原文地址 https://blog.csdn.net/gzzaigcnforever/article/details/49070703
前沿：
爲了更好的梳理preview下buffer數據流的操作過程，前一文中對surface下的buffer相關的操作架構進行了描述。本文主要以此爲基礎，重點分析再Camera2Client和Camera3Device下是如何維護並讀寫這些視頻幀緩存的。
1. Camera3Device::convertMetadataListToRequestListLocked函數
結合上一博文中關於preview的控制流，定位到數據流主要的操作主要是對preview模式下將CameraMetadata mPreviewRequest轉換爲CaptureRequest的過程之中，回顧到mPreviewRequest是主要包含了當前preview下所需要Camera3Device來操作的OutputStream的index值。
2. Camera3Device::configureStreamsLocked函數
在configureStreamsLocked的函數中，主要關注的是Camera3Device對當前所具有的所有的mInputStreams和mOutputStreams進行Config的操作，分別包括startConfiguration/finishConfiguration兩個狀態。
2.1 mOutputStreams.editValueAt(i)->startConfiguration()
這裏的遍歷所有輸出stream即最終調用的函數入口爲Camera3Stream::startConfiguration()，這裏需要先看下Camera3OutputStream的整個結構，出現了Camera3Stream和Camera3IOStreamBase，兩者是Input和Output stream所共有的，前者提供的更多的是對buffer的config、get/retrun buffer的操作，後者以維護當前的stream所擁有的buffer數目。另一個支路camera3_stream_t是一個和Camera HAL3底層進行stream信息交互的入口。
startConfiguration函數首先是判斷當前stream的狀態，對於已經config的不作處理，config的主要操作是getEndpointUsage：
1 2 3 4 5 6 7 8 9 10 | 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; returnres;} |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | /* 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是一個camera3_stream_configuration數據結構，他記錄了一次和HAL3交互的stream的數量，已經當前每一個stream的屬性配置相關的信息camer3_stream_t，包括stream中每一個buffer的屬性值，stream的類型值等等，提交這些信息供hal3去分析處理。在高通平臺中你可以看到，對於每一個stream在HAL3平臺下均以一個Channel的形式存在。
1 2 3 4 | 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主要是指當前buffer支持的像素點存儲格式，以HAL_PIXEL_FORMAT_IMPLEMENTATION_DEFINED居多，表明數據格式是由Gralloc模塊來決定的。
對於HAL3中對configureStreams接口的實現會放在後續介紹高通平臺的實現機制時再做分析。
2.3 Camera3Stream::finishConfiguration
該函數主要執行configureQueueLocked和registerBuffersLocked兩個函數
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 | status_t Camera3OutputStream::configureQueueLocked() { status_t res; mTraceFirstBuffer = true; if((res = Camera3IOStreamBase::configureQueueLocked()) != OK) { returnres; } 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 nativewindow forstream %d, __FUNCTION__, mId); returnres; } res = native_window_set_usage(mConsumer.get(), camera3_stream::usage); if(res != OK) { ALOGE(%s: Unable to configure usage %08x forstream %d, __FUNCTION__, camera3_stream::usage, mId); returnres; } 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); returnres; } 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) forstream %d, __FUNCTION__, camera3_stream::width, camera3_stream::height, mMaxSize, mId); returnres; } res = native_window_set_buffers_format(mConsumer.get(), camera3_stream::format); if(res != OK) { ALOGE(%s: Unable to configure stream buffer format %#x forstream %d, __FUNCTION__, camera3_stream::format, mId); returnres; } intmaxConsumerBuffers; res = mConsumer->query(mConsumer.get(), NATIVE_WINDOW_MIN_UNDEQUEUED_BUFFERS, &maxConsumerBuffers);//支持的最大buffer數量 if(res != OK) { ALOGE(%s: Unable to query consumer undequeued buffer count forstream %d, __FUNCTION__, mId); returnres; } 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); returnINVALID_OPERATION; } mTotalBufferCount = maxConsumerBuffers + camera3_stream::max_buffers;//至少2個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 forstream %d, __FUNCTION__, mId); returnres; } 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); } returnOK;} |
這裏重點關注以下幾個buffer的相關屬性信息：
比如native_window_set_buffer_count是設置當前Window所需要的buffer數目：
總的當前stream下的buffer個數總數爲mTotalBufferCount = maxConsumerBuffers + camera3_stream::max_buffers。其中camera3_stream::max_buffer需要的buffer總數由configureStreams時HAL3底層的Device來決定的，高通平臺下定義的camera3_stream::max_buffer數爲7個，而maxConsumerBuffers指的是在所有buffer被dequeue時還應該保留的處於queue操作的buffer個數，即全dequeue時至少有maxConsumerBuffers個buffer是處於queue狀態在被Consumer使用的。通過query NATIVE_WINDOW_MIN_UNDEQUEUED_BUFFERS來完成，一般默認是1個，即每個stream可以認爲需要由8個buffer緩存塊組成，實際可dequeue的爲8個。
比如native_window_set_buffers_transform一般是指定buffer的Consumer，即當前buffer顯示的90/180/270°角度。
該過程本質是結合HAL3的底層buffer配置需求，反過來請求Buffer的Consumer端BufferQueueConsumer來設置相關的buffer屬性。
registerBuffersLocked是一個比較重要的處理過程：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 | 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__); returnINVALID_OPERATION; }else{ ALOGD(%s: Skipping NULL check fordeprecated register_stream_buffers, __FUNCTION__); } returnOK; }else{ ALOGV(%s: register_stream_buffers using deprecated code path, __FUNCTION__); } status_t res; size_t bufferCount = getBufferCountLocked();//獲取buffer的數量,mTotalBufferCount，最少2個buffer Vector<buffer_handle_t*> 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;//當前stream下的buffer數 bufferSet.buffers = buffers.editArray(); Vector<camera3_stream_buffer_t> 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出來的所有buffer if(res != OK) { ALOGE(%s: Unable to get buffer %d forregistration with HAL, __FUNCTION__, bufferIdx); // Skip registering, go straight to cleanup break; } sp<fence> fence = newFence(streamBuffers[bufferIdx].acquire_fence); fence->waitForever(Camera3Stream::registerBuffers);//等待可寫 buffers.editItemAt(bufferIdx) = streamBuffers[bufferIdx].buffer;//dequeue buffer出來的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綁定並register到hal層 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後進行queue buffer } returnres;}</fence></camera3_stream_buffer_t></buffer_handle_t*> |
a 可以明確看到CAMERA_DEVICE_API_VERSION_3_2的版本才支持這個Device ops接口
b getBufferCountLocked獲取當前stream下的允許的buffer總數
c camera3_stream_buffer_t、camera3_stream_buffer_set和buffer_handle_t
首先需要關注的結構是camera3_stream_buffer_t，用於描述每一個stream下的buffer自身的特性值，其中關鍵結構是buffer_handle_t值是每一個buffer在不同進程間共享的handle，此外acquire_fence和release_fence用來不同硬件模塊對buffer讀寫時的同步。
camera3_stream_buffer_set是封裝了當前stream下所有的buffer的信息：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | 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; |
d getBufferLocked獲取當前buffer
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 | status_t Camera3OutputStream::getBufferLocked(camera3_stream_buffer *buffer) { ATRACE_CALL(); status_t res; if((res = getBufferPreconditionCheckLocked()) != OK) { returnres; } ANativeWindowBuffer* anb; intfenceFd; /** * 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); returnres; } /** * 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); returnOK;}</anativewindow> |
接着執行handoutBufferLocked，填充camera3_stream_buffer這個結構體，其中設置的acquireFence爲-1值表明hal3的這個buffer可被Framewrok直接使用，而acquireFence表示HAL3如何想使用這個buffer時需要等待其變爲1，因爲buffer分配和handler返回不一定是一致同步的。還會切換當前buffer的狀態CAMERA3_BUFFER_STATUS_OK。
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | voidCamera3IOStreamBase::handoutBufferLocked(camera3_stream_buffer &buffer, buffer_handle_t *handle, intacquireFence, intreleaseFence, 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<hal3.2statustracker=""> statusTracker = mStatusTracker.promote(); if(statusTracker != 0) { statusTracker->markComponentActive(mStatusId); } } mHandoutTotalBufferCount++;//統計dequeuebuffer的數量 if(output) { mHandoutOutputBufferCount++; }}</hal3.2> |
e hal3Device->ops->register_stream_buffers(hal3Device,&bufferSet);//buffer綁定並register到hal層
