相机原生代码底层逻辑

我试图更好地理解相机本机代码的底层逻辑，但在寻找方法定义时我似乎陷入了死胡同Camera::connect()和其他声明的函数Camera.h.

我遵循的步骤如下：

1. In the master branch I located Camera.java https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/hardware/Camera.java, which contains the logic for resolving cameras, selecting CameraInfo.CAMERA_FACING_BACK when it is encountered:
   • Camera.open() calls Camera.getCameraInfo(int, CameraInfo)对于每个 intCamera.getNumberOfCameras().
   • Camera.getCameraInfo(int, CameraInfo)依次调用原生函数Camera._getCameraInfo(int, CameraInfo).

2. Delving 进入JNI https://android.googlesource.com/platform/frameworks/base/+/master/core/jni/android_hardware_Camera.cpp:

   • android_hardware_Camera_getCameraInfo(JNIEnv*, jobject, jint, jobject)然后调用静态方法Camera::getCameraInfo(jint, CameraInfo*)，它似乎是通过以下方式声明的：

     #include <camera/Camera.h>
     

3. 浏览和搜索主分支似乎没有给出任何点击camera/Camera.h。例如，我能找到的唯一结果是旧标签在姜饼分支 https://android.googlesource.com/platform/frameworks/base/+/gingerbread/include/camera/Camera.h。这里只有一个方法声明：

   static  status_t    getCameraInfo(int cameraId,
                                 struct CameraInfo* cameraInfo);
   

4. 但是，方法主体似乎没有在任何地方定义。

最后两步是我感到困惑的地方。哪里camera/Camera.h为更新版本的 Android 定义的？最后，方法体在哪里Camera实际上定义了？

在ICS中，Camera::getCameraInfo(jint, CameraInfo*)在frameworks/av/camera/Camera.cpp中定义为

status_t Camera::getCameraInfo(int cameraId,
                               struct CameraInfo* cameraInfo) {
    const sp<ICameraService>& cs = getCameraService();
    if (cs == 0) return UNKNOWN_ERROR;
    return cs->getCameraInfo(cameraId, cameraInfo);
}

然后它抓取一个活页夹对象CameraService并致电getCameraInfo on CameraService.

status_t CameraService::getCameraInfo(int cameraId,
                                      struct CameraInfo* cameraInfo) {
    ...
    struct camera_info info;
    status_t rc = mModule->get_camera_info(cameraId, &info);
    ...
    return rc;
}

The mModule包含您设备上相机的实际实现。不同的设备可能有不同的实现。例如你可以找到QualcommCamera under 硬件/高通/相机/QualcommCamera.cpp https://android.googlesource.com/platform/hardware/qcom/camera/+/android-4.2.2_r1/QualcommCamera.cpp.

然后看一下connect. The connect做了类似的工作并最终调用CameraService::connect。在该方法中，有一个CameraClient初始化由mModule。因此，当您使用客户端执行某些操作时，您实际上是在使用特定于设备的实现。

多说一句，mModule的初始化是hw_get_module in CameraService::onFirstRef.