由上节的内容可知，SurfaceComposerClient是应用程序与surfaceflinger之间的通信桥梁，不过SurfaceComposerClient只是一个封装，实质是通过内部的ISurfaceComposerClient来执行的，ISurfaceComposerClient对应的服务端实现是Client。
SurfaceComposerClient.h sp<ISurfaceComposerClient> mClient; SurfaceComposerClient.cpp void SurfaceComposerClient::onFirstRef() { sp<ISurfaceComposer> sf(ComposerService::getComposerService()); if (sf != nullptr && mStatus == NO_INIT) { sp<ISurfaceComposerClient> conn; conn = sf->createConnection(); if (conn != nullptr) { mClient = conn; mStatus = NO_ERROR; } } } ISurfaceComposer.cpp class BpSurfaceComposer : public BpInterface<ISurfaceComposer> { ... virtual sp<ISurfaceComposerClient> createConnection() { Parcel data, reply; data.writeInterfaceToken(ISurfaceComposer::getInterfaceDescriptor()); remote()->transact(BnSurfaceComposer::CREATE_CONNECTION, data, &reply); //返回的类型ISurfaceComposerClient return interface_cast<ISurfaceComposerClient>(reply.readStrongBinder()); } ... } Client类的继承关系 class Client : public BnSurfaceComposerClient class BnSurfaceComposerClient : public SafeBnInterface<ISurfaceComposerClient>Client将应用程序创建Surface的请求转交给SurfaceFlinger。
Client.cpp status_t Client::createSurface(const String8& name, uint32_t w, uint32_t h, PixelFormat format, uint32_t flags, const sp<IBinder>& parentHandle, LayerMetadata metadata, sp<IBinder>* handle, sp<IGraphicBufferProducer>* gbp) { // We rely on createLayer to check permissions. return mFlinger->createLayer(name, this, w, h, format, flags, std::move(metadata), handle, gbp, parentHandle); } SurfaceFlinger.cpp status_t SurfaceFlinger::createLayer(const String8& name, const sp<Client>& client, uint32_t w, uint32_t h, PixelFormat format, uint32_t flags, LayerMetadata metadata, sp<IBinder>* handle, sp<IGraphicBufferProducer>* gbp, const sp<IBinder>& parentHandle, const sp<Layer>& parentLayer) {Layer ... status_t result = NO_ERROR; sp<Layer> layer; ... switch (flags & ISurfaceComposerClient::eFXSurfaceMask) { case ISurfaceComposerClient::eFXSurfaceBufferQueue: result = createBufferQueueLayer(client, uniqueName, w, h, flags, std::move(metadata), format, handle, gbp, &layer); break; case ISurfaceComposerClient::eFXSurfaceBufferState: result = createBufferStateLayer(client, uniqueName, w, h, flags, std::move(metadata), handle, &layer); break; case ISurfaceComposerClient::eFXSurfaceColor: // check if buffer size is set for color layer. if (w > 0 || h > 0) { ALOGE("createLayer() failed, w or h cannot be set for color layer (w=%d, h=%d)", int(w), int(h)); return BAD_VALUE; } result = createColorLayer(client, uniqueName, w, h, flags, std::move(metadata), handle, &layer); break; case ISurfaceComposerClient::eFXSurfaceContainer: // check if buffer size is set for container layer. if (w > 0 || h > 0) { ALOGE("createLayer() failed, w or h cannot be set for container layer (w=%d, h=%d)", int(w), int(h)); return BAD_VALUE; } result = createContainerLayer(client, uniqueName, w, h, flags, std::move(metadata), handle, &layer); break; default: result = BAD_VALUE; break; } ... result = addClientLayer(client, *handle, *gbp, layer, parentHandle, parentLayer, addToCurrentState); ... return result; }该函数中根据flag创建不同的Layer，Layer用于标示一个图层。SurfaceFlinger为应用程序创建好Layer后，需要统一管理这些Layer对象，因此通过函数addClientLayer将创建的Layer保存到当前State的Z秩序列表layersSortedByZ中，同时将这个Layer所对应的IGraphicBufferProducer本地Binder对象gbp保存到SurfaceFlinger的成员变量mGraphicBufferProducerList中。除了SurfaceFlinger需要统一管理系统中创建的所有Layer对象外，专门为每个应用程序进程服务的Client也需要统一管理当前应用程序进程所创建的Layer，因此在addClientLayer函数里还会通过Client::attachLayer将创建的Layer和该类对应的handle以键值对的方式保存到Client的成员变量mLayers表中。
SurfaceFlinger.cpp status_t SurfaceFlinger::addClientLayer(const sp<Client>& client, const sp<IBinder>& handle, const sp<IGraphicBufferProducer>& gbc, const sp<Layer>& lbc, const sp<IBinder>& parentHandle, const sp<Layer>& parentLayer, bool addToCurrentState) { // add this layer to the current state list { ... if (parent == nullptr && addToCurrentState) { mCurrentState.layersSortedByZ.add(lbc); } else if (parent == nullptr) { lbc->onRemovedFromCurrentState(); } else if (parent->isRemovedFromCurrentState()) { parent->addChild(lbc); lbc->onRemovedFromCurrentState(); } else { parent->addChild(lbc); } if (gbc != nullptr) { mGraphicBufferProducerList.insert(IInterface::asBinder(gbc).get()); ... } ... } // attach this layer to the client client->attachLayer(handle, lbc); return NO_ERROR; } Client.cpp void Client::attachLayer(const sp<IBinder>& handle, const sp<Layer>& layer) { Mutex::Autolock _l(mLock); mLayers.add(handle, layer); }以createBufferQueueLayer为例，继续后续过程的分析。
SurfaceFlinger.cpp status_t SurfaceFlinger::createBufferQueueLayer(const sp<Client>& client, const String8& name, uint32_t w, uint32_t h, uint32_t flags, LayerMetadata metadata, PixelFormat& format, sp<IBinder>* handle, sp<IGraphicBufferProducer>* gbp, sp<Layer>* outLayer) { // initialize the surfaces switch (format) { case PIXEL_FORMAT_TRANSPARENT: case PIXEL_FORMAT_TRANSLUCENT: format = PIXEL_FORMAT_RGBA_8888; break; case PIXEL_FORMAT_OPAQUE: format = PIXEL_FORMAT_RGBX_8888; break; } sp<BufferQueueLayer> layer = getFactory().createBufferQueueLayer( LayerCreationArgs(this, client, name, w, h, flags, std::move(metadata))); status_t err = layer->setDefaultBufferProperties(w, h, format); if (err == NO_ERROR) { *handle = layer->getHandle(); *gbp = layer->getProducer(); *outLayer = layer; } ... return err; } SurfaceFlingerFactory.cpp sp<BufferQueueLayer> createBufferQueueLayer(const LayerCreationArgs& args) override { return new BufferQueueLayer(args); } BufferQueueLayer.cpp void BufferQueueLayer::onFirstRef() { BufferLayer::onFirstRef(); // Creates a custom BufferQueue for SurfaceFlingerConsumer to use sp<IGraphicBufferProducer> producer; sp<IGraphicBufferConsumer> consumer; BufferQueue::createBufferQueue(&producer, &consumer, true); mProducer = new MonitoredProducer(producer, mFlinger, this); { // Grab the SF state lock during this since it's the only safe way to access RenderEngine Mutex::Autolock lock(mFlinger->mStateLock); mConsumer = new BufferLayerConsumer(consumer, mFlinger->getRenderEngine(), mTextureName, this); } mConsumer->setConsumerUsageBits(getEffectiveUsage(0)); mConsumer->setContentsChangedListener(this); mConsumer->setName(mName); // BufferQueueCore::mMaxDequeuedBufferCount is default to 1 if (!mFlinger->isLayerTripleBufferingDisabled()) { mProducer->setMaxDequeuedBufferCount(2); } if (const auto display = mFlinger->getDefaultDisplayDevice()) { updateTransformHint(display); } } BufferQueue.cpp void BufferQueue::createBufferQueue(sp<IGraphicBufferProducer>* outProducer, sp<IGraphicBufferConsumer>* outConsumer, bool consumerIsSurfaceFlinger) { ... sp<BufferQueueCore> core(new BufferQueueCore()); ... sp<IGraphicBufferProducer> producer(new BufferQueueProducer(core, consumerIsSurfaceFlinger)); ... sp<IGraphicBufferConsumer> consumer(new BufferQueueConsumer(core)); ... *outProducer = producer; *outConsumer = consumer; }1) BufferQueue
可以认为BufferQueue是一个服务中心，IGraphicBufferProducer和IGraphicBufferConsumer 所需要使用的buffer必须要通过它来管理。比如说当IGraphicBufferProducer想要获取一个buffer时，它不能越过BufferQueue直接与IGraphicBufferConsumer进行联系，反之亦然。这有点像房产中介一样，房主与买方的任何交易都需要经过中介的同意，私自达成的协议都是违反规定的 2) IGraphicBufferProducer
IGraphicBufferProducer就是“填充”buffer空间的人，通常情况下是应用程序。因为应用程序不断地刷新UI，从而将产生的显示数据源源不断地写到buffer中。当IGraphicBufferProducer需要使用一块buffer时，它首先会向中介BufferQueue发起dequeueBuffer申请，然后才能对指定的buffer进行操作。此时buffer就只属于IGraphicBufferProducer一个人的了，它可以对buffer进行任何必要的操作，而IGraphicBufferConsumer此刻绝不能操作这块buffer。当IGraphicBufferProducer认为一块buffer已经写入完成后，它进一步调用queueBuffer函数。从字面上看这个函数是“入列”的意思，形象地表达了buffer此时的操作，把buffer归还到BufferQueue的队列中。一旦queue成功后，buffer的owner也就随之改变为BufferQueue了。 3) IGraphicBufferConsumer
IGraphicBufferConsumer是与IGraphicBufferProducer相对应的，它的操作同样受到BufferQueue的管控。当一块buffer已经就绪后，IGraphicBufferConsumer就可以开始工作了。
