本内容基于自己对于代码的理解以及网上大牛的博客参考写的，作为回顾时的参考之用。
1. handlePageFlip
bool SurfaceFlinger::handleMessageInvalidate() {
ATRACE_CALL();
return handlePageFlip();
}
page flip 意思是翻页
bool SurfaceFlinger::handlePageFlip()
{
Region dirtyRegion;
nsecs_t pageFlipTimestamp = systemTime();
mAnimFrameTracker.setPageFlipTime(pageFlipTimestamp);
bool visibleRegions = false;
const LayerVector& layers(mDrawingState.layersSortedByZ);
bool frameQueued = false;
#ifdef USE_PHS
mAdd->phsHints.onPreHandlePageFlip();
#endif
// Store the set of layers that need updates. This set must not change as
// buffers are being latched, as this could result in a deadlock.
// Example: Two producers share the same command stream and:
// 1.) Layer 0 is latched
// 2.) Layer 0 gets a new frame
// 2.) Layer 1 gets a new frame
// 3.) Layer 1 is latched.
// Display is now waiting on Layer 1's frame, which is behind layer 0's
// second frame. But layer 0's second frame could be waiting on display.
Vector<Layer*> layersWithQueuedFrames;
for (size_t i = 0, count = layers.size(); i<count ; i++) {
const sp<Layer>& layer(layers[i]);
if (layer->hasQueuedFrame()) {//该Layer是否有 QUEUED buffer
frameQueued = true;
layer->decrementSwapInterval(); //一个vsync来了，就表示需要swap一次。 Consumer的mSwapInterval如果大于0就减1
if (layer->shouldPresentNow(mPrimaryDispSync)) { //是否需要显示该Layer
layersWithQueuedFrames.push_back(layer.get());
} else {
layer->useEmptyDamage();//如果不需要显示，则该Layer的脏区域为empty
}
} else {
layer->useEmptyDamage();
}
#ifdef USE_PHS
mAdd->phsHints.sendHintsPreLatch(layer);
#endif
}
bool layerHadDirtyRegion = false;
//layersWithQueuedFrames保存需要进行合成的Layer
for (size_t i = 0, count = layersWithQueuedFrames.size() ; i<count ; i++) {
Layer* layer = layersWithQueuedFrames[i];
//计算Layer的脏区域
const Region dirty(layer->latchBuffer(visibleRegions, pageFlipTimestamp));
layer->useSurfaceDamage();
layerHadDirtyRegion |= !dirty.isEmpty();
const Layer::State& s(layer->getDrawingState());
//修改Layer所在的Display上的脏区域
invalidateLayerStack(s.layerStack, dirty);
#ifdef USE_PHS
mAdd->phsHints.sendHintsPostLatch(layer);
#endif
}
mVisibleRegionsDirty |= visibleRegions;
if (layerHadDirtyRegion) {
mDebugHandlePageFlipHadDirtyRegionCount++;
}
// If we will need to wake up at some time in the future to deal with a
// queued frame that shouldn't be displayed during this vsync period, wake
// up during the next vsync period to check again.
