Android 源码 图形系统之创建 Layer

层 Layer 创建起点是 new 一个 Layer 对象，当对象第一次被引用的时候就会触发其 onFirstRef() 方法。

Layer 构造器中初始化了一大堆成员变量。

onFirstRef() 方法中看到了几个重量级选手，这里创建了 BufferQueue 和 SurfaceFlingerConsumer。

Layer 类首次引用图层时，将创建新的 BufferQueue 和新的 SurfaceFlingerConsumer。它还实现了 onFrameAvailable()，该函数通知 SurfaceFlinger 新数据已到达。

frameworks/native/services/surfaceflinger/Layer.cpp

Layer::Layer(SurfaceFlinger* flinger, const sp<Client>& client,
        const String8& name, uint32_t w, uint32_t h, uint32_t flags)
    :   contentDirty(false),
        sequence(uint32_t(android_atomic_inc(&sSequence))),
        mFlinger(flinger),
        mTextureName(-1U),
        mPremultipliedAlpha(true),
        mName("unnamed"),
        mFormat(PIXEL_FORMAT_NONE),
        mTransactionFlags(0),
        mQueuedFrames(0),
        mSidebandStreamChanged(false),
        mCurrentTransform(0),
        mCurrentScalingMode(NATIVE_WINDOW_SCALING_MODE_FREEZE),
        mCurrentOpacity(true),
        mRefreshPending(false),
        mFrameLatencyNeeded(false),
        mFiltering(false),
        mNeedsFiltering(false),
        mMesh(Mesh::TRIANGLE_FAN, 4, 2, 2),
        mProtectedByApp(false),
        mHasSurface(false),
        mClientRef(client),
        mPotentialCursor(false),
        mQueueItemLock(),
        mQueueItemCondition(),
        mQueueItems(),
        mLastFrameNumberReceived(0),
        mUpdateTexImageFailed(false)
{
    mCurrentCrop.makeInvalid();
    mFlinger->getRenderEngine().genTextures(1, &mTextureName);
    mTexture.init(Texture::TEXTURE_EXTERNAL, mTextureName);

    uint32_t layerFlags = 0;
    if (flags & ISurfaceComposerClient::eHidden)
        layerFlags |= layer_state_t::eLayerHidden;
    if (flags & ISurfaceComposerClient::eOpaque)
        layerFlags |= layer_state_t::eLayerOpaque;
    if (flags & ISurfaceComposerClient::eSecure)
        layerFlags |= layer_state_t::eLayerSecure;

    if (flags & ISurfaceComposerClient::eNonPremultiplied)
        mPremultipliedAlpha = false;

    mName = name;

    mCurrentState.active.w = w;
    mCurrentState.active.h = h;
    mCurrentState.active.crop.makeInvalid();
    mCurrentState.z = 0;
    mCurrentState.alpha = 0xFF;
    mCurrentState.layerStack = 0;
    mCurrentState.flags = layerFlags;
    mCurrentState.sequence = 0;
    mCurrentState.transform.set(0, 0);
    mCurrentState.requested = mCurrentState.active;

    // 绘制状态与当前状态相同
    mDrawingState = mCurrentState;

    nsecs_t displayPeriod =
            flinger->getHwComposer().getRefreshPeriod(HWC_DISPLAY_PRIMARY);
    mFrameTracker.setDisplayRefreshPeriod(displayPeriod);
}

void Layer::onFirstRef() {
    // 创建一个自定义 BufferQueue 供 SurfaceFlingerConsumer 使用
    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);
}

BufferQueue 管理供生产者和消费者使用的 gralloc 内存 slot 池。分配器（allocator）用于分配所有需要的 gralloc 缓冲区。

1. 创建 BufferQueueCore 对象
2. 创建 BufferQueueProducer （生产者）对象
3. 创建 BufferQueueConsumer （消费者）对象

frameworks/native/libs/gui/BufferQueue.cpp

void BufferQueue::createBufferQueue(sp<IGraphicBufferProducer>* outProducer,
        sp<IGraphicBufferConsumer>* outConsumer,
        const sp<IGraphicBufferAlloc>& allocator) {
    LOG_ALWAYS_FATAL_IF(outProducer == NULL,
            "BufferQueue: outProducer must not be NULL");
    LOG_ALWAYS_FATAL_IF(outConsumer == NULL,
            "BufferQueue: outConsumer must not be NULL");

    sp<BufferQueueCore> core(new BufferQueueCore(allocator));
    LOG_ALWAYS_FATAL_IF(core == NULL,
            "BufferQueue: failed to create BufferQueueCore");

    sp<IGraphicBufferProducer> producer(new BufferQueueProducer(core));
    LOG_ALWAYS_FATAL_IF(producer == NULL,
            "BufferQueue: failed to create BufferQueueProducer");

    sp<IGraphicBufferConsumer> consumer(new BufferQueueConsumer(core));
    LOG_ALWAYS_FATAL_IF(consumer == NULL,
            "BufferQueue: failed to create BufferQueueConsumer");

    *outProducer = producer;
    *outConsumer = consumer;
}

1. 由于传入的 allocator 为 NULL，因此会调用 BpSurfaceComposer 类 createGraphicBufferAlloc() 方法创建分配器
2. 填充 mFreeSlots（包含所有空闲的和当前没有 attach 缓冲区的 slot）

frameworks/native/libs/gui/BufferQueueCore.cpp

BufferQueueCore::BufferQueueCore(const sp<IGraphicBufferAlloc>& allocator) :
    mAllocator(allocator),
    mMutex(),
    mIsAbandoned(false),
    mConsumerControlledByApp(false),
    mConsumerName(getUniqueName()),
    mConsumerListener(),
    mConsumerUsageBits(0),
    mConnectedApi(NO_CONNECTED_API),
    mConnectedProducerListener(),
    mSlots(),
    mQueue(),
    mFreeSlots(),
    mFreeBuffers(),
    mOverrideMaxBufferCount(0),
    mDequeueCondition(),
    mUseAsyncBuffer(true),
    mDequeueBufferCannotBlock(false),
    mDefaultBufferFormat(PIXEL_FORMAT_RGBA_8888),
    mDefaultWidth(1),
    mDefaultHeight(1),
    mDefaultBufferDataSpace(HAL_DATASPACE_UNKNOWN),
    mDefaultMaxBufferCount(2),
    mMaxAcquiredBufferCount(1),
    mBufferHasBeenQueued(false),
    mFrameCounter(0),
    mTransformHint(0),
    mIsAllocating(false),
    mIsAllocatingCondition(),
    mAllowAllocation(true),
    mBufferAge(0),
    mGenerationNumber(0)
{
    if (allocator == NULL) {
        sp<ISurfaceComposer> composer(ComposerService::getComposerService());
        mAllocator = composer->createGraphicBufferAlloc();
        if (mAllocator == NULL) {
            BQ_LOGE("createGraphicBufferAlloc failed");
        }
    }
    for (int slot = 0; slot < BufferQueueDefs::NUM_BUFFER_SLOTS; ++slot) {
        mFreeSlots.insert(slot);
    }
}

Bn 端实现位于 SurfaceFlinger 中，因此实际会调用 SurfaceFlinger 类 createGraphicBufferAlloc() 方法。

frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

sp<IGraphicBufferAlloc> SurfaceFlinger::createGraphicBufferAlloc()
{
    sp<GraphicBufferAlloc> gba(new GraphicBufferAlloc());
    return gba;
}

现在来看创建 BufferQueueProducer 对象和创建 BufferQueueConsumer 对象。

frameworks/native/libs/gui/BufferQueueProducer.cpp

BufferQueueProducer::BufferQueueProducer(const sp<BufferQueueCore>& core) :
    mCore(core),
    mSlots(core->mSlots),
    mConsumerName(),
    mStickyTransform(0),
    mLastQueueBufferFence(Fence::NO_FENCE),
    mCallbackMutex(),
    mNextCallbackTicket(0),
    mCurrentCallbackTicket(0),
    mCallbackCondition() {}

frameworks/native/libs/gui/BufferQueueConsumer.cpp

BufferQueueConsumer::BufferQueueConsumer(const sp<BufferQueueCore>& core) :
    mCore(core),
    mSlots(core->mSlots),
    mConsumerName() {}

MonitoredProducer 包装了一个 IGraphicBufferProducer，以便在销毁 SurfaceFlinger 时通知它。

frameworks/native/services/surfaceflinger/MonitoredProducer.cpp

MonitoredProducer::MonitoredProducer(const sp<IGraphicBufferProducer>& producer,
        const sp<SurfaceFlinger>& flinger) :
    mProducer(producer),
    mFlinger(flinger) {}

SurfaceFlingerConsumer 是 GLConsumer 的瘦包装。

frameworks/native/services/surfaceflinger/SurfaceFlingerConsumer.cpp

class SurfaceFlingerConsumer : public GLConsumer {
public:
    ......
    SurfaceFlingerConsumer(const sp<IGraphicBufferConsumer>& consumer,
            uint32_t tex)
        : GLConsumer(consumer, tex, GLConsumer::TEXTURE_EXTERNAL, false, false),
          mTransformToDisplayInverse(false), mSurfaceDamage()
    {}
    ......
}

GLConsumer 消费 BufferQueue 中的图形数据缓冲区，并使它们作为纹理可用于 OpenGL。

典型的使用模式是使用所需选项设置 GLConsumer，并在需要新帧时调用 updateTexImage()。 如果有新帧可用，则纹理将被更新。如果不是，则保留先前的内容。

默认情况下，在调用 updateTexImage() 的第一个线程的 EGL 上下文中，纹理将 attach 到 GL_TEXTURE_EXTERNAL_OES 纹理目标。

该类以前称为 SurfaceTexture。

frameworks/native/libs/gui/GLConsumer.cpp

GLConsumer::GLConsumer(const sp<IGraphicBufferConsumer>& bq, uint32_t tex,
        uint32_t texTarget, bool useFenceSync, bool isControlledByApp) :
    ConsumerBase(bq, isControlledByApp),
    mCurrentTransform(0),
    mCurrentScalingMode(NATIVE_WINDOW_SCALING_MODE_FREEZE),
    mCurrentFence(Fence::NO_FENCE),
    mCurrentTimestamp(0),
    mCurrentFrameNumber(0),
    mDefaultWidth(1),
    mDefaultHeight(1),
    mFilteringEnabled(true),
    mTexName(tex),
    mUseFenceSync(useFenceSync),
    mTexTarget(texTarget),
    mEglDisplay(EGL_NO_DISPLAY),
    mEglContext(EGL_NO_CONTEXT),
    mCurrentTexture(BufferQueue::INVALID_BUFFER_SLOT),
    mAttached(true)
{
    GLC_LOGV("GLConsumer");

    memcpy(mCurrentTransformMatrix, mtxIdentity,
            sizeof(mCurrentTransformMatrix));

    mConsumer->setConsumerUsageBits(DEFAULT_USAGE_FLAGS);
}