android4.2.2 Camera HAL的结构
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时间：2015年06月11日
本文均属自己阅读源码的点滴总结，转账请注明出处谢谢。
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Android源码版本Version：4.2.2; 硬件平台 全志A31
这里单独以preview的控制和数据流来进行相关的camera的调用处理，主要先引入Camera 的HAL层的处理结构。
调用还是先从camera的JNI和HAL两个方面来分析：
step1：启动预览startPreview()
// start preview mode
status_t Camera::startPreview()
{
ALOGV("startPreview");
sp <ICamera> c = mCamera;
if (c == 0) return NO_INIT;
return c->startPreview();
}这里的mCamera是之前connect请求CameraService建立，该类是匿名的BpCamera直接和CameraService处的CameraClient（该类继承了CameraService的内部类Client，Client继承了BnCamera）进行交互。
step2:调用CameraService侧的CameraClient里的startpreview()
status_t CameraClient::startPreviewMode() {
LOG1("startPreviewMode");
status_t result = NO_ERROR;
// if preview has been enabled, nothing needs to be done
if (mHardware->previewEnabled()) {//使能预览
return NO_ERROR;
}
if (mPreviewWindow != 0) {
native_window_set_scaling_mode(mPreviewWindow.get(),
NATIVE_WINDOW_SCALING_MODE_SCALE_TO_WINDOW);
native_window_set_buffers_transform(mPreviewWindow.get(),
mOrientation);
}
mHardware->setPreviewWindow(mPreviewWindow);//mPreviewWindow为一个本地窗口ANativeWindow
result = mHardware->startPreview();
return result;
}这里出现了一个mPreviewWIndow对象，其类为ANativeWindow，很熟悉的一个应用端的本地窗口。那么这个窗口的初始化过程呢，即这个变量是哪里来的？
step3:探秘本地预览窗口mPreviewWinodw对象
java处：
public final void setPreviewDisplay(SurfaceHolder holder) throws IOException {
if (holder != null) {
setPreviewDisplay(holder.getSurface());
} else {
setPreviewDisplay((Surface)null);
}
}
这个getSurface()的获取调用如下
static sp<Surface> getSurface(JNIEnv* env, jobject surfaceObj) {
sp<Surface> result(android_view_Surface_getSurface(env, surfaceObj));
if (result == NULL) {
/*
* if this method is called from the WindowManager‘s process, it means
* the client is is not remote, and therefore is allowed to have
* a Surface (data), so we create it here.
* If we don‘t have a SurfaceControl, it means we‘re in a different
* process.
*/
SurfaceControl* const control = reinterpret_cast<SurfaceControl*>(
env->GetIntField(surfaceObj, gSurfaceClassInfo.mNativeSurfaceControl));
if (control) {
result = control->getSurface();
if (result != NULL) {
result->incStrong(surfaceObj);
env->SetIntField(surfaceObj, gSurfaceClassInfo.mNativeSurface,
reinterpret_cast<jint>(result.get()));
}
}
}
return result;
}
看到这里可以回顾到从Android Bootanimation理解SurfaceFlinger的客户端建立这一文中，对客户端的一个Surface建立，这里的过程几乎一摸一样，最终返回一个客户端需要的Surface用来绘图使用。
而这个surface最终也将进一步传递到JNI，HAL供实时的预览等。
JNI处：
static void android_hardware_Camera_setPreviewDisplay(JNIEnv *env, jobject thiz, jobject jSurface)
{
ALOGV("setPreviewDisplay");
sp<Camera> camera = get_native_camera(env, thiz, NULL);
if (camera == 0) return;
sp<Surface> surface = NULL;
if (jSurface != NULL) {
surface = reinterpret_cast<Surface*>(env->GetIntField(jSurface, fields.surface));
}
if (camera->setPreviewDisplay(surface) != NO_ERROR) {
jniThrowException(env, "java/io/IOException", "setPreviewDisplay failed");
}
}
来到JNI层的实现，获取之前由CameraService创作的Camera对象，该类继承了BpCamera用于进一步和CameraService端的CameraClient进行交互。
step4:CameraService处的响应
status_t BnCamera::onTransact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
.....
case SET_PREVIEW_DISPLAY: {
ALOGV("SET_PREVIEW_DISPLAY");
CHECK_INTERFACE(ICamera, data, reply);
sp<Surface> surface = Surface::readFromParcel(data);
reply->writeInt32(setPreviewDisplay(surface));
return NO_ERROR;
} break;
......