if (frameQueued && layersWithQueuedFrames.empty()) {
//如果Layer中有QUEUED的帧，但是在该VSYNC检查出来不需要显示Layer, 那么说明QUEUED的帧要显示的条件还不满足，则触发下一个 VSYNC
signalLayerUpdate();
}
// Only continue with the refresh if there is actually new work to do
// 返回值确定是否需要刷新显示
return !layersWithQueuedFrames.empty();
}
2. shouldPresentNow
bool Layer::shouldPresentNow(const DispSync& dispSync) const {
//如果是自动刷新，或是sideband buffer(Tv相关的)发生变化了, mSidebandStreamChanged主要是通过setSidebandStream改变的，
if (mSidebandStreamChanged || mAutoRefresh) {
return true;
}
// 如果swap的间隔还大于0，表示还需多个VSYNC，则不需要刷新
if (mSurfaceFlingerConsumer->getSwapInterval() > 0) {
return false;
}
Mutex::Autolock lock(mQueueItemLock);
//Layer都没有Queued的frame，就不需要显示了
if (mQueueItems.empty()) {
return false;
}
//第一个QUEUED的帧刷新时间
auto timestamp = mQueueItems[0].mTimestamp;
nsecs_t expectedPresent =
mSurfaceFlingerConsumer->computeExpectedPresent(dispSync);
// Ignore timestamps more than a second in the future
//如果第一个queued的frame在未来1s之内显示，这个是比较可信的，
//反之，一个frame要求在1S后显示，这个可能就有问题，所以此时就让它显示
bool isPlausible = timestamp < (expectedPresent + s2ns(1));
//如果超时了赶紧刷新出来
bool isDue = timestamp < expectedPresent;
return isDue || !isPlausible;
}
3. latchBuffer
Layer.cpp
Region Layer::latchBuffer(bool& recomputeVisibleRegions, nsecs_t pageFlipTimestamp)
{
ATRACE_CALL();
//如果sideband surface改变了，表示该layer是sideband buffer了， 然后将 mSidebandStreamChanged置为false
if (android_atomic_acquire_cas(true, false, &mSidebandStreamChanged) == 0) {
// mSidebandStreamChanged was true
mSidebandStream = mSurfaceFlingerConsumer->getSidebandStream();
if (mSidebandStream != NULL) {
setTransactionFlags(eTransactionNeeded);
mFlinger->setTransactionFlags(eTraversalNeeded);
}
// sideband的情况，需要重新 计算可视区域
recomputeVisibleRegions = true;
const State& s(getDrawingState());
return s.active.transform.transform(Region(Rect(s.active.w, s.active.h)));
}
Region outDirtyRegion;
//当前Layer中有QUEUED的帧，或者Layer是自动刷新的情况
if (mQueuedFrames > 0 || mAutoRefresh) {
// if we've already called updateTexImage() without going through
// a composition step, we have to skip this layer at this point
// because we cannot call updateTeximage() without a corresponding
// compositionComplete() call.
// we'll trigger an update in onPreComposition().
if (mRefreshPending) {
return outDirtyRegion;
}
// Capture the old state of the layer for comparisons later
const State& s(getDrawingState());
const bool oldOpacity = isOpaque(s);
sp<GraphicBuffer> oldActiveBuffer = mActiveBuffer;
...
//生成一个Reject
Reject r(mDrawingState, getCurrentState(), recomputeVisibleRegions,
getProducerStickyTransform() != 0, mName.string(),
mOverrideScalingMode);
// Check all of our local sync points to ensure that all transactions
// which need to have been applied prior to the frame which is about to
// be latched have signaled
//获得QUEUED队列中第一个Frame号
auto headFrameNumber = getHeadFrameNumber();
bool matchingFramesFound = false;
bool allTransactionsApplied = true;
{
//看下延迟的buffer是否到了延迟点了，(根据frame number来判断)
Mutex::Autolock lock(mLocalSyncPointMutex);
for (auto& point : mLocalSyncPoints) {
//还不是defer的那个Frame
if (point->getFrameNumber() > headFrameNumber) {
break;
}
//代码走到这里，说明Defer的那个Frame已经来了
matchingFramesFound = true;
if (!point->frameIsAvailable()) { //这个在Layer处理事务中已经设置过了
// We haven't notified the remote layer that the frame for
// this point is available yet. Notify it now, and then
// abort this attempt to latch.
point->setFrameAvailable();
allTransactionsApplied = false;
break;
}
allTransactionsApplied &= point->transactionIsApplied();
}
}
//DEFER的帧已经到来，但是还没有apply transaction (这个发生在applyPendingStates),
//这时需要触发下一个VSYNC，先去apply transaction
if (matchingFramesFound && !allTransactionsApplied) {
mFlinger->signalLayerUpdate();
return outDirtyRegion;
}
// This boolean is used to make sure that SurfaceFlinger's shadow copy
// of the buffer queue isn't modified when the buffer queue is returning
// BufferItem's that weren't actually queued. This can happen in shared
// buffer mode.
bool queuedBuffer = false;
status_t updateResult = mSurfaceFlingerConsumer->updateTexImage(&r,
mFlinger->mPrimaryDispSync, &mAutoRefresh, &queuedBuffer,
mLastFrameNumberReceived);
if (updateResult == BufferQueue::PRESENT_LATER) {
// Producer doesn't want buffer to be displayed yet. Signal a
// layer update so we check again at the next opportunity.
