Android 12(S) 图像显示系统 – SurfaceFlinger GPU合成/CLIENT合成方式 – 随笔1



必读:

Android 12(S) 图像显示系统 - 开篇


 

一、前言

SurfaceFlinger中的图层选择GPU合成(CLIENT合成方式)时,会把待合成的图层Layers通过renderengine(SkiaGLRenderEngine)绘制到一块GraphicBuffer中,然后把这块GraphicBuffer图形缓存通过调用setClientTarget传递给HWC模块,HWC进一步处理后把这个GraphicBuffer中的图像呈现到屏幕上。

本篇文章,我们先聚焦一点做介绍:用于存储GPU合成后的图形数据的GraphicBuffer是从哪里来的?下面的讲解会围绕这个问题展开。

 

二、从dumpsys SurfaceFlinger中的信息谈起

如果你查看过dumpsys SurfaceFlinger的信息,也许你注意过一些GraphicBufferAllocator/GraphicBufferMapper打印出的一些信息,这些信息记录了所有通过Gralloc模块allocate和import的图形缓存的信息。

如下是在我的平台下截取的dumpsys SurfaceFlinger部分信息:

GraphicBufferAllocator buffers:     Handle |        Size |     W (Stride) x H | Layers |   Format |      Usage | Requestor 0xf3042b90 | 8100.00 KiB | 1920 (1920) x 1080 |      1 |        1 | 0x    1b00 | FramebufferSurface 0xf3042f30 | 8100.00 KiB | 1920 (1920) x 1080 |      1 |        1 | 0x    1b00 | FramebufferSurface 0xf3046020 | 8100.00 KiB | 1920 (1920) x 1080 |      1 |        1 | 0x    1b00 | FramebufferSurface Total allocated by GraphicBufferAllocator (estimate): 24300.00 KB Imported gralloc buffers: + name:FramebufferSurface, id:e100000000, size:8.3e+03KiB, w/h:780x438, usage: 0x40001b00, req fmt:5, fourcc/mod:875713089/576460752303423505, dataspace: 0x0, compressed: true 	planes: B/G/R/A:	 w/h:780x440, stride:1e00 bytes, size:818000 + name:FramebufferSurface, id:e100000001, size:8.3e+03KiB, w/h:780x438, usage: 0x40001b00, req fmt:5, fourcc/mod:875713089/576460752303423505, dataspace: 0x0, compressed: true 	planes: B/G/R/A:	 w/h:780x440, stride:1e00 bytes, size:818000 + name:FramebufferSurface, id:e100000002, size:8.3e+03KiB, w/h:780x438, usage: 0x40001b00, req fmt:5, fourcc/mod:875713089/576460752303423505, dataspace: 0x0, compressed: true 	planes: B/G/R/A:	 w/h:780x440, stride:1e00 bytes, size:818000 Total imported by gralloc: 5e+04KiB

上面的信息中可以看到一些儿冥冥之中貌似、似乎、好像很有意思的字眼:FramebufferSurface

作为Requestor的FramebufferSurface去请求分配了三块图形缓存,还规定了width、height、format、usage等信息。


 

如上你看到的这3块GraphicBuffer,就是用来存储CPU合成后的图形数据的。

 


 

三、创建与初始化FramebufferSurface的流程

FramebufferSurface的初始化逻辑需要从SurfaceFlinger的初始化谈起,在文章Android 12(S) 图像显示系统 - SurfaceFlinger的启动和消息队列处理机制(四)

中,曾分析过,SurfaceFlinger::init()中会去注册HWC的回调函数mCompositionEngine->getHwComposer().setCallback(this),当第一次注册callback时,onComposerHalHotplug()会立即在调用registerCallback()的线程中被调用,并跨进程回调到SurfaceFlinger::onComposerHalHotplug。然后一路飞奔:

Android 12(S) 图像显示系统 - SurfaceFlinger  GPU合成/CLIENT合成方式 - 随笔1

SurfaceFlinger::processDisplayAdded这个方法中去创建了BufferQueue和FramebufferSurface,简单理解为连接上了显示屏幕(Display),那就要给准备一个BufferQueue,以便GPU合成UI等图层时,可以向这个BufferQueue索要GraphicBuffer来存储合成后的图形数据,再呈现到屏幕上去(我的傻瓜式理解)

