Android Camera HAL3中预览preview模式下的数据流

来源:转载

 

前沿:

为了更好的梳理preview下buffer数据流的操作过程,前一文中对surface下的buffer相关的操作架构进行了描述。本文主要以此为基础,重点分析再Camera2Client和Camera3Device下是如何维护并读写这些视频帧缓存的。

 

1. Camera3Device::convertMetadataListToRequestListLocked函数

结合上一博文中关于preview的控制流,定位到数据流主要的操作主要是对preview模式下将CameraMetadata mPreviewRequest转换为CaptureRequest的过程之中,回顾到mPreviewRequest是主要包含了当前preview下所需要Camera3Device来操作的OutputStream的index值。

 

2. Camera3Device::configureStreamsLocked函数

在configureStreamsLocked的函数中,主要关注的是Camera3Device对当前所具有的所有的mInputStreams和mOutputStreams进行Config的操作,分别包括startConfiguration/finishConfiguration两个状态。

 

2.1 mOutputStreams.editValueAt(i)->startConfiguration()

这里的遍历所有输出stream即最终调用的函数入口为Camera3Stream::startConfiguration(),这里需要先看下Camera3OutputStream的整个结构,出现了Camera3Stream和Camera3IOStreamBase,两者是Input和Output stream所共有的,前者提供的更多的是对buffer的config、get/retrun buffer的操作,后者以维护当前的stream所拥有的buffer数目。另一个支路camera3_stream_t是一个和Camera HAL3底层进行stream信息交互的入口。

startConfiguration函数首先是判断当前stream的状态,对于已经config的不作处理,config的主要操作是getEndpointUsage:

status_t Camera3OutputStream::getEndpointUsage(uint32_t *usage) { status_t res; int32_t u = 0; res = mConsumer->query(mConsumer.get(), NATIVE_WINDOW_CONSUMER_USAGE_BITS, &u); *usage = u; return res;}
这里的mConsumer其实就是之前创建的Surface的本体,每一个Stream在建立时createStream,都会传入一个ANativeWIndow类似的Consumer绑定到当前的stream中去。这里主要是完成当前window所管理的buffer的USAGE值,可参看grallo.h中的定义,由Gralloc模块负责指定当前buffer操作是由HW还是SW来完成以及不同的应用场合,在Gralloc模块中不同模块需求的buffer亦会有不同的分配、定义与处理方式:

 

 

 /* buffer will be used as an OpenGL ES texture */ GRALLOC_USAGE_HW_TEXTURE = 0x00000100, /* buffer will be used as an OpenGL ES render target */ GRALLOC_USAGE_HW_RENDER = 0x00000200, /* buffer will be used by the 2D hardware blitter */ GRALLOC_USAGE_HW_2D = 0x00000400, /* buffer will be used by the HWComposer HAL module */ GRALLOC_USAGE_HW_COMPOSER = 0x00000800, /* buffer will be used with the framebuffer device */ GRALLOC_USAGE_HW_FB = 0x00001000, /* buffer will be used with the HW video encoder */ GRALLOC_USAGE_HW_VIDEO_ENCODER = 0x00010000, /* buffer will be written by the HW camera pipeline */ GRALLOC_USAGE_HW_CAMERA_WRITE = 0x00020000, /* buffer will be read by the HW camera pipeline */ GRALLOC_USAGE_HW_CAMERA_READ = 0x00040000, /* buffer will be used as part of zero-shutter-lag queue */ GRALLOC_USAGE_HW_CAMERA_ZSL = 0x00060000, /* mask for the camera access values */ GRALLOC_USAGE_HW_CAMERA_MASK = 0x00060000, /* mask for the software usage bit-mask */ GRALLOC_USAGE_HW_MASK = 0x00071F00,

 

