Android显示系统SurfaceFlinger分析
本文详细讲解了Android显示系统SurfaceFlinger，文中通过示例代码介绍的非常详细。对大家的学习或工作具有一定的参考借鉴价值，需要的朋友可以参考下
目录
一 Surfaceflinger介绍
surfaceflinger作用是接受多个来源的图形显示数据，将他们合成，然后发送到显示设备。比如打开应用，常见的有三层显示，顶部的statusbar底部或者侧面的导航栏以及应用的界面，每个层是单独更新和渲染，这些界面都是有surfaceflinger合成一个刷新到硬件显示。在显示过程中使用到了bufferqueue，surfaceflinger作为consumer方，比如windwomanager管理的surface作为生产方产生页面，交由surfaceflinger进行合成。
二 bufferqueue 原理
bufferqueue分为生产者和消费者
比如应用通过windowsmanager分配一个surface，需要分配(dequeueBuffer)显示空间在上面进行绘图，在图形绘制完成后需要推送（queueBuffer）到surfaceflinger进行合成显示。
surfaceflinger作为消费者，通过acquireBuffer（）得到一个要合成的图形，在合成完毕后再releaseBuffer（）将图形释放。
bufferqueue类图关系如下：
三 surfaceflinger 关系图
ComposerService 为单例模式负责与surfaceflinger建立binder连接代码如下：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 | class ComposerService : public Singleton<ComposerService>{ sp<ISurfaceComposer> mComposerService; sp<IBinder::DeathRecipient> mDeathObserver; Mutex mLock; ComposerService(); void connectLocked(); void composerServiceDied(); friend class Singleton<ComposerService>;public: // Get a connection to the Composer Service. This will block until // a connection is established. static sp<ISurfaceComposer> getComposerService();};void ComposerService::connectLocked() { const String16 name("SurfaceFlinger"); while (getService(name, &mComposerService) != NO_ERROR) { usleep(250000); } assert(mComposerService != NULL); // Create the death listener. class DeathObserver : public IBinder::DeathRecipient { ComposerService& mComposerService; virtual void binderDied(const wp<IBinder>& who) { ALOGW("ComposerService remote (surfaceflinger) died [%p]", who.unsafe_get()); mComposerService.composerServiceDied(); } public: DeathObserver(ComposerService& mgr) : mComposerService(mgr) { } }; mDeathObserver = new DeathObserver(*const_cast<ComposerService*>(this)); mComposerService->asBinder()->linkToDeath(mDeathObserver);}/*static*/ sp<ISurfaceComposer> ComposerService::getComposerService() { ComposerService& instance = ComposerService::getInstance(); Mutex::Autolock _l(instance.mLock); if (instance.mComposerService == NULL) { ComposerService::getInstance().connectLocked(); assert(instance.mComposerService != NULL); ALOGD("ComposerService reconnected"); } return instance.mComposerService;} |
SurfaceComposerClient则在于surfaceflinger建立连接后建立与Client的连接，通过client调用createSurface，然后返回SurfaceControl
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | sp<SurfaceControl> SurfaceComposerClient::createSurface( const String8& name, uint32_t w, uint32_t h, PixelFormat format, uint32_t flags){ sp<SurfaceControl> sur; if (mStatus == NO_ERROR) { sp<IBinder> handle; sp<IGraphicBufferProducer> gbp; status_t err = mClient->createSurface(name, w, h, format, flags, &handle, &gbp); ALOGE_IF(err, "SurfaceComposerClient::createSurface error %s", strerror(-err)); if (err == NO_ERROR) { sur = new SurfaceControl(this, handle, gbp); } } return sur;} |
SurfaceControl负责这个显示层的控制。
1 2 3 4 5 6 7 8 9 10 | sp<Surface> SurfaceControl::getSurface() const{ Mutex::Autolock _l(mLock); if (mSurfaceData == 0) { // This surface is always consumed by SurfaceFlinger, so the // producerControlledByApp value doesn't matter; using false. mSurfaceData = new Surface(mGraphicBufferProducer, false); } return mSurfaceData;} |
通过SurfaceControl::getSurface()，得到的真正的显示层，这样之后可以通过Lock和unlock将surface空间分配绘图，再返回给surfaceflinger
