SurfaceFinger layer创建过程

引言

本篇博客重点分析app创建Surface时候，SurfaceFlinger是如何构建对应的Layer的主要工作有那些！

这里参考的Android源码是Android 13 aosp！

app端创建Surface

其核心流程可以分为如下接部分:

app使用w,h,format等参数，调用SurfaceComposerClient::createSurface
createSurface调用SurfaceComposerClient::createSurfaceChecked；createSurfaceChecked调用mClient->createSurface；mClient是surfaceflinger client的代理；mClient的初始化还没介绍，后面单独写一篇介绍。
mClient->createSurface会调用到android12\frameworks\native\services\surfaceflinger\Client.cpp 中Client::createSurface
Client::createSurface调用mFlinger->createLayer

核心逻辑代码如下:

surfaceComposerClient->createSurface(String8("SurfaceTestDemo"), resolution.getWidth(),resolution.getHeight(), PIXEL_FORMAT_RGBA_8888,ISurfaceComposerClient::eFXSurfaceBufferState,/*parent*/ nullptr);sp<SurfaceControl> SurfaceComposerClient::createSurface(const String8& name, uint32_t w, uint32_t h,PixelFormat format, uint32_t flags,const sp<IBinder>& parentHandle,LayerMetadata metadata,uint32_t* outTransformHint) {sp<SurfaceControl> s;createSurfaceChecked(name, w, h, format, &s, flags, parentHandle, std::move(metadata),outTransformHint);return s;
}status_t SurfaceComposerClient::createSurfaceChecked(const String8& name, uint32_t w, uint32_t h,PixelFormat format,sp<SurfaceControl>* outSurface, uint32_t flags,const sp<IBinder>& parentHandle,LayerMetadata metadata,uint32_t* outTransformHint) {status_t err = mStatus;if (mStatus == NO_ERROR) {sp<IBinder> handle;sp<IGraphicBufferProducer> gbp;err = mClient->createSurface(name, w, h, format, flags, parentHandle, std::move(metadata),&handle, &gbp, &id, &transformHint);*outSurface =new SurfaceControl(this, handle, gbp, id, w, h, format, transformHint, flags);}return err;
}

SurfaceFlinger端创建layer过程

SurfaceFlinger构建Layer的核心流程如下:

根据app的flags确定创建layer类型createBufferStateLayer；createEffectLayer还是createContainerLayer；目前尚不清楚不同layer之间的区别，以createBufferStateLayer为例
将传入参数放入LayerCreationArgs args，调用getFactory().createBufferStateLayer(args)创建BufferStateLayer；获取layer handle，并返回
调用SurfaceFlinger::addClientLayer，创建LayerCreatedState，放入mCreatedLayers[handle->localBinder()]；使用handle等参数创建composerState，并传入SurfaceFlinger::setTransactionState
创建TransactionState state，并将其放入mTransactionQueue.emplace(state)

这里我们重点看下SurfaceFlinger::addClientLayer的实现，因为后面会用到它。

status_t SurfaceFlinger::addClientLayer(const sp<Client>& client, const sp<IBinder>& handle,const sp<Layer>& layer, const wp<Layer>& parent,bool addToRoot, uint32_t* outTransformHint) {
...                                        {std::scoped_lock<std::mutex> lock(mCreatedLayersLock);mCreatedLayers.emplace_back(layer, parent, addToRoot);}       // attach this layer to the clientif (client != nullptr) {client->attachLayer(handle, layer);mLayers.add(handle, layer);        }   setTransactionFlags(eTransactionNeeded) //提交eTransactionNeeded...    
}//这个什么时候会触发这个transaction呢，大概流程如下:MessageQueue::Handler::handleMessage(...)//frameworks/native/services/surfaceflinger/Scheduler/MessageQueue.cppcompositor.commit()//这里的compositor指向SurfaceFlingerif (clearTransactionFlags(eTransactionFlushNeeded)) {needsTraversal |= commitCreatedLayers();needsTraversal |= flushTransactionQueues(vsyncId);}bool SurfaceFlinger::commitCreatedLayers() {for (const auto& createdLayer : createdLayers) {handleLayerCreatedLocked(createdLayer);}    
}void SurfaceFlinger::handleLayerCreatedLocked(const LayerCreatedState& state) {sp<Layer> layer = state.layer.promote();if (!layer) {ALOGD("Layer was destroyed soon after creation %p", state.layer.unsafe_get());return;}sp<Layer> parent;bool addToRoot = state.addToRoot;if (state.initialParent != nullptr) {parent = state.initialParent.promote();if (parent == nullptr) {ALOGD("Parent was destroyed soon after creation %p", state.initialParent.unsafe_get());addToRoot = false;}}if (parent == nullptr && addToRoot) {layer->setIsAtRoot(true);mCurrentState.layersSortedByZ.add(layer);//注意这里对应的Layer是BufferStateLayer} else if (parent == nullptr) {layer->onRemovedFromCurrentState();} else if (parent->isRemovedFromCurrentState()) {parent->addChild(layer);layer->onRemovedFromCurrentState();} else {parent->addChild(layer);}layer->updateTransformHint(mActiveDisplayTransformHint);mInterceptor->saveSurfaceCreation(layer);
}