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--- |
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Vsync 信号机制 |
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--- |
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|
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1. Vsync 信号的生成机制 |
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2. Vsync 在 SurfaceFlinger 中的分发流程 |
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3. Vsync 信号的分发原理 |
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|
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![](https://i.loli.net/2020/03/26/XIw6DvOa2MTRKoj.png) |
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|
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```c++ |
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void SurfaceFlinger::init(){ |
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sp<VsyncSource> vsyncSrc = new DispSyncSource(&mPrimaryDispSync, vsyncPhaseOffsetNs, true, "app"); |
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mEventThread = new EventThread(vsyncSrc); |
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sp<VsyncSource> sfVsyncSrc = new DisSyncSource(&mPrimaryDispSync, sfVsyncPhaseOffsetNs, true, "sf"); |
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mSFEventThread = new EventThread(sfVsyncSrc); |
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mHwc = new HWComposer(this, *static_cast<HWCompiser::EventHandler *>(this)); |
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} |
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// 主要用于生成 Vsync 信号 |
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HWComposer::HWComposer(const sp<SurfaceFlinger>& flinger, ...){ |
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bool needVsyncThread = true; |
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loadHwcModule(); |
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if(mHwc){ |
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mCBContext->procs.vsync = &hook_vsync; |
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needVsyncThread = false; |
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} |
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if(needVsyncThread){ |
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mVsyncThread = new VsyncThread(*this); |
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} |
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} |
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// hook_vsync |
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void HWComposer::vsync(int disp, int64_t timestamp){ |
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mEventHandler.onVSyncReceived(disp, timestamp); |
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} |
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// 软件分发 |
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bool HWComposer::VSyncThread::threadLoop(){ |
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clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &spec, NULL); |
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mHwc.mEventHandler.onVSyncReceived(0, next_vsync); |
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return true; |
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} |
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|
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void SurfaceFlinger::onVSyncReceived(int type, nsece_t timestamp){ |
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mPrimaryDispSync.addResyncSample(timestamp); |
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} |
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bool DispSync::addResyncSample(nsecs_t timestamp){ |
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mResyncSamples[idx] = timestamp; |
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updateModelLocked(); |
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} |
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void DispSync::updateModelLocked(){ |
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mThread->updateModel(mPeriod, mPhase); |
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} |
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DispSync::DispSync():mThread(new DispSyncThread()){ |
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mThread->run("DispSync", ...); |
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} |
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// 工作线程的处理流程 |
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virtual bool threadLoop(){ |
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while(true){ |
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if(mPeriod == 0){ |
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mCond.wait(mMutex); |
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continue; |
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} |
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now = systemTime(SYSTEM_TIME_MONOTONIC); |
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callbackInvocations = gatherCallbackInvocationsLocked(now); |
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fireCallbackInvocations(callbackInvocations); |
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} |
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return false; |
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} |
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``` |
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|
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```c++ |
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void EventThread::onVSyncEvent(nsecs_t timestamp){ |
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mVSyncEvent[0].header.timestamp = timestamp; |
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mCondition.broadcast(); |
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} |
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Vector<sp<EventThread::Connection>> EventThread::waitForEvent(...){ |
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do{ |
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// 检查 mVSyncEvent 数组,看有没有 VSync 触发 |
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// 如果有就遍历所有注册的 connection |
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// 如果 count>=0 就加到 signalConnections 里,加的时候重置为 -1 |
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if(!timestamp){ |
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if(waitForVSync){ |
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mCondition.waitRelative(mLock, timeout); |
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} |
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} |
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}while(signalConnections.isEmpty()); |
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return signalConnections; |
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} |
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``` |
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|
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```c++ |
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status_t EventThread::Connection::postEvent(...){ |
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DisplayEventReceiver::sendEvents(mChannel, &event, 1); |
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} |
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ssize_t DisplayEventReceiver::sendEvents(const sp<BitTube>&dataChannel, Event const* events, size_t count){ |
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return BitTube::sendObjects(dataChannel, events, count); |
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} |
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ssize_t BitTube::sendObjects(const sp<BitTube>&tube, void const* events, size_t count, size_t objSize){ |
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const char* vaddr = reinterpret_cast<const char*>(events); |
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sszie_t size = tube->write(vaddr, count*objSize); |
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} |
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``` |
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![](https://i.loli.net/2020/03/26/gsG1Jlv8cxmCzIE.png) |
After Width: | Height: | Size: 123 KiB |
After Width: | Height: | Size: 274 KiB |
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