前言
经过前两篇文章的解析，我们彻底的理解GraphicBuffer的生产端究竟做了什么。本文就来讨论GraphicBuffer是怎么消费。
整个图元的消费到合成，最后到通过hwc发送到fb。由于整个流程十分长，中间有许多细节，我将会挑出核心的思想来和大家聊聊其中的原理。
还记得，我在GraphicBuffer的诞生里面具体了聊了queuebuffer最后会通过IConsumerListener的回调通知消费者进行消费。
我们接着继续看看接下来的逻辑。
如果遇到问题，可以到本文讨论https://www.jianshu.com/p/67c1e350fe0d
正文
让我们先来回忆一下，在图元缓冲队列初始化一文中曾经总结的UML图。
文件：frameworks/native/libs/gui/BufferQueueProducer.cpp
frameAvailableListener = mCore->mConsumerListener;
}
Mutex::Autolock lock(mCallbackMutex);
while (callbackTicket != mCurrentCallbackTicket) {
mCallbackCondition.wait(mCallbackMutex);
}
if (frameAvailableListener != NULL) {
frameAvailableListener->onFrameAvailable(item);
} else if (frameReplacedListener != NULL) {
frameReplacedListener->onFrameReplaced(item);
}frameAvailableListener就是ProxyConsumerListener。这个对象持有ConsumeBase。当进行回调时候就会回调到ConsumeBase的mFrameAvailableListener。
void ConsumerBase::onFrameAvailable(const BufferItem& item) {
sp<FrameAvailableListener> listener;
{ // scope for the lock
Mutex::Autolock lock(mFrameAvailableMutex);
listener = mFrameAvailableListener.promote();
}
if (listener != NULL) {
listener-> (item);
}
}而ConsumeBase的mFrameAvailableListener是BufferLayer注册进来的。到这里倒在缓冲队列的初始化聊过。
BufferLayer onFrameAvailable
文件：/frameworks/native/services/surfaceflinger/BufferLayer.cpp
void BufferLayer::onFrameAvailable(const BufferItem& item) {
// Add this buffer from our internal queue tracker
{ // Autolock scope
Mutex::Autolock lock(mQueueItemLock);
mFlinger->mInterceptor->saveBufferUpdate(this, item.mGraphicBuffer->getWidth(),
item.mGraphicBuffer->getHeight(),
item.mFrameNumber);
if (item.mFrameNumber == 1) {
mLastFrameNumberReceived = 0;
}
// Ensure that callbacks are handled in order
while (item.mFrameNumber != mLastFrameNumberReceived + 1) {
status_t result = mQueueItemCondition.waitRelative(mQueueItemLock,
ms2ns(500));
...
}
mQueueItems.push_back(item);
android_atomic_inc(&mQueuedFrames);
mLastFrameNumberReceived = item.mFrameNumber;
mQueueItemCondition.broadcast();
}
mFlinger->signalLayerUpdate();
}这里做的事情很简单，增加mQueuedFrames的计数，mQueueItems添加一个BufferItem，并唤醒其他线程入队的阻塞。接着调用SF的signalLayerUpdate。
SurfaceFlinger signalLayerUpdate
文件：rameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
void SurfaceFlinger::signalLayerUpdate() {
mEventQueue->invalidate();
}接着调用到MessageQueue的invalidate
void MessageQueue::invalidate() {
mEvents->requestNextVsync();
}在MessageQueue中请求下一个同步信号
EventThread::Connection::requestNextVsync
void EventThread::Connection::requestNextVsync() {
mEventThread->requestNextVsync(this);
}void EventThread::requestNextVsync(const sp<EventThread::Connection>& connection) {
std::lock_guard<std::mutex> lock(mMutex);
if (mResyncWithRateLimitCallback) {
mResyncWithRateLimitCallback();
}
if (connection->count < 0) {
connection->count = 0;
mCondition.notify_all();
}
}EventThread::Connection的count的标志位实际上是指vysnc事件是每隔几个事件通知。此时是count在初始化的时候是-1.此时强制设置为0，说明只有调用requestNextVsync强制唤醒才会返回vysnc通知。
整体设计可以看我写第一篇SurfaceFlinger 的初始化。mResyncWithRateLimitCallback这个方法用于调整DispSync的时间戳。假如是第一次初始化，因此count还是-1.因此直接唤醒waitForEventLocked中的等待。
if (!timestamp && !eventPending) {
// wait for something to happen
if (waitForVSync) {
bool softwareSync = mUseSoftwareVSync;
auto timeout = softwareSync ? 16ms : 1000ms;
if (mCondition.wait_for(*lock, timeout) == std::cv_status::timeout) {
if (!softwareSync) {
ALOGW("Timed out waiting for hw vsync; faking it");
}
// FIXME: how do we decide which display id the fake
// vsync came from ?
mVSyncEvent[0].header.type = DisplayEventReceiver::DISPLAY_EVENT_VSYNC;
mVSyncEvent[0].header.id = DisplayDevice::DISPLAY_PRIMARY;
mVSyncEvent[0].header.timestamp = systemTime(SYSTEM_TIME_MONOTONIC);
mVSyncEvent[0].vsync.count++;
}
} else {
mCondition.wait(*lock);
}此时timestamp一开始是0，当设置了时间戳，将不会直接等待跳出死循环，为0则会。eventPending是由接进来的屏幕的mPendingEvents判断是否为空，不为空则是true。 如果EventThread有Connection接进来进行监听将会设置为waitForVSync为true。
当我们进行初始化的时候，由于没有屏幕接进来。因此第一个信号是DISPLAY_EVENT_VSYNC。进行刷新。
MessageQueue的回调
int MessageQueue::eventReceiver(int /*fd*/, int /*events*/) {
ssize_t n;
DisplayEventReceiver::Event buffer[8];
while ((n = DisplayEventReceiver::getEvents(&mEventTube, buffer, 8)) > 0) {
for (int i = 0; i < n; i++) {
if (buffer[i].header.type == DisplayEventReceiver::DISPLAY_EVENT_VSYNC) {
mHandler->dispatchInvalidate();
break;
}
}
}
return 1;
}能看到整个MessageQueue的回调只接受DISPLAY_EVENT_VSYNC，进行刷新。
void MessageQueue::Handler::dispatchInvalidate() {
if ((android_atomic_or(eventMaskInvalidate, &mEventMask) & eventMaskInvalidate) == 0) {
mQueue.mLooper->sendMessage(this, Message(MessageQueue::INVALIDATE));
}
}
void MessageQueue::Handler::handleMessage(const Message& message) {
switch (message.what) {
case INVALIDATE:
android_atomic_and(~eventMaskInvalidate, &mEventMask);
mQueue.mFlinger->onMessageReceived(message.what);
break;
case REFRESH:
android_atomic_and(~eventMaskRefresh, &mEventMask);
mQueue.mFlinger->onMessageReceived(message.what);
break;
}
}发送了一个INVALIDATE消息交给SF的onMessageReceive处理。
SF onMessageReceive 处理 INVALIDATE消息
void SurfaceFlinger::onMessageReceived(int32_t what) {
ATRACE_CALL();
switch (what) {
case MessageQueue::INVALIDATE: {
bool frameMissed = !mHadClientComposition &&
mPreviousPresentFence != Fence::NO_FENCE &&
(mPreviousPresentFence->getSignalTime() ==
Fence::SIGNAL_TIME_PENDING);
if (frameMissed) {
mTimeStats.incrementMissedFrames();
if (mPropagateBackpressure) {
signalLayerUpdate();
break;
}
}
updateVrFlinger();
bool refreshNeeded = handleMessageTransaction();
refreshNeeded |= handleMessageInvalidate();
refreshNeeded |= mRepaintEverything;
if (refreshNeeded) {
signalRefresh();
}
break;
}
case MessageQueue::REFRESH: {
handleMessageRefresh();
break;
}
}
}MessageQueue的消息处理函数中SF处理了两种消息一种是INVALIDATE校验无效的区域。校验方式两个步骤：
- 1.handleMessageTransaction 处理事务，如交换绘制mDrawState和mCurrentState的焦点状态，记录每一个Layer当前需要绘制的各自的Layer，如果判断到已经添加了Layer进来，则需要打开判断可视区域标志位。发现Layer被移除了需要更新脏(已经变动)区域
- 2.handleMessageInvalidate 核心就是latch每一个Layer中的图元进行acquire的操作。一旦判断到每一Layer中有latch了图元，说有新的图元需要消费，或者还有图元没有消费的，则需要主动调用signalLayerUpdate()进行下一个循环的INVALIDATE发送。
最后是否需要调用signalRefresh，handleMessageTransaction需要处理事务或者handleMessageInvalidate判断到有新图元。则会通过signalRefresh进入下一个循环进行Refresh消息的发送。
void SurfaceFlinger::signalRefresh() {
mRefreshPending = true;
mEventQueue->refresh();
}知道核心思想，我们再来每一个步骤中做了什么。
handleMessageTransaction
uint32_t SurfaceFlinger::peekTransactionFlags() {
return android_atomic_release_load(&mTransactionFlags);
}
bool SurfaceFlinger::handleMessageTransaction() {
uint32_t transactionFlags = peekTransactionFlags();
if (transactionFlags) {
handleTransaction(transactionFlags);
return true;
}
return false;
}我们先讨论打开了mTransactionFlags事务的标志位。一旦Layer，Display等和显示相关的数据结构发生变化都需要打开这个标志位。
void SurfaceFlinger::handleTransaction(uint32_t transactionFlags)
{
State drawingState(mDrawingState);
Mutex::Autolock _l(mStateLock);
const nsecs_t now = systemTime();
...
mVsyncModulator.onTransactionHandled();
transactionFlags = getTransactionFlags(eTransactionMask);
handleTransactionLocked(transactionFlags);
mLastTransactionTime = systemTime() - now;
invalidateHwcGeometry();
}
void SurfaceFlinger::invalidateHwcGeometry()
{
mGeometryInvalid = true;
}核心是handleTransactionLocked。
void SurfaceFlinger::handleTransactionLocked(uint32_t transactionFlags)
{
// 通知所有的Layer可以进行合成
mCurrentState.traverseInZOrder([](Layer* layer) {
layer->notifyAvailableFrames();
});
if (transactionFlags & eTraversalNeeded) {
mCurrentState.traverseInZOrder([&](Layer* layer) {
uint32_t trFlags = layer->getTransactionFlags(eTransactionNeeded);
if (!trFlags) return;
const uint32_t flags = layer->doTransaction(0);
if (flags & Layer::eVisibleRegion)
mVisibleRegionsDirty = true;
});
}
/*
* Perform display own transactions if needed
*/
if (transactionFlags & eDisplayTransactionNeeded) {
processDisplayChangesLocked();
processDisplayHotplugEventsLocked();
}
if (transactionFlags & (eDisplayLayerStackChanged|eDisplayTransactionNeeded)) {
sp<const DisplayDevice> disp;
uint32_t currentlayerStack = 0;
bool first = true;
mCurrentState.traverseInZOrder([&](Layer* layer) {
uint32_t layerStack = layer->getLayerStack();
if (first || currentlayerStack != layerStack) {
currentlayerStack = layerStack;
disp.clear();
for (size_t dpy=0 ; dpy<mDisplays.size() ; dpy++) {
sp<const DisplayDevice> hw(mDisplays[dpy]);
if (layer->belongsToDisplay(hw->getLayerStack(), hw->isPrimary())) {
if (disp == nullptr) {
disp = std::move(hw);
} else {
disp = nullptr;
break;
}
}
}
}
if (disp == nullptr) {
disp = getDefaultDisplayDeviceLocked();
}
if (disp != nullptr) {
layer->updateTransformHint(disp);
}
first = false;
});
}
if (mLayersAdded) {
mLayersAdded = false;
mVisibleRegionsDirty = true;
}
if (mLayersRemoved) {
mLayersRemoved = false;
mVisibleRegionsDirty = true;
mDrawingState.traverseInZOrder([&](Layer* layer) {
if (mLayersPendingRemoval.indexOf(layer) >= 0) {
Region visibleReg;
visibleReg.set(layer->computeScreenBounds());
invalidateLayerStack(layer, visibleReg);
}
});
}
commitTransaction();
updateCursorAsync();
}1.第一个从底部向顶部循环遍历mCurrentState中的Layer，通知每一个被SyncPoint完成了doTransaction步骤而阻塞的Layer。让Layer可以进行合成的准备。
void BufferLayer::notifyAvailableFrames() { auto headFrameNumber = getHeadFrameNumber(); bool headFenceSignaled = headFenceHasSignaled(); Mutex::Autolock lock(mLocalSyncPointMutex); for (auto& point : mLocalSyncPoints) { if (headFrameNumber >= point->getFrameNumber() && headFenceSignaled) { point->setFrameAvailable(); } } }2.从底部遍历每一个Layer的doTransaction方法。处理可视区域。
3.检查每一个Layer中的所对应的显示屏id类型，同时更新里面的变换矩阵。
4.如果通过Client添加过Layer就会打上mLayersAdded，此时将会关闭这个标志位，同时打开mVisibleRegionsDirty，让后续的步骤检测变动的可视区域。
5.如果Layer有移除，则调用invalidateLayerStack更新DisplayDevice中原有的可视脏区。
void SurfaceFlinger::invalidateLayerStack(const sp<const Layer>& layer, const Region& dirty) { for (size_t dpy=0 ; dpy<mDisplays.size() ; dpy++) { const sp<DisplayDevice>& hw(mDisplays[dpy]); if (layer->belongsToDisplay(hw->getLayerStack(), hw->isPrimary())) { hw->dirtyRegion.orSelf(dirty); } } }
让我们看看doTransaction核心方法。
Layer doTransaction
文件：/frameworks/native/services/surfaceflinger/Layer.cpp
uint32_t Layer::doTransaction(uint32_t flags) {
pushPendingState();
Layer::State c = getCurrentState();
if (!applyPendingStates(&c)) {
return 0;
}
const Layer::State& s(getDrawingState());
const bool sizeChanged = (c.requested.w != s.requested.w) || (c.requested.h != s.requested.h);
if (sizeChanged) {
...
setDefaultBufferSize(c.requested.w, c.requested.h);
}
const bool resizePending = ((c.requested.w != c.active.w) || (c.requested.h != c.active.h)) &&
(getBE().compositionInfo.mBuffer != nullptr);
if (!isFixedSize()) {
if (resizePending && getBE().compositionInfo.hwc.sidebandStream == nullptr) {
flags |= eDontUpdateGeometryState;
}
}
if (!(flags & eDontUpdateGeometryState)) {
Layer::State& editCurrentState(getCurrentState());
if (mFreezeGeometryUpdates) {
float tx = c.active.transform.tx();
float ty = c.active.transform.ty();
c.active = c.requested;
c.active.transform.set(tx, ty);
editCurrentState.active = c.active;
} else {
editCurrentState.active = editCurrentState.requested;
c.active = c.requested;
}
}
if (s.active != c.active) {
flags |= Layer::eVisibleRegion;
}
if (c.sequence != s.sequence) {
// invalidate and recompute the visible regions if needed
flags |= eVisibleRegion;
this->contentDirty = true;
const uint8_t type = c.active.transform.getType();
mNeedsFiltering = (!c.active.transform.preserveRects() || (type >= Transform::SCALE));
}
if (c.flags & layer_state_t::eLayerHidden) {
clearSyncPoints();
}
// Commit the transaction
commitTransaction(c);
return flags;
}
void Layer::commitTransaction(const State& stateToCommit) {
mDrawingState = stateToCommit;
}
1.就是检测BufferLayer中的mCurrentState和上一帧已经绘制了的mDrawState的差距。如果发现两者的requested的区域发生了变动，则会调用setDefaultBufferSize，重新定义图元消费BufferLayerConsumer的默认宽高。
void BufferLayer::setDefaultBufferSize(uint32_t w, uint32_t h) { mConsumer->setDefaultBufferSize(w, h); }- 检测mCurrentState中requested和active之间的几何宽高。在每一个Layer::State中都会存在两个几何结构体requested和active。当我们设置了Surface了postion等在屏幕上显示的几何参数会先设置到mCurrentState.requested中。也就是说requested等待绘制的参数。active则是显示中的几何参数。一旦发生变化则设resizePending为true。
- isFixedSize则是判断当前对应的Layer是否被冻结不允许变化大小，假设此时是关闭的，且sidebandStream是空的。此时不会立即更新requested和active的区域。回到后面acquire步骤时候进行处理。
- 最后更新mCurrentState为mDrawState。
这里需要注意，和SF的State不一样。Layer::State将会记录Layer显示相关的参数。
SF commitTransaction
void SurfaceFlinger::commitTransaction()
{
if (!mLayersPendingRemoval.isEmpty()) {
// Notify removed layers now that they can't be drawn from
for (const auto& l : mLayersPendingRemoval) {
recordBufferingStats(l->getName().string(),
l->getOccupancyHistory(true));
l->onRemoved();
}
mLayersPendingRemoval.clear();
}
mAnimCompositionPending = mAnimTransactionPending;
mDrawingState = mCurrentState;
mCurrentState.colorMatrixChanged = false;
mDrawingState.traverseInZOrder([](Layer* layer) {
layer->commitChildList();
});
mTransactionPending = false;
mAnimTransactionPending = false;
mTransactionCV.broadcast();
}此时也会更新SF中的mDrawingState，同时会更新每一个Layer中对应处理完的事务状态。
BufferLayer commitChildList
void Layer::commitChildList() {
for (size_t i = 0; i < mCurrentChildren.size(); i++) {
const auto& child = mCurrentChildren[i];
child->commitChildList();
}
mDrawingChildren = mCurrentChildren;
mDrawingParent = mCurrentParent;
}对应的每一个Layer同时会更新之后需要绘制的父Layer和子Layer。
handleMessageInvalidate 检测变动区域
文件：/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
bool SurfaceFlinger::handleMessageInvalidate() {
return handlePageFlip();
}bool SurfaceFlinger::handlePageFlip()
{
nsecs_t latchTime = systemTime();
bool visibleRegions = false;
bool frameQueued = false;
bool newDataLatched = false;
mDrawingState.traverseInZOrder([&](Layer* layer) {
if (layer->hasQueuedFrame()) {
frameQueued = true;
if (layer->shouldPresentNow(mPrimaryDispSync)) {
mLayersWithQueuedFrames.push_back(layer);
} else {
layer->useEmptyDamage();
}
} else {
layer->useEmptyDamage();
}
});
for (auto& layer : mLayersWithQueuedFrames) {
const Region dirty(layer->latchBuffer(visibleRegions, latchTime));
layer->useSurfaceDamage();
invalidateLayerStack(layer, dirty);
if (layer->isBufferLatched()) {
newDataLatched = true;
}
}
mVisibleRegionsDirty |= visibleRegions;
if (frameQueued && (mLayersWithQueuedFrames.empty() || !newDataLatched)) {
signalLayerUpdate();
}
return !mLayersWithQueuedFrames.empty() && newDataLatched;
}首先要注意，在这个方法开始SF需要正式消费图元。此时会有一个问题，比如有个Layer.此时线程1通知了Layer有了一个新的图元进来了，还没来的消费又进来了一个图元。此时我们需要再进行消费？假如出现了宽高变化怎么办？那不就浪费了doTransaction步骤的宽高变化记录吗。因此我们需要一个latch方法，锁住图元。
一旦检测到图元还有没有消费的或者还没有到了需要显示时候，就会调用signalLayerUpdate，让下一个循环回来消费。
这个方法判断是否需要refresh的依据，其实就是判断两个情况同时成立，第一个是mLayersWithQueuedFrames不为空，有需要显示的Layer。同时latch上锁图元成功了。
BufferLayer shouldPresentNow
文件：/frameworks/native/services/surfaceflinger/BufferLayer.cpp
bool BufferLayer::shouldPresentNow(const DispSync& dispSync) const {
if (mSidebandStreamChanged || mAutoRefresh) {
return true;
}
Mutex::Autolock lock(mQueueItemLock);
if (mQueueItems.empty()) {
return false;
}
auto timestamp = mQueueItems[0].mTimestamp;
nsecs_t expectedPresent = mConsumer->computeExpectedPresent(dispSync);
// Ignore timestamps more than a second in the future
bool isPlausible = timestamp < (expectedPresent + s2ns(1));
bool isDue = timestamp < expectedPresent;
return isDue || !isPlausible;
}该方法会通过computeExpectedPresent通过DispSync计算这一帧应该是什么显示。是否显示由下面的公式决定：
预期显示 - 入队时间 < 1s && 入队时间<预期时间
一旦允许显示则往mLayersWithQueuedFrames添加Layer。这个Layer集合就是需要绘制的图层。
BufferLayer latchBuffer
接着会遍历mLayersWithQueuedFrames每一层的Layer，并且调用latchBuffer进行图元锁定。
接下来这个方法很长。我把它拆开2部分来聊
Region BufferLayer::latchBuffer(bool& recomputeVisibleRegions, nsecs_t latchTime) {
...
Region outDirtyRegion;
if (mQueuedFrames <= 0 && !mAutoRefresh) {
return outDirtyRegion;
}
//已经latch过了就不需要了
if (mRefreshPending) {
return outDirtyRegion;
}
//fence已经唤醒了，也不需要了
if (!headFenceHasSignaled()) {
mFlinger->signalLayerUpdate();
return outDirtyRegion;
}
const State& s(getDrawingState());
const bool oldOpacity = isOpaque(s);
sp<GraphicBuffer> oldBuffer = getBE().compositionInfo.mBuffer;
if (!allTransactionsSignaled()) {
mFlinger->signalLayerUpdate();
return outDirtyRegion;
}
bool queuedBuffer = false;
LayerRejecter r(mDrawingState, getCurrentState(), recomputeVisibleRegions,
getProducerStickyTransform() != 0, mName.string(),
mOverrideScalingMode, mFreezeGeometryUpdates);
//核心
status_t updateResult =
mConsumer->updateTexImage(&r, mFlinger->mPrimaryDispSync,
&mAutoRefresh, &queuedBuffer,
mLastFrameNumberReceived);
//根据消费返回的状态做处理
if (updateResult == BufferQueue::PRESENT_LATER) {
mFlinger->signalLayerUpdate();
return outDirtyRegion;
} else if (updateResult == BufferLayerConsumer::BUFFER_REJECTED) {
if (queuedBuffer) {
Mutex::Autolock lock(mQueueItemLock);
mTimeStats.removeTimeRecord(getName().c_str(), mQueueItems[0].mFrameNumber);
mQueueItems.removeAt(0);
android_atomic_dec(&mQueuedFrames);
}
return outDirtyRegion;
} else if (updateResult != NO_ERROR || mUpdateTexImageFailed) {
if (queuedBuffer) {
Mutex::Autolock lock(mQueueItemLock);
mQueueItems.clear();
android_atomic_and(0, &mQueuedFrames);
mTimeStats.clearLayerRecord(getName().c_str());
}
mUpdateTexImageFailed = true;
return outDirtyRegion;
}
//从入队到这里的queuedBuffer 都为true
if (queuedBuffer) {
// Autolock scope
auto currentFrameNumber = mConsumer->getFrameNumber();
Mutex::Autolock lock(mQueueItemLock);
while (mQueueItems[0].mFrameNumber != currentFrameNumber) {
mTimeStats.removeTimeRecord(getName().c_str(), mQueueItems[0].mFrameNumber);
mQueueItems.removeAt(0);
android_atomic_dec(&mQueuedFrames);
}
const std::string layerName(getName().c_str());
mTimeStats.setAcquireFence(layerName, currentFrameNumber, mQueueItems[0].mFenceTime);
mTimeStats.setLatchTime(layerName, currentFrameNumber, latchTime);
mQueueItems.removeAt(0);
}
if ((queuedBuffer && android_atomic_dec(&mQueuedFrames) > 1) ||
mAutoRefresh) {
mFlinger->signalLayerUpdate();
}
//把已经消费的图元保存到SurfaceFlingerBE里面
getBE().compositionInfo.mBuffer =
mConsumer->getCurrentBuffer(&getBE().compositionInfo.mBufferSlot);
mActiveBuffer = getBE().compositionInfo.mBuffer;
if (getBE().compositionInfo.mBuffer == nullptr) {
// this can only happen if the very first buffer was rejected.
return outDirtyRegion;
}
mBufferLatched = true;
...
}整个核心就是updateTexImage方法。在这里面经过判断，latch过的Layer就不会再进行latch。
经过updateTexImage处理后，会判断返回的状态码。如果需要延迟显示则直接返回空的脏区域。如果发现需要拒绝显示这个帧，将会丢弃mQueueItem中对应的图元参数和索引。如果消费失败了，则会处理清除mQueueItem中所有等待消费的图元。最后返回空脏区。
成功消费后，如果是从queueBuffer的步骤到这里的，将会移除mQueueItem第一项图元数据。剩下的图元还有剩下的，则需要进行下一轮invalidate消息。
最后会把消费后的图元，作为当前需要显示的图元保存在getBE().compositionInfo.mBuffer和mActiveBuffer，并且设置mBufferLatched。
核心的updateTexImage方法我们稍后注重考究。
//记录上一帧序列
mPreviousFrameNumber = mCurrentFrameNumber;
//记录当前这一帧的序列
mCurrentFrameNumber = mConsumer->getFrameNumber();
{
//记录上锁时间
Mutex::Autolock lock(mFrameEventHistoryMutex);
mFrameEventHistory.addLatch(mCurrentFrameNumber, latchTime);
}
mRefreshPending = true;
mFrameLatencyNeeded = true;
if (oldBuffer == nullptr) {
recomputeVisibleRegions = true;
}
//记录DataSpace
ui::Dataspace dataSpace = mConsumer->getCurrentDataSpace();
switch (dataSpace) {
case ui::Dataspace::V0_SRGB:
dataSpace = ui::Dataspace::SRGB;
break;
case ui::Dataspace::V0_SRGB_LINEAR:
dataSpace = ui::Dataspace::SRGB_LINEAR;
break;
case ui::Dataspace::V0_JFIF:
dataSpace = ui::Dataspace::JFIF;
break;
case ui::Dataspace::V0_BT601_625:
dataSpace = ui::Dataspace::BT601_625;
break;
case ui::Dataspace::V0_BT601_525:
dataSpace = ui::Dataspace::BT601_525;
break;
case ui::Dataspace::V0_BT709:
dataSpace = ui::Dataspace::BT709;
break;
default:
break;
}
mCurrentDataSpace = dataSpace;
Rect crop(mConsumer->getCurrentCrop());
const uint32_t transform(mConsumer->getCurrentTransform());
const uint32_t scalingMode(mConsumer->getCurrentScalingMode());
if ((crop != mCurrentCrop) ||
(transform != mCurrentTransform) ||
(scalingMode != mCurrentScalingMode)) {
mCurrentCrop = crop;
mCurrentTransform = transform;
mCurrentScalingMode = scalingMode;
recomputeVisibleRegions = true;
}
if (oldBuffer != nullptr) {
uint32_t bufWidth = getBE().compositionInfo.mBuffer->getWidth();
uint32_t bufHeight = getBE().compositionInfo.mBuffer->getHeight();
if (bufWidth != uint32_t(oldBuffer->width) ||
bufHeight != uint32_t(oldBuffer->height)) {
recomputeVisibleRegions = true;
}
}
//记录透明参数
mCurrentOpacity = getOpacityForFormat(getBE().compositionInfo.mBuffer->format);
if (oldOpacity != isOpaque(s)) {
recomputeVisibleRegions = true;
}
//移除mLocalSyncPoints中的阻塞
{
Mutex::Autolock lock(mLocalSyncPointMutex);
auto point = mLocalSyncPoints.begin();
while (point != mLocalSyncPoints.end()) {
if (!(*point)->frameIsAvailable() || !(*point)->transactionIsApplied()) {
// This sync point must have been added since we started
// latching. Don't drop it yet.
++point;
continue;
}
if ((*point)->getFrameNumber() <= mCurrentFrameNumber) {
point = mLocalSyncPoints.erase(point);
} else {
++point;
}
}
}
// FIXME: postedRegion should be dirty & bounds
Region dirtyRegion(Rect(s.active.w, s.active.h));
// transform the dirty region to window-manager space
outDirtyRegion = (getTransform().transform(dirtyRegion));
return outDirtyRegion;1.设置相关的参数，如帧数，裁剪参数，DataSpace，透明参数等。并且移除了代表当帧数之前mLocalSyncPoints。
2.计算脏区是由mDrawState对应的active参数确定(此时requested和active已经交换了)。最后调用transform转化转化为脏区
Transform Layer::getTransform() const { Transform t; const auto& p = mDrawingParent.promote(); if (p != nullptr) { t = p->getTransform(); if (p->isFixedSize() && p->getBE().compositionInfo.mBuffer != nullptr) { int bufferWidth; int bufferHeight; if ((p->mCurrentTransform & NATIVE_WINDOW_TRANSFORM_ROT_90) == 0) { bufferWidth = p->getBE().compositionInfo.mBuffer->getWidth(); bufferHeight = p->getBE().compositionInfo.mBuffer->getHeight(); } else { bufferHeight = p->getBE().compositionInfo.mBuffer->getWidth(); bufferWidth = p->getBE().compositionInfo.mBuffer->getHeight(); } float sx = p->getDrawingState().active.w / static_cast<float>(bufferWidth); float sy = p->getDrawingState().active.h / static_cast<float>(bufferHeight); Transform extraParentScaling; extraParentScaling.set(sx, 0, 0, sy); t = t * extraParentScaling; } } return t * getDrawingState().active.transform; }其实这个转化是查找每一个Layer的父Layer，并且根据父Layer的宽高和当前Layer比进行一次等比例缩小。
换句话说，实际上脏区的计算，从App进程角度来看是以Surface为一个单位进行计算。
BufferLayerConsumer updateTexImage
文件：/frameworks/native/services/surfaceflinger/BufferLayerConsumer.cpp
status_t BufferLayerConsumer::updateTexImage(BufferRejecter* rejecter, const DispSync& dispSync,
bool* autoRefresh, bool* queuedBuffer,
uint64_t maxFrameNumber) {
ATRACE_CALL();
Mutex::Autolock lock(mMutex);
if (mAbandoned) {
return NO_INIT;
}
// Make sure RenderEngine is current
if (!mRE.isCurrent()) {
return INVALID_OPERATION;
}
BufferItem item;
status_t err = acquireBufferLocked(&item, computeExpectedPresent(dispSync), maxFrameNumber);
if (err != NO_ERROR) {
if (err == BufferQueue::NO_BUFFER_AVAILABLE) {
err = NO_ERROR;
} else if (err == BufferQueue::PRESENT_LATER) {
// return the error, without logging
} else {
BLC_LOGE("updateTexImage: acquire failed: %s (%d)", strerror(-err), err);
}
return err;
}
if (autoRefresh) {
*autoRefresh = item.mAutoRefresh;
}
if (queuedBuffer) {
*queuedBuffer = item.mQueuedBuffer;
}
int slot = item.mSlot;
if (rejecter && rejecter->reject(mSlots[slot].mGraphicBuffer, item)) {
releaseBufferLocked(slot, mSlots[slot].mGraphicBuffer);
return BUFFER_REJECTED;
}
// Release the previous buffer.
err = updateAndReleaseLocked(item, &mPendingRelease);
if (err != NO_ERROR) {
return err;
}
if (!SyncFeatures::getInstance().useNativeFenceSync()) {
err = bindTextureImageLocked();
}
return err;
}在这个方法中有两个核心：
- 1.acquireBufferLocked消费图元。
- 2.LayerReject 判断是否需要拒绝显示当前已经消费的图元。
- 3.updateAndReleaseLocked更新当前Layer中需要显示的图元，同时释放之前的图元为Free状态。
- 4.最后判断OpenGL es是否携带EGL_KHR_fence_sync标志位，代表OpenGL es的同步栅。如果是，则提前通过OpenGL es绘制Image。
BufferLayerConsumer acquireBufferLocked
文件：meworks/native/services/surfaceflinger/BufferLayerConsumer.cpp
status_t BufferLayerConsumer::acquireBufferLocked(BufferItem* item, nsecs_t presentWhen,
uint64_t maxFrameNumber) {
status_t err = ConsumerBase::acquireBufferLocked(item, presentWhen, maxFrameNumber);
if (err != NO_ERROR) {
return err;
}
if (item->mGraphicBuffer != nullptr) {
mImages[item->mSlot] = new Image(item->mGraphicBuffer, mRE);
}
return NO_ERROR;
}- 1.ConsumerBase::acquireBufferLocked 从基类还是处理图元消费。
- 2.通过GraphicBuffer生成Image对象保存在mImages数组中。
先来看看image对象对应的头文件：
class Image : public LightRefBase<Image> {
public:
Image(sp<GraphicBuffer> graphicBuffer, RE::RenderEngine& engine);
Image(const Image& rhs) = delete;
Image& operator=(const Image& rhs) = delete;
status_t createIfNeeded(const Rect& imageCrop);
const sp<GraphicBuffer>& graphicBuffer() { return mGraphicBuffer; }
const native_handle* graphicBufferHandle() {
return mGraphicBuffer == nullptr ? nullptr : mGraphicBuffer->handle;
}
const RE::Image& image() const { return *mImage; }
private:
friend class LightRefBase<Image>;
virtual ~Image();
// mGraphicBuffer is the buffer that was used to create this image.
sp<GraphicBuffer> mGraphicBuffer;
std::unique_ptr<RE::Image> mImage;
bool mCreated;
int32_t mCropWidth;
int32_t mCropHeight;
};其实很简单，核心是持有了GraphicBuffer和RE::Image两个对象。GraphicBuffer图元，我们去看看RE::Image对象是怎么生成的。
BufferLayerConsumer::Image::Image(sp<GraphicBuffer> graphicBuffer, RE::RenderEngine& engine)
: mGraphicBuffer(graphicBuffer),
mImage{engine.createImage()},
mCreated(false),
mCropWidth(0),
mCropHeight(0) {}std::unique_ptr<RE::Image> RenderEngine::createImage() {
return std::make_unique<Image>(*this);
}class Image {
public:
virtual ~Image() = 0;
virtual bool setNativeWindowBuffer(ANativeWindowBuffer* buffer, bool isProtected,
int32_t cropWidth, int32_t cropHeight) = 0;
};
namespace impl {
class RenderEngine;
class Image : public RE::Image {
public:
explicit Image(const RenderEngine& engine);
~Image() override;
Image(const Image&) = delete;
Image& operator=(const Image&) = delete;
bool setNativeWindowBuffer(ANativeWindowBuffer* buffer, bool isProtected, int32_t cropWidth,
int32_t cropHeight) override;
private:
friend class RenderEngine;
EGLSurface getEGLImage() const { return mEGLImage; }
EGLDisplay mEGLDisplay;
EGLImageKHR mEGLImage = EGL_NO_IMAGE_KHR;
};
} // namespace impl其实Image对象实际上就是控制NativeBuffer，EGLDisplay，EGLSurface对象。这些对象实际上都是OpenGL es绘制的核心对象。所有的操作都是透过这个Image绘制。
ConsumerBase acquireBufferLocked
文件：/frameworks/native/libs/gui/ConsumerBase.cpp
status_t ConsumerBase::acquireBufferLocked(BufferItem *item,
nsecs_t presentWhen, uint64_t maxFrameNumber) {
...
status_t err = mConsumer->acquireBuffer(item, presentWhen, maxFrameNumber);
...
if (item->mGraphicBuffer != NULL) {
if (mSlots[item->mSlot].mGraphicBuffer != NULL) {
freeBufferLocked(item->mSlot);
}
mSlots[item->mSlot].mGraphicBuffer = item->mGraphicBuffer;
}
mSlots[item->mSlot].mFrameNumber = item->mFrameNumber;
mSlots[item->mSlot].mFence = item->mFence;
return OK;
}这里调用了BufferQueueConsumer的acquireBuffer。并且把消费的值赋值到新的item对应的mSlots下标中。因为这个过程可能会选择一些丢帧或者跳帧处理。
BufferQueueConsumer acquireBuffer
文件：/frameworks/native/libs/gui/BufferQueueConsumer.cpp
status_t BufferQueueConsumer::acquireBuffer(BufferItem* outBuffer,
nsecs_t expectedPresent, uint64_t maxFrameNumber) {
ATRACE_CALL();
int numDroppedBuffers = 0;
sp<IProducerListener> listener;
{
Mutex::Autolock lock(mCore->mMutex);
int numAcquiredBuffers = 0;
for (int s : mCore->mActiveBuffers) {
if (mSlots[s].mBufferState.isAcquired()) {
++numAcquiredBuffers;
}
}
if (numAcquiredBuffers >= mCore->mMaxAcquiredBufferCount + 1) {
return INVALID_OPERATION;
}
bool sharedBufferAvailable = mCore->mSharedBufferMode &&
mCore->mAutoRefresh && mCore->mSharedBufferSlot !=
BufferQueueCore::INVALID_BUFFER_SLOT;
if (mCore->mQueue.empty() && !sharedBufferAvailable) {
return NO_BUFFER_AVAILABLE;
}
BufferQueueCore::Fifo::iterator front(mCore->mQueue.begin());
if (expectedPresent != 0 && !mCore->mQueue.empty()) {
const int MAX_REASONABLE_NSEC = 1000000000ULL; // 1 second
while (mCore->mQueue.size() > 1 && !mCore->mQueue[0].mIsAutoTimestamp) {
const BufferItem& bufferItem(mCore->mQueue[1]);
if (maxFrameNumber && bufferItem.mFrameNumber > maxFrameNumber) {
break;
}
nsecs_t desiredPresent = bufferItem.mTimestamp;
if (desiredPresent < expectedPresent - MAX_REASONABLE_NSEC ||
desiredPresent > expectedPresent) {
break;
}
if (!front->mIsStale) {
// Front buffer is still in mSlots, so mark the slot as free
mSlots[front->mSlot].mBufferState.freeQueued();
if (!mCore->mSharedBufferMode &&
mSlots[front->mSlot].mBufferState.isFree()) {
mSlots[front->mSlot].mBufferState.mShared = false;
}
// Don't put the shared buffer on the free list
if (!mSlots[front->mSlot].mBufferState.isShared()) {
mCore->mActiveBuffers.erase(front->mSlot);
mCore->mFreeBuffers.push_back(front->mSlot);
}
listener = mCore->mConnectedProducerListener;
++numDroppedBuffers;
}
mCore->mQueue.erase(front);
front = mCore->mQueue.begin();
}
nsecs_t desiredPresent = front->mTimestamp;
bool bufferIsDue = desiredPresent <= expectedPresent ||
desiredPresent > expectedPresent + MAX_REASONABLE_NSEC;
bool consumerIsReady = maxFrameNumber > 0 ?
front->mFrameNumber <= maxFrameNumber : true;
if (!bufferIsDue || !consumerIsReady) {
return PRESENT_LATER;
}
}
int slot = BufferQueueCore::INVALID_BUFFER_SLOT;
if (sharedBufferAvailable && mCore->mQueue.empty()) {
....
} else {
slot = front->mSlot;
*outBuffer = *front;
}
if (!outBuffer->mIsStale) {
mSlots[slot].mAcquireCalled = true;
if (mCore->mQueue.empty()) {
mSlots[slot].mBufferState.acquireNotInQueue();
} else {
mSlots[slot].mBufferState.acquire();
}
mSlots[slot].mFence = Fence::NO_FENCE;
}
if (outBuffer->mAcquireCalled) {
outBuffer->mGraphicBuffer = NULL;
}
mCore->mQueue.erase(front);
mCore->mDequeueCondition.broadcast();
mCore->mOccupancyTracker.registerOccupancyChange(mCore->mQueue.size());
VALIDATE_CONSISTENCY();
}
if (listener != NULL) {
for (int i = 0; i < numDroppedBuffers; ++i) {
listener->onBufferReleased();
}
}
return NO_ERROR;
}- 处理图元之前，首先检测mActiveBuffers中活跃的图元究竟有多少个。如果超出mMaxAcquiredBufferCount限制，则不允许继续。
- 获取之前入队到mQueue的第一项front进行循环处理。首先获取之前计算出来的期待显示时间和当前入队的时间比较，找出和当前时间最接近的入队图元。如果入队的时间比期待的小一秒，并且入队的时间比期待的时间小。这样就会直接跳出mQueue处理的处理循环。
如果front.mIsStale为false说明这个图元已经过期了。将把mSlot的索引从mActiveBuffers转移到mFreeBuffer。同时计算为一个numDroppedBuffers丢帧计数处理。获取mQueue的下一项图元。
最后把当前的front图元返回，并且释放那些已经丢帧的图元。
LayerRejecter 判断是否需要拒绝显示当前已经消费的图元
文件：/frameworks/native/services/surfaceflinger/LayerRejecter.cpp
bool LayerRejecter::reject(const sp<GraphicBuffer>& buf, const BufferItem& item) {
if (buf == nullptr) {
return false;
}
uint32_t bufWidth = buf->getWidth();
uint32_t bufHeight = buf->getHeight();
if (item.mTransform & Transform::ROT_90) {
swap(bufWidth, bufHeight);
}
int actualScalingMode = mOverrideScalingMode >= 0 ? mOverrideScalingMode : item.mScalingMode;
bool isFixedSize = actualScalingMode != NATIVE_WINDOW_SCALING_MODE_FREEZE;
if (mFront.active != mFront.requested) {
if (isFixedSize || (bufWidth == mFront.requested.w && bufHeight == mFront.requested.h)) {
mFront.active = mFront.requested;
mCurrent.active = mFront.active;
mCurrent.modified = true;
mRecomputeVisibleRegions = true;
mFreezeGeometryUpdates = false;
if (mFront.crop != mFront.requestedCrop) {
mFront.crop = mFront.requestedCrop;
mCurrent.crop = mFront.requestedCrop;
mRecomputeVisibleRegions = true;
}
if (mFront.finalCrop != mFront.requestedFinalCrop) {
mFront.finalCrop = mFront.requestedFinalCrop;
mCurrent.finalCrop = mFront.requestedFinalCrop;
mRecomputeVisibleRegions = true;
}
}
}
if (!isFixedSize && !mStickyTransformSet) {
if (mFront.active.w != bufWidth || mFront.active.h != bufHeight) {
return true;
}
}
if (!mFront.activeTransparentRegion.isTriviallyEqual(mFront.requestedTransparentRegion)) {
mFront.activeTransparentRegion = mFront.requestedTransparentRegion;
mCurrent.activeTransparentRegion = mFront.activeTransparentRegion;
mRecomputeVisibleRegions = true;
}
return false;
}拒绝检测图元显示。mFront其实就是上文通过doTransaction的mDrawState，此时已经进行交换，所以mDrawState是这一帧的内容。一旦发现requested和active的几何不一致。如果此时不是NATIVE_WINDOW_SCALING_MODE_FREEZE(冻结屏幕)。同时图元的宽高和requested相同，才会进行requested和active的交换。
如果是NATIVE_WINDOW_SCALING_MODE_FREEZE(冻结屏幕)，则但是发现requested的宽高和图元需要的宽高不一致就会拒绝绘制，丢掉当前帧。其实思想很简单，实际上就这种NATIVE_WINDOW_SCALING_MODE_FREEZE模式下就是只绘制和当前窗口一样大小的图元。其他都不设置。
updateAndReleaseLocked更新当前Layer中需要显示的图元，同时释放之前的图元为Free状态
status_t BufferLayerConsumer::updateAndReleaseLocked(const BufferItem& item,
PendingRelease* pendingRelease) {
status_t err = NO_ERROR;
int slot = item.mSlot;
if (slot != mCurrentTexture) {
err = syncForReleaseLocked();
if (err != NO_ERROR) {
releaseBufferLocked(slot, mSlots[slot].mGraphicBuffer);
return err;
}
}
sp<Image> nextTextureImage = mImages[slot];
if (mCurrentTexture != BufferQueue::INVALID_BUFFER_SLOT) {
if (pendingRelease == nullptr) {
status_t status =
releaseBufferLocked(mCurrentTexture, mCurrentTextureImage->graphicBuffer());
if (status < NO_ERROR) {
err = status;
}
} else {
pendingRelease->currentTexture = mCurrentTexture;
pendingRelease->graphicBuffer = mCurrentTextureImage->graphicBuffer();
pendingRelease->isPending = true;
}
}
// Update the BufferLayerConsumer state.
mCurrentTexture = slot;
mCurrentTextureImage = nextTextureImage;
mCurrentCrop = item.mCrop;
mCurrentTransform = item.mTransform;
mCurrentScalingMode = item.mScalingMode;
mCurrentTimestamp = item.mTimestamp;
mCurrentDataSpace = static_cast<ui::Dataspace>(item.mDataSpace);
mCurrentHdrMetadata = item.mHdrMetadata;
mCurrentFence = item.mFence;
mCurrentFenceTime = item.mFenceTime;
mCurrentFrameNumber = item.mFrameNumber;
mCurrentTransformToDisplayInverse = item.mTransformToDisplayInverse;
mCurrentSurfaceDamage = item.mSurfaceDamage;
mCurrentApi = item.mApi;
computeCurrentTransformMatrixLocked();
return err;
}- 1.syncForReleaseLocked 实际上是一次Fence阻塞，等待所有的Fence的监听都达到了NO_ERROR,返回Signal状态。就进行下一步，同时进行释放上一帧的图元，进入到free状态。
- 2.记录上一帧的数据到pendingRelease，以及本次准备渲染的帧数中相关的参数，如DataSpace，mSlot插槽中对应的index，以及携带GraphicBuffer的Image。
DataSpace小知识的记录
有了RGB，Ycbcr这些颜色format，为什么还需要DataSpace，色彩的数据空间呢？这里需要借助一篇文章
，这里稍作总结。
在现实世界中，当光强一倍，则亮度也会提升一倍，是一个线性关系。但是由于最早的显示器(阴极射线管)显示图像的时候，输出亮度和电压并不是成线性关系的，而是亮度等于电压的2.2次幂的非线性关系：$l = u^{2.2}$.
这个2.2也叫做Gama值。为了尽可能的达到现实世界的效果。因此需要一个Gama的纠正。也就是去除2.2次幂，因此会在处理之前先进行一次0.45次幂的处理，抵消这个2.2次幂的造成的异常。
而我们常用的sRGB的色彩空间也是这么一回事，就是指的是0.45次幂。而在上文中所有记录的DataSpace也是这个意思。
总结
bool refreshNeeded = handleMessageTransaction();
refreshNeeded |= handleMessageInvalidate();
refreshNeeded |= mRepaintEverything;
if (refreshNeeded) {
signalRefresh();
}此时我们已经分析接收到Invalidate消息之后判断是否需要刷新的判断处理。
- 1.handleMessageTransaction将会处理每一个Layer的事务，最核心的事情就是把每一个Layer中的上一帧的mDrawState被当前帧的mCurrentState替代。一旦有事务需要处理，说明有Surface发生了状态的变化，如宽高如位置。此时就必须重新刷新整个界面。
- 2.handleMessageInvalidate处理的核心：
- 首先检测哪一些图元需要显示，需要的则会添加到mLayersWithQueuedFrames。条件是入队时间不能超过预期时间的一秒，也能不能超过预期时间（mQueueItems是onFrameAvailable回调添加）。
- 遍历每一个需要显示的Layer，调用latchBuffer方法。这个方法核心是updateTexImage。这个方法分为3个步骤：
1) acquireBufferLocked 本质上是获取mQueue的第一个加进来的图元作为即将显示的图元。但是如果遇到显示的时间和预期时间差大于1秒，同时发现这个图元已经过期了(free状态),则会跳帧，直到找到最近时间的一帧。
2) LayerRejecter 判断是否有打开冻结窗口模式，打开了但是发现图元的大小不对则拒绝显示。相反，则会mDrawState的requested赋值给active。
3) updateAndReleaseLocked 释放前一帧的图元，同时准备设置当前消费的图元作为准备绘制的画面。
我们回头来看看handleMessageInvalidate，它其实也是判断是否需要全局刷新。如果发现图元锁定之后有Layer消费了图元，则会决定进行调用refresh页面。发送Refresh消息。最后dirty区域将会依赖父Layer 的宽高。mVisibleRegions标志位最后是依赖latchBuffer返回的脏区和Layer是否有添加过。
我们最后来看看Refresh做了什么？
case MessageQueue::REFRESH: {
handleMessageRefresh();
break;
}void SurfaceFlinger::handleMessageRefresh() {
mRefreshPending = false;
nsecs_t refreshStartTime = systemTime(SYSTEM_TIME_MONOTONIC);
preComposition(refreshStartTime);
rebuildLayerStacks();
setUpHWComposer();
doDebugFlashRegions();
doTracing("handleRefresh");
logLayerStats();
doComposition();
postComposition(refreshStartTime);
...
mLayersWithQueuedFrames.clear();
}大致上，刷新屏幕分为7步骤：
- 1.preComposition 预处理合成
- 2.rebuildLayerStacks 重新构建Layer栈
- 3.setUpHWComposer HWC的渲染或者准备
- 4.doDebugFlashRegions 打开debug绘制模式
- 5.doTracing 跟踪打印
- 6.doComposition 合成图元
- 7.postComposition 图元合成后的vysnc等收尾工作。
下一篇文章将会和大家聊聊。