case START_PREVIEW: {
ALOGV("START_PREVIEW");
CHECK_INTERFACE(ICamera, data, reply);
reply->writeInt32(startPreview());//调用服务端的cameraclient处的函数，为该类的派生类
return NO_ERROR;
} break;
}由于之前connect写入的Binder本地实体类对象为CameraClient，则由该类对象的成员函数来实现。
status_t CameraClient::setPreviewDisplay(const sp<Surface>& surface) {
LOG1("setPreviewDisplay(%p) (pid %d)", surface.get(), getCallingPid());
sp<IBinder> binder(surface != 0 ? surface->asBinder() : 0);
sp<ANativeWindow> window(surface);
return setPreviewWindow(binder, window);
}
再调用SetPreviewWindow(),传入的Binder分别为Surface对象和一个ANativeWindow对象window。status_t CameraClient::setPreviewWindow(const sp<IBinder>& binder,
const sp<ANativeWindow>& window) {
Mutex::Autolock lock(mLock);
status_t result = checkPidAndHardware();
if (result != NO_ERROR) return result;
// return if no change in surface.
if (binder == mSurface) {
return NO_ERROR;
}
if (window != 0) {
result = native_window_api_connect(window.get(), NATIVE_WINDOW_API_CAMERA);
if (result != NO_ERROR) {
ALOGE("native_window_api_connect failed: %s (%d)", strerror(-result),
result);
return result;
}
}
// If preview has been already started, register preview buffers now.
if (mHardware->previewEnabled()) {
if (window != 0) {
native_window_set_scaling_mode(window.get(),
NATIVE_WINDOW_SCALING_MODE_SCALE_TO_WINDOW);
native_window_set_buffers_transform(window.get(), mOrientation);
result = mHardware->setPreviewWindow(window);
}
}
if (result == NO_ERROR) {
// Everything has succeeded. Disconnect the old window and remember the
// new window.
disconnectWindow(mPreviewWindow);
mSurface = binder;// This is a binder of Surface or SurfaceTexture.
mPreviewWindow = window;//获取了预览的数据窗口
} else {
// Something went wrong after we connected to the new window, so
// disconnect here.
disconnectWindow(window);
}
return result;
}调用mHardware这个硬件接口将本地的一个Window窗口传递到HAL层。并将这个windw记录到mPreviewWindow中。
Camera的HAL相关的具体实现结构
到了这里已经非讲不可的是mHardware啦，因为这个接口类将不得不访问HAL层。如最之前的result = mHardware->startPreview();函数。
status_t startPreview()
{
ALOGV("%s(%s)", __FUNCTION__, mName.string());
if (mDevice->ops->start_preview)
return mDevice->ops->start_preview(mDevice);
return INVALID_OPERATION;
}这是一个典型的底层设备的调用。因此将和大家分享Camera的HAL层的相关操作。
1.参考当前平台的Camera源码，CameraService启动时会调用Camera的HAL模块，第一次open操作的最终调用如下：
int HALCameraFactory::device_open(const hw_module_t* module,
const char* name,
hw_device_t** device)//最先被framework层调用
{
/*
* Simply verify the parameters, and dispatch the call inside the
* HALCameraFactory instance.
*/
.....
return gEmulatedCameraFactory.cameraDeviceOpen(atoi(name), device);
}该Camera模块中gEmulatedCameraFactory是一个静态的全局对象。来看该对象的构造过程：
HALCameraFactory::HALCameraFactory()
: mHardwareCameras(NULL),
mAttachedCamerasNum(0),
mRemovableCamerasNum(0),
mConstructedOK(false)
{
F_LOG;
LOGD("camera hal version: %s", CAMERA_HAL_VERSION);
/* Make sure that array is allocated. */
if (mHardwareCameras == NULL) {
mHardwareCameras = new CameraHardware*[MAX_NUM_OF_CAMERAS];
if (mHardwareCameras == NULL) {
LOGE("%s: Unable to allocate V4L2Camera array for %d entries",
__FUNCTION__, MAX_NUM_OF_CAMERAS);
return;
}
memset(mHardwareCameras, 0, MAX_NUM_OF_CAMERAS * sizeof(CameraHardware*));
}
/* Create the cameras */
for (int id = 0; id < MAX_NUM_OF_CAMERAS; id++)
{
// camera config information
mCameraConfig[id] = new CCameraConfig(id);//读取camera配置文件.cfg
if(mCameraConfig[id] == 0)
{
LOGW("create CCameraConfig failed");
}
else
{
mCameraConfig[id]->initParameters();
mCameraConfig[id]->dumpParameters();
}
mHardwareCameras[id] = new CameraHardware(&HAL_MODULE_INFO_SYM.common, mCameraConfig[id]);//创建CameraHardware
if (mHardwareCameras[id] == NULL)
{
mHardwareCameras--;
LOGE("%s: Unable to instantiate fake camera class", __FUNCTION__);
return;
}
}
// check camera cfg
if (mCameraConfig[0] != NULL)
{
mAttachedCamerasNum = mCameraConfig[0]->numberOfCamera();
if ((mAttachedCamerasNum == 2)
&& (mCameraConfig[1] == NULL))
{
return;
}
}
mConstructedOK = true;
}
这个全局对象是新建并初始化CameraHardware对象，而这里的Camera支持数目为2个。CameraHardware表示的是一个完整的摄像头类型，该类继承了camera_device这个结构体类：
CameraHardware::CameraHardware(struct hw_module_t* module, CCameraConfig* pCameraCfg)
: mPreviewWindow(),
mCallbackNotifier(),
mCameraConfig(pCameraCfg),
mIsCameraIdle(true),
mFirstSetParameters(true),
mFullSizeWidth(0),
mFullSizeHeight(0),
mCaptureWidth(0),
mCaptureHeight(0),
mVideoCaptureWidth(0),
mVideoCaptureHeight(0),
mUseHwEncoder(false),
mFaceDetection(NULL),
mFocusStatus(FOCUS_STATUS_IDLE),
mIsSingleFocus(false),
mOriention(0),
mAutoFocusThreadExit(true),
mIsImageCaptureIntent(false)
{
/*
* Initialize camera_device descriptor for this object.