2.2 mHal3Device->ops->configure_streams(mHal3Device, &config);

config是一个camera3_stream_configuration数据结构,他记录了一次和HAL3交互的stream的数量,已经当前每一个stream的属性配置相关的信息camer3_stream_t,包括stream中每一个buffer的属性值,stream的类型值等等,提交这些信息供hal3去分析处理。在高通平台中你可以看到,对于每一个stream在HAL3平台下均以一个Channel的形式存在。

typedef struct camera3_stream_configuration { uint32_t num_streams; camera3_stream_t **streams;} camera3_stream_configuration_t;

 

stream_type包括:CAMERA3_STREAM_OUTPUT、CAMERA3_STREAM_INPUT、CAMERA3_STREAM_BIDIRECTIONAL。

format主要是指当前buffer支持的像素点存储格式,以HAL_PIXEL_FORMAT_IMPLEMENTATION_DEFINED居多,表明数据格式是由Gralloc模块来决定的。

对于HAL3中对configureStreams接口的实现会放在后续介绍高通平台的实现机制时再做分析。

 

2.3 Camera3Stream::finishConfiguration

该函数主要执行configureQueueLocked和registerBuffersLocked两个函数

 

status_t Camera3OutputStream::configureQueueLocked() { status_t res; mTraceFirstBuffer = true; if ((res = Camera3IOStreamBase::configureQueueLocked()) != OK) { return res; } ALOG_ASSERT(mConsumer != 0, mConsumer should never be NULL); // Configure consumer-side ANativeWindow interface res = native_window_api_connect(mConsumer.get(), NATIVE_WINDOW_API_CAMERA); if (res != OK) { ALOGE(%s: Unable to connect to native window for stream %d, __FUNCTION__, mId); return res; } res = native_window_set_usage(mConsumer.get(), camera3_stream::usage); if (res != OK) { ALOGE(%s: Unable to configure usage %08x for stream %d, __FUNCTION__, camera3_stream::usage, mId); return res; } res = native_window_set_scaling_mode(mConsumer.get(), NATIVE_WINDOW_SCALING_MODE_SCALE_TO_WINDOW); if (res != OK) { ALOGE(%s: Unable to configure stream scaling: %s (%d), __FUNCTION__, strerror(-res), res); return res; } if (mMaxSize == 0) { // For buffers of known size res = native_window_set_buffers_dimensions(mConsumer.get(), camera3_stream::width, camera3_stream::height); } else { // For buffers with bounded size res = native_window_set_buffers_dimensions(mConsumer.get(), mMaxSize, 1); } if (res != OK) { ALOGE(%s: Unable to configure stream buffer dimensions %d x %d (maxSize %zu) for stream %d, __FUNCTION__, camera3_stream::width, camera3_stream::height, mMaxSize, mId); return res; } res = native_window_set_buffers_format(mConsumer.get(), camera3_stream::format); if (res != OK) { ALOGE(%s: Unable to configure stream buffer format %#x for stream %d, __FUNCTION__, camera3_stream::format, mId); return res; } int maxConsumerBuffers; res = mConsumer->query(mConsumer.get(), NATIVE_WINDOW_MIN_UNDEQUEUED_BUFFERS, &maxConsumerBuffers);//支持的最大buffer数量 if (res != OK) { ALOGE(%s: Unable to query consumer undequeued buffer count for stream %d, __FUNCTION__, mId); return res; } ALOGV(%s: Consumer wants %d buffers, HAL wants %d, __FUNCTION__, maxConsumerBuffers, camera3_stream::max_buffers); if (camera3_stream::max_buffers == 0) { ALOGE(%s: Camera HAL requested max_buffer count: %d, requires at least 1, __FUNCTION__, camera3_stream::max_buffers); return INVALID_OPERATION; } mTotalBufferCount = maxConsumerBuffers + camera3_stream::max_buffers;//至少2个buffer mHandoutTotalBufferCount = 0; mFrameCount = 0; mLastTimestamp = 0; res = native_window_set_buffer_count(mConsumer.get(), mTotalBufferCount); if (res != OK) { ALOGE(%s: Unable to set buffer count for stream %d, __FUNCTION__, mId); return res; } res = native_window_set_buffers_transform(mConsumer.get(), mTransform); if (res != OK) { ALOGE(%s: Unable to configure stream transform to %x: %s (%d), __FUNCTION__, mTransform, strerror(-res), res); } return OK;}
如果你对SurfaceFlinger的架构熟悉的话,该代码会相对比较好理解。本质是根据当前stream设置的buffer属性,将这些属性值通过ANativeWindow这个接口传递给Consumer侧去维护:

 

这里重点关注以下几个buffer的相关属性信息:

比如native_window_set_buffer_count是设置当前Window所需要的buffer数目:

总的当前stream下的buffer个数总数为mTotalBufferCount = maxConsumerBuffers + camera3_stream::max_buffers。其中camera3_stream::max_buffer需要的buffer总数由configureStreams时HAL3底层的Device来决定的,高通平台下定义的camera3_stream::max_buffer数为7个,而maxConsumerBuffers指的是在所有buffer被dequeue时还应该保留的处于queue操作的buffer个数,即全dequeue时至少有maxConsumerBuffers个buffer是处于queue状态在被Consumer使用的。通过query NATIVE_WINDOW_MIN_UNDEQUEUED_BUFFERS来完成,一般默认是1个,即每个stream可以认为需要由8个buffer缓存块组成,实际可dequeue的为8个。

比如native_window_set_buffers_transform一般是指定buffer的Consumer,即当前buffer显示的90/180/270°角度。

 

该过程本质是结合HAL3的底层buffer配置需求,反过来请求Buffer的Consumer端BufferQueueConsumer来设置相关的buffer属性。

 

registerBuffersLocked是一个比较重要的处理过程:

 

status_t Camera3Stream::registerBuffersLocked(camera3_device *hal3Device) { ATRACE_CALL(); /** * >= CAMERA_DEVICE_API_VERSION_3_2: * * camera3_device_t->ops->register_stream_buffers() is not called and must * be NULL. */ if (hal3Device->common.version >= CAMERA_DEVICE_API_VERSION_3_2) { ALOGV(%s: register_stream_buffers unused as of HAL3.2, __FUNCTION__); if (hal3Device->ops->register_stream_buffers != NULL) { ALOGE(%s: register_stream_buffers is deprecated in HAL3.2; must be set to NULL in camera3_device::ops, __FUNCTION__); return INVALID_OPERATION; } else { ALOGD(%s: Skipping NULL check for deprecated register_stream_buffers, __FUNCTION__); } return OK; } else { ALOGV(%s: register_stream_buffers using deprecated code path, __FUNCTION__); } status_t res; size_t bufferCount = getBufferCountLocked();//获取buffer的数量,mTotalBufferCount,最少2个buffer Vector buffers; buffers.insertAt(/*prototype_item*/NULL, /*index*/0, bufferCount); camera3_stream_buffer_set bufferSet = camera3_stream_buffer_set(); bufferSet.stream = this;//新的bufferset指向camera3_stream_t bufferSet.num_buffers = bufferCount;//当前stream下的buffer数 bufferSet.buffers = buffers.editArray(); Vector streamBuffers; streamBuffers.insertAt(camera3_stream_buffer_t(), /*index*/0, bufferCount); // Register all buffers with the HAL. This means getting all the buffers // from the stream, providing them to the HAL with the // register_stream_buffers() method, and then returning them back to the // stream in the error state, since they won't have valid data. // // Only registered buffers can be sent to the HAL. uint32_t bufferIdx = 0; for (; bufferIdx < bufferCount; bufferIdx++) { res = getBufferLocked( &streamBuffers.editItemAt(bufferIdx) );//返回dequeue buffer出来的所有buffer if (res != OK) { ALOGE(%s: Unable to get buffer %d for registration with HAL, __FUNCTION__, bufferIdx); // Skip registering, go straight to cleanup break; } sp fence = new Fence(streamBuffers[bufferIdx].acquire_fence); fence->waitForever(Camera3Stream::registerBuffers);//等待可写 buffers.editItemAt(bufferIdx) = streamBuffers[bufferIdx].buffer;//dequeue buffer出来的buffer handle } if (bufferIdx == bufferCount) { // Got all buffers, register with HAL ALOGV(%s: Registering %zu buffers with camera HAL, __FUNCTION__, bufferCount); ATRACE_BEGIN(camera3->register_stream_buffers); res = hal3Device->ops->register_stream_buffers(hal3Device, &bufferSet);//buffer绑定并register到hal层 ATRACE_END(); } // Return all valid buffers to stream, in ERROR state to indicate // they weren't filled. for (size_t i = 0; i < bufferIdx; i++) { streamBuffers.editItemAt(i).release_fence = -1; streamBuffers.editItemAt(i).status = CAMERA3_BUFFER_STATUS_ERROR; returnBufferLocked(streamBuffers[i], 0);//register后进行queue buffer } return res;}