// 延迟显示，触发下一个VSYNC， 即Buffer显示的时间还没到
mFlinger->signalLayerUpdate();
return outDirtyRegion;
} else if (updateResult == SurfaceFlingerConsumer::BUFFER_REJECTED) {
// If the buffer has been rejected, remove it from the shadow queue
// and return early
// Buffer被Reject掉的情况
if (queuedBuffer) {
Mutex::Autolock lock(mQueueItemLock);
mQueueItems.removeAt(0); //从Layer的 mQueueItems列队中移除
android_atomic_dec(&mQueuedFrames);
}
return outDirtyRegion;
} else if (updateResult != NO_ERROR || mUpdateTexImageFailed) {
// This can occur if something goes wrong when trying to create the
// EGLImage for this buffer. If this happens, the buffer has already
// been released, so we need to clean up the queue and bug out
// early.
// 创建 EGLImage 失败的情况
if (queuedBuffer) {
Mutex::Autolock lock(mQueueItemLock);
mQueueItems.clear();
android_atomic_and(0, &mQueuedFrames);
}
// Once we have hit this state, the shadow queue may no longer
// correctly reflect the incoming BufferQueue's contents, so even if
// updateTexImage starts working, the only safe course of action is
// to continue to ignore updates.
mUpdateTexImageFailed = true;
return outDirtyRegion;
}
//queuedBuffer在非buffer shared模式时为true
if (queuedBuffer) {
// Autolock scope
//这个是GLConsumer里的Frame number号， 在updateAndReleaseLocked里赋值, 即当前需要显示的Frame
auto currentFrameNumber = mSurfaceFlingerConsumer->getFrameNumber();
Mutex::Autolock lock(mQueueItemLock);
// Remove any stale buffers that have been dropped during
// updateTexImage
//马上要显示的Frame号是currentFrameNumber, 那么之前QUEUED的frame就过期了，直接移除掉
while (mQueueItems[0].mFrameNumber != currentFrameNumber) {
//移除掉过时的 Buffer
mQueueItems.removeAt(0);
android_atomic_dec(&mQueuedFrames);
}
//现在第一个显示frame了
mQueueItems.removeAt(0);
}
// Decrement the queued-frames count. Signal another event if we
// have more frames pending.
if ((queuedBuffer && android_atomic_dec(&mQueuedFrames) > 1)
|| mAutoRefresh) {
//如果还有Queued的Buffer，那么通知 SurfaceFlinger在下一个VSYNC时进行更新
mFlinger->signalLayerUpdate();
}
// Trigger another wake up to decrement our swap interval
if (mSurfaceFlingerConsumer->getSwapInterval() > 1) {
//如果 swap 间隔还大于1， 表示还需要多个vsync还能显示该buffer，触发 VSYNC
mFlinger->signalLayerUpdate();
}
if (updateResult != NO_ERROR) {
// something happened!
//异常发生
recomputeVisibleRegions = true;
return outDirtyRegion;
}
// update the active buffer
//mActiveBuffer表示马上要显示的buffer,
mActiveBuffer = mSurfaceFlingerConsumer->getCurrentBuffer();
if (mActiveBuffer == NULL) {
// this can only happen if the very first buffer was rejected.
return outDirtyRegion;
}
//即将进入 refresh的阶段
mRefreshPending = true;
mFrameLatencyNeeded = true;
mFrameTracker.setPageFlipTime(pageFlipTimestamp);
if (oldActiveBuffer == NULL) {
// the first time we receive a buffer, we need to trigger a
// geometry invalidation.
