Android 12(S) 圖像顯示系統 - Surface 一點補充知識（十二）

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必讀：

Android 12(S) 圖像顯示系統 - 開篇

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一、前言

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因為個人工作主要是Android多媒體播放的內容，在工作中查看源碼或設計程序經常會遇到調用API：

static inline int native_window_api_connect(struct ANativeWindow* window, int api)
static inline int native_window_api_disconnect(struct ANativeWindow* window, int api)

所以也一直好奇這兩個方法都做了什么事情？這篇文章就來一探究竟。

 

二、native_window_api_connect 解析

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Android系統中，開始播放視頻並設置Surface后，都會做一次 connectToSurface 的操作，比如MediaCodec中，在初始化階段setSurface后就會調用方法：

status_t MediaCodec::connectToSurface(const sp<Surface> &surface) {
    ...
    err = nativeWindowConnect(surface.get(), "connectToSurface");
    ...
}

這里就是去調用了 /frameworks/av/media/libstagefright/SurfaceUtils.cpp  中的方法：

status_t nativeWindowConnect(ANativeWindow *surface, const char *reason) {
    ALOGD("connecting to surface %p, reason %s", surface, reason);

    status_t err = native_window_api_connect(surface, NATIVE_WINDOW_API_MEDIA);
    ALOGE_IF(err != OK, "Failed to connect to surface %p, err %d", surface, err);

    return err;
}

是不是看到了 native_window_api_connect ，其中參數 NATIVE_WINDOW_API_MEDIA 表明 video decoder會作為生產者來生成buffer數據。

再接着往下走，看看到底做了什么？

大體的調用流程如下：

 /frameworks/native/libs/gui/Surface.cpp

 /frameworks/native/libs/gui/BufferQueueProducer.cpp

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>>> static inline int native_window_api_connect(struct ANativeWindow* window, int api)

>>> int Surface::hook_perform(ANativeWindow* window, int operation, ...)

>>> int Surface::perform(int operation, va_list args)

>>> int Surface::dispatchConnect(va_list args)

>>> int Surface::connect(int api)

>>> int Surface::connect(int api, const sp<IProducerListener>& listener)

>>> int Surface::connect(int api, const sp<IProducerListener>& listener, bool reportBufferRemoval)

>>> status_t BufferQueueProducer::connect(const sp<IProducerListener>& listener,
                int api, bool producerControlledByApp, QueueBufferOutput *output) 

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最終進入到了BufferQueueProducer::connect函數中，看起來這里應該就是做具體事情的地方了

老規矩，看源碼：

status_t BufferQueueProducer::connect(const sp<IProducerListener>& listener,
        int api, bool producerControlledByApp, QueueBufferOutput *output) {
    ATRACE_CALL();
    std::lock_guard<std::mutex> lock(mCore->mMutex);
    mConsumerName = mCore->mConsumerName; // 消費者名字
    BQ_LOGV("connect: api=%d producerControlledByApp=%s", api,
            producerControlledByApp ? "true" : "false");
    // 對一些條件進行判斷，必要時直接返回return
    if (mCore->mIsAbandoned) {
        BQ_LOGE("connect: BufferQueue has been abandoned");
        return NO_INIT;
    }

    if (mCore->mConsumerListener == nullptr) {
        BQ_LOGE("connect: BufferQueue has no consumer");
        return NO_INIT;
    }

    if (output == nullptr) {
        BQ_LOGE("connect: output was NULL");
        return BAD_VALUE;
    }

    if (mCore->mConnectedApi != BufferQueueCore::NO_CONNECTED_API) {
        BQ_LOGE("connect: already connected (cur=%d req=%d)",
                mCore->mConnectedApi, api);
        return BAD_VALUE;
    }

    int delta = mCore->getMaxBufferCountLocked(mCore->mAsyncMode,
            mDequeueTimeout < 0 ?
            mCore->mConsumerControlledByApp && producerControlledByApp : false,
            mCore->mMaxBufferCount) -
            mCore->getMaxBufferCountLocked();
    if (!mCore->adjustAvailableSlotsLocked(delta)) {
        BQ_LOGE("connect: BufferQueue failed to adjust the number of available "
                "slots. Delta = %d", delta);
        return BAD_VALUE;
    }

    int status = NO_ERROR;
    switch (api) {
        case NATIVE_WINDOW_API_EGL:
        case NATIVE_WINDOW_API_CPU:
        case NATIVE_WINDOW_API_MEDIA:
        case NATIVE_WINDOW_API_CAMERA:
            mCore->mConnectedApi = api;

            output->width = mCore->mDefaultWidth;
            output->height = mCore->mDefaultHeight;
            output->transformHint = mCore->mTransformHintInUse = mCore->mTransformHint;
            output->numPendingBuffers =
                    static_cast<uint32_t>(mCore->mQueue.size());
            output->nextFrameNumber = mCore->mFrameCounter + 1;
            output->bufferReplaced = false;
            output->maxBufferCount = mCore->mMaxBufferCount;

            if (listener != nullptr) {
                // Set up a death notification so that we can disconnect
                // automatically if the remote producer dies
#ifndef NO_BINDER
                if (IInterface::asBinder(listener)->remoteBinder() != nullptr) {
                    status = IInterface::asBinder(listener)->linkToDeath(
                            static_cast<IBinder::DeathRecipient*>(this));
                    if (status != NO_ERROR) {
                        BQ_LOGE("connect: linkToDeath failed: %s (%d)",
                                strerror(-status), status);
                    }
                    mCore->mLinkedToDeath = listener;
                }
#endif
                mCore->mConnectedProducerListener = listener; // 設置producer listener
                mCore->mBufferReleasedCbEnabled = listener->needsReleaseNotify();
            }
            break;
        default:
            BQ_LOGE("connect: unknown API %d", api);
            status = BAD_VALUE;
            break;
    }
    mCore->mConnectedPid = BufferQueueThreadState::getCallingPid();
    mCore->mBufferHasBeenQueued = false;
    mCore->mDequeueBufferCannotBlock = false;
    mCore->mQueueBufferCanDrop = false;
    mCore->mLegacyBufferDrop = true;
    if (mCore->mConsumerControlledByApp && producerControlledByApp) {
        mCore->mDequeueBufferCannotBlock = mDequeueTimeout < 0;
        mCore->mQueueBufferCanDrop = mDequeueTimeout <= 0;
    }

    mCore->mAllowAllocation = true; // 允許分配 graphic buffer
    VALIDATE_CONSISTENCY();
    return status;
}

我才疏學淺，按我理解，就是完成了一些初始化的操作，貌似也沒啥了，這之后應該produder就可以 dequeue buffer 了

另外一點，這里有設置producer listener，之前文章中也講過，貌似也沒啥作用(也許我錯了)

    mCore->mConnectedProducerListener = listener;
    mCore->mBufferReleasedCbEnabled = listener->needsReleaseNotify();

三、native_window_api_disconnect 解析

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disconnect的調用流程和connect的流程類似。

 

 

 

 

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