 

a 可以明确看到CAMERA_DEVICE_API_VERSION_3_2的版本才支持这个Device ops接口

b getBufferCountLocked

获取当前stream下的允许的buffer总数

c camera3_stream_buffer_t、camera3_stream_buffer_set和buffer_handle_t

 

首先需要关注的结构是camera3_stream_buffer_t,用于描述每一个stream下的buffer自身的特性值,其中关键结构是buffer_handle_t值是每一个buffer在不同进程间共享的handle,此外acquire_fence和release_fence用来不同硬件模块对buffer读写时的同步。

 

camera3_stream_buffer_set是封装了当前stream下所有的buffer的信息:

 

typedef struct camera3_stream_buffer_set { /** * The stream handle for the stream these buffers belong to */ camera3_stream_t *stream; /** * The number of buffers in this stream. It is guaranteed to be at least * stream->max_buffers. */ uint32_t num_buffers; /** * The array of gralloc buffer handles for this stream. If the stream format * is set to HAL_PIXEL_FORMAT_IMPLEMENTATION_DEFINED, the camera HAL device * should inspect the passed-in buffers to determine any platform-private * pixel format information. */ buffer_handle_t **buffers;} camera3_stream_buffer_set_t;
三个变量分别保存stream的buffer个数,当前这个set集合所属的stream,以及他所包含的所有buffer的handle信息列表。

 

 

d getBufferLocked获取当前buffer

 

status_t Camera3OutputStream::getBufferLocked(camera3_stream_buffer *buffer) { ATRACE_CALL(); status_t res; if ((res = getBufferPreconditionCheckLocked()) != OK) { return res; } ANativeWindowBuffer* anb; int fenceFd; /** * Release the lock briefly to avoid deadlock for below scenario: * Thread 1: StreamingProcessor::startStream -> Camera3Stream::isConfiguring(). * This thread acquired StreamingProcessor lock and try to lock Camera3Stream lock. * Thread 2: Camera3Stream::returnBuffer->StreamingProcessor::onFrameAvailable(). * This thread acquired Camera3Stream lock and bufferQueue lock, and try to lock * StreamingProcessor lock. * Thread 3: Camera3Stream::getBuffer(). This thread acquired Camera3Stream lock * and try to lock bufferQueue lock. * Then there is circular locking dependency. */ sp currentConsumer = mConsumer; mLock.unlock(); res = currentConsumer->dequeueBuffer(currentConsumer.get(), &anb, &fenceFd); mLock.lock(); if (res != OK) { ALOGE(%s: Stream %d: Can't dequeue next output buffer: %s (%d), __FUNCTION__, mId, strerror(-res), res); return res; } /** * FenceFD now owned by HAL except in case of error, * in which case we reassign it to acquire_fence */ handoutBufferLocked(*buffer, &(anb->handle), /*acquireFence*/fenceFd, /*releaseFence*/-1, CAMERA3_BUFFER_STATUS_OK, /*output*/true); return OK;}
该函数主要是从由ANativeWindow从Consumer端dequeue获取一个buffer,本质上这个过程中首次执行是会有Consumer端去分配一个由实际物理空间的给当前的一个buffer的。

