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Android顯示系統(tǒng)SurfaceFlinger分析_Android

作者：Little熊貓 ? 更新時(shí)間： 2022-03-07 編程語(yǔ)言

一 Surfaceflinger介紹

surfaceflinger作用是接受多個(gè)來(lái)源的圖形顯示數(shù)據(jù)，將他們合成，然后發(fā)送到顯示設(shè)備。比如打開(kāi)應(yīng)用，常見(jiàn)的有三層顯示，頂部的statusbar底部或者側(cè)面的導(dǎo)航欄以及應(yīng)用的界面，每個(gè)層是單獨(dú)更新和渲染，這些界面都是有surfaceflinger合成一個(gè)刷新到硬件顯示。在顯示過(guò)程中使用到了bufferqueue，surfaceflinger作為consumer方，比如windwomanager管理的surface作為生產(chǎn)方產(chǎn)生頁(yè)面，交由surfaceflinger進(jìn)行合成。

二 bufferqueue 原理

bufferqueue分為生產(chǎn)者和消費(fèi)者

比如應(yīng)用通過(guò)windowsmanager分配一個(gè)surface，需要分配(dequeueBuffer)顯示空間在上面進(jìn)行繪圖，在圖形繪制完成后需要推送（queueBuffer）到surfaceflinger進(jìn)行合成顯示。

surfaceflinger作為消費(fèi)者，通過(guò)acquireBuffer（）得到一個(gè)要合成的圖形，在合成完畢后再releaseBuffer（）將圖形釋放。

bufferqueue類(lèi)圖關(guān)系如下：

三 surfaceflinger 關(guān)系圖

ComposerService 為單例模式負(fù)責(zé)與surfaceflinger建立binder連接代碼如下：

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則在于surfaceflinger建立連接后建立與Client的連接，通過(guò)client調(diào)用createSurface，然后返回SurfaceControl

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負(fù)責(zé)這個(gè)顯示層的控制。

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;
}

通過(guò)SurfaceControl::getSurface()，得到的真正的顯示層，這樣之后可以通過(guò)Lock和unlock將surface空間分配繪圖，再返回給surfaceflinger

上面只是cpp側(cè)的分析，上層比如WMS是java層，他的管理也是同底層一樣，只不過(guò)是有層JNI的封裝。

四 layer顯示內(nèi)存分配

surface創(chuàng)建后得到 mGraphicBufferProducer,通過(guò)mGraphicBufferProducer dequeubuffer在surfaceflinger的BnGraphicBufferProducer dequeuebuffer

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側(cè),new GraphicBuffer分配一個(gè)GraphicBuffer

    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中就是分配一個(gè)共享內(nèi)存

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進(jìn)行內(nèi)存分配，分配完成后，得到bufferIdx 將他發(fā)給client端也就是surface端

    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;

返回虛擬地址給上層

        void* vaddr;
        status_t res = backBuffer->lockAsync(
                GRALLOC_USAGE_SW_READ_OFTEN | GRALLOC_USAGE_SW_WRITE_OFTEN,
                newDirtyRegion.bounds(), &vaddr, fenceFd);

五 surfaceflinger Layer

上面創(chuàng)建一個(gè)surface后，surfaceflinger對(duì)應(yīng)的是一個(gè)layer，當(dāng)上層layer調(diào)用刷新后，onFrameAvailable被調(diào)用，通知surfaceflinger有l(wèi)ayer更新

void BufferLayer::onFrameAvailable(const BufferItem& item) {
    mFlinger->signalLayerUpdate();
}

原文鏈接：https://www.jianshu.com/p/656fb878f9ee

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