Android5.0 显示系统（三）————Surface的创建

程序员文章站 2022-03-29 14:07:25

...

sp<SurfaceControl> surfaceControl = client->createSurface(String8("resize"),
        160, 240, PIXEL_FORMAT_RGB_565, 0);
sp<Surface> surface = surfaceControl->getSurface();

frameworks\native\libs\gui\SurfaceComposerClient.cpp
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;
		/*Step1: 创建服务端Layer*/
        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) {
            /*Step2: 创建SurfaceControl对象*/
            sur = new SurfaceControl(this, handle, gbp);
        }
    }
    return sur;
}

handle和gbp是Binder对象，他们的值都是在SurfaceFlinger中设置，其中gdp就是图像缓冲区对象。这个handle对象的作用和前面介绍Activity中的token作用类似，也是利用Binder的唯一性为Surface生成一个唯一标识。

/*Step1*/
frameworks\native\libs\gui\ISurfaceComposerClient.cpp
virtual status_t createSurface(const String8& name, uint32_t w,
            uint32_t h, PixelFormat format, uint32_t flags,
            sp<IBinder>* handle,
            sp<IGraphicBufferProducer>* gbp) {
        Parcel data, reply;
        data.writeInterfaceToken(ISurfaceComposerClient::getInterfaceDescriptor());
        data.writeString8(name);
        data.writeInt32(w);
        data.writeInt32(h);
        data.writeInt32(format);
        data.writeInt32(flags);
        remote()->transact(CREATE_SURFACE, data, &reply);
        *handle = reply.readStrongBinder();
        *gbp = interface_cast<IGraphicBufferProducer>(reply.readStrongBinder());
        return reply.readInt32();
    }
}

frameworks\native\libs\gui\ISurfaceComposerClient.cpp
status_t BnSurfaceComposerClient::onTransact(
    uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
     switch(code) {
        case CREATE_SURFACE: {
            CHECK_INTERFACE(ISurfaceComposerClient, data, reply);
            String8 name = data.readString8();
            uint32_t w = data.readInt32();
            uint32_t h = data.readInt32();
            PixelFormat format = data.readInt32();
            uint32_t flags = data.readInt32();
            sp<IBinder> handle;
            sp<IGraphicBufferProducer> gbp;
            status_t result = createSurface(name, w, h, format, flags,
                    &handle, &gbp);
            reply->writeStrongBinder(handle);
            reply->writeStrongBinder(gbp->asBinder());
            reply->writeInt32(result);
            return NO_ERROR;
        } break;
      ......
}

frameworks\native\services\surfaceflinger\Client.cpp
status_t Client::createSurface(
        const String8& name,
        uint32_t w, uint32_t h, PixelFormat format, uint32_t flags,
        sp<IBinder>* handle,
        sp<IGraphicBufferProducer>* gbp)
{

    class MessageCreateLayer : public MessageBase {
        SurfaceFlinger* flinger;
        Client* client;
        sp<IBinder>* handle;
        sp<IGraphicBufferProducer>* gbp;
        status_t result;
        const String8& name;
        uint32_t w, h;
        PixelFormat format;
        uint32_t flags;
    public:
        MessageCreateLayer(SurfaceFlinger* flinger,
                const String8& name, Client* client,
                uint32_t w, uint32_t h, PixelFormat format, uint32_t flags,
                sp<IBinder>* handle,
                sp<IGraphicBufferProducer>* gbp)
            : flinger(flinger), client(client),
              handle(handle), gbp(gbp),
              name(name), w(w), h(h), format(format), flags(flags) {
        }
        status_t getResult() const { return result; }
        virtual bool handler() {//消息处理函数
            result = flinger->createLayer(name, client, w, h, format, flags,
                    handle, gbp);
            return true;
        }
    };
	/*创建消息对象*/
    sp<MessageBase> msg = new MessageCreateLayer(mFlinger.get(),
            name, this, w, h, format, flags, handle, gbp);
    mFlinger->postMessageSync(msg);//发送同步消息
    return static_cast<MessageCreateLayer*>( msg.get() )->getResult(); //返回结果
}