 

接着执行handoutBufferLocked,填充camera3_stream_buffer这个结构体,其中设置的acquireFence为-1值表明hal3的这个buffer可被Framewrok直接使用,而acquireFence表示HAL3如何想使用这个buffer时需要等待其变为1,因为buffer分配和handler返回不一定是一致同步的。还会切换当前buffer的状态CAMERA3_BUFFER_STATUS_OK。

 

void Camera3IOStreamBase::handoutBufferLocked(camera3_stream_buffer &buffer, buffer_handle_t *handle, int acquireFence, int releaseFence, camera3_buffer_status_t status, bool output) { /** * Note that all fences are now owned by HAL. */ // Handing out a raw pointer to this object. Increment internal refcount. incStrong(this); buffer.stream = this; buffer.buffer = handle; buffer.acquire_fence = acquireFence; buffer.release_fence = releaseFence; buffer.status = status; // Inform tracker about becoming busy if (mHandoutTotalBufferCount == 0 && mState != STATE_IN_CONFIG && mState != STATE_IN_RECONFIG) { /** * Avoid a spurious IDLE->ACTIVE->IDLE transition when using buffers * before/after register_stream_buffers during initial configuration * or re-configuration. * * TODO: IN_CONFIG and IN_RECONFIG checks only make sense for  statusTracker = mStatusTracker.promote(); if (statusTracker != 0) { statusTracker->markComponentActive(mStatusId); } } mHandoutTotalBufferCount++;//统计dequeuebuffer的数量 if (output) { mHandoutOutputBufferCount++; }}

 

e hal3Device->ops->register_stream_buffers(hal3Device,&bufferSet);//buffer绑定并register到hal层

将所属的stream下的所有buffer有关的信息,主要是每个buffer的buffer_handle_t值,交给HAL3层去实现。比如高通HAL3平台每一个Channel对应于Camera3Device端的stream,而每一个stream的buffer在不同的Channel下面却是一个个的stream,这是高通的实现方式。

 

f 在完成register所有buffer后,设置每一个buffer状态为从CAMERA3_BUFFER_STATUS_OK切换到CAMERA3_BUFFER_STATUS_ERROR表明这个buffer都是可用的,目的在于执行returnBufferLocked是为了将这些因为register而出列的所有buffer再次cancelbuffer操作。

Camera3OutputStream::returnBufferLocked->Camera3IOStreamBase::returnAnyBufferLocked->Camera3OutputStream::returnBufferCheckedLocked

 

