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 client
    if (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.cpp
    compositor.commit()//这里的compositor指向SurfaceFlinger
        if (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);
}