暫時(shí)跳過(guò)SurfaceFlinger的初始化污秆，根據(jù)systrace的函數(shù)調(diào)用來(lái)分析SurfaceFlinger運(yùn)行的原理腹泌，看SurfaceFlinger做了哪些工作授滓。
sf trace.png
前面說(shuō)的當(dāng)應(yīng)用queueBuffer過(guò)來(lái)時(shí)會(huì)請(qǐng)求vsync來(lái)刷新粒没，首先會(huì)執(zhí)行onMessageInvalidate 函數(shù)揩抡，看下這個(gè)函數(shù)做了哪些工作。
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回調(diào)帶過(guò)來(lái)的時(shí)間戳却邓，通過(guò)nextAnticipatedVSyncTimeFrom 計(jì)算得到
if (expectedVSyncTime >= frameStart) {
mExpectedPresentTime = expectedVSyncTime;
} else {
mExpectedPresentTime = mScheduler->getDispSyncExpectedPresentTime(frameStart);
}
// 存儲(chǔ)上一幀的expectedVSyncTime
const nsecs_t lastScheduledPresentTime = mScheduledPresentTime;
mScheduledPresentTime = expectedVSyncTime;
...
// 根據(jù)上一幀的present fence判斷當(dāng)前這一幀是否pending
const TracedOrdinal<bool> framePending = {"PrevFramePending",
previousFramePending(graceTimeForPresentFenceMs)};
// 若framePending 或者 上一幀present fence釋放的時(shí)間 > 上一幀vsync計(jì)算的時(shí)間戳 + vsync周期的一半
// 則當(dāng)前幀要丟掉
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))};
// 根據(jù)合成類(lèi)型判斷丟幀的類(lèi)型
const TracedOrdinal<bool> hwcFrameMissed = {"PrevHwcFrameMissed",
mHadDeviceComposition && frameMissed};
const TracedOrdinal<bool> gpuFrameMissed = {"PrevGpuFrameMissed",
mHadClientComposition && frameMissed};
...
// 這部分涉及幀率切換硕糊，先是通過(guò)performSetActiveConfig 將新的幀率給到hwc，然后下一幀再更新sf這邊的狀態(tài)
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 可以通過(guò)adb shell setprop debug.sf.disable_backpressure x 來(lái)控制,表示系統(tǒng)是否允許丟幀
// 若允許丟幀則skip這次刷幀
if (framePending && mPropagateBackpressure) {
if ((hwcFrameMissed && !gpuFrameMissed) || mPropagateBackpressureClientComposition) {
signalLayerUpdate();
return;
}
}
....
bool refreshNeeded;
{
ConditionalLockGuard<std::mutex> lock(mTracingLock, mTracingEnabled);
// 主要的邏輯在這兩個(gè)函數(shù)腊徙，簡(jiǎn)單理解為處理layer或者display的事務(wù)和layer的buffer
refreshNeeded = handleMessageTransaction();
refreshNeeded |= handleMessageInvalidate();
...
}
// 幀率切換简十，SurfaceFlinger主線程執(zhí)行
ON_MAIN_THREAD(performSetActiveConfig());
...