*/
F_LOG;
/* Common header */
common.tag = HARDWARE_DEVICE_TAG;
common.version = 0;
common.module = module;
common.close = CameraHardware::close;
/* camera_device fields. */
ops = &mDeviceOps;
priv = this;
// instance V4L2CameraDevice object
mV4L2CameraDevice = new V4L2CameraDevice(this, &mPreviewWindow, &mCallbackNotifier);//初始化V4L2CameraDevice
if (mV4L2CameraDevice == NULL)
{
LOGE("Failed to create V4L2Camera instance");
return ;
}
memset((void*)mCallingProcessName, 0, sizeof(mCallingProcessName));
memset(&mFrameRectCrop, 0, sizeof(mFrameRectCrop));
memset((void*)mFocusAreasStr, 0, sizeof(mFocusAreasStr));
memset((void*)&mLastFocusAreas, 0, sizeof(mLastFocusAreas));
// init command queue
OSAL_QueueCreate(&mQueueCommand, CMD_QUEUE_MAX);
memset((void*)mQueueElement, 0, sizeof(mQueueElement));
// init command thread
pthread_mutex_init(&mCommandMutex, NULL);
pthread_cond_init(&mCommandCond, NULL);
mCommandThread = new DoCommandThread(this);
mCommandThread->startThread();
// init auto focus thread
pthread_mutex_init(&mAutoFocusMutex, NULL);
pthread_cond_init(&mAutoFocusCond, NULL);
mAutoFocusThread = new DoAutoFocusThread(this);
}这里对这个CameraHardware对象进行了成员变量的初始化，其中包括camera_device_t结构体的初始化，其中ops是对Camera模块操作的核心所在。
typedef struct camera_device {
/**
* camera_device.common.version must be in the range
* HARDWARE_DEVICE_API_VERSION(0,0)-(1,FF). CAMERA_DEVICE_API_VERSION_1_0 is
* recommended.
*/
hw_device_t common;
camera_device_ops_t *ops;
void *priv;
} camera_device_t;这里有出息了一个V4L2CameraDevice对象，真正的和底层内核打交道的地方，基于V4L2的架构实现。
V4L2CameraDevice::V4L2CameraDevice(CameraHardware* camera_hal,
PreviewWindow * preview_window,
CallbackNotifier * cb)
: mCameraHardware(camera_hal),
.......
{
LOGV("V4L2CameraDevice construct");
memset(&mHalCameraInfo, 0, sizeof(mHalCameraInfo));
memset(&mRectCrop, 0, sizeof(Rect));
// init preview buffer queue
OSAL_QueueCreate(&mQueueBufferPreview, NB_BUFFER);//建立10个预览帧
OSAL_QueueCreate(&mQueueBufferPicture, 2);//建立2个图片帧buffer
// init capture thread
mCaptureThread = new DoCaptureThread(this);
pthread_mutex_init(&mCaptureMutex, NULL);
pthread_cond_init(&mCaptureCond, NULL);
mCaptureThreadState = CAPTURE_STATE_PAUSED;
mCaptureThread->startThread();//启动视频采集
// init preview thread
mPreviewThread = new DoPreviewThread(this);
pthread_mutex_init(&mPreviewMutex, NULL);
pthread_cond_init(&mPreviewCond, NULL);
mPreviewThread->startThread();//启动预览
// init picture thread
mPictureThread = new DoPictureThread(this);
pthread_mutex_init(&mPictureMutex, NULL);
pthread_cond_init(&mPictureCond, NULL);
mPictureThread->startThread();//启动拍照
pthread_mutex_init(&mConnectMutex, NULL);
pthread_cond_init(&mConnectCond, NULL);
// init continuous picture thread
mContinuousPictureThread = new DoContinuousPictureThread(this);
pthread_mutex_init(&mContinuousPictureMutex, NULL);
pthread_cond_init(&mContinuousPictureCond, NULL);
mContinuousPictureThread->startThread();//启动连续拍照
}
创建预览mQueueBufferPreview队列，初始化并启动了Camera需要的几个线程：视频采集，预览，拍照，以及连续的拍照等。
通过以上的几个对象构造后Camera的硬件信息维护到了全局类HALCameraFactory的mHardwareCameras[id]成员变量当中。
在客户端的connect，最终调用HAL的cameraDeviceOpen打开真正的设备:
int HALCameraFactory::cameraDeviceOpen(int camera_id, hw_device_t** device)
{
.....
