从AndroidP 开始，高通camera系统全面使用HAL3，之前的HAL1已经被移除，对应HAL3主流的相机开发接口是camera API2 ，但是依然存在大量的使用Camera API 1开发的相机应用，为此Android专门设计了一套兼容API1调用HAL3的中间转换接口，本门主要从几个方面简要介绍下这部分相关的知识。**

opencamera
startpreview
takepicture
setparameter、getparameter

1. opencamera

相机应用在调用

Camera open(int cameraId)

时, 经过Binder IPC进入CameraService.cpp，调用的接口是

CameraService::connectHelper(....){ALOGI("CameraService::connect call (PID %d \"%s\", camera ID %s) for HAL version %s and ""Camera API version %d");

ret = makeClient(......))

err <span class="token operator">=</span> client<span class="token operator">-&gt;</span><span class="token function">initialize</span><span class="token punctuation">(</span>mCameraProviderManager<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//重点分析</span>

}

通过makeClient会创建相应的client

Status CameraService::makeClient(.....) {......// Default path: HAL version is unspecified by caller, create CameraClient// based on device version reported by the HAL.switch(deviceVersion) {//Android P 之后不再存在CAMERA_DEVICE_API_VERSION_1_0case CAMERA_DEVICE_API_VERSION_1_0:if (effectiveApiLevel == API_1) {  // Camera1 API route *client = new CameraClient(....),} else { // Camera2 API route}break;case CAMERA_DEVICE_API_VERSION_3_0:case CAMERA_DEVICE_API_VERSION_3_1:case CAMERA_DEVICE_API_VERSION_3_2:case CAMERA_DEVICE_API_VERSION_3_3:case CAMERA_DEVICE_API_VERSION_3_4://API1+HAL3 对应的clientif (effectiveApiLevel == API_1) { // Camera1 API route*client = new Camera2Client(.....);} else { // Camera2 API route//API2+HAL3 对应的client*client = new CameraDeviceClient(.....);}break;default:// Should not be reachableALOGE("Unknown camera device HAL version: %d", deviceVersion);.....}
}

通过上述代码分析发现API1+HAL3对用的client是Camera2Client
其类图如下：

从上边看Camera2Client继承实现了ICamera定义的camera API1接口，但是其内部的成员变量mDevice是`Camera3Device 类型,其是针对HAL3设计的，其类的备注如下：

/*** CameraDevice for HAL devices with version CAMERA_DEVICE_API_VERSION_3_0 or higher.*/
class Camera3Device :public CameraDeviceBase,virtual public hardware::camera::device::V3_2::ICameraDeviceCallback,private camera3_callback_ops

Camera3Device类图如下：

Camera3Device内部类HalInterface中的sp<hardware::camera::device::V3_2::ICameraDeviceSession>mHidlSession成员变量，是在opencamera是获取的对象，之后所有的constructDefaultRequestSettings，configureStreams等操作，都是通过该对象与HAL3进行通信完成的。
下边给出ICameraDeviceSession类图：

该类是定义在hardware\interfaces\camera\device中，是cameraservice与cameraprovider通信的接口。
下边分析 openCamera具体流程

从流程图上看，opencamera主要完成了两件事：

makeclient 创建camera2client对象及Camera3Device对象
初始化camera2client，真正完成打开相机的地方

从上述过程看，Camera2Client实现的是Camera API1的接口，在opencamera时，通过Camera3Device中的BpHwCameraDevice类型对象deviceInfo3->mInterface的open方法完成与HAL3通信来打开相机，并该方法返回结果为ICameraDeviceSession类型对象session，表示相机成功打开，之后所有的相机相关操作全是通过该对象完成。

2. startpreview

startPreview时序图如下：

从上述时序图看，startpreive过程主要有两个过程，

configureStreams
将request插入到mRepeatingRequests队列中，并启动RequestThread，向HAL层不断发送processCaptureRequest申请

3. takepicture

开启相机后会启动一个拍照处理线程mCaptureSequencer:

template<typename TProviderPtr>
status_t Camera2Client::initializeImpl(TProviderPtr providerPtr)
{ATRACE_CALL();ALOGV("%s: Initializing client for camera %d", __FUNCTION__, mCameraId);status_t res;

res <span class="token operator">=</span> Camera2ClientBase<span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">initialize</span><span class="token punctuation">(</span>providerPtr<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>