//如果是第一次接收到Buffer, 需要重新计算可视区域
recomputeVisibleRegions = true;
}
Rect crop(mSurfaceFlingerConsumer->getCurrentCrop());
const uint32_t transform(mSurfaceFlingerConsumer->getCurrentTransform());
const uint32_t scalingMode(mSurfaceFlingerConsumer->getCurrentScalingMode());
if ((crop != mCurrentCrop) ||
(transform != mCurrentTransform) ||
(scalingMode != mCurrentScalingMode))
{
//保存最新的 crop 与transform 这些变量
mCurrentCrop = crop;
mCurrentTransform = transform;
mCurrentScalingMode = scalingMode;
recomputeVisibleRegions = true;
}
if (oldActiveBuffer != NULL) {
uint32_t bufWidth = mActiveBuffer->getWidth();
uint32_t bufHeight = mActiveBuffer->getHeight();
if (bufWidth != uint32_t(oldActiveBuffer->width) ||
bufHeight != uint32_t(oldActiveBuffer->height)) {
recomputeVisibleRegions = true; //最新的buffer和上一个渲染的buffer的尺寸不一样的，这时需要重新计算可视化区域
mFreezePositionUpdates = false;
}
}
//透明度相关
mCurrentOpacity = getOpacityForFormat(mActiveBuffer->format);
if (oldOpacity != isOpaque(s)) {
recomputeVisibleRegions = true;
}
mCurrentFrameNumber = mSurfaceFlingerConsumer->getFrameNumber();
// Remove any sync points corresponding to the buffer which was just
// latched
{
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;
}
// mCurrentFrameNumber是即将要显示的Frame，如果要显示的Frame已经超过了DEFER的帧，则移除掉sync point
if ((*point)->getFrameNumber() <= mCurrentFrameNumber) {
point = mLocalSyncPoints.erase(point);
} else {
++point;
}
}
}
//计算出脏区域
// FIXME: postedRegion should be dirty & bounds
Region dirtyRegion(Rect(s.active.w, s.active.h));
// transform the dirty region to window-manager space
outDirtyRegion = (s.active.transform.transform(dirtyRegion));
}
return outDirtyRegion;
}
4. updateTexImage
status_t SurfaceFlingerConsumer::updateTexImage(BufferRejecter* rejecter,
const DispSync& dispSync, bool* autoRefresh, bool* queuedBuffer,
uint64_t maxFrameNumber)
{
ATRACE_CALL();
ALOGV("updateTexImage");
Mutex::Autolock lock(mMutex);
if (mAbandoned) {
return NO_INIT;
}
// Make sure the EGL state is the same as in previous calls.
// egl环境检查
status_t err = checkAndUpdateEglStateLocked();
if (err != NO_ERROR) {
return err;
}
BufferItem item;
// Acquire the next buffer.
// In asynchronous mode the list is guaranteed to be one buffer
// deep, while in synchronous mode we use the oldest buffer.
//获得要显示出来的Buffer
// maxFrameNumber是 Layer onFrameAvailable/onFrameReplaced 里的那个Frame号，也就是Layer中的mLastFrameNumberReceived
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 {
ALOGE("updateTexImage: acquire failed: %s (%d)",
strerror(-err), err);
}
return err;
}
// We call the rejecter here, in case the caller has a reason to
// not accept this buffer. This is used by SurfaceFlinger to
// reject buffers which have the wrong size
int slot = item.mSlot;
// 检查是否需要 reject buffer
if (rejecter && rejecter->reject(mSlots[slot].mGraphicBuffer, item)) {
releaseBufferLocked(slot, mSlots[slot].mGraphicBuffer, EGL_NO_SYNC_KHR);
return BUFFER_REJECTED;
}
if (autoRefresh) {
*autoRefresh = item.mAutoRefresh;
}
// mQueuedBuffer 表示是否该Buffer还被Producer queued, 在shared buffer模式才为false
if (queuedBuffer) {
*queuedBuffer = item.mQueuedBuffer;
}
// release 旧的buffer, 创建GLConsumer里新的EGLImage
err = updateAndReleaseLocked(item);
if (err != NO_ERROR) {
return err;
}
if (!SyncFeatures::getInstance().useNativeFenceSync()) {
// Bind the new buffer to the GL texture.