摘取关键代码如下:

[/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp] void SurfaceFlinger::processDisplayAdded(const wp<IBinder>& displayToken,                                          const DisplayDeviceState& state) {     ......     sp<compositionengine::DisplaySurface> displaySurface;      sp<IGraphicBufferProducer> producer;     // 创建BufferQueue,获取到生产者和消费者,而且消费者不是SurfaceFlinger哦     sp<IGraphicBufferProducer> bqProducer;     sp<IGraphicBufferConsumer> bqConsumer;     getFactory().createBufferQueue(&bqProducer, &bqConsumer, /*consumerIsSurfaceFlinger =*/false);      if (state.isVirtual()) { // 虚拟屏幕,不管它         const auto displayId = VirtualDisplayId::tryCast(compositionDisplay->getId());         LOG_FATAL_IF(!displayId);         auto surface = sp<VirtualDisplaySurface>::make(getHwComposer(), *displayId, state.surface,                                                        bqProducer, bqConsumer, state.displayName);         displaySurface = surface;         producer = std::move(surface);     } else { // 看这个case         ALOGE_IF(state.surface != nullptr,                  "adding a supported display, but rendering "                  "surface is provided (%p), ignoring it",                  state.surface.get());         const auto displayId = PhysicalDisplayId::tryCast(compositionDisplay->getId());         LOG_FATAL_IF(!displayId);         // 创建了FramebufferSurface对象,FramebufferSurface继承自compositionengine::DisplaySurface         // FramebufferSurface是作为消费者的角色工作的,消费SF GPU合成后的图形数据         displaySurface =                 sp<FramebufferSurface>::make(getHwComposer(), *displayId, bqConsumer,                                              state.physical->activeMode->getSize(),                                              ui::Size(maxGraphicsWidth, maxGraphicsHeight));         producer = bqProducer;     }      LOG_FATAL_IF(!displaySurface);     // 创建DisplayDevice,其又去创建RenderSurface,作为生产者角色工作,displaySurface就是FramebufferSurface对象     const auto display = setupNewDisplayDeviceInternal(displayToken, std::move(compositionDisplay),                                                        state, displaySurface, producer);     mDisplays.emplace(displayToken, display);     ......    }

瞅一瞅 FramebufferSuraface的构造函数,没啥复杂的,就是一些设置,初始化一些成员

FramebufferSurface::FramebufferSurface(HWComposer& hwc, PhysicalDisplayId displayId,                                        const sp<IGraphicBufferConsumer>& consumer,                                        const ui::Size& size, const ui::Size& maxSize)       : ConsumerBase(consumer),         mDisplayId(displayId),         mMaxSize(maxSize),         mCurrentBufferSlot(-1),         mCurrentBuffer(),         mCurrentFence(Fence::NO_FENCE),         mHwc(hwc),         mHasPendingRelease(false),         mPreviousBufferSlot(BufferQueue::INVALID_BUFFER_SLOT),         mPreviousBuffer() {     ALOGV("Creating for display %s", to_string(displayId).c_str());      mName = "FramebufferSurface";     mConsumer->setConsumerName(mName); // 设置消费者的名字是 "FramebufferSurface"     mConsumer->setConsumerUsageBits(GRALLOC_USAGE_HW_FB |  // 设置usage                                        GRALLOC_USAGE_HW_RENDER |                                        GRALLOC_USAGE_HW_COMPOSER);     const auto limitedSize = limitSize(size);     mConsumer->setDefaultBufferSize(limitedSize.width, limitedSize.height); // 设置buffer 大小     mConsumer->setMaxAcquiredBufferCount(              SurfaceFlinger::maxFrameBufferAcquiredBuffers - 1); }

 

再进到SurfaceFlinger::setupNewDisplayDeviceInternal中看看相关的逻辑:

[/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp] sp<DisplayDevice> SurfaceFlinger::setupNewDisplayDeviceInternal(         const wp<IBinder>& displayToken,         std::shared_ptr<compositionengine::Display> compositionDisplay,         const DisplayDeviceState& state,         const sp<compositionengine::DisplaySurface>& displaySurface,          const sp<IGraphicBufferProducer>& producer) {     ......     creationArgs.displaySurface = displaySurface;  // displaySurface就是FramebufferSurface对象             // producer是前面processDisplayAdded中创建的     auto nativeWindowSurface = getFactory().createNativeWindowSurface(producer);     auto nativeWindow = nativeWindowSurface->getNativeWindow();     creationArgs.nativeWindow = nativeWindow;      ....     // 前面一大坨代码是在初始话creationArgs,这些参数用来创建DisplayDevice     // creationArgs.nativeWindow会把前面创建的producer关联到了DisplayDevice     sp<DisplayDevice> display = getFactory().createDisplayDevice(creationArgs);          // 后面一大坨,对display进行了些设置     if (!state.isVirtual()) {         display->setActiveMode(state.physical->activeMode->getId());         display->setDeviceProductInfo(state.physical->deviceProductInfo);     }     .... }

 

接下来就是 DisplayDevice 的构造函数了,里面主要是创建了RenderSurface对象,然后对其进行初始化

[/frameworks/native/services/surfaceflinger/DisplayDevice.cpp] DisplayDevice::DisplayDevice(DisplayDeviceCreationArgs& args)       : mFlinger(args.flinger),         mHwComposer(args.hwComposer),         mDisplayToken(args.displayToken),         mSequenceId(args.sequenceId),         mConnectionType(args.connectionType),         mCompositionDisplay{args.compositionDisplay},         mPhysicalOrientation(args.physicalOrientation),         mSupportedModes(std::move(args.supportedModes)),         mIsPrimary(args.isPrimary) {     mCompositionDisplay->editState().isSecure = args.isSecure;     // 创建RenderSurface,args.nativeWindow 即为producer,指向生产者     mCompositionDisplay->createRenderSurface(             compositionengine::RenderSurfaceCreationArgsBuilder()                     .setDisplayWidth(ANativeWindow_getWidth(args.nativeWindow.get()))                     .setDisplayHeight(ANativeWindow_getHeight(args.nativeWindow.get()))                     .setNativeWindow(std::move(args.nativeWindow))                     .setDisplaySurface(std::move(args.displaySurface)) // displaySurface就是FramebufferSurface对象                     .setMaxTextureCacheSize(                             static_cast<size_t>(SurfaceFlinger::maxFrameBufferAcquiredBuffers))                     .build());      if (!mFlinger->mDisableClientCompositionCache &&         SurfaceFlinger::maxFrameBufferAcquiredBuffers > 0) {         mCompositionDisplay->createClientCompositionCache(                 static_cast<uint32_t>(SurfaceFlinger::maxFrameBufferAcquiredBuffers));     }      mCompositionDisplay->createDisplayColorProfile(             compositionengine::DisplayColorProfileCreationArgs{args.hasWideColorGamut,                                                                std::move(args.hdrCapabilities),                                                                args.supportedPerFrameMetadata,                                                                args.hwcColorModes});      if (!mCompositionDisplay->isValid()) {         ALOGE("Composition Display did not validate!");     }     // 初始化RenderSurface     mCompositionDisplay->getRenderSurface()->initialize();      setPowerMode(args.initialPowerMode);      // initialize the display orientation transform.     setProjection(ui::ROTATION_0, Rect::INVALID_RECT, Rect::INVALID_RECT); }

本文作者@二的次方  2022-05-10 发布于博客园

RenderSurface作为生产者的角色工作,构造函数如下,留意启成员displaySurface就是SurfaceFlinger中创建的FramebufferSurface对象

也就是 作为生产者的RenderSurface中持有 消费者的引用 displaySurface,可以呼叫FramebufferSurface的方法

[ /frameworks/native/services/surfaceflinger/CompositionEngine/src/RenderSurface.cpp] RenderSurface::RenderSurface(const CompositionEngine& compositionEngine, Display& display,                              const RenderSurfaceCreationArgs& args)       : mCompositionEngine(compositionEngine),         mDisplay(display),         mNativeWindow(args.nativeWindow),         mDisplaySurface(args.displaySurface),  // displaySurface就是FramebufferSurface对象         mSize(args.displayWidth, args.displayHeight),         mMaxTextureCacheSize(args.maxTextureCacheSize) {     LOG_ALWAYS_FATAL_IF(!mNativeWindow); }

 

我们看看他的RenderSurface::initialize()方法

[/frameworks/native/services/surfaceflinger/CompositionEngine/src/RenderSurface.cpp] void RenderSurface::initialize() {     ANativeWindow* const window = mNativeWindow.get();      int status = native_window_api_connect(window, NATIVE_WINDOW_API_EGL);     ALOGE_IF(status != NO_ERROR, "Unable to connect BQ producer: %d", status);     status = native_window_set_buffers_format(window, HAL_PIXEL_FORMAT_RGBA_8888);     ALOGE_IF(status != NO_ERROR, "Unable to set BQ format to RGBA888: %d", status);     status = native_window_set_usage(window, DEFAULT_USAGE);     ALOGE_IF(status != NO_ERROR, "Unable to set BQ usage bits for GPU rendering: %d", status); }

上述方法也很简单,就是作为producer去和BufferQueue建立connect,并设置format为RGBA_8888,设置usage为GRALLOC_USAGE_HW_RENDER | GRALLOC_USAGE_HW_TEXTURE

 


为了验证上述分析的流程是正确的,我在BufferQueueProducer::connect中加log来打印调用栈的信息,如下,是不是和分析的一样啊

11-13 00:52:58.497   227   227 D BufferQueueProducer: connect[1303] /vendor/bin/hw/android.hardware.graphics.composer@2.4-service start 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#00 pc 0005e77f  /system/lib/libgui.so (android::BufferQueueProducer::connect(android::sp<android::IProducerListener> const&, int, bool, android::IGraphicBufferProducer::QueueBufferOutput*)+1282) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#01 pc 000a276b  /system/lib/libgui.so (android::Surface::connect(int, android::sp<android::IProducerListener> const&, bool)+138) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#02 pc 0009de41  /system/lib/libgui.so (android::Surface::hook_perform(ANativeWindow*, int, ...)+128) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#03 pc 00121b1d  /system/bin/surfaceflinger (android::compositionengine::impl::RenderSurface::initialize()+12) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#04 pc 00083cc5  /system/bin/surfaceflinger (android::DisplayDevice::DisplayDevice(android::DisplayDeviceCreationArgs&)+1168) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#05 pc 000d8bed  /system/bin/surfaceflinger (android::SurfaceFlinger::processDisplayAdded(android::wp<android::IBinder> const&, android::DisplayDeviceState const&)+4440) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#06 pc 000d0db5  /system/bin/surfaceflinger (android::SurfaceFlinger::processDisplayChangesLocked()+2436) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#07 pc 000cef6b  /system/bin/surfaceflinger (android::SurfaceFlinger::processDisplayHotplugEventsLocked()+6422) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#08 pc 000d2c7f  /system/bin/surfaceflinger (android::SurfaceFlinger::onComposerHalHotplug(unsigned long long, android::hardware::graphics::composer::V2_1::IComposerCallback::Connection)+334) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#09 pc 0009afab  /system/bin/surfaceflinger (_ZN7android12_GLOBAL__N_122ComposerCallbackBridge9onHotplugEyNS_8hardware8graphics8composer4V2_117IComposerCallback10ConnectionE$d689f7ac1c60e4abeed02ca92a51bdcd+20) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#10 pc 0001bb97  /system/lib/android.hardware.graphics.composer@2.1.so (android::hardware::graphics::composer::V2_1::BnHwComposerCallback::_hidl_onHotplug(android::hidl::base::V1_0::BnHwBase*, android::hardware::Parcel const&, android::hardware::Parcel*, std::__1::function<void (android::hardware::Parcel&)>)+166) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#11 pc 000275e9  /system/lib/android.hardware.graphics.composer@2.4.so (android::hardware::graphics::composer::V2_4::BnHwComposerCallback::onTransact(unsigned int, android::hardware::Parcel const&, android::hardware::Parcel*, unsigned int, std::__1::function<void (android::hardware::Parