Android下SF合成流程重学习之onMessageInvalidate

引言

虽然看了很多关于Android Graphics图形栈的文章和博客，但是都没有形成自己的知识点。每次学习了，仅仅是学习了而已，没有形成自己的知识体系，这次趁着有时间，这次必须把这个事情干透彻了！

本篇引用的代码，主要是Android R的。

并且Android下Graphics图形栈牵涉的点，太多了，这篇博客我们着重分析SF合成流程重学习之onMessageInvalidate的处理流程！

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SurfaceFlinger layer之间的对应关系

先用一张图来看下各个部分之间layer的对应关系。接下来会根据这个图来解析是如何进行转换的,如下:

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一. SF处理事务和处理Buffer

在SF的onMessageInvalidate主要是用来，处理事物和处理相关Buffer的，我们在下面的博客中详细分析！

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1.1 onMessageInvalidate

文件： frameworks/native/services/surfaceflinger/Surfaceflinger.cpp

void SurfaceFlinger::onMessageInvalidate(nsecs_t expectedVSyncTime) {
    ATRACE_CALL();
    const nsecs_t frameStart = systemTime();
    // expectedVSyncTime 是vsync回调带过来的时间戳，通过nextAnticipatedVSyncTimeFrom 计算得到
    if (expectedVSyncTime >= frameStart) {
        mExpectedPresentTime = expectedVSyncTime;
    } else {
        mExpectedPresentTime = mScheduler->getDispSyncExpectedPresentTime(frameStart);
    }
     // 存储上一帧的expectedVSyncTime
    const nsecs_t lastScheduledPresentTime = mScheduledPresentTime;
    mScheduledPresentTime = expectedVSyncTime;

   ...
     // 根据上一帧的present fence判断当前这一帧是否pending
    const TracedOrdinal<bool> framePending = {"PrevFramePending",
                                              previousFramePending(graceTimeForPresentFenceMs)};

    // 若framePending  或者 上一帧present fence释放的时间  > 上一帧vsync计算的时间戳 + vsync周期的一半
    // 则当前帧要丢掉
    DisplayStatInfo stats;
    mScheduler->getDisplayStatInfo(&stats);
    const nsecs_t frameMissedSlop = stats.vsyncPeriod / 2;
    const nsecs_t previousPresentTime = previousFramePresentTime();
    const TracedOrdinal<bool> frameMissed = {"PrevFrameMissed",
                                             framePending ||
                                                     (previousPresentTime >= 0 &&
                                                      (lastScheduledPresentTime <
                                                       previousPresentTime - frameMissedSlop))};
    // 根据合成类型判断丢帧的类型
    const TracedOrdinal<bool> hwcFrameMissed = {"PrevHwcFrameMissed",
                                                mHadDeviceComposition && frameMissed};
    const TracedOrdinal<bool> gpuFrameMissed = {"PrevGpuFrameMissed",
                                                mHadClientComposition && frameMissed};
   
    ...
    // 这部分涉及帧率切换，先是通过performSetActiveConfig 将新的帧率给到hwc，然后下一帧再更新sf这边的状态
    if (mSetActiveConfigPending) {
        if (framePending) {
            mEventQueue->invalidate();
            return;
        }

        // We received the present fence from the HWC, so we assume it successfully updated
        // the config, hence we update SF.
        mSetActiveConfigPending = false;
        ON_MAIN_THREAD(setActiveConfigInternal());
    }
}
  //  mPropagateBackpressure 可以通过adb shell setprop debug.sf.disable_backpressure x 来控制,表示系统是否允许丢帧
  //  若允许丢帧则skip这次刷帧
  if (framePending && mPropagateBackpressure) {
        if ((hwcFrameMissed && !gpuFrameMissed) || mPropagateBackpressureClientComposition) {
            signalLayerUpdate();
            return;
        }
    }
 ....
   bool refreshNeeded;
    {
        ConditionalLockGuard<std::mutex> lock(mTracingLock, mTracingEnabled);
        // 主要的逻辑在这两个函数，简单理解为处理layer或者display的事务和layer的buffer
        refreshNeeded = handleMessageTransaction();
        refreshNeeded |= handleMessageInvalidate();
       ...
    }
    // 帧率切换，SurfaceFlinger主线程执行
   ON_MAIN_THREAD(performSetActiveConfig());
   ...
   // 若layer的事务有变化或者有新的buffer，则触发refresh
   signalRefresh();
}

上述onMessageInvalidate概括来说，其主要处理的事情如下:

• 判断当前帧是否丢掉
• handleMessageTransaction 处理layer或者display事务
• handleMessageInvalidate 处理应用queue过来的Buffer
• 帧率切换
• 触发刷新流程

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1.2 handleMessageTransaction

文件： frameworks/native/services/surfaceflinger/Surfaceflinger.cpp

bool SurfaceFlinger::handleMessageTransaction() {
    ATRACE_CALL();
    // 获取当前的mTransactionFlags，mTransactionFlags 由setTransactionFlags 赋值，比如CreateLayer时会给mTransactionFlags 赋值eTransactionNeeded
    // createDisplay 时会给mTransactionFlags 赋值 eDisplayTransactionNeeded
    uint32_t transactionFlags = peekTransactionFlags();
    // flushTransactionQueues 会消费transactionQueue，transactionQueue 是上层通过SurfaceComposerClient 设的，然后再通过binder设置给sf这边
    // setDisplayStateLocked： 处理display的事务
    // setClientStateLocked： 处理layer的事务
    // 这两部分事务都存放在surfaceflinger的mCurrentState 里面
    bool flushedATransaction = flushTransactionQueues();
    // 有新的事务则要执行handleTransaction
    bool runHandleTransaction =
            (transactionFlags && (transactionFlags != eTransactionFlushNeeded)) ||
            flushedATransaction ||
            mForceTraversal;
    // 处理layer和display的事务
    if (runHandleTransaction) {
        handleTransaction(eTransactionMask);
    } else {
        getTransactionFlags(eTransactionFlushNeeded);
    }

    if (transactionFlushNeeded()) {
        setTransactionFlags(eTransactionFlushNeeded);
    }
 
    return runHandleTransaction;
}

//来看下display和layer有哪些事务处理

文件： frameworks/native/services/surfaceflinger/Surfaceflinger.cpp

// display的事务，包括display Surface, layerStack , Projection , viewport, Size发生变化时附上eDisplayTransactionNeeded 这个flags
uint32_t SurfaceFlinger::setDisplayStateLocked(const DisplayState& s) {
    const ssize_t index = mCurrentState.displays.indexOfKey(s.token);
    if (index < 0) return 0;

    uint32_t flags = 0;
    DisplayDeviceState& state = mCurrentState.displays.editValueAt(index);

    const uint32_t what = s.what;
    if (what & DisplayState::eSurfaceChanged) {
        if (IInterface::asBinder(state.surface) != IInterface::asBinder(s.surface)) {
            state.surface = s.surface;
            flags |= eDisplayTransactionNeeded;
        }
    }
    if (what & DisplayState::eLayerStackChanged) {
        if (state.layerStack != s.layerStack) {
            state.layerStack = s.layerStack;
            flags |= eDisplayTransactionNeeded;
        }
    }
    if (what & DisplayState::eDisplayProjectionChanged) {
        if (state.orientation != s.orientation) {
            state.orientation = s.orientation;
            flags |= eDisplayTransactionNeeded;
        }
        if (state.frame != s.frame) {
            state.frame = s.frame;
            flags |= eDisplayTransactionNeeded;
        }
        if (state.viewport != s.viewport) {
            state.viewport = s.viewport;
            flags |= eDisplayTransactionNeeded;
        }
    }
    if (what & DisplayState::eDisplaySizeChanged) {
        if (state.width != s.width) {
            state.width = s.width;
            flags |= eDisplayTransactionNeeded;
        }
        if (state.height != s.height) {
            state.height = s.height;
            flags |= eDisplayTransactionNeeded;
        }
    }

    return flags;
}

文件： frameworks/native/services/surfaceflinger/Surfaceflinger.cpp

// layer的事务，包括ePositionChanged, eLayerChanged, eAlphaChanged 等等，跟上层的surface设置一样，同样的事务同步给layer
uint32_t SurfaceFlinger::setClientStateLocked(
        const ComposerState& composerState, int64_t desiredPresentTime, int64_t postTime,
        bool privileged,
        std::unordered_set<ListenerCallbacks, ListenerCallbacksHash>& listenerCallbacks) {
...  
   sp<Layer> layer = nullptr;
    if (s.surface) {
        layer = fromHandleLocked(s.surface).promote();
    ...

    if (what & layer_state_t::eDeferTransaction_legacy) {
        layer->pushPendingState();
    }

    // Only set by BLAST adapter layers
    if (what & layer_state_t::eProducerDisconnect) {
        layer->onDisconnect();
    }

    if (what & layer_state_t::ePositionChanged) {
        if (layer->setPosition(s.x, s.y)) {
            flags |= eTraversalNeeded;
        }
    }
...
}

通过setDisplayStateLocked 和 setClientStateLocked 获取了display和layer的事务变化的flag，并且setClientStateLocked还将layer与surface进行了事务的同步。

文件：  frameworks/native/services/surfaceflinger/Surfaceflinger.cpp

void SurfaceFlinger::handleTransactionLocked(uint32_t transactionFlags)
{
    ...
    if ((transactionFlags & eTraversalNeeded) || mForceTraversal) {
        mForceTraversal = false;
         // 遍历mCurrentState 里面的layer，对有事务变化的layer进行处理，doTransaction 主要的处理逻辑是对sync ponit的处理，
        // sync ponit用于延迟显示的一些layer，根据FrameNumber进行同步，如果当前帧数达到了设定值，latchBuffer就可以消费这个layer
        mCurrentState.traverse([&](Layer* layer) {
            uint32_t trFlags = layer->getTransactionFlags(eTransactionNeeded);
            if (!trFlags) return;

            const uint32_t flags = layer->doTransaction(0);
            if (flags & Layer::eVisibleRegion)
                mVisibleRegionsDirty = true;

            if (flags & Layer::eInputInfoChanged) {
                mInputInfoChanged = true;
            }
        });
    }

    // 处理 display的 事务逻辑
    if (transactionFlags & eDisplayTransactionNeeded) {
        processDisplayChangesLocked();
        processDisplayHotplugEventsLocked();
    }
   ...
    // SurfaceFlinger维持mCurrentState 和 mDrawingState 两个状态，是个大的结构体，mCurrentState 可以理解为下一帧的
    // layer和display的状态， mDrawingState 可以理解为当前帧的状态，commitTransaction 将 mCurrentState 更新到这一帧的状态
    commitTransaction();
}

handleMessageTransaction主要的作用是处理display和layer的事物，将上层的surface和底层的layer属性做个同步，涉及到很多的细节以后遇到具体场景来分析，最后将mCurrentState 赋给 mDrawingState 更新到当前这一帧的状态。

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1.3 handleMessageInvalidate

我们接着继续往下看，累啊，学习，搞起来~

文件：frameworks/native/services/surfaceflinger/Surfaceflinger.cpp

bool SurfaceFlinger::handleMessageInvalidate() {
    ATRACE_CALL();
    // 处理queue过来的Buffer
    bool refreshNeeded = handlePageFlip();

    if (mVisibleRegionsDirty) {
        // 如果可见区域有变化，则重新计算layer的范围
        computeLayerBounds();
    }
    //判断需要刷新的layer是否属于当前Output
    for (auto& layer : mLayersPendingRefresh) {
        Region visibleReg;
        visibleReg.set(layer->getScreenBounds());
        invalidateLayerStack(layer, visibleReg);
    }
    mLayersPendingRefresh.clear();
    return refreshNeeded;
}

bool SurfaceFlinger::handlePageFlip()
{
   ...
    // 遍历 mDrawingState里面的layer，判断该layer是否可在当前vsync内显示，如果queueBuffer带过来的时间戳大于Vsync的时间戳，则表示该layer不能在当前vsync内显示
    // 能够显示的layer放到mLayersWithQueuedFrames 里面
    mDrawingState.traverse([&](Layer* layer) {
        if (layer->hasReadyFrame()) {
            frameQueued = true;
            if (layer->shouldPresentNow(expectedPresentTime)) {
                mLayersWithQueuedFrames.push_back(layer);
            } else {
                ATRACE_NAME("!layer->shouldPresentNow()");
                layer->useEmptyDamage();
            }
        } else {
            layer->useEmptyDamage();
        }
    });
   ...
    // 遍历mLayersWithQueuedFrames 里面的layer，执行latchBuffer，在latchBuffer里面消费Buffer
    // 成功消费的layer放到mLayersPendingRefresh 里面
     for (auto& layer : mLayersWithQueuedFrames) {
            if (layer->latchBuffer(visibleRegions, latchTime, expectedPresentTime)) {
                mLayersPendingRefresh.push_back(layer);
            }
            layer->useSurfaceDamage();
            if (layer->isBufferLatched()) {
                newDataLatched = true;
            }
     ...
    // 当有需要消费Buffer的layer则返回true
   return !mLayersWithQueuedFrames.empty() && newDataLatched;

文件： frameworks/native/services/surfaceflinger/BufferLayer.cpp

bool BufferLayer::latchBuffer(bool& recomputeVisibleRegions, nsecs_t latchTime,
                              nsecs_t expectedPresentTime) {
   ...
   // 执行顺序BufferQueueLayer-> updateTexImage ==> BufferLayerConsumer-> updateTexImage,具体逻辑在
   // BufferLayerConsumer 里面
   status_t err = updateTexImage(recomputeVisibleRegions, latchTime, expectedPresentTime);
   // 更新mBufferInfo里的buffer，这个变量是在BufferQueueLayer里面维护
    err = updateActiveBuffer();
    if (err != NO_ERROR) {
        return false;
    }
    //更新mBufferInfo的FrameNumber
    err = updateFrameNumber(latchTime);
    if (err != NO_ERROR) {
        return false;
    }
    // 更新到mBufferInfo
    gatherBufferInfo();
    ...
}

文件： frameworks/native/services/surfaceflinger/BufferLayerConsumer.cpp

status_t BufferLayerConsumer::updateTexImage(BufferRejecter* rejecter, nsecs_t expectedPresentTime,
                                             bool* autoRefresh, bool* queuedBuffer,
                                             uint64_t maxFrameNumber) {
  ...
    BufferItem item;

   // acquireBuffer：消费queue过来的Buffer,放到item里面
    status_t err = acquireBufferLocked(&item, expectedPresentTime, maxFrameNumber);
    ...
    // 更新BufferLayerConsumer 状态，都是从queueBuffer设置而来
    err = updateAndReleaseLocked(item, &mPendingRelease);
    ...
}

status_t BufferLayerConsumer::acquireBufferLocked(BufferItem* item, nsecs_t presentWhen,
                                                  uint64_t maxFrameNumber) {
    status_t err = ConsumerBase::acquireBufferLocked(item, presentWhen, maxFrameNumber);
    ...
    if (item->mGraphicBuffer != nullptr) {
        std::lock_guard<std::mutex> lock(mImagesMutex);
        if (mImages[item->mSlot] == nullptr || mImages[item->mSlot]->graphicBuffer() == nullptr ||
            mImages[item->mSlot]->graphicBuffer()->getId() != item->mGraphicBuffer->getId()) {
            // 将acquire出来的Buffer做成EGLImage，为了后面GPU合成
            mImages[item->mSlot] = std::make_shared<Image>(item->mGraphicBuffer, mRE);
        }
    }

    return NO_ERROR;
}

文件： frameworks/native/libs/gui/ConsumerBase.cpp

status_t ConsumerBase::acquireBufferLocked(BufferItem *item,
        nsecs_t presentWhen, uint64_t maxFrameNumber) {
     ...
    // 实现在BufferQueueConsumer的 acquireBuffer
    status_t err = mConsumer->acquireBuffer(item, presentWhen, maxFrameNumber);
    if (err != NO_ERROR) {
        return err;
    }

    if (item->mGraphicBuffer != nullptr) {
        if (mSlots[item->mSlot].mGraphicBuffer != nullptr) {
            freeBufferLocked(item->mSlot);
        }
        //更新Bufferslot里面的GraphicsBuffer，这个Buffer的owner是GPU在处理
        mSlots[item->mSlot].mGraphicBuffer = item->mGraphicBuffer;
    }
    // 更新Bufferslot里面的frameNumber和fence，与queueBuffer设置保持一致，这里的fence为acquireFence
    mSlots[item->mSlot].mFrameNumber = item->mFrameNumber;
    mSlots[item->mSlot].mFence = item->mFence;

    CB_LOGV("acquireBufferLocked: -> slot=%d/%" PRIu64,
            item->mSlot, item->mFrameNumber);

    return OK;
}

文件： frameworks/native/libs/gui/BufferQueueConsumer.cpp

//跳过一些特殊情况代码细节，把主线code拎出来分析
status_t BufferQueueConsumer::acquireBuffer(BufferItem* outBuffer,
        nsecs_t expectedPresent, uint64_t maxFrameNumber) {
   ...
   // queueBuffer时入的队列
   BufferQueueCore::Fifo::iterator front(mCore->mQueue.begin());
   ...
   // 拿到queueBuffer对应的slot和BufferItem
   slot = front->mSlot;
   *outBuffer = *front;
    ...
   if (!outBuffer->mIsStale) {
            mSlots[slot].mAcquireCalled = true;
            // Don't decrease the queue count if the BufferItem wasn't
            // previously in the queue. This happens in shared buffer mode when
            // the queue is empty and the BufferItem is created above.
            if (mCore->mQueue.empty()) {
                mSlots[slot].mBufferState.acquireNotInQueue();
            } else {
                 // 更新状态为acquire
                mSlots[slot].mBufferState.acquire();
            }
      // queueBuffer入队，acquireBuffer出队
     mCore->mQueue.erase(front);
     ...
}

handleMessageInvalidate主要作用是执行 latchBuffer 去 acquire 应用queue过来的Buffer，然后拿到queueBuffer时设的Bufferslot一些状态属性给到BufferQueueLayer的mBufferInfo，同时还把这个Buffer做成EGLImage为后面的GPU合成做准备，期间都是数据之间的传递，所以说SurfaceFlinger并未真正触碰Buffer的内容。

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写在最后

好了今天的博客Android下SF合成流程重学习之onMessageInvalidate就到这里了。总之，青山不改绿水长流先到这里了。如果本博客对你有所帮助，麻烦关注或者点个赞，如果觉得很烂也可以踩一脚！谢谢各位了！！