Android开发之fsl在HAL层Camera的实现

通过前面分析Camera我们知道在framework层主要就用到了两个结构体：

struct camera_module_t；struct camera_device_t；通过这两个结构体我们就和hal层联系起来了。下面我们通过fsl的HAL层源码来分析下Camera在HAL的具体实现。

 <span style="font-size:14px;">static struct hw_module_methods_t camera_module_methods = { open: camera_device_open };
 camera_module_t HAL_MODULE_INFO_SYM = {
     common: {
         tag: HARDWARE_MODULE_TAG,
         version_major: 1,
         version_minor: 0,
         id: CAMERA_HARDWARE_MODULE_ID,
         name: "Freescale CameraHal Module",
         author: "Freescale"
         methods: &camera_module_methods,
         dso: NULL
         reserved: {0}
     },
     get_number_of_cameras: camera_get_number_of_cameras,
     get_camera_info: camera_get_camera_info,
 };

 typedef struct fsl_camera_device {
     camera_device_t base;
     int cameraid;
 } fsl_camera_device_t;span>

我们知道前面hw_get_modules就是从/system/lib/hw/camera.xx.so加载动态库，查找HMI符号的地址，保存到hw_module_t结构体中。找到的就是这个地方的camera_module_t HAL_MODULE_INFO_SYM。

1）mModule->get_camera_info

  调用的就是当前文件中的camera_get_camera_info函数

2）mModule->common->methods->open(mModule->common, name, (hw_device_t**)mDevice);

  调用的就是当前文件的camera_device_open(hw_module_t* module, char* name, hw_device_t** device)

 typedef struct hw_device_t {
     uint32_t tag;
     uint32_t version;
     struct hw_module_t* module;
     uint32_t reserved[12];
     int (*close)(struct hw_device_t* device);
 } hw_device_t;

 

 typedef struct camera_device {
     hw_device_t common;
     camera_device_opts_t *ops;
     void* priv;
 } camera_device_t;

这里根据主要初始化话hw_device_t **device和camera_device_opts_t *ops这两个指针。

我们来看看camera_device_open这个函数：

 int camera_device_open(const hw_module_t* module, const char* name, hw_device_t** device)
 {
     int num_cameras = 0;
     int cameraid;
     fsl_camera_device_t* camera_device = NULL;
     camera_device_ops_t* camera_ops = NULL;
     android::CameraHal* camera = NULL;
     char *SelectedCameraName;
     android::sp<android::CaptureDeviceInterface> pCaptureDevice = NULL;
     android::sp<android::JpegEncoderInterface>pJpegEncoder = NULL;

     android::Mutex::Autolock lock(gCameraHalDeviceLock);

     LOGI("camera_device open: %s", name);

     if (name != NULL) {
         cameraid = atoi(name);
         num_cameras = camera_get_number_of_cameras();
         //判断是否有前摄像头gCameraName[0]、后摄像头gCameraName[1], 返回gCameraNum摄像头总个数(最大为2)，摄像头文件路径gCameraDevPath[2]

         camera_device = (fsl_camera_device_t*)malloc(sizeof(*camera_device));
         camera_ops = (camera_device_ops_t*)malloc(sizeof(*camera_ops));

         memset(camera_device, 0, sizeof(*camera_device));
         memset(camera_ops, 0, sizeof(*camera_ops));

         camera_device->base.common.tag = HARDWARE_DEVICE_TAG;
         camera_device->base.common.version = 0;
         camera_device->base.common.module = (hw_module_t *)(module);
         camera_device->base.common.close = camera_device_close;
         camera_device->base.ops = camera_ops;
         // 下面这些函数非常重要，是我们apk中最终会调用到的业务函数，都是与驱动直接交互
         camera_ops->set_preview_window = camera_set_preview_window;
         camera_ops->set_callbacks = camera_set_callbacks;
         camera_ops->enable_msg_type = camera_enable_msg_type;
         camera_ops->disable_msg_type = camera_disable_msg_type;
         camera_ops->msg_type_enabled = camera_msg_type_enabled;
         camera_ops->start_preview = camera_start_preview;
         camera_ops->stop_preview = camera_stop_preview;
         camera_ops->preview_enabled = camera_preview_enabled;
         camera_ops->store_meta_data_in_buffers = camera_store_meta_data_in_buffers;
         camera_ops->start_recording = camera_start_recording;
         camera_ops->stop_recording = camera_stop_recording;
         camera_ops->recording_enabled = camera_recording_enabled;
         camera_ops->release_recording_frame = camera_release_recording_frame;
         camera_ops->auto_focus = camera_auto_focus;
         camera_ops->cancel_auto_focus = camera_cancel_auto_focus;
         camera_ops->take_picture = camera_take_picture;
         camera_ops->cancel_picture = camera_cancel_picture;
         camera_ops->set_parameters = camera_set_parameters;
         camera_ops->get_parameters = camera_get_parameters;
         camera_ops->put_parameters = camera_put_parameters;
         camera_ops->send_command = camera_send_command;
         camera_ops->release = camera_release;
         camera_ops->dump = camera_dump;