status_t Camera3OutputStream::returnBufferCheckedLocked(//result返回时调用 const camera3_stream_buffer &buffer, nsecs_t timestamp, bool output, /*out*/ sp *releaseFenceOut) { (void)output; ALOG_ASSERT(output, Expected output to be true); status_t res; sp releaseFence; /** * Fence management - calculate Release Fence */ if (buffer.status == CAMERA3_BUFFER_STATUS_ERROR) { if (buffer.release_fence != -1) { ALOGE(%s: Stream %d: HAL should not set release_fence(%d) when there is an error, __FUNCTION__, mId, buffer.release_fence); close(buffer.release_fence); } /** * Reassign release fence as the acquire fence in case of error */ releaseFence = new Fence(buffer.acquire_fence); } else { res = native_window_set_buffers_timestamp(mConsumer.get(), timestamp); if (res != OK) { ALOGE(%s: Stream %d: Error setting timestamp: %s (%d), __FUNCTION__, mId, strerror(-res), res); return res; } releaseFence = new Fence(buffer.release_fence); } int anwReleaseFence = releaseFence->dup(); /** * Release the lock briefly to avoid deadlock with * StreamingProcessor::startStream -> Camera3Stream::isConfiguring (this * thread will go into StreamingProcessor::onFrameAvailable) during * queueBuffer */ sp currentConsumer = mConsumer; mLock.unlock(); /** * Return buffer back to ANativeWindow */ if (buffer.status == CAMERA3_BUFFER_STATUS_ERROR) { // Cancel buffer res = currentConsumer->cancelBuffer(currentConsumer.get(), container_of(buffer.buffer, ANativeWindowBuffer, handle), anwReleaseFence);//Register buffer locked所在的事情,cancelbuffer dequeue的buffer if (res != OK) { ALOGE(%s: Stream %d: Error cancelling buffer to native window: %s (%d), __FUNCTION__, mId, strerror(-res), res); } } else { if (mTraceFirstBuffer && (stream_type == CAMERA3_STREAM_OUTPUT)) { { char traceLog[48]; snprintf(traceLog, sizeof(traceLog), Stream %d: first full buffer, mId); ATRACE_NAME(traceLog); } mTraceFirstBuffer = false; } res = currentConsumer->queueBuffer(currentConsumer.get(), container_of(buffer.buffer, ANativeWindowBuffer, handle), anwReleaseFence);//queuebuffer,送显ANativeWindowBuffer if (res != OK) { ALOGE(%s: Stream %d: Error queueing buffer to native window: %s (%d), __FUNCTION__, mId, strerror(-res), res); } } mLock.lock(); if (res != OK) { close(anwReleaseFence); } *releaseFenceOut = releaseFence; return res;}

 

该函数对于首次register的处理来说,他处理的buffer均是CAMERA3_BUFFER_STATUS_ERROR,调用了cancelBuffer将所有buffer的状态都还原为free的状态,依次说明目前的buffer均是可用的,之前均不涉及到对buffer的数据流的操作。

 

3 buffer数据流的dequeue操作

上述步骤2主要是将每一个Stream下全部的buffer信息全部register到下层的HAL3中,为后续对buffer的数据流读写操作奠定基础。

那么preview模式下我们又是如何去获得一帧完成的视频流的呢?

触发点就是preview模式下的Request,前面提到过一个mPreviewRequest至少包含一个StreamProcessor和一个CallbackProcessor的两路stream,每路stream拥有不同的buffer数量。比如要从HAL3获取一帧图像数据,最简单的思路就是从StreamProcessor下的Outputstream流中下发一个可用的buffer地址,然后HAL3填充下数据,Framework就可以拥有一帧数据了。

根据这个思路,回顾到前一博文中每次会不断的下发一个Request命令包到HAL3中,在这里我们就可以看到这个buffer地址身影。

Camera3Device::RequestThread::threadLoop() 下的部分代码:

 

 outputBuffers.insertAt(camera3_stream_buffer_t(), 0, nextRequest->mOutputStreams.size());//Streamprocess,Callbackprocessor request.output_buffers = outputBuffers.array();//camera3_stream_buffer_t for (size_t i = 0; i < nextRequest->mOutputStreams.size(); i++) { res = nextRequest->mOutputStreams.editItemAt(i)-> getBuffer(&outputBuffers.editItemAt(i));//等待获取buffer,内部是dequeue一根buffer填充到camera3_stream_buffer_t if (res != OK) { // Can't get output buffer from gralloc queue - this could be due to // abandoned queue or other consumer misbehavior, so not a fatal // error ALOGE(RequestThread: Can't get output buffer, skipping request: %s (%d), strerror(-res), res); Mutex::Autolock l(mRequestLock); if (mListener != NULL) { mListener->notifyError( ICameraDeviceCallbacks::ERROR_CAMERA_REQUEST, nextRequest->mResultExtras); } cleanUpFailedRequest(request, nextRequest, outputBuffers); return true; } request.num_output_buffers++;//一般一根OutStream对应一个buffer,故总的out_buffer数目 }
在这个下发到HAL3的camera3_capture_request中,可以看到 const camera3_stream_buffer_t *output_buffers,下面的代码可以说明这一次的Request的output_buffers是打包了当前Camera3Device所拥有的mOutputStreams。

