括的每个输出表面。这些是相对于输出CaptureResult异步生成的，有时基本上稍晚。

            CameraCaptureSession.CaptureCallback CaptureCallback
                    = new CameraCaptureSession.CaptureCallback() {

                @Override
                public void onCaptureCompleted(@NonNull CameraCaptureSession session,
                                               @NonNull CaptureRequest request,
                                               @NonNull TotalCaptureResult result) {
                    showToast("Saved: " + mFile);
                    Log.d(TAG, mFile.toString());
                    unlockFocus();
                }
            };

参考资料：

android.hardware.camera2 使用指南