         *device = &camera_device->base.common;

         camera_device->cameraid = cameraid;
         SelectedCameraName = gCameraName[sCameraInfo[cameraid].facing];

         // 根据当前选中的cameraName和设备路径来创建一个合适的捕获图像的设备
         pCaptureDevice = android::createCaptureDevice(SelectedCameraName,
                 gCameraDevPath[sCameraInfo[cameraid].facing]);
         // 创建相应的图片编码器
         pJpegEncoder = android::createJpegEncoder(android::SOFTWARE_JPEG_ENC);

         // 创建HAL层的代理
         camera = new android::CameraHal(cameraid);

         // 设置为HAL层
         if (camera->setCaptureDevice(pCaptureDevice) < 0 ||
                 camera->setJpegEncoder(pJpegEncoder) < 0) {
             rv = -EINVAL;
             goto fail;
         }

         // HAL层初始化
         if (camera->Init() < 0) {
             rv = -EINVAL;
             goto fail;
         }

         gCameraHals[cameraid] = camera;
         gCamerasOpen++;
     }
     return rv;
 }

下面我主要分析几个函数：

1）sp pCaptureDevice = createCaptureDevice()

      sp device(new V412UVCDevice());

       device->SetDevName(deviceName);

       return device;

   这里就是通过V412UVCDevice类来构造一个对象，初始化sp device。

   我们发现CaptureDeviceInterface 这个类里面包含很多业务函数，但是都是纯虚函数，肯定有子类负责实现它。找到它的子类V412CapDeviceBase,的确实现了这些函数。但是我们的V412UVCDevice类又继承于V412CapDeviceBase，而这里我们是new 一个V412UVCDevice对象，所以根据C++的动态联编我们确定最终调用的函数都是类V412UVCDevice的实现。

 

2）sp pJpegEncoder = createJpegEncoder()

        return JpegEncoderSoftware::createInstance();

     这里也是通过new 一个JpegEncoderSoftware对象，初始化sp hardware这个指针。

      而JpegEncoderSoftware也是继承与JpegEncoderInterface类。

 

3）CameraHal *camera = new CameraHal(cameraid)

      这个类特别复杂，仅仅是构造函数中初始化的变量就有50多个，我们主要关注几个内部线程类：

       注意：下面几个类中的mHardware指向CameraHal* camera。

      (1) class CaptureFrameThread : public Thread

             线程函数为：mHardware->captureframeThreadWrapper();

             负责处理的消息队列为：CMessageQueue mCaptureThreadQueue

 

      (2) class PostProcessThread : public Thread

             线程函数为：mHardware->postprocessThreadWrapper();

             负责处理的消息队列为：CMessageQueue mPostProcessThreadQueue

 

      (3) class PreviewShowFrameThread : public Thread

             线程函数为：mHardware->previewshowframeThreadWrapper()             负责处理的消息队列为：CMessageQueue mPreviewThreadQueue

 

      (4) class EncoderFrameThread : public Thread

            线程函数为：mHardware->encoderframeThreadWrapper()           负责处理的消息队列为：CMessageQueue mEncoderThreadQueue

 

      (5) class AutoFocusThread : public Thread

             线程函数为：mHardware->autoFocusThread();

 

      (6) class TakePicThread : public Thread

             线程函数为：mHardware->takepicThread();

 

4）camera->setCaptureDevice(pCaptureDevice)

          mCaptureDevice = pCaptureDevice;

 

5）camera->setJpegEncoder(pJpegEncoder)

           mJpegEncoder = pJpegEncoder;

 

6）camera->Init()

 CAMERA_HAL_RET CameraHal::Init()
 {
     mCameraReady == true;
     mCaptureDevice->GetDevType(&mSensorType);

     if ((ret = AllocInterBuf())<0)
         return ret;
     if ((ret = InitCameraHalParam()) < 0)
         return ret;
     if ((ret = CameraMiscInit()) < 0)
         return ret;

     return ret;
 }