这个函数中定义了一个消息类MessageCreateLayer，然后把它的对象通过postMessageSync()方法发送出去，这个消息是以同步的方式发送，因此函数结束后可以直接返回结果。因此就直接到了handler函数，在这个函数中调用了SurfaceFlinger的createLayer()函数。

frameworks\native\services\surfaceflinger\SurfaceFlinger.cpp
status_t SurfaceFlinger::createLayer(
        const String8& name,
        const sp<Client>& client,
        uint32_t w, uint32_t h, PixelFormat format, uint32_t flags,
        sp<IBinder>* handle, sp<IGraphicBufferProducer>* gbp)
{
    if (int32_t(w|h) < 0) {
        ALOGE("createLayer() failed, w or h is negative (w=%d, h=%d)",
                int(w), int(h));
        return BAD_VALUE;
    }

    status_t result = NO_ERROR;

    sp<Layer> layer;

	/*根据传进来的flags来创建普通的的Layer还是模糊的Layer。*/
    switch (flags & ISurfaceComposerClient::eFXSurfaceMask) {
        case ISurfaceComposerClient::eFXSurfaceNormal:   //普通的Surface
        	
            result = createNormalLayer(client,
                    name, w, h, flags, format,
                    handle, gbp, &layer);
            break;
        case ISurfaceComposerClient::eFXSurfaceDim:	   //模糊的Surface
            result = createDimLayer(client,
                    name, w, h, flags,
                    handle, gbp, &layer);
            break;
        default:
            result = BAD_VALUE;
            break;
    }

    if (result == NO_ERROR) {
    	/*Step1.2 绑定Layer对象*/
        addClientLayer(client, *handle, *gbp, layer);
        setTransactionFlags(eTransactionNeeded);
    }
    return result;
}

/*Step1.1 创建Layer对象*/
我们先来看看创建普通的Layer，根据传入的format参数，选择不同格式。然后创建一个Layer对象，具体Layer我们后续介绍。然后获取handle和gbp。

frameworks\native\services\surfaceflinger\SurfaceFlinger.cpp
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;
    }
	/*创建一个Layer*/
    *outLayer = new Layer(this, client, name, w, h, flags);
	/*Surface中的handle和gbp从这里得到*/
    status_t err = (*outLayer)->setBuffers(w, h, format, flags);
    if (err == NO_ERROR) {
		/*返回Layer的文件句柄*/
		/*Handle标识Surface全局变量的唯一性，其他没有什么实际意思*/
        *handle = (*outLayer)->getHandle();
		/*返回生产者*/
        *gbp = (*outLayer)->getProducer();
    }

    ALOGE_IF(err, "createNormalLayer() failed (%s)", strerror(-err));
    return err;
}

获取handle

下面我们再来看handle的获取，只是新建一个Handle，而这个Handle只是一个Binder的实现，就是标识Surface的全局唯一性，还有就是当Layer被销毁时，会调用LayerCleaner的析构函数进行一些处理。

createNormalLayer()->getHandle()
sp<IBinder> Layer::getHandle() {  
    Mutex::Autolock _l(mLock);  
  
    LOG_ALWAYS_FATAL_IF(mHasSurface,  
            "Layer::getHandle() has already been called");  
  
    mHasSurface = true;  
  
    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);  
}

gbp图像缓冲区
那么我们再来看看gbp的获取,就是Layer中mProducer成员变量。

createNormalLayer()->getProducer()
sp<IGraphicBufferProducer> Layer::getProducer() const {  
    return mProducer;  
}

/*Step1.2 */
先假设我们已经创建了Layer对象，并且layer对象对应的handle和gbp。这样我们只是创建了Layer对象，但是我们还没有把创建的Layer对象告诉其他对象，这部分工作是addClientLayer()方法来完成的。addClientLayer(client, *handle, *gbp, layer);为应用程序申请Layer，一方面需要告诉SurfaceFlinger，另一方面要记录到各Client内部中。这两个步骤是由addClientLayer()分别调用Client::attachLayer()和SurfaceFlinger::addLayer_1()完成。

void SurfaceFlinger::addClientLayer(const sp<Client>& client,
        const sp<IBinder>& handle,
        const sp<IGraphicBufferProducer>& gbc,
        const sp<Layer>& lbc)
{
    // attach this layer to the client
    client->attachLayer(handle, lbc);//让此Layer与Client相关联

    // add this layer to the current state list
    Mutex::Autolock _l(mStateLock);
    mCurrentState.layersSortedByZ.add(lbc);//将Layer按顺序添加到全局变量中
    mGraphicBufferProducerList.add(gbc->asBinder());//将gdb也添加到全局变量中
}
void Client::attachLayer(const sp<IBinder>& handle, const sp<Layer>& layer)
{
    Mutex::Autolock _l(mLock);
    mLayers.add(handle, layer);//添加到client的mLayers变量中
}
ssize_t SortedVectorImpl::add(const void* item)
{
    size_t order;
    ssize_t index = _indexOrderOf(item, &order);
    if (index < 0) {
        index = VectorImpl::insertAt(item, order, 1);
    } else {
        index = VectorImpl::replaceAt(item, index);
    }
    return index;
}

/*Step2*/

//sur = new SurfaceControl(this, handle, gbp);
frameworks\native\libs\gui\SurfaceControl.cpp
SurfaceControl::SurfaceControl(
        const sp<SurfaceComposerClient>& client,
        const sp<IBinder>& handle,
        const sp<IGraphicBufferProducer>& gbp)
    : mClient(client), mHandle(handle), mGraphicBufferProducer(gbp)
{
}



sp<Surface> surface = surfaceControl->getSurface();
frameworks\native\libs\gui\SurfaceControl.cpp
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;
}


frameworks\native\libs\gui\Surface.cpp
Surface::Surface(
        const sp<IGraphicBufferProducer>& bufferProducer,
        bool controlledByApp)
    : mGraphicBufferProducer(bufferProducer)
{
    // Initialize the ANativeWindow function pointers.
    ANativeWindow::setSwapInterval  = hook_setSwapInterval;
    ANativeWindow::dequeueBuffer    = hook_dequeueBuffer;
    ANativeWindow::cancelBuffer     = hook_cancelBuffer;
    ANativeWindow::queueBuffer      = hook_queueBuffer;
    ANativeWindow::query            = hook_query;
    ANativeWindow::perform          = hook_perform;

    ANativeWindow::dequeueBuffer_DEPRECATED = hook_dequeueBuffer_DEPRECATED;
    ANativeWindow::cancelBuffer_DEPRECATED  = hook_cancelBuffer_DEPRECATED;
    ANativeWindow::lockBuffer_DEPRECATED    = hook_lockBuffer_DEPRECATED;
    ANativeWindow::queueBuffer_DEPRECATED   = hook_queueBuffer_DEPRECATED;

    const_cast<int&>(ANativeWindow::minSwapInterval) = 0;
    const_cast<int&>(ANativeWindow::maxSwapInterval) = 1;

    mReqWidth = 0;
    mReqHeight = 0;
    mReqFormat = 0;
    mReqUsage = 0;
    mTimestamp = NATIVE_WINDOW_TIMESTAMP_AUTO;
    mCrop.clear();
    mScalingMode = NATIVE_WINDOW_SCALING_MODE_FREEZE;
    mTransform = 0;
    mStickyTransform = 0;
    mDefaultWidth = 0;
    mDefaultHeight = 0;
    mUserWidth = 0;
    mUserHeight = 0;
    mTransformHint = 0;
    mConsumerRunningBehind = false;
    mConnectedToCpu = false;
    mProducerControlledByApp = controlledByApp;
    mSwapIntervalZero = false;
}

而mProducer是在Layer的onFirstRef()中赋值的，我们注意MonitoredProducer构造函数的一个参数producer，事实上MonitoredProducer只是一个代理类，真正的实现在这个producer参数。

总结：surfaceControl->getSurface()创建了一个surfaceControl对象，该对象有三个参数，第一个参数是SurfaceComposerClient对象；第二个参数是handle，表示SurfaceControl的唯一性；第三个参数是gbp,表示Layer对象的GraphicBufferProducer的binder对象。

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