// 若layer的事務(wù)有變化或者有新的buffer，則觸發(fā)refresh
signalRefresh();
}
onMessageInvalidate主要處理的事情1. 判斷當(dāng)前幀是否丟掉 2. handleMessageTransaction 處理layer或者display事務(wù) 3. handleMessageInvalidate 處理應(yīng)用queue過(guò)來(lái)的Buffer 4. 幀率切換 5. 觸發(fā)刷新流程
handleMessageTransaction
文件： frameworks/native/services/surfaceflinger/Surfaceflinger.cpp
bool SurfaceFlinger::handleMessageTransaction() {
ATRACE_CALL();
// 獲取當(dāng)前的mTransactionFlags撬腾，mTransactionFlags 由setTransactionFlags 賦值螟蝙，比如CreateLayer時(shí)會(huì)給mTransactionFlags 賦值eTransactionNeeded
// createDisplay 時(shí)會(huì)給mTransactionFlags 賦值 eDisplayTransactionNeeded
uint32_t transactionFlags = peekTransactionFlags();
// flushTransactionQueues 會(huì)消費(fèi)transactionQueue，transactionQueue 是上層通過(guò)SurfaceComposerClient 設(shè)的民傻，然后再通過(guò)binder設(shè)置給sf這邊
// setDisplayStateLocked： 處理display的事務(wù)
// setClientStateLocked： 處理layer的事務(wù)
// 這兩部分事務(wù)都存放在surfaceflinger的mCurrentState 里面
bool flushedATransaction = flushTransactionQueues();
// 有新的事務(wù)則要執(zhí)行handleTransaction
bool runHandleTransaction =
(transactionFlags && (transactionFlags != eTransactionFlushNeeded)) ||
flushedATransaction ||
mForceTraversal;
// 處理layer和display的事務(wù)
if (runHandleTransaction) {
handleTransaction(eTransactionMask);
} else {
getTransactionFlags(eTransactionFlushNeeded);
}
if (transactionFlushNeeded()) {
setTransactionFlags(eTransactionFlushNeeded);
}
return runHandleTransaction;
}
//來(lái)看下display和layer有哪些事務(wù)處理
文件： frameworks/native/services/surfaceflinger/Surfaceflinger.cpp
// display的事務(wù)胰默，包括display Surface, layerStack , Projection , viewport, Size發(fā)生變化時(shí)附上eDisplayTransactionNeeded 這個(gè)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的事務(wù)，包括ePositionChanged, eLayerChanged, eAlphaChanged 等等漓踢，跟上層的surface設(shè)置一樣牵署，同樣的事務(wù)同步給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;
}
}
...
}
通過(guò)setDisplayStateLocked 和 setClientStateLocked 獲取了display和layer的事務(wù)變化的flag，并且setClientStateLocked還將layer與surface進(jìn)行了事務(wù)的同步喧半。
文件： frameworks/native/services/surfaceflinger/Surfaceflinger.cpp
void SurfaceFlinger::handleTransactionLocked(uint32_t transactionFlags)
{
...
if ((transactionFlags & eTraversalNeeded) || mForceTraversal) {
mForceTraversal = false;
// 遍歷mCurrentState 里面的layer碟刺，對(duì)有事務(wù)變化的layer進(jìn)行處理，doTransaction 主要的處理邏輯是對(duì)sync ponit的處理薯酝，
// sync ponit用于延遲顯示的一些layer半沽，根據(jù)FrameNumber進(jìn)行同步爽柒，如果當(dāng)前幀數(shù)達(dá)到了設(shè)定值，latchBuffer就可以消費(fèi)這個(gè)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;
}
});
}
// 處理 display的 事務(wù)邏輯
if (transactionFlags & eDisplayTransactionNeeded) {
processDisplayChangesLocked();
processDisplayHotplugEventsLocked();
}
...
// SurfaceFlinger維持mCurrentState 和 mDrawingState 兩個(gè)狀態(tài)者填，是個(gè)大的結(jié)構(gòu)體浩村，mCurrentState 可以理解為下一幀的
// layer和display的狀態(tài)， mDrawingState 可以理解為當(dāng)前幀的狀態(tài)占哟，commitTransaction 將 mCurrentState 更新到這一幀的狀態(tài)
commitTransaction();
}
handleMessageTransaction 主要的作用是處理display和layer的事務(wù)心墅，將上層的surface和底層的layer屬性做個(gè)同步，涉及到很多的細(xì)節(jié)以后遇到具體場(chǎng)景來(lái)分析榨乎，最后將mCurrentState 賦給 mDrawingState 更新到當(dāng)前這一幀的狀態(tài)怎燥。
handleMessageInvalidate
文件：frameworks/native/services/surfaceflinger/Surfaceflinger.cpp
bool SurfaceFlinger::handleMessageInvalidate() {
ATRACE_CALL();
// 處理queue過(guò)來(lái)的Buffer
bool refreshNeeded = handlePageFlip();
if (mVisibleRegionsDirty) {
// 如果可見(jiàn)區(qū)域有變化，則重新計(jì)算layer的范圍
computeLayerBounds();
}
for (auto& layer : mLayersPendingRefresh) {
Region visibleReg;
visibleReg.set(layer->getScreenBounds());
invalidateLayerStack(layer, visibleReg);
}
mLayersPendingRefresh.clear();
return refreshNeeded;
}
bool SurfaceFlinger::handlePageFlip()
{
...
// 遍歷 mDrawingState里面的layer蜜暑，判斷該layer是否可在當(dāng)前vsync內(nèi)顯示铐姚，如果queueBuffer帶過(guò)來(lái)的時(shí)間戳大于Vsync的時(shí)間戳，則表示該layer不能在當(dāng)前vsync內(nèi)顯示
// 能夠顯示的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();
}
});
...
// 遍歷mLayersWithQueuedFrames 里面的layer肛捍，執(zhí)行l(wèi)atchBuffer隐绵，在latchBuffer里面消費(fèi)Buffer
// 成功消費(fèi)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;
}
...
// 當(dāng)有需要消費(fèi)Buffer的layer則返回true
return !mLayersWithQueuedFrames.empty() && newDataLatched;
文件： frameworks/native/services/surfaceflinger/BufferLayer.cpp
bool BufferLayer::latchBuffer(bool& recomputeVisibleRegions, nsecs_t latchTime,
nsecs_t expectedPresentTime) {
...
// 執(zhí)行順序BufferQueueLayer-> updateTexImage ==> BufferLayerConsumer-> updateTexImage,具體邏輯在
// BufferLayerConsumer 里面
status_t err = updateTexImage(recomputeVisibleRegions, latchTime, expectedPresentTime);
// 更新mBufferInfo里的buffer，這個(gè)變量是在BufferQueueLayer里面維護(hù)
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：消費(fèi)queue過(guò)來(lái)的Buffer,放到item里面
status_t err = acquireBufferLocked(&item, expectedPresentTime, maxFrameNumber);
...
// 更新BufferLayerConsumer 狀態(tài)拙毫，都是從queueBuffer設(shè)置而來(lái)
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()) {
// 將acquire出來(lái)的Buffer做成EGLImage依许，為了后面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) {
...
// 實(shí)現(xiàn)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，這個(gè)Buffer的owner是GPU在處理
mSlots[item->mSlot].mGraphicBuffer = item->mGraphicBuffer;
}
// 更新Bufferslot里面的frameNumber和fence缀蹄，與queueBuffer設(shè)置保持一致峭跳，這里的fence為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
//跳過(guò)一些特殊情況代碼細(xì)節(jié)，把主線code拎出來(lái)分析
status_t BufferQueueConsumer::acquireBuffer(BufferItem* outBuffer,
nsecs_t expectedPresent, uint64_t maxFrameNumber) {
...
// queueBuffer時(shí)入的隊(duì)列
BufferQueueCore::Fifo::iterator front(mCore->mQueue.begin());
...
// 拿到queueBuffer對(duì)應(yīng)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?tīng)顟B(tài)為acquire
mSlots[slot].mBufferState.acquire();
}
// queueBuffer入隊(duì)缺前，acquireBuffer出隊(duì)
mCore->mQueue.erase(front);
...
}
handleMessageInvalidate 主要作用是執(zhí)行 latchBuffer 去 acquire 應(yīng)用queue過(guò)來(lái)的Buffer蛀醉，然后拿到queueBuffer時(shí)設(shè)的Bufferslot一些狀態(tài)屬性給到BufferQueueLayer的mBufferInfo，同時(shí)還把這個(gè)Buffer做成EGLImage為后面的GPU合成做準(zhǔn)備诡延，期間都是數(shù)據(jù)之間的傳遞滞欠，所以說(shuō)SurfaceFlinger并未真正觸碰Buffer的內(nèi)容古胆。
Buffer消費(fèi)流程.png
