// queueBuffer returns a filled buffer to the BufferQueue.
//
// Additional data is provided in the QueueBufferInput struct.  Notably,
// a timestamp must be provided for the buffer. The timestamp is in
// nanoseconds, and must be monotonically increasing. Its other semantics
// (zero point, etc) are producer-specific and should be documented by the
// producer.
//
// The caller may provide a fence that signals when all rendering
// operations have completed.  Alternatively, NO_FENCE may be used,
// indicating that the buffer is ready immediately.
//
// Some values are returned in the output struct: the current settings
// for default width and height, the current transform hint, and the
// number of queued buffers.
status_t BufferQueueProducer::queueBuffer(int slot,
        const QueueBufferInput &input, QueueBufferOutput *output) {

• queueBuffer() 把已填充的 buffer 返还给 BufferQueue。
• 额外信息通过 QueueBufferInput 提供。生产者可以提供一个 fence 来通知绘制完成。NO_FENCE 表示可以立即被消费。
• 返回信息信息通过结构体 QueueBufferOutput。

    int64_t requestedPresentTimestamp;
    bool isAutoTimestamp;
    android_dataspace dataSpace;
    Rect crop(Rect::EMPTY_RECT);
    int scalingMode;
    uint32_t transform;
    uint32_t stickyTransform;
    sp<Fence> acquireFence;
    bool getFrameTimestamps = false;
    input.deflate(&requestedPresentTimestamp, &isAutoTimestamp, &dataSpace,
            &crop, &scalingMode, &transform, &acquireFence, &stickyTransform,
            &getFrameTimestamps);
    const Region& surfaceDamage = input.getSurfaceDamage();
    const HdrMetadata& hdrMetadata = input.getHdrMetadata();

• 从 input 读取信息。

    sp<IConsumerListener> frameAvailableListener;
    sp<IConsumerListener> frameReplacedListener;
    int callbackTicket = 0;
    uint64_t currentFrameNumber = 0;
    BufferItem item;
    { // Autolock scope
        std::lock_guard<std::mutex> lock(mCore->mMutex);

        if (mCore->mIsAbandoned) {
            BQ_LOGE("queueBuffer: BufferQueue has been abandoned");
            return NO_INIT;
        }

        if (mCore->mConnectedApi == BufferQueueCore::NO_CONNECTED_API) {
            BQ_LOGE("queueBuffer: BufferQueue has no connected producer");
            return NO_INIT;
        }

        if (slot < 0 || slot >= BufferQueueDefs::NUM_BUFFER_SLOTS) {
            BQ_LOGE("queueBuffer: slot index %d out of range [0, %d)",
                    slot, BufferQueueDefs::NUM_BUFFER_SLOTS);
            return BAD_VALUE;
        } else if (!mSlots[slot].mBufferState.isDequeued()) {
            BQ_LOGE("queueBuffer: slot %d is not owned by the producer "
                    "(state = %s)", slot, mSlots[slot].mBufferState.string());
            return BAD_VALUE;
        } else if (!mSlots[slot].mRequestBufferCalled) {
            BQ_LOGE("queueBuffer: slot %d was queued without requesting "
                    "a buffer", slot);
            return BAD_VALUE;
        }

• 检查一些状态。
  • isDequeued() 返回 false，说明该 slot 所有权不在生产者，返回 BAD_VALUE。
  • 在 BufferSlot 中描述了mRequestBufferCalled 是 false 时返回 BAD_VALUE，

        mSlots[slot].mFence = acquireFence;
        mSlots[slot].mBufferState.queue();

• 设置 mFence。调用 queue() 变更 BufferState 状态为 QUEUED。

        // Increment the frame counter and store a local version of it
        // for use outside the lock on mCore->mMutex.
        ++mCore->mFrameCounter;
        currentFrameNumber = mCore->mFrameCounter;
        mSlots[slot].mFrameNumber = currentFrameNumber;

• 递增 BufferQueueCore::mFrameCount，然后更新 BufferSlot 的 mFrameNumber。

        item.mAcquireCalled = mSlots[slot].mAcquireCalled;
        item.mGraphicBuffer = mSlots[slot].mGraphicBuffer;
        item.mCrop = crop;
        item.mTransform = transform &
                ~static_cast<uint32_t>(NATIVE_WINDOW_TRANSFORM_INVERSE_DISPLAY);
        item.mTransformToDisplayInverse =
                (transform & NATIVE_WINDOW_TRANSFORM_INVERSE_DISPLAY) != 0;
        item.mScalingMode = static_cast<uint32_t>(scalingMode);
        item.mTimestamp = requestedPresentTimestamp;
        item.mIsAutoTimestamp = isAutoTimestamp;
        item.mDataSpace = dataSpace;
        item.mHdrMetadata = hdrMetadata;
        item.mFrameNumber = currentFrameNumber;
        item.mSlot = slot;
        item.mFence = acquireFence;
        item.mFenceTime = acquireFenceTime;
        item.mIsDroppable = mCore->mAsyncMode ||
                (mConsumerIsSurfaceFlinger && mCore->mQueueBufferCanDrop) ||
                (mCore->mLegacyBufferDrop && mCore->mQueueBufferCanDrop) ||
                (mCore->mSharedBufferMode && mCore->mSharedBufferSlot == slot);
        item.mSurfaceDamage = surfaceDamage;
        item.mQueuedBuffer = true;
        item.mAutoRefresh = mCore->mSharedBufferMode && mCore->mAutoRefresh;
        item.mApi = mCore->mConnectedApi;

设置 BufferItem 的成员。

• mAcquireCalled 和 mGraphicBuffer 的来源是 BufferSlot。