//
// Older devices require the "implicit" synchronization provided
// by glEGLImageTargetTexture2DOES, which this method calls. Newer
// devices will either call this in Layer::onDraw, or (if it's not
// a GL-composited layer) not at all.
err = bindTextureImageLocked();
}
if (err == NO_ERROR) {
mSwapInterval = item.mInterval == 1 ? 0 : (item.mInterval+2)>>1;
}
return err;
}
5. acquireBuffer
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);
// Check that the consumer doesn't currently have the maximum number of
// buffers acquired. We allow the max buffer count to be exceeded by one
// buffer so that the consumer can successfully set up the newly acquired
// buffer before releasing the old one.
int numAcquiredBuffers = 0;
for (int s : mCore->mActiveBuffers) { //统计mActiveBuffers中已经是 ACQUIRED 的Frame 个数
if (mSlots[s].mBufferState.isAcquired()) { //是否已经是 ACQUIRED 的Buffer
++numAcquiredBuffers;
}
}
//异常检测
if (numAcquiredBuffers >= mCore->mMaxAcquiredBufferCount + 1) {
return INVALID_OPERATION;
}
bool sharedBufferAvailable = mCore->mSharedBufferMode &&
mCore->mAutoRefresh && mCore->mSharedBufferSlot !=
BufferQueueCore::INVALID_BUFFER_SLOT;
// In asynchronous mode the list is guaranteed to be one buffer deep,
// while in synchronous mode we use the oldest buffer.
//既不是shared buffer mode，而且也没有Queued 的buffer
if (mCore->mQueue.empty() && !sharedBufferAvailable) {
return NO_BUFFER_AVAILABLE;
}
//queue中的第一个 buffer
BufferQueueCore::Fifo::iterator front(mCore->mQueue.begin());
// If expectedPresent is specified, we may not want to return a buffer yet.
// If it's specified and there's more than one buffer queued, we may want
// to drop a buffer.
// Skip this if we're in shared buffer mode and the queue is empty,
// since in that case we'll just return the shared buffer.
if (expectedPresent != 0 && !mCore->mQueue.empty()) {
const int MAX_REASONABLE_NSEC = 1000000000ULL; // 1 second
// The 'expectedPresent' argument indicates when the buffer is expected
// to be presented on-screen. If the buffer's desired present time is
// earlier (less) than expectedPresent -- meaning it will be displayed
// on time or possibly late if we show it as soon as possible -- we
// acquire and return it. If we don't want to display it until after the
// expectedPresent time, we return PRESENT_LATER without acquiring it.
//
// To be safe, we don't defer acquisition if expectedPresent is more
// than one second in the future beyond the desired present time
// (i.e., we'd be holding the buffer for a long time).
//
// NOTE: Code assumes monotonic time values from the system clock
// are positive.
// Start by checking to see if we can drop frames. We skip this check if
// the timestamps are being auto-generated by Surface. If the app isn't
// generating timestamps explicitly, it probably doesn't want frames to
// be discarded based on them.
// 检查后面的 Queue, 找到最近需要显示的Buffer,
while (mCore->mQueue.size() > 1 && !mCore->mQueue[0].mIsAutoTimestamp) {
const BufferItem& bufferItem(mCore->mQueue[1]);
// If dropping entry[0] would leave us with a buffer that the
// consumer is not yet ready for, don't drop it.
// maxFrameNumber是这次REFERSH中Layer收到的最近的那个FRAME,
// 但是这个BUFFERITEM还在后面才显示，所以说明后面的Buffer都还没过期
// Consumer 还没有准备好，没必要把上一个buffer drop掉，break掉，显示上一个buffer
if (maxFrameNumber && bufferItem.mFrameNumber > maxFrameNumber) {
break;
}
// If entry[1] is timely, drop entry[0] (and repeat). We apply an
// additional criterion here: we only drop the earlier buffer if our
// desiredPresent falls within +/- 1 second of the expected present.
// Otherwise, bogus desiredPresent times (e.g., 0 or a small
// relative timestamp), which normally mean "ignore the timestamp
// and acquire immediately", would cause us to drop frames.
//
// We may want to add an additional criterion: don't drop the
// earlier buffer if entry[1]'s fence hasn't signaled yet.
nsecs_t desiredPresent = bufferItem.mTimestamp;
//如果这个buffer显示的时间在expected之后，并在将来的1s内会，那么也没有drop掉上一个.
// break掉直接显示上一个buffer
if (desiredPresent < expectedPresent - MAX_REASONABLE_NSEC ||
desiredPresent > expectedPresent) {
// This buffer is set to display in the near future, or
// desiredPresent is garbage. Either way we don't want to drop
// the previous buffer just to get this on the screen sooner.
break;
}
//没有过期的Buffer, 一般disconnect后才会过期
if (!front->mIsStale) {
// Front buffer is still in mSlots, so mark the slot as free
mSlots[front->mSlot].mBufferState.freeQueued(); //将会从queue里删除
// 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[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;
}
//上一个已经没有必要显示了, 重新找一个显示的
mCore->mQueue.erase(front);
front = mCore->mQueue.begin();
}
// See if the front buffer is ready to be acquired
nsecs_t desiredPresent = front->mTimestamp;
bool bufferIsDue = desiredPresent <= expectedPresent ||
desiredPresent > expectedPresent + MAX_REASONABLE_NSEC;
bool consumerIsReady = maxFrameNumber > 0 ?
front->mFrameNumber <= maxFrameNumber : true;
// buffer要显示的时间还没到，或者 consumer 还没有准备好,
if (!bufferIsDue || !consumerIsReady) {
if(bVQ_StatsEnable && (mCore->mConnectedApi == NATIVE_WINDOW_API_MEDIA)) {
}
return PRESENT_LATER;
}
}
int slot = BufferQueueCore::INVALID_BUFFER_SLOT;
//如果是shared buffer的情况
if (sharedBufferAvailable && mCore->mQueue.empty()) {
// make sure the buffer has finished allocating before acquiring it
mCore->waitWhileAllocatingLocked();
slot = mCore->mSharedBufferSlot;
// Recreate the BufferItem for the shared buffer from the data that
// was cached when it was last queued.
outBuffer->mGraphicBuffer = mSlots[slot].mGraphicBuffer;
outBuffer->mFence = Fence::NO_FENCE;
outBuffer->mCrop = mCore->mSharedBufferCache.crop;
outBuffer->mTransform = mCore->mSharedBufferCache.transform &
~static_cast<uint32_t>(
NATIVE_WINDOW_TRANSFORM_INVERSE_DISPLAY);
outBuffer->mScalingMode = mCore->mSharedBufferCache.scalingMode;
outBuffer->mDataSpace = mCore->mSharedBufferCache.dataspace;
outBuffer->mFrameNumber = mCore->mFrameCounter;
outBuffer->mSlot = slot;
outBuffer->mAcquireCalled = mSlots[slot].mAcquireCalled;
outBuffer->mTransformToDisplayInverse =
(mCore->mSharedBufferCache.transform &
NATIVE_WINDOW_TRANSFORM_INVERSE_DISPLAY) != 0;
outBuffer->mSurfaceDamage = Region::INVALID_REGION;
outBuffer->mQueuedBuffer = false;
outBuffer->mIsStale = false;
outBuffer->mAutoRefresh = mCore->mSharedBufferMode &&
mCore->mAutoRefresh;
} else {
//找到了即将要显示的Buffer
slot = front->mSlot;
*outBuffer = *front;
}
ATRACE_BUFFER_INDEX(slot);
//即将要显示的Buffer没有过期
if (!outBuffer->mIsStale) {
mSlots[slot].mAcquireCalled = true; //BUFFER的状态已经是 ACQUIRED 的了
// 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.
// 状态变为 ACQUIRED
if (mCore->mQueue.empty()) {
mSlots[slot].mBufferState.acquireNotInQueue();
} else {
//
mSlots[slot].mBufferState.acquire();
}
mSlots[slot].mFence = Fence::NO_FENCE;
}
// If the buffer has previously been acquired by the consumer, set
// mGraphicBuffer to NULL to avoid unnecessarily remapping this buffer
// on the consumer side
if (outBuffer->mAcquireCalled) {
outBuffer->mGraphicBuffer = NULL;
}
//将Buffer从 BufferQueueCore列队里移除
mCore->mQueue.erase(front);
// We might have freed a slot while dropping old buffers, or the producer
// may be blocked waiting for the number of buffers in the queue to
// decrease.
mCore->mDequeueCondition.broadcast();
ATRACE_INT(mCore->mConsumerName.string(), mCore->mQueue.size());
VALIDATE_CONSISTENCY();
}
if (listener != NULL) {
//对丢掉的buffer进行回调
for (int i = 0; i < numDroppedBuffers; ++i) {
listener->onBufferReleased();
}
}
return NO_ERROR;
}
5. updateAndReleaseLocked
GLConsumer.cpp
status_t GLConsumer::updateAndReleaseLocked(const BufferItem& item,
PendingRelease* pendingRelease)
{
status_t err = NO_ERROR;
//找出slot
int slot = item.mSlot;
if (!mAttached) { //Open GL ES attach
releaseBufferLocked(slot, mSlots[slot].mGraphicBuffer,
mEglDisplay, EGL_NO_SYNC_KHR);
return INVALID_OPERATION;
}
// Confirm state.
err = checkAndUpdateEglStateLocked();
if (err != NO_ERROR) {
releaseBufferLocked(slot, mSlots[slot].mGraphicBuffer,
mEglDisplay, EGL_NO_SYNC_KHR);
return err;
}
// Ensure we have a valid EglImageKHR for the slot, creating an EglImage
// if nessessary, for the gralloc buffer currently in the slot in
// ConsumerBase.
// We may have to do this even when item.mGraphicBuffer == NULL (which
// means the buffer was previously acquired).
//创建 EGLImage 此时 mEglImage 已经有acquireBufferLocked中找到的即将要显示的 BufferItem 的 GraphicBuffer
err = mEglSlots[slot].mEglImage->createIfNeeded(mEglDisplay, item.mCrop);
if (err != NO_ERROR) {
releaseBufferLocked(slot, mSlots[slot].mGraphicBuffer,
mEglDisplay, EGL_NO_SYNC_KHR);
return UNKNOWN_ERROR;
}
// Do whatever sync ops we need to do before releasing the old slot.
if (slot != mCurrentTexture) {
err = syncForReleaseLocked(mEglDisplay); //egl 同步相关
if (err != NO_ERROR) {
// Release the buffer we just acquired. It's not safe to
// release the old buffer, so instead we just drop the new frame.
// As we are still under lock since acquireBuffer, it is safe to
// release by slot.
releaseBufferLocked(slot, mSlots[slot].mGraphicBuffer,
mEglDisplay, EGL_NO_SYNC_KHR);
return err;
}
}
// Hang onto the pointer so that it isn't freed in the call to
// releaseBufferLocked() if we're in shared buffer mode and both buffers are
// the same.
sp<EglImage> nextTextureImage = mEglSlots[slot].mEglImage;
// release old buffer
if (mCurrentTexture != BufferQueue::INVALID_BUFFER_SLOT) {
if (pendingRelease == nullptr) {
status_t status = releaseBufferLocked(
mCurrentTexture, mCurrentTextureImage->graphicBuffer(),
mEglDisplay, mEglSlots[mCurrentTexture].mEglFence);
if (status < NO_ERROR) {
GLC_LOGE("updateAndRelease: failed to release buffer: %s (%d)",
strerror(-status), status);
err = status;
// keep going, with error raised [?]
}
} else {
pendingRelease->currentTexture = mCurrentTexture;
pendingRelease->graphicBuffer =
mCurrentTextureImage->graphicBuffer();
pendingRelease->display = mEglDisplay;
pendingRelease->fence = mEglSlots[mCurrentTexture].mEglFence;
pendingRelease->isPending = true;
}
}
// Update the GLConsumer state.
// 更新 GLConsumer 状态
mCurrentTexture = slot;
mCurrentTextureImage = nextTextureImage;
mCurrentCrop = item.mCrop;
mCurrentTransform = item.mTransform;
mCurrentScalingMode = item.mScalingMode;
mCurrentTimestamp = item.mTimestamp;
mCurrentQueueBufferTimestamp = item.mQueueBufferTimestamp;
mCurrentFence = item.mFence;
mCurrentFrameNumber = item.mFrameNumber;
computeCurrentTransformMatrixLocked();
return err;
}