將所屬的stream下的所有buffer有關的信息，主要是每個buffer的buffer_handle_t值，交給HAL3層去實現。比如高通HAL3平臺每一個Channel對應於Camera3Device端的stream，而每一個stream的buffer在不同的Channel下面卻是一個個的stream，這是高通的實現方式。
f 在完成register所有buffer後，設置每一個buffer狀態爲從CAMERA3_BUFFER_STATUS_OK切換到CAMERA3_BUFFER_STATUS_ERROR表明這個buffer都是可用的，目的在於執行returnBufferLocked是爲了將這些因爲register而出列的所有buffer再次cancelbuffer操作。
Camera3OutputStream::returnBufferLocked->Camera3IOStreamBase::returnAnyBufferLocked->Camera3OutputStream::returnBufferCheckedLocked
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 | status_t Camera3OutputStream::returnBufferCheckedLocked(//result返回時調用 constcamera3_stream_buffer &buffer, nsecs_t timestamp, bool output, /*out*/ sp<fence> *releaseFenceOut) { (void)output; ALOG_ASSERT(output, Expected output to be true); status_t res; sp<fence> 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 = newFence(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); returnres; } releaseFence = newFence(buffer.release_fence); } intanwReleaseFence = 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 nativewindow: %s (%d), __FUNCTION__, mId, strerror(-res), res); } }else{ if(mTraceFirstBuffer && (stream_type == CAMERA3_STREAM_OUTPUT)) { { chartraceLog[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，送顯ANativeWindowBuffer if(res != OK) { ALOGE(%s: Stream %d: Error queueing buffer to nativewindow: %s (%d), __FUNCTION__, mId, strerror(-res), res); } } mLock.lock(); if(res != OK) { close(anwReleaseFence); } *releaseFenceOut = releaseFence; returnres;}</anativewindow></fence></fence> |
該函數對於首次register的處理來說，他處理的buffer均是CAMERA3_BUFFER_STATUS_ERROR，調用了cancelBuffer將所有buffer的狀態都還原爲free的狀態，依次說明目前的buffer均是可用的，之前均不涉及到對buffer的數據流的操作。
3 buffer數據流的dequeue操作
上述步驟2主要是將每一個Stream下全部的buffer信息全部register到下層的HAL3中，爲後續對buffer的數據流讀寫操作奠定基礎。
那麼preview模式下我們又是如何去獲得一幀完成的視頻流的呢？
觸發點就是preview模式下的Request，前面提到過一個mPreviewRequest至少包含一個StreamProcessor和一個CallbackProcessor的兩路stream，每路stream擁有不同的buffer數量。比如要從HAL3獲取一幀圖像數據，最簡單的思路就是從StreamProcessor下的Outputstream流中下發一個可用的buffer地址，然後HAL3填充下數據，Framework就可以擁有一幀數據了。
根據這個思路，回顧到前一博文中每次會不斷的下發一個Request命令包到HAL3中，在這裏我們就可以看到這個buffer地址身影。
Camera3Device::RequestThread::threadLoop() 下的部分代碼：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | outputBuffers.insertAt(camera3_stream_buffer_t(),0, nextRequest->mOutputStreams.size());//Streamprocess,Callbackprocessorrequest.output_buffers = outputBuffers.array();//camera3_stream_buffer_tfor(size_t i = 0; i < nextRequest->mOutputStreams.size(); i++) { res = nextRequest->mOutputStreams.editItemAt(i)-> getBuffer(&outputBuffers.editItemAt(i));//等待獲取buffer,內部是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); returntrue; } request.num_output_buffers++;//一般一根OutStream對應一個buffer,故總的out_buffer數目} |
1 2 | outputBuffers.insertAt(camera3_stream_buffer_t(),0, nextRequest->mOutputStreams.size());//Streamprocess,Callbackprocessor |
1 2 | nextRequest->mOutputStreams.editItemAt(i)-> getBuffer(&outputBuffers.editItemAt(i)) |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 | 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 ifstream is not in CONFIGURED state %d, __FUNCTION__, mId, mState); returnINVALID_OPERATION; } // Wait for new buffer returned back if we are running into the limit. if(getHandoutOutputBufferCountLocked() == camera3_stream::max_buffers) {//dequeue過多時等待queue的釋放 ALOGV(%s: Already dequeued max output buffers (%d), wait fornext returned one., __FUNCTION__, camera3_stream::max_buffers); res = mOutputBufferReturnedSignal.waitRelative(mLock, kWaitForBufferDuration); if(res != OK) { if(res == TIMED_OUT) { ALOGE(%s: wait foroutput buffer returntimed out after %lldms, __FUNCTION__, kWaitForBufferDuration / 1000000LL); } returnres; } } res = getBufferLocked(buffer); if(res == OK) { fireBufferListenersLocked(*buffer,/*acquired*/true,/*output*/true); } returnres;} |