 

 

 outputBuffers.insertAt(camera3_stream_buffer_t(), 0, nextRequest->mOutputStreams.size());//Streamprocess,Callbackprocessor
对于每一个OutputStream他会给她分配一个buffer handle。关注下面的处理代码:

 

 

nextRequest->mOutputStreams.editItemAt(i)-> getBuffer(&outputBuffers.editItemAt(i))
nextRequest->mOutputStreams.editItemAt(i)是获取一个Camera3OutputStream对象,然后对getBuffer而言传入的是这个Camera3OutputStream所对应的这次buffer的输入位置,这个camera3_stream_buffer是需要从Camera3OutputStream对象中去获取的。

 

 

status_t Camera3Stream::getBuffer(camera3_stream_buffer *buffer) { ATRACE_CALL(); Mutex::Autolock l(mLock); status_t res = OK; // This function should be only called when the stream is configured already. if (mState != STATE_CONFIGURED) { ALOGE(%s: Stream %d: Can't get buffers if stream is not in CONFIGURED state %d, __FUNCTION__, mId, mState); return INVALID_OPERATION; } // Wait for new buffer returned back if we are running into the limit. if (getHandoutOutputBufferCountLocked() == camera3_stream::max_buffers) {//dequeue过多时等待queue的释放 ALOGV(%s: Already dequeued max output buffers (%d), wait for next returned one., __FUNCTION__, camera3_stream::max_buffers); res = mOutputBufferReturnedSignal.waitRelative(mLock, kWaitForBufferDuration); if (res != OK) { if (res == TIMED_OUT) { ALOGE(%s: wait for output buffer return timed out after %lldms, __FUNCTION__, kWaitForBufferDuration / 1000000LL); } return res; } } res = getBufferLocked(buffer); if (res == OK) { fireBufferListenersLocked(*buffer, /*acquired*/true, /*output*/true); } return res;}
上述的代码先是检查dequeue了的buffer是否已经达到本stream申请的buffer数目的最大值,如果已经全部dequeue的话就得wait到当前已经有buffer return并且queue操作后,在处理完成后才允许将从buffer队列中再次执行dequeue操作。

 

随后调用getBufferLocked通过2.2(d)小节可以知道是从buffer队列中获取一个可用的buffer,并填充这个camera3_stream_buffer值。

这样处理完的结果是,下发的Request包含所有模块下的outputstream,同时每个stream都配备了一个camera3_stream_buffer供底层HAL3.0去处理,而这个buffer在Camera3Device模式下,可以是交互的是帧图像数据,可以是参数控制命令,也可以是其他的3A信息,这些不同的信息一般归不同的模块管理,也就是不同的stream来处理。

 

4 buffer数据流的queue操作

dequeue出来的buffer信息已经随着Request下发到了HAL3层,在Camera3Device架构下,可以使用一个Callback接口将数据从HAL3回传到Camera所在的Framework层。Camera3Device私有继承了一个Callback接口camera3_callback_ops数据结构,分别预留了notify和process_capture_result。前者是用于回调一些shutter已经error等信息,后者以Callback数据流为主,这个回调接口通过device->initialize(camera3_device, this)来完成注册。

