Camera api2 frameworks

Camera 工作结构

Camera 工作结构.png

• Camera Device：代表一个摄像头，在一部手机上有可能有多个摄像头，如前置摄像头，后置摄像头等。
• CameraCaptureSession：表式Android Device（APP）与CameraDevice之间的会话层，类似于 http中的 session。
• CaptureRequest：APP要想拍照，摄像都是向 CameraDevice 发送CaptureRequest请求。这个请求是通过上面的 Session发送出去的。
• CameraMetadata：CameraDevice将捕获到的数据封装成CameraMetadata通过Session传给 APP。其实这一步基本是隐藏起来的，在API中我们很少直接用它。
• Android Device：可以把它想象成我们自己的APP应用。
• Surface：存放数据的类，在实际的操作中，我们只要把 surface告诉CaptureRequest.Builder，当有数据到来之后，系统底层就会将数据存放到 surface中。

摘自：https://www.jianshu.com/p/22d2c76698da

frameworks 实现预览拍照流程图

预览拍照.png

AndroidCamera2AgentImpl.java

CameraManager 对象初始化

private final CameraManager mCameraManager;
AndroidCamera2AgentImpl(Context context) {
    ...
    mCameraManager = (CameraManager) context.getSystemService(Context.CAMERA_SERVICE);
    ...
}

CameraDevice 对象初始化

protected CameraDevice mCamera;

mCameraManager.openCamera(mCameraId, mCameraDeviceStateCallback, this);

// This callback monitors our connection to and disconnection from camera devices.
private CameraDevice.StateCallback mCameraDeviceStateCallback =
        new CameraDevice.StateCallback() {
    @Override 
    public void onOpened(CameraDevice camera) {
    ...
    mCamera = camera;
    ...
    }

    @Override
    public void onDisconnected(CameraDevice camera) {
    }

    @Override
    public void onError(CameraDevice camera, int error) {
    }
};

CameraCaptureSession 对象初始化

protected CameraCaptureSession mSession;

mCamera.createCaptureSession(
        Arrays.asList(mPreviewSurface,mCaptureReader.getSurface()),
        mCameraPreviewStateCallback,this);

// This callback monitors our camera session (i.e. our transition into and out of preview).
protected CameraCaptureSession.StateCallback mCameraPreviewStateCallback=
        new CameraCaptureSession.StateCallback(){
    @Override
    public void onConfigured(CameraCaptureSession session){
        mSession=session;
        ...
    }

    @Override
    public void onConfigureFailed(CameraCaptureSession session){
    }

    @Override
    public void onActive(CameraCaptureSession session){
    }
};

CameraRequest 对象初始化

mPersistentSettings.createRequest(mCamera,
        CameraDevice.TEMPLATE_STILL_CAPTURE,
        mCaptureReader.getSurface())
    
// Camera2RequestSettingsSet.java    
public CaptureRequest createRequest(CameraDevice camera,int template,Surface...targets)
        throws CameraAccessException{
    ...
    Builder reqBuilder=camera.createCaptureRequest(template);
    ...
    return reqBuilder.build();
}

CameraDevice.java

CameraDevice 常量解释

public abstract class CameraDevice implements AutoCloseable {
    // 用于创建一个相机预览窗口的请求
    public static final int TEMPLATE_PREVIEW = 1;

    // 用于创建静态图像捕获的请求
    public static final int TEMPLATE_STILL_CAPTURE = 2;

    // 用于创建录像请求
    public static final int TEMPLATE_RECORD  = 3;

    // 用于在录制视频时创建静态图像捕获的请求
    public static final int TEMPLATE_VIDEO_SNAPSHOT = 4;

    // 用于创建零延迟拍照请求
    public static final int TEMPLATE_ZERO_SHUTTER_LAG = 5;

    // 用于创建一个直接控制相机拍照参数的请求(需支持 MANUAL_SENSOR 功能)
    public static final int TEMPLATE_MANUAL = 6;
}    

CameraCaptureSession.java

CameraCaptureSession 方法介绍

/**
* 
Submit a request for an image to be captured by the camera device.
* 提交捕获图像请求,即拍照
*/
public abstract int capture(@NonNull CaptureRequest request,
            @Nullable CaptureCallback listener, @Nullable Handler handler)
            throws CameraAccessException;

/**
* Request endlessly repeating capture of images by this capture session.
*/
public abstract int captureBurst(@NonNull List requests,
            @Nullable CaptureCallback listener, @Nullable Handler handler)
            throws CameraAccessException;

/**
* 
Request endlessly repeating capture of a sequence of images by this
* capture session.
*/
public abstract int setRepeatingBurst(@NonNull List requests,
            @Nullable CaptureCallback listener, @Nullable Handler handler)
            throws CameraAccessException;

/**
* Request endlessly repeating capture of images by this capture session.
* 请求不断重复捕获图像，即实现预览
*/
public abstract int setRepeatingRequest(@NonNull CaptureRequest request,
            @Nullable CaptureCallback listener, @Nullable Handler handler)
            throws CameraAccessException;

/**
* 
Cancel any ongoing repeating capture set by either
* 停止捕获图像，即停止预览
*/
public abstract void stopRepeating() throws CameraAccessException;

注意：

• capture() 和 setRepeatingRequest() 方法都是向相机设备发送获取图像的请求
• capture() 的功能是获取一次，一般用于拍照，图像会停在那里；setRepeatingRequest() 是不停的发出 capture 请求，不断重复的获取图像，一般用于预览或录制视频
• capture() 比 setRepeatingRequest() 的优先级高，当在 setRepeatingRequest() 时执行capture() ，会先处理capture()，然后继续处理 setRepeatingRequest()