隨後調用getBufferLocked通過2.2(d）小節可以知道是從buffer隊列中獲取一個可用的buffer，並填充這個camera3_stream_buffer值。
這樣處理完的結果是，下發的Request包含所有模塊下的outputstream，同時每個stream都配備了一個camera3_stream_buffer供底層HAL3.0去處理，而這個buffer在Camera3Device模式下，可以是交互的是幀圖像數據，可以是參數控制命令，也可以是其他的3A信息，這些不同的信息一般歸不同的模塊管理，也就是不同的stream來處理。
4 buffer數據流的queue操作
dequeue出來的buffer信息已經隨着Request下發到了HAL3層，在Camera3Device架構下，可以使用一個Callback接口將數據從HAL3回傳到Camera所在的Framework層。Camera3Device私有繼承了一個Callback接口camera3_callback_ops數據結構，分別預留了notify和process_capture_result。前者是用於回調一些shutter已經error等信息，後者以Callback數據流爲主，這個回調接口通過device->initialize(camera3_device, this)來完成註冊。
1 2 3 4 5 6 7 | voidCamera3Device::sProcessCaptureResult(constcamera3_callback_ops *cb, constcamera3_capture_result *result) { Camera3Device *d = const_cast<camera3device*>(static_cast<const>(cb)); d->processCaptureResult(result);}</const></camera3device*> |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | voidCamera3Device::returnOutputBuffers( constcamera3_stream_buffer_t *outputBuffers, size_t numBuffers, nsecs_t timestamp) { for(size_t i = 0; i < numBuffers; i++)//對每一個buffer所屬的stream進行分析 { Camera3Stream *stream = Camera3Stream::cast(outputBuffers[i].stream);//該buffer對應的camera3_stream status_t res = stream->returnBuffer(outputBuffers[i], timestamp);//Camera3OutPutStream，每一各stream對應的return // Note: stream may be deallocated at this point, if this buffer was // the last reference to it. if(res != OK) { ALOGE(Can'treturnbuffer to its stream: %s (%d), strerror(-res), res); } }} |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | status_t Camera3Stream::returnBuffer(constcamera3_stream_buffer &buffer, nsecs_t timestamp) { ATRACE_CALL(); Mutex::Autolock l(mLock); /** * TODO: Check that the state is valid first. * * <hal3.2 addition="" and="" configured.="" in="" in_config="" in_reconfig="" to="">= HAL3.2 CONFIGURED only * * Do this for getBuffer as well. */ status_t res = returnBufferLocked(buffer, timestamp);//以queue buffer爲主 if(res == OK) { fireBufferListenersLocked(buffer,/*acquired*/false,/*output*/true); mOutputBufferReturnedSignal.signal(); } returnres;}</hal3.2> |
5 buffer數據真正的被Consumer處理
在queuebuffer的操作時，參考前一博文Android5.1中surface和CpuConsumer下生產者和消費者間的處理框架簡述很容易知道真正的Consumer需要開始工作了，對於preview模式下的當然是由SurfaceFlinger的那套機制去處理。而在Camera2Client和Camera3Device下你還可以看到CPUConsumer的存在，比如：
1 2 3 4 5 6 7 | voidCallbackProcessor::onFrameAvailable(constBufferItem& /*item*/) { Mutex::Autolock l(mInputMutex); if(!mCallbackAvailable) { mCallbackAvailable = true; mCallbackAvailableSignal.signal();//數據callback線程處理 }} |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | bool CallbackProcessor::threadLoop() { status_t res; { Mutex::Autolock l(mInputMutex); while(!mCallbackAvailable) { res = mCallbackAvailableSignal.waitRelative(mInputMutex, kWaitDuration); if(res == TIMED_OUT) returntrue; } mCallbackAvailable = false; } do{ sp<camera2client> client = mClient.promote(); if(client == 0) { res = discardNewCallback(); }else{ res = processNewCallback(client);//callback 處理新的一幀 } }while(res == OK); returntrue;}</camera2client> |
1 2 | l.mRemoteCallback->dataCallback(CAMERA_MSG_PREVIEW_FRAME, callbackHeap->mBuffers[heapIdx], NULL);//處理成API的需求後，回調Preview frame |
6 總結
到這裏，整個preview預覽的視頻流基本介紹完畢了，主要框架雖然負責，但仔細看看也就是buffer的queue與dequeue操作，真正的HAL3的實現纔是最爲複雜的。後續還會簡單介紹下整個take picture的過程，數據的回調處理在後續中還會繼續分析。
下面貼一圖是整個Camera3架構下基於Request和result的處理流序圖：
