AndroidQ 图形系统（4）queueBuffer函数分析

上一篇文章分析了dequeueBuffer函数的过程，本篇接着分析queueBuffer函数，当我们需要绘制图像时，调用dequeueBuffer函数获取到可用的GraphicBuffer之后就可以开始绘制了，最常见的绘制操作就是Android上层View的draw方法了，其他还有OpenGL ES、 mediaserver 视频解码器都可以作为图形数据的来源。

当对GraphicBuffer的绘制操作完成之后就需要调用queueBuffer函数将这块buffer放入BufferQueue队列中并通过回调通知消费者使用这块buffer，图形数据最常见的消耗方就是SurfaceFlinger，该系统服务会消耗当前可见的 Surface（核心是GraphicBuffer），合成到显示部分。
具体实的合成流程是SurfaceFlinger使用 OpenGL和Hardware Composer来合成一组 Surface。
其他 OpenGL ES 应用也可以消耗图像流，例如相机应用会消耗相机预览图像流。非 GL 应用也可以是使用方，例如 ImageReader 类。（引自Android官网）。

我们从Surface.cpp的queueBuffer函数开始看，这个函数比较长我们分为三部分来看。

Surface::queueBuffer

int Surface::queueBuffer(android_native_buffer_t* buffer, int fenceFd) {
	......
    int i = getSlotFromBufferLocked(buffer);
    if (i < 0) {
        if (fenceFd >= 0) {
            close(fenceFd);
        }
        return i;
    }
    if (mSharedBufferSlot == i && mSharedBufferHasBeenQueued) {
        if (fenceFd >= 0) {
            close(fenceFd);
        }
        return OK;
    }


    // Make sure the crop rectangle is entirely inside the buffer.
    Rect crop(Rect::EMPTY_RECT);
    mCrop.intersect(Rect(buffer->width, buffer->height), &crop);

    sp<Fence> fence(fenceFd >= 0 ? new Fence(fenceFd) : Fence::NO_FENCE);
    IGraphicBufferProducer::QueueBufferOutput output;
    IGraphicBufferProducer::QueueBufferInput input(timestamp, isAutoTimestamp,
            static_cast<android_dataspace>(mDataSpace), crop, mScalingMode,
            mTransform ^ mStickyTransform, fence, mStickyTransform,
            mEnableFrameTimestamps);

    // we should send HDR metadata as needed if this becomes a bottleneck
    input.setHdrMetadata(mHdrMetadata);
    ALOGE("dongjiao...mConnectedToCpu = :%d,INVALID_RECT = :%d",mConnectedToCpu,(mDirtyRegion.bounds() == Rect::INVALID_RECT));
    if (mConnectedToCpu || mDirtyRegion.bounds() == Rect::INVALID_RECT) {
        input.setSurfaceDamage(Region::INVALID_REGION);
    } else {
        // Here we do two things:
        // 1) The surface damage was specified using the OpenGL ES convention of
        //    the origin being in the bottom-left corner. Here we flip to the
        //    convention that the rest of the system uses (top-left corner) by
        //    subtracting all top/bottom coordinates from the buffer height.
        // 2) If the buffer is coming in rotated (for example, because the EGL
        //    implementation is reacting to the transform hint coming back from
        //    SurfaceFlinger), the surface damage needs to be rotated the
        //    opposite direction, since it was generated assuming an unrotated
        //    buffer (the app doesn't know that the EGL implementation is
        //    reacting to the transform hint behind its back). The
        //    transformations in the switch statement below apply those
        //    complementary rotations (e.g., if 90 degrees, rotate 270 degrees).

        int width = buffer->width;
        int height = buffer->height;
        bool rotated90 = (mTransform ^ mStickyTransform) &
                NATIVE_WINDOW_TRANSFORM_ROT_90;
        if (rotated90) {
            std::swap(width, height);
        }

        Region flippedRegion;
        for (auto rect : mDirtyRegion) {
            int left = rect.left;
            int right = rect.right;
            int top = height - rect.bottom; // Flip from OpenGL convention
            int bottom = height - rect.top; // Flip from OpenGL convention
            switch (mTransform ^ mStickyTransform) {
                case NATIVE_WINDOW_TRANSFORM_ROT_90: {
                    // Rotate 270 degrees
                    Rect flippedRect{top, width - right, bottom, width - left};
                    flippedRegion.orSelf(flippedRect);
                    break;
                }
                case NATIVE_WINDOW_TRANSFORM_ROT_180: {
                    // Rotate 180 degrees
                    Rect flippedRect{width - right, height - bottom,
                            width - left, height - top};
                    flippedRegion.orSelf(flippedRect);
                    break;
                }
                case NATIVE_WINDOW_TRANSFORM_ROT_270: {
                    // Rotate 90 degrees
                    Rect flippedRect{height - bottom, left,
                            height - top, right};
                    flippedRegion.orSelf(flippedRect);
                    break;
                }
                default: {
                    Rect flippedRect{left, top, right, bottom};
                    flippedRegion.orSelf(flippedRect);
                    break;
                }
            }
        }

        input.setSurfaceDamage(flippedRegion);
    }
    .....
  }

首先第一部分，queueBuffer的第一个参数buffer就是当前绘制完成的GraphicBuffer，第二个参数fenceFd是一种用作同步的工具。

1. 首先来看函数getSlotFromBufferLocked：

int Surface::getSlotFromBufferLocked(
        android_native_buffer_t* buffer) const {
    for (int i = 0; i < NUM_BUFFER_SLOTS; i++) {
        if (mSlots[i].buffer != nullptr &&
                mSlots[i].buffer->handle == buffer->handle) {
            return i;
        }
    }
    ALOGE("getSlotFromBufferLocked: unknown buffer: %p", buffer->handle);
    return BAD_VALUE;
}

这个函数很简单，就是找到buffer在mSlots中的下标，mSlots为所有BufferSlot集合，得到下标之后进行一些合法性判断，如果是mSharedBufferSlot并且mSharedBufferHasBeenQueued代码当前使用的是共享buffer模式则直接返回OK，不太了解共享buffer模式，就跳过了。

2. 接着定义一个空的Rect crop矩形，mCrop也是一个Rect对象，用于buffer的裁剪，我们看它的intersect函数：

bool Rect::intersect(const Rect& with, Rect* result) const {
    result->left = max(left, with.left);
    result->top = max(top, with.top);
    result->right = min(right, with.right);
    result->bottom = min(bottom, with.bottom);
    return !(result->isEmpty());
}

这个函数用于获取两个矩形相交的部分，并将相交部分赋值给result，再看看调用intersect传递的参数：
mCrop.intersect(Rect(buffer->width, buffer->height), &crop);
其实就是将mCrop和Rect(buffer->width, buffer->height)相交部分赋值给crop。

3. 接着创建了两个QueueBufferOutput对象，input作为输入参数传递到BufferQueueProducer，input里面封装的这些信息很多都是外部应用程序设置的，如mDataSpace，mScalingMode，mStickyTransform这些都会应用到最终的显示，而output会作为BufferQueueProducer的返回值。

4. 接着有一个判断，mConnectedToCpu的含义是：CPU生产者(在CPU上运行并生成图形数据的代码，如上层的2Dcanvas绘图)连接到BufferQueue，可以通过函数native_window_api_connect传入参数NATIVE_WINDOW_API_CPU设置CPU生产者，但现在所用的图形数据更多来自OpenGL ES、 mediaserver 视频解码器和camera API，对应连接的API为NATIVE_WINDOW_API_EGL，NATIVE_WINDOW_API_MEDIA，
   NATIVE_WINDOW_API_CAMERA，所以mConnectedToCpu大多数为false。

mDirtyRegion：脏区域，需要更新图形数据的区域，如果没有需要更新的脏区域则设置无效脏区域。
否则就根据buffer宽高以及旋转角度按一定规则创建flippedRegion，并设置给input传递到BufferQueueProducer。

setSurfaceDamage设置脏区域，对于非脏区域，会直接从之前的buffer中复制，仅仅更新指定的脏区域部分，提高效率。

我们可以看到所有的图形数据都被封装在了input中。

Surface::queueBuffer第一部分分析完了，接着看第二部分：

int Surface::queueBuffer(android_native_buffer_t* buffer, int fenceFd) {
	......
		status_t err = mGraphicBufferProducer->queueBuffer(i, input, &output);
	......
	 return err; 
	}

这部分就是本篇的核心，调用生产者queueBuffer函数，传递的依然是BufferSlot下标，到了BufferQueueProducer中通过下标就能找到绑定的GraphicBuffer。

BufferQueueProducer::queueBuffer

status_t BufferQueueProducer::queueBuffer(int slot,
        const QueueBufferInput &input, QueueBufferOutput *output) {
    ATRACE_CALL();
    ATRACE_BUFFER_INDEX(slot);

    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();

    if (acquireFence == nullptr) {
        BQ_LOGE("queueBuffer: fence is NULL");
        return BAD_VALUE;
    }

    auto acquireFenceTime = std::make_shared<FenceTime>(acquireFence);

    switch (scalingMode) {
        case NATIVE_WINDOW_SCALING_MODE_FREEZE:
        case NATIVE_WINDOW_SCALING_MODE_SCALE_TO_WINDOW:
        case NATIVE_WINDOW_SCALING_MODE_SCALE_CROP:
        case NATIVE_WINDOW_SCALING_MODE_NO_SCALE_CROP:
            break;
        default:
            BQ_LOGE("queueBuffer: unknown scaling mode %d", scalingMode);
            return BAD_VALUE;
    }

    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;
        }

        // If shared buffer mode has just been enabled, cache the slot of the
        // first buffer that is queued and mark it as the shared buffer.
        if (mCore->mSharedBufferMode && mCore->mSharedBufferSlot ==
                BufferQueueCore::INVALID_BUFFER_SLOT) {
            mCore->mSharedBufferSlot = slot;
            mSlots[slot].mBufferState.mShared = true;
        }

        BQ_LOGV("queueBuffer: slot=%d/%" PRIu64 " time=%" PRIu64 " dataSpace=%d"
                " validHdrMetadataTypes=0x%x crop=[%d,%d,%d,%d] transform=%#x scale=%s",
                slot, mCore->mFrameCounter + 1, requestedPresentTimestamp, dataSpace,
                hdrMetadata.validTypes, crop.left, crop.top, crop.right, crop.bottom,
                transform,
                BufferItem::scalingModeName(static_cast<uint32_t>(scalingMode)));

        const sp<GraphicBuffer>& graphicBuffer(mSlots[slot].mGraphicBuffer);
        Rect bufferRect(graphicBuffer->getWidth(), graphicBuffer->getHeight());
        Rect croppedRect(Rect::EMPTY_RECT);
        crop.intersect(bufferRect, &croppedRect);
        if (croppedRect != crop) {
            BQ_LOGE("queueBuffer: crop rect is not contained within the "
                    "buffer in slot %d", slot);
            return BAD_VALUE;
        }

        // Override UNKNOWN dataspace with consumer default
        if (dataSpace == HAL_DATASPACE_UNKNOWN) {
            dataSpace = mCore->mDefaultBufferDataSpace;
        }

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

        // 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;

        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;

        mStickyTransform = stickyTransform;

        // Cache the shared buffer data so that the BufferItem can be recreated.
        if (mCore->mSharedBufferMode) {
            mCore->mSharedBufferCache.crop = crop;
            mCore->mSharedBufferCache.transform = transform;
            mCore->mSharedBufferCache.scalingMode = static_cast<uint32_t>(
                    scalingMode);
            mCore->mSharedBufferCache.dataspace = dataSpace;
        }
        output->bufferReplaced = false;
        if (mCore->mQueue.empty()) {
            // When the queue is empty, we can ignore mDequeueBufferCannotBlock
            // and simply queue this buffer
            mCore->mQueue.push_back(item);
            frameAvailableListener = mCore->mConsumerListener;
        } else {
            // When the queue is not empty, we need to look at the last buffer
            // in the queue to see if we need to replace it
            const BufferItem& last = mCore->mQueue.itemAt(
                    mCore->mQueue.size() - 1);
            if (last.mIsDroppable) {

                if (!last.mIsStale) {
                    mSlots[last.mSlot].mBufferState.freeQueued();

                    // After leaving shared buffer mode, the shared buffer will
                    // still be around. Mark it as no longer shared if this
                    // operation causes it to be free.
                    if (!mCore->mSharedBufferMode &&
                            mSlots[last.mSlot].mBufferState.isFree()) {
                        mSlots[last.mSlot].mBufferState.mShared = false;
                    }
                    // Don't put the shared buffer on the free list.
                    if (!mSlots[last.mSlot].mBufferState.isShared()) {
                        mCore->mActiveBuffers.erase(last.mSlot);
                        mCore->mFreeBuffers.push_back(last.mSlot);
                        output->bufferReplaced = true;
                    }
                }

                // Make sure to merge the damage rect from the frame we're about
                // to drop into the new frame's damage rect.
                if (last.mSurfaceDamage.bounds() == Rect::INVALID_RECT ||
                    item.mSurfaceDamage.bounds() == Rect::INVALID_RECT) {
                    item.mSurfaceDamage = Region::INVALID_REGION;
                } else {
                    item.mSurfaceDamage |= last.mSurfaceDamage;
                }

                // Overwrite the droppable buffer with the incoming one
                mCore->mQueue.editItemAt(mCore->mQueue.size() - 1) = item;
                frameReplacedListener = mCore->mConsumerListener;
            } else {
                mCore->mQueue.push_back(item);
                frameAvailableListener = mCore->mConsumerListener;
            }
        }
        ......
        }

这个函数也比较多，同样分部分来看，首先看第一部分：

1. 定义了一堆变量，用来保存Surface传递过来的input里面封装的buffer信息。
2. 接着需要检测scalingMode，缩放模式，当buffer内容和屏幕不成比例时采用什么方式处理，scalingMode可以通过函数native_window_set_scaling_mode进行设置，如果没有设置直接返回BAD_VALUE。
3. 又进行一堆检测： BufferQueue是否被弃用，buffer是否连接到BufferQueue，BufferSlot下标是否合法，当前这个BufferSlot状态是否是DEQUEUE，mRequestBufferCalled是否为true（即此BufferSlot是否调用了requestBuffer函数）。
4. 接着又创建了三个对象，graphicBuffer（此次queue的具体buffer），bufferRect（根据当前graphicBuffer创建的矩形区域），croppedRect（裁剪区域，值为crop和bufferRect相交部分，其实这里的crop.intersect(bufferRect, &croppedRect)和前面Surface里面mCrop.intersect(Rect(buffer->width, buffer->height), &crop)会得到同样的裁剪区域，只要裁剪的部分包含在当前buffer之内）。
5. 接着将当前BufferSlot状态修改为QUEUE，并修改一些状态值。
6. 将BufferSlot以及GraphicBuffer的信息进一步封装到BufferItem，而BufferItem又存储在BufferQueueCore的mQueue中，所以一般我们说的生产者-消费者模型中的buffer队列，更具体的话就是mQueue。如果mQueue为空就直接将BufferItem添加进去，并将BufferQueueCore的mConsumerListener给到frameAvailableListener，从AndroidQ 图形系统（2）生产者-消费者模型知道，mConsumerListener是在ConsumerBase的构造函数中传递的BufferQueue::ProxyConsumerListener。
   对于mQueue非空的情况，首先取到mQueue尾部的BufferItem，根据mIsDroppable值查看是否需要丢弃，什么情况下需要丢弃？有很多种情况，常见就是同步模式即mAsyncMode为true，至于需要丢弃的情况怎么处理的我这里不去看了，对于不需要丢弃的情况总是将BufferItem放入mQueue的尾部。
   此部分已经分析完了，主要做的事情就是上面这六点。

接着看剩下的部分：

status_t BufferQueueProducer::queueBuffer(int slot,
        const QueueBufferInput &input, QueueBufferOutput *output) {
	......
	    mCore->mBufferHasBeenQueued = true;
        mCore->mDequeueCondition.notify_all();
        mCore->mLastQueuedSlot = slot;

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

        ATRACE_INT(mCore->mConsumerName.string(),
                static_cast<int32_t>(mCore->mQueue.size()));
        mCore->mOccupancyTracker.registerOccupancyChange(mCore->mQueue.size());

        // Take a ticket for the callback functions
        callbackTicket = mNextCallbackTicket++;

        VALIDATE_CONSISTENCY();
    } // Autolock scope

    // It is okay not to clear the GraphicBuffer when the consumer is SurfaceFlinger because
    // it is guaranteed that the BufferQueue is inside SurfaceFlinger's process and
    // there will be no Binder call
    if (!mConsumerIsSurfaceFlinger) {
        item.mGraphicBuffer.clear();
    }

    // Call back without the main BufferQueue lock held, but with the callback
    // lock held so we can ensure that callbacks occur in order

    int connectedApi;
    sp<Fence> lastQueuedFence;

    { // scope for the lock
        std::unique_lock<std::mutex> lock(mCallbackMutex);
        while (callbackTicket != mCurrentCallbackTicket) {
            mCallbackCondition.wait(lock);
        }

        if (frameAvailableListener != nullptr) {
            frameAvailableListener->onFrameAvailable(item);
        } else if (frameReplacedListener != nullptr) {
            frameReplacedListener->onFrameReplaced(item);
        }

        connectedApi = mCore->mConnectedApi;
        lastQueuedFence = std::move(mLastQueueBufferFence);

        mLastQueueBufferFence = std::move(acquireFence);
        mLastQueuedCrop = item.mCrop;
        mLastQueuedTransform = item.mTransform;

        ++mCurrentCallbackTicket;
        mCallbackCondition.notify_all();
    }

    // Update and get FrameEventHistory.
    nsecs_t postedTime = systemTime(SYSTEM_TIME_MONOTONIC);
    NewFrameEventsEntry newFrameEventsEntry = {
        currentFrameNumber,
        postedTime,
        requestedPresentTimestamp,
        std::move(acquireFenceTime)
    };
    addAndGetFrameTimestamps(&newFrameEventsEntry,
            getFrameTimestamps ? &output->frameTimestamps : nullptr);

    // Wait without lock held
    if (connectedApi == NATIVE_WINDOW_API_EGL) {
        // Waiting here allows for two full buffers to be queued but not a
        // third. In the event that frames take varying time, this makes a
        // small trade-off in favor of latency rather than throughput.
        lastQueuedFence->waitForever("Throttling EGL Production");
    }
    return NO_ERROR;
}

这部分主要做了如下事情：

1. mBufferHasBeenQueued一个状态值，代表buffer已经queued，mDequeueCondition是C++条件变量用作等待/唤醒，这里调用notify_all会唤醒调用了wait的线程，即在dequeueBuffer函数中因为tooManyBuffers而陷入等待状态的线程，当一块buffer被queued之后就可以继续dequeue了，output最终会返回给Surface进程，mConsumerIsSurfaceFlinger表示消费者是否SurfaceFlinger进程，默认值为true。
2. frameAvailableListener不为空则调用onFrameAvailable回调函数通知有buffer可以进行消费，这个函数会经过一系列调用，最终的实现类是BufferQueueLayer（一种最常用的Layer），最后如果连接BufferQueue的方式为NATIVE_WINDOW_API_EGL，会通过Fence陷入等待，这里会一直等，知道上一帧绘制完成，图形系统的生产消费非常依赖Fence同步机制，Android引入三重缓冲之后，GPU，CPU，显示硬件可以各持有一个buffer工作，例如当CPU持有的buffer数据已经处理完了，但此时GUP，显示硬件还在使用buffer，CPU并不能立马申请下一个buffer，需要等待，我这里对Fence不了解，所以文中出现的和Fence同步相关的代码就略过了。

到此queueBuffer函数已经分析完毕，代码看着多，逻辑比较简单，就是将Surface进程数据传过来，然后封装成BufferItem，放入BufferQueueCore的mQueue中，再通过frameAvailableListener通知消费者去消费。

接着回到Surface看剩下的代码，

int Surface::queueBuffer(android_native_buffer_t* buffer, int fenceFd) {
		......
		
		if (err != OK)  {
        	ALOGE("queueBuffer: error queuing buffer to SurfaceTexture, %d", err);
   		 }

    if (mEnableFrameTimestamps) {
        mFrameEventHistory->applyDelta(output.frameTimestamps);
        // Update timestamps with the local acquire fence.
        // The consumer doesn't send it back to prevent us from having two
        // file descriptors of the same fence.
        mFrameEventHistory->updateAcquireFence(mNextFrameNumber,
                std::make_shared<FenceTime>(fence));

        // Cache timestamps of signaled fences so we can close their file
        // descriptors.
        mFrameEventHistory->updateSignalTimes();
    }

    mLastFrameNumber = mNextFrameNumber;

    mDefaultWidth = output.width;
    mDefaultHeight = output.height;
    mNextFrameNumber = output.nextFrameNumber;

    // Ignore transform hint if sticky transform is set or transform to display inverse flag is
    // set.
    if (mStickyTransform == 0 && !transformToDisplayInverse()) {
        mTransformHint = output.transformHint;
    }

    mConsumerRunningBehind = (output.numPendingBuffers >= 2);

    if (!mConnectedToCpu) {
        // Clear surface damage back to full-buffer
        mDirtyRegion = Region::INVALID_REGION;
    }

    if (mSharedBufferMode && mAutoRefresh && mSharedBufferSlot == i) {
        mSharedBufferHasBeenQueued = true;
    }

    mQueueBufferCondition.broadcast();

    if (CC_UNLIKELY(atrace_is_tag_enabled(ATRACE_TAG_GRAPHICS))) {
        static FenceMonitor gpuCompletionThread("GPU completion");
        gpuCompletionThread.queueFence(fence);
    }

    return err;

这后面部分其实没什么好说的了，会更新一些变量，清空脏区域，通过条件变量mQueueBufferCondition唤醒等待下一帧的线程，处理一下Fence。