上面只是cpp侧的分析，上层比如WMS是java层，他的管理也是同底层一样，只不过是有层JNI的封装。
四 layer显示内存分配
surface创建后得到 mGraphicBufferProducer,通过mGraphicBufferProducer dequeubuffer在surfaceflinger的BnGraphicBufferProducer dequeuebuffer
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | int Surface::dequeueBuffer(android_native_buffer_t** buffer, int* fenceFd) { status_t result = mGraphicBufferProducer->dequeueBuffer(&buf, &fence, mSwapIntervalZero, reqW, reqH, mReqFormat, mReqUsage); sp<GraphicBuffer>& gbuf(mSlots[buf].buffer); if ((result & IGraphicBufferProducer::BUFFER_NEEDS_REALLOCATION) || gbuf == 0) { result = mGraphicBufferProducer->requestBuffer(buf, &gbuf); if (result != NO_ERROR) { ALOGE("dequeueBuffer: IGraphicBufferProducer::requestBuffer failed: %d", result); return result; } *buffer = gbuf.get(); }} |
在producer的server侧,new GraphicBuffer分配一个GraphicBuffer
1 2 3 4 5 | if (returnFlags & BUFFER_NEEDS_REALLOCATION) { BQ_LOGV("dequeueBuffer: allocating a new buffer for slot %d", *outSlot); sp<GraphicBuffer> graphicBuffer = new GraphicBuffer( width, height, format, BQ_LAYER_COUNT, usage, {mConsumerName.string(), mConsumerName.size()}); |
在graphicbuffer中就是分配一个共享内存
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | GraphicBuffer::GraphicBuffer(uint32_t inWidth, uint32_t inHeight, PixelFormat inFormat, uint32_t inLayerCount, uint64_t usage, std::string requestorName) : GraphicBuffer(){ mInitCheck = initWithSize(inWidth, inHeight, inFormat, inLayerCount, usage, std::move(requestorName));}status_t GraphicBuffer::initWithSize(uint32_t inWidth, uint32_t inHeight, PixelFormat inFormat, uint32_t inLayerCount, uint64_t inUsage, std::string requestorName){ GraphicBufferAllocator& allocator = GraphicBufferAllocator::get(); uint32_t outStride = 0; status_t err = allocator.allocate(inWidth, inHeight, inFormat, inLayerCount, inUsage, &handle, &outStride, mId, std::move(requestorName)); if (err == NO_ERROR) { mBufferMapper.getTransportSize(handle, &mTransportNumFds, &mTransportNumInts); width = static_cast<int>(inWidth); height = static_cast<int>(inHeight); format = inFormat; layerCount = inLayerCount; usage = inUsage; usage_deprecated = int(usage); stride = static_cast<int>(outStride); } return err;} |
GraphicBufferAllocator::get() 使用gralloc进行内存分配，分配完成后，得到bufferIdx 将他发给client端也就是surface端
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | virtual status_t requestBuffer(int bufferIdx, sp<GraphicBuffer>* buf) { Parcel data, reply; data.writeInterfaceToken(IGraphicBufferProducer::getInterfaceDescriptor()); data.writeInt32(bufferIdx); status_t result =remote()->transact(REQUEST_BUFFER, data, &reply); if (result != NO_ERROR) { return result; } bool nonNull = reply.readInt32(); if (nonNull) { *buf = new GraphicBuffer(); result = reply.read(**buf); if(result != NO_ERROR) { (*buf).clear(); return result; } } result = reply.readInt32(); return result; |
返回虚拟地址给上层
1 2 3 4 | void* vaddr;status_t res = backBuffer->lockAsync( GRALLOC_USAGE_SW_READ_OFTEN | GRALLOC_USAGE_SW_WRITE_OFTEN, newDirtyRegion.bounds(), &vaddr, fenceFd); |
五 surfaceflinger Layer
上面创建一个surface后，surfaceflinger对应的是一个layer，当上层layer调用刷新后，onFrameAvailable被调用，通知surfaceflinger有layer更新
1 2 3 | void BufferLayer::onFrameAvailable(const BufferItem& item) { mFlinger->signalLayerUpdate();} |
到此这篇关于Android显示系统SurfaceFlinger分析的文章就介绍到这了。
原文链接：https://www.jianshu.com/p/656fb878f9ee