Android P Camera架构

古城微笑少年丶 2022-04-25 02:22 272阅读 0赞

Camera架构

一、APP层  
获取摄像头ID列表：getCameraIdList()  
打开摄像头：openCamera();

二、frameworks层：  
CameraManager：  
代码路径：\\frameworks\\base\\core\\java\\android\\hardware\\camera2\\CameraManager.java

private CameraDevice openCameraDeviceUserAsync(String cameraId,
            CameraDevice.StateCallback callback, Executor executor, final int uid)
            throws CameraAccessException { 
    
    	//省略一部分代码
    	//...
    
       // Use cameraservice's cameradeviceclient implementation for HAL3.2+ devices
       ICameraService cameraService = CameraManagerGlobal.get().getCameraService();
       if (cameraService == null) { 
           throw new ServiceSpecificException(
               ICameraService.ERROR_DISCONNECTED,
               "Camera service is currently unavailable");
       }
       //通过CameraService连接摄像头设备
       cameraUser = cameraService.connectDevice(callbacks, cameraId,
               mContext.getOpPackageName(), uid);
    
    	//省略一部分代码
    	//...
     }

三、C++ Libraries层代码：  
CameraService  
代码路径：frameworks\\av\\services\\camera\\libcameraservice\\CameraService.cpp

// CameraService::connectDevice流程
    { 
    	//省略一部分代码
    	//...
    	
    	// 创建不同HAL版本对应的相机Client
    	sp<BasicClient> tmp = nullptr;
    	if(!(ret = makeClient(this, cameraCb, clientPackageName,
    	        cameraId, api1CameraId, facing,
    	        clientPid, clientUid, getpid(), legacyMode,
    	        halVersion, deviceVersion, effectiveApiLevel,
    	        /*out*/&tmp)).isOk()) { 
    	    return ret;
    	}
    	
    	//省略一部分代码
    	//...
    }
    
    // 根据HAL版本创建对应的相机Clinet，这里以创建最新版本的CAMERA_DEVICE_API_VERSION_3_4版本，
    // 以Camera2 API为例的版本
    Status CameraService::makeClient() { 
    
    	//省略一部分代码
    	//...
    
    	// Camera2 API route
    	sp<hardware::camera2::ICameraDeviceCallbacks> tmp = static_cast<hardware::camera2::ICameraDeviceCallbacks*>(cameraCb.get());
    	
    	*client = new CameraDeviceClient(cameraService, tmp, packageName, cameraId, facing, clientPid, clientUid, servicePid);
    
    	//省略一部分代码
    	//...
    }

frameworks\\av\\services\\camera\\libcameraservice\\api2\\CameraDeviceClient.cpp  
frameworks\\av\\services\\camera\\libcameraservice\\common\\Camera2ClientBase.cpp  
frameworks\\av\\services\\camera\\libcameraservice\\device3\\Camera3Device.cpp

status_t Camera3Device::initialize(sp<CameraProviderManager> manager) { 
    
    	//在初始化时，调用了 CameraProviderManager 的 openSession 方法，开启了远端的 Session
        sp<ICameraDeviceSession> session;
        ATRACE_BEGIN("CameraHal::openSession");
        status_t res = manager->openSession(mId.string(), this,
                /*out*/ &session);
        ATRACE_END();
        if (res != OK) { 
            SET_ERR_L("Could not open camera session: %s (%d)", strerror(-res), res);
            return res;
        }
    
    	//生成HIDL接口层对象
    	mInterface = new HalInterface(session, queue);
    }

frameworks\\av\\services\\camera\\libcameraservice\\common\\CameraProviderManager.cpp

//V3_2::ICameraDeviceCallback 调用V3.2版本的HIDL接口
    status_t CameraProviderManager::openSession(const std::string &id,
            const sp<hardware::camera::device::V3_2::ICameraDeviceCallback>& callback,
            /*out*/
            sp<hardware::camera::device::V3_2::ICameraDeviceSession> *session) { 
    
        std::lock_guard<std::mutex> lock(mInterfaceMutex);
    
        auto deviceInfo = findDeviceInfoLocked(id,
                /*minVersion*/ { 3,0}, /*maxVersion*/ { 4,0});
        if (deviceInfo == nullptr) return NAME_NOT_FOUND;
    
        auto *deviceInfo3 = static_cast<ProviderInfo::DeviceInfo3*>(deviceInfo);
    
        Status status;
        hardware::Return<void> ret;
        //通过HIDL层接口调用open()
        ret = deviceInfo3->mInterface->open(callback, [&status, &session]
                (Status s, const sp<device::V3_2::ICameraDeviceSession>& cameraSession) { 
                    status = s;
                    if (status == Status::OK) { 
                        *session = cameraSession;
                    }
                });
        if (!ret.isOk()) { 
            ALOGE("%s: Transaction error opening a session for camera device %s: %s",
                    __FUNCTION__, id.c_str(), ret.description().c_str());
            return DEAD_OBJECT;
        }
        return mapToStatusT(status);
    }

四、HIDL层和HAL层  
文件路径：  
hardware\\interfaces\\camera\\device\\3.2\\default\\CameraDevice.cpp

Return<void> CameraDevice::open(const sp<ICameraDeviceCallback>& callback, open_cb _hidl_cb)  { 
    	/** Open HAL device */
    	status_t res;
    	camera3_device_t *device;
    	
    	ATRACE_BEGIN("camera3->open");
    	//调用CameraModule中的open
    	res = mModule->open(mCameraId.c_str(), reinterpret_cast<hw_device_t**>(&device));
    	ATRACE_END();
    }

hardware\\interfaces\\camera\\common\\1.0\\default\\CameraModule.cpp

int CameraModule::open(const char* id, struct hw_device_t** device) { 
        int res;
        ATRACE_BEGIN("camera_module->open");
        //mModule是一个camera_module_t对象，此openfa方法将调用Driver层代码进行打开摄像头操作
        res = filterOpenErrorCode(mModule->common.methods->open(&mModule->common, id, device));
        ATRACE_END();
        return res;
    }

//camera\_module\_t涉及到CAMERA\_HARDWARE\_MODULE\_ID的创建和绑定  
camera\_module\_t文件路径：hardware\\libhardware\\include\\hardware\\camera\_common.h

五、Driver层  
Driver层是硬件厂商定制的，所以，不同的芯片厂商，Driver层代码不一样。

驱动层执行一些跟摄像头设备相关和图形显示，视频数据的一些操作，涉及到一些设备文件操作。

主要方法和解析如下：  
// open camera dev nodes, etc  
int32\_t ret = mVideoStream->openDev(mDevPath);  
主要执行：

// name为"/dev/video0"摄像头设备，
    	mDev = open(name, O_RDWR);

// flush camera dev nodes.  
return mVideoStream->flushDev();  
主要执行：

// 这里执行了两个重要的操作VIDIOC_DQBUF和VIDIOC_QBUF，取出摄像头视频图像Buffer
        ret = ioctl(mDev, VIDIOC_DQBUF, &cfilledbuffer);
        if (ret < 0) { 
            ALOGE("%s: VIDIOC_DQBUF Failed: %s (%d)", __func__, strerror(errno), errno);
            return BAD_VALUE;
        }
        ret = ioctl(mDev, VIDIOC_QBUF, &cfilledbuffer);
        if (ret < 0) { 
            ALOGE("%s: VIDIOC_QBUF Failed: %s (%d)", __func__, strerror(errno), errno);
            return BAD_VALUE;
        }

// close camera dev nodes, etc  
mVideoStream->closeDev();  
主要执行：