 

void Camera3Device::sProcessCaptureResult(const camera3_callback_ops *cb, const camera3_capture_result *result) { Camera3Device *d = const_cast(static_cast(cb)); d->processCaptureResult(result);}
返回的buffer所有信息均包含在camera3_capture_result中,该函数的处理过程相对比较复杂,如果只定位queue buffer的入口可直接到returnOutputBuffers中去:

 

 

void Camera3Device::returnOutputBuffers( const camera3_stream_buffer_t *outputBuffers, size_t numBuffers, nsecs_t timestamp) { for (size_t i = 0; i < numBuffers; i++)//对每一个buffer所属的stream进行分析 { Camera3Stream *stream = Camera3Stream::cast(outputBuffers[i].stream);//该buffer对应的camera3_stream status_t res = stream->returnBuffer(outputBuffers[i], timestamp);//Camera3OutPutStream,每一各stream对应的return // Note: stream may be deallocated at this point, if this buffer was // the last reference to it. if (res != OK) { ALOGE(Can't return buffer to its stream: %s (%d), strerror(-res), res); } }}
因为在下发Request时,每一个buffer均包含所述的stream信息,当buffer数据返回到Framework层时,我们又可以转到Camera3OutPutStream来处理这个return的buffer。

 

 

status_t Camera3Stream::returnBuffer(const camera3_stream_buffer &buffer, nsecs_t timestamp) { ATRACE_CALL(); Mutex::Autolock l(mLock); /** * TODO: Check that the state is valid first. * * = HAL3.2 CONFIGURED only * * Do this for getBuffer as well. */ status_t res = returnBufferLocked(buffer, timestamp);//以queue buffer为主 if (res == OK) { fireBufferListenersLocked(buffer, /*acquired*/false, /*output*/true); mOutputBufferReturnedSignal.signal(); } return res;}
在这里看看registerBuffersLocked,参考前面对这个函数他是register完所有的buffer时被调用,在这里其本质处理的buffer状态不在是CAMERA3_BUFFER_STATUS_ERROR,而是CAMERA3_BUFFER_STATUS_OK故执行的是将会queuebuffer的操作。

 

 

5 buffer数据真正的被Consumer处理

在queuebuffer的操作时,参考前一博文Android5.1中surface和CpuConsumer下生产者和消费者间的处理框架简述很容易知道真正的Consumer需要开始工作了,对于preview模式下的当然是由SurfaceFlinger的那套机制去处理。而在Camera2Client和Camera3Device下你还可以看到CPUConsumer的存在,比如:

 

void CallbackProcessor::onFrameAvailable(const BufferItem& /*item*/) { Mutex::Autolock l(mInputMutex); if (!mCallbackAvailable) { mCallbackAvailable = true; mCallbackAvailableSignal.signal();//数据callback线程处理 }}
在这里,你就可以去处理那些处于queue状态的buffer数据,比如这里的Callback将这帧数据上传会APP。

 

 

bool CallbackProcessor::threadLoop() { status_t res; { Mutex::Autolock l(mInputMutex); while (!mCallbackAvailable) { res = mCallbackAvailableSignal.waitRelative(mInputMutex, kWaitDuration); if (res == TIMED_OUT) return true; } mCallbackAvailable = false; } do { sp client = mClient.promote(); if (client == 0) { res = discardNewCallback(); } else { res = processNewCallback(client);//callback 处理新的一帧 } } while (res == OK); return true;}
 l.mRemoteCallback->dataCallback(CAMERA_MSG_PREVIEW_FRAME, callbackHeap->mBuffers[heapIdx], NULL);//处理成API的需求后,回调Preview frame

 

 

 

6 总结

到这里,整个preview预览的视频流基本介绍完毕了,主要框架虽然负责,但仔细看看也就是buffer的queue与dequeue操作,真正的HAL3的实现才是最为复杂的。后续还会简单介绍下整个take picture的过程,数据的回调处理在后续中还会继续分析。

 

下面贴一图是整个Camera3架构下基于Request和result的处理流序图:





 

 

 

 

 



 


 

 



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