#ifdef USE_QTI_CAMERA2CLIENT
mQTICamera2Client = new QTICamera2Client(this);
#endif

mStreamingProcessor <span class="token operator">=</span> new <span class="token function">StreamingProcessor</span><span class="token punctuation">(</span>this<span class="token punctuation">)</span><span class="token punctuation">;</span>
threadName <span class="token operator">=</span> String8<span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">format</span><span class="token punctuation">(</span><span class="token string">"C2-%d-StreamProc"</span><span class="token punctuation">,</span>mCameraId<span class="token punctuation">)</span><span class="token punctuation">;</span>mFrameProcessor <span class="token operator">=</span> new <span class="token function">FrameProcessor</span><span class="token punctuation">(</span>mDevice<span class="token punctuation">,</span> this<span class="token punctuation">)</span><span class="token punctuation">;</span>
threadName <span class="token operator">=</span> String8<span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">format</span><span class="token punctuation">(</span><span class="token string">"C2-%d-FrameProc"</span><span class="token punctuation">,</span>mCameraId<span class="token punctuation">)</span><span class="token punctuation">;</span>
mFrameProcessor<span class="token operator">-&gt;</span><span class="token function">run</span><span class="token punctuation">(</span>threadName<span class="token punctuation">.</span><span class="token function">string</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//创建拍照处理线程并启动</span>
mCaptureSequencer <span class="token operator">=</span> new <span class="token function">CaptureSequencer</span><span class="token punctuation">(</span>this<span class="token punctuation">)</span><span class="token punctuation">;</span>
threadName <span class="token operator">=</span> String8<span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">format</span><span class="token punctuation">(</span><span class="token string">"C2-%d-CaptureSeq"</span><span class="token punctuation">,</span>mCameraId<span class="token punctuation">)</span><span class="token punctuation">;</span>
mCaptureSequencer<span class="token operator">-&gt;</span><span class="token function">run</span><span class="token punctuation">(</span>threadName<span class="token punctuation">.</span><span class="token function">string</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>mJpegProcessor <span class="token operator">=</span> new <span class="token function">JpegProcessor</span><span class="token punctuation">(</span>this<span class="token punctuation">,</span> mCaptureSequencer<span class="token punctuation">)</span><span class="token punctuation">;</span>
threadName <span class="token operator">=</span> String8<span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">format</span><span class="token punctuation">(</span><span class="token string">"C2-%d-JpegProc"</span><span class="token punctuation">,</span>mCameraId<span class="token punctuation">)</span><span class="token punctuation">;</span>
mJpegProcessor<span class="token operator">-&gt;</span><span class="token function">run</span><span class="token punctuation">(</span>threadName<span class="token punctuation">.</span><span class="token function">string</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

#ifdef USE_QTI_CAMERA2CLIENT
mRawProcessor = new RawProcessor(this, mCaptureSequencer);
threadName = String8::format(“C2-%d-RawProc”,
mCameraId);
mRawProcessor->run(threadName.string());
#endif

mZslProcessor <span class="token operator">=</span> new <span class="token function">ZslProcessor</span><span class="token punctuation">(</span>this<span class="token punctuation">,</span> mCaptureSequencer<span class="token punctuation">)</span><span class="token punctuation">;</span>threadName <span class="token operator">=</span> String8<span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">format</span><span class="token punctuation">(</span><span class="token string">"C2-%d-ZslProc"</span><span class="token punctuation">,</span>mCameraId<span class="token punctuation">)</span><span class="token punctuation">;</span>
mZslProcessor<span class="token operator">-&gt;</span><span class="token function">run</span><span class="token punctuation">(</span>threadName<span class="token punctuation">.</span><span class="token function">string</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>mCallbackProcessor <span class="token operator">=</span> new <span class="token function">CallbackProcessor</span><span class="token punctuation">(</span>this<span class="token punctuation">)</span><span class="token punctuation">;</span>
threadName <span class="token operator">=</span> String8<span class="token punctuation">:</span><span class="token punctuation">:</span><span class="token function">format</span><span class="token punctuation">(</span><span class="token string">"C2-%d-CallbkProc"</span><span class="token punctuation">,</span>mCameraId<span class="token punctuation">)</span><span class="token punctuation">;</span>
mCallbackProcessor<span class="token operator">-&gt;</span><span class="token function">run</span><span class="token punctuation">(</span>threadName<span class="token punctuation">.</span><span class="token function">string</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token keyword">return</span> OK<span class="token punctuation">;</span>

}

线程中包含有一个状态机，不断检测是否有拍照命令下发，
状态机状态定义如下：

    enum CaptureState {IDLE,START,ZSL_START,ZSL_WAITING,ZSL_REPROCESSING,STANDARD_START,STANDARD_PRECAPTURE_WAIT,STANDARD_CAPTURE,STANDARD_CAPTURE_WAIT,DONE,ERROR,NUM_CAPTURE_STATES} mCaptureState;

对应的状态处理函数定义如下：

const CaptureSequencer::StateManagerCaptureSequencer::kStateManagers[CaptureSequencer::NUM_CAPTURE_STATES-1] = {&CaptureSequencer::manageIdle,&CaptureSequencer::manageStart,&CaptureSequencer::manageZslStart,&CaptureSequencer::manageZslWaiting,&CaptureSequencer::manageZslReprocessing,&CaptureSequencer::manageStandardStart,&CaptureSequencer::manageStandardPrecaptureWait,&CaptureSequencer::manageStandardCapture,&CaptureSequencer::manageStandardCaptureWait,&CaptureSequencer::manageDone,
};

在有拍照命令下发时，状态机进入下一状态START，否则一直停留在IDLE状态


bool CaptureSequencer::threadLoop() {

sp<span class="token operator">&lt;</span>Camera2Client<span class="token operator">&gt;</span> client <span class="token operator">=</span> mClient<span class="token punctuation">.</span><span class="token function">promote</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>client <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token keyword">return</span> false<span class="token punctuation">;</span>CaptureState currentState<span class="token punctuation">;</span>
<span class="token punctuation">{</span>Mutex<span class="token punctuation">:</span><span class="token punctuation">:</span>Autolock <span class="token function">l</span><span class="token punctuation">(</span>mStateMutex<span class="token punctuation">)</span><span class="token punctuation">;</span>currentState <span class="token operator">=</span> mCaptureState<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">//状态机处理流程</span>
currentState <span class="token operator">=</span> <span class="token punctuation">(</span>this<span class="token operator">-&gt;</span><span class="token operator">*</span>kStateManagers<span class="token punctuation">[</span>currentState<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">(</span>client<span class="token punctuation">)</span><span class="token punctuation">;</span>Mutex<span class="token punctuation">:</span><span class="token punctuation">:</span>Autolock <span class="token function">l</span><span class="token punctuation">(</span>mStateMutex<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>currentState <span class="token operator">!=</span> mCaptureState<span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token keyword">if</span> <span class="token punctuation">(</span>mCaptureState <span class="token operator">!=</span> IDLE<span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token function">ATRACE_ASYNC_END</span><span class="token punctuation">(</span>kStateNames<span class="token punctuation">[</span>mCaptureState<span class="token punctuation">]</span><span class="token punctuation">,</span> mStateTransitionCount<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token punctuation">}</span>mCaptureState <span class="token operator">=</span> currentState<span class="token punctuation">;</span>mStateTransitionCount<span class="token operator">++</span><span class="token punctuation">;</span><span class="token keyword">if</span> <span class="token punctuation">(</span>mCaptureState <span class="token operator">!=</span> IDLE<span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token function">ATRACE_ASYNC_BEGIN</span><span class="token punctuation">(</span>kStateNames<span class="token punctuation">[</span>mCaptureState<span class="token punctuation">]</span><span class="token punctuation">,</span> mStateTransitionCount<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token punctuation">}</span><span class="token function">ALOGV</span><span class="token punctuation">(</span><span class="token string">"Camera %d: New capture state %s"</span><span class="token punctuation">,</span>client<span class="token operator">-&gt;</span><span class="token function">getCameraId</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> kStateNames<span class="token punctuation">[</span>mCaptureState<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>mStateChanged<span class="token punctuation">.</span><span class="token function">signal</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token keyword">if</span> <span class="token punctuation">(</span>mCaptureState <span class="token operator">==</span> ERRORmanageStart<span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token function">ALOGE</span><span class="token punctuation">(</span><span class="token string">"Camera %d: Stopping capture sequencer due to error"</span><span class="token punctuation">,</span>client<span class="token operator">-&gt;</span><span class="token function">getCameraId</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token keyword">return</span> false<span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token keyword">return</span> true<span class="token punctuation">;</span>

}

状态图如下：

4. setparameter、getparameter

待续。。。。

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android camera API1调用camera HAL3流程学习总结

1. opencamera

2. startpreview

3. takepicture

4. setparameter、getparameter

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