if (!mHardwareCameras[0]->isCameraIdle()
|| !mHardwareCameras[1]->isCameraIdle())
{
LOGW("camera device is busy, wait a moment");
usleep(500000);
}
mHardwareCameras[camera_id]->setCameraHardwareInfo(&mHalCameraInfo[camera_id]);
if (mHardwareCameras[camera_id]->connectCamera(device) != NO_ERROR)//连接camera硬件设备
{
LOGE("%s: Unable to connect camera", __FUNCTION__);
return -EINVAL;
}
if (mHardwareCameras[camera_id]->Initialize() != NO_ERROR) //camera硬件设备参数等初始化
{
LOGE("%s: Unable to Initialize camera", __FUNCTION__);
return -EINVAL;
}
return NO_ERROR;
}初始化的流程依次调用HAL的HardwareCamera的connectCamera函数，其实这里最终的核心是返回一个camera device给上层调用camera的具体操作:最终将CameraHardware的基类camera_devcie_t返回给device。
status_t CameraHardware::connectCamera(hw_device_t** device)
{
F_LOG;
status_t res = EINVAL;
{
Mutex::Autolock locker(&mCameraIdleLock);
mIsCameraIdle = false;
}
if (mV4L2CameraDevice != NULL)
{
res = mV4L2CameraDevice->connectDevice(&mHalCameraInfo);
if (res == NO_ERROR)
{
*device = &common;
......
}mV4L2CameraDevice->connectDevice()，真正的开启V4l2的相关Camera启动，内部通过openCameraDev来实现
status_t V4L2CameraDevice::connectDevice(HALCameraInfo * halInfo)
{
F_LOG;
.....
// open v4l2 camera device
int ret = openCameraDev(halInfo);//调用v4l2的camera标准接口
if (ret != OK)
{
return ret;
}
memcpy((void*)&mHalCameraInfo, (void*)halInfo, sizeof(HALCameraInfo));
.......
}
openCameraDev()函数内部的实现就是V4L2的典型的API流程，通过ioctl来完成对内核Camera视频采集的驱动的控制。该流程可以参考DM6446的视频前端VPFE驱动之ioctl控制（视频缓存区，CCDC，decoder)解析
int V4L2CameraDevice::openCameraDev(HALCameraInfo * halInfo)
{
F_LOG;
int ret = -1;
struct v4l2_input inp;
struct v4l2_capability cap;
if (halInfo == NULL)
{
LOGE("error HAL camera info");
return -1;
}
// open V4L2 device
mCameraFd = open(halInfo->device_name, O_RDWR | O_NONBLOCK, 0);
if (mCameraFd == -1)
{
LOGE("ERROR opening %s: %s", halInfo->device_name, strerror(errno));
return -1;
}
// check v4l2 device capabilities
ret = ioctl (mCameraFd, VIDIOC_QUERYCAP, &cap);
if (ret < 0)
{
LOGE("Error opening device: unable to query device.");
goto END_ERROR;
}
if ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == 0)
{
LOGE("Error opening device: video capture not supported.");
goto END_ERROR;
}
if ((cap.capabilities & V4L2_CAP_STREAMING) == 0)
{
LOGE("Capture device does not support streaming i/o");
goto END_ERROR;
}
if (!strcmp((char *)cap.driver, "uvcvideo"))
{
mIsUsbCamera = true;
}
if (!mIsUsbCamera)
{
// uvc do not need to set input
inp.index = halInfo->device_id;
if (-1 == ioctl (mCameraFd, VIDIOC_S_INPUT, &inp))
{
LOGE("VIDIOC_S_INPUT error!");
goto END_ERROR;
}
}
// try to support this format: NV21, YUYV
.....
}到这里为止一共典型的Camera从应用侧到CameraService再到Camera HAL处的初始化流程基本完成。
总结下的是HAL层建立了一个基于V4L2的V4L2CameraDevice对象来完成和内核视频采集模块的互动，返回一个camera_device_t结构体对象mDevice来为后续对Camera设备的进一步控制。
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