Android SurfaceFlinger服務（三） ----- 本地圖層Layer建立

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在上一篇文章中，主要分析了Surface的建立過程，對於Layer圖層的建立並沒有深入跟蹤分析。這篇文章將分析Layer圖層的建立，並分析handle gbp這兩個變數的來源。

在SurfaceFlinger中會根據flags的值建立不同的layer。這裡主要以建立普通layer為例進行分析。

status_t SurfaceFlinger::createNormalLayer(const sp<Client>& client,        const String8& name, uint32_t w, uint32_t h, uint32_t flags, 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;    }    *outLayer = new Layer(this, client, name, w, h, flags);    status_t err = (*outLayer)->setBuffers(w, h, format, flags);    if (err == NO_ERROR) {        *handle = (*outLayer)->getHandle();        *gbp = (*outLayer)->getProducer();    }    ALOGE_IF(err, "createNormalLayer() failed (%s)", strerror(-err));    return err;}

• 建立一個Layer對象outLayer
• 調用Layer對象的getHandle()方法賦值給handle
• 調用Layer對象的getProducer()方法賦值給gbp

感覺快到源頭了，在來看看Layer類的onFirstRef方法

void Layer::onFirstRef() {    // Creates a custom BufferQueue for SurfaceFlingerConsumer to use    sp<IGraphicBufferProducer> producer;    sp<IGraphicBufferConsumer> consumer;    BufferQueue::createBufferQueue(&producer, &consumer);    mProducer = new MonitoredProducer(producer, mFlinger);    mSurfaceFlingerConsumer = new SurfaceFlingerConsumer(consumer, mTextureName);    mSurfaceFlingerConsumer->setConsumerUsageBits(getEffectiveUsage(0));    mSurfaceFlingerConsumer->setContentsChangedListener(this);    mSurfaceFlingerConsumer->setName(mName);#ifdef TARGET_DISABLE_TRIPLE_BUFFERING#warning "disabling triple buffering"    mSurfaceFlingerConsumer->setDefaultMaxBufferCount(2);#else    mSurfaceFlingerConsumer->setDefaultMaxBufferCount(3);#endif    const sp<const DisplayDevice> hw(mFlinger->getDefaultDisplayDevice());    updateTransformHint(hw);}

• 調用BufferQueue::createBufferQueue()方法建立映像緩衝區隊列
• 建立產生者對象MonitoredProducer，並賦值給mProducer
• 建立消費者對象SurfaceFlingerConsumer，並賦值給mSurfaceFlingerConsumer

在來看看Layer的getHandle方法

sp<IBinder> Layer::getHandle() {            Mutex::Autolock _l(mLock);    LOG_ALWAYS_FATAL_IF(mHasSurface,            "Layer::getHandle() has already been called");    mHasSurface = true;    /*      * The layer handle is just a BBinder object passed to the client     * (remote process) -- we don‘t keep any reference on our side such that     * the dtor is called when the remote side let go of its reference.     *      * LayerCleaner ensures that mFlinger->onLayerDestroyed() is called for     * this layer when the handle is destroyed.     */    class Handle : public BBinder, public LayerCleaner {        wp<const Layer> mOwner;    public:        Handle(const sp<SurfaceFlinger>& flinger, const sp<Layer>& layer)            : LayerCleaner(flinger, layer), mOwner(layer) {        }    };     return new Handle(mFlinger, this);}

• 最終返回一個Handle類的binder對象，不知道有什麼用

總結，當用戶端建立Surface的時候，SurfaceFlinger服務端為會之建立對應的圖層Layer。並且把Layer的映像緩衝區的生產者介面賦值給Surface對象的成員變數mGraphicBufferProducer。這樣用戶端就能將畫好的映像提交給SurfaceFlinger服務去處理了。

Android SurfaceFlinger服務（三） ----- 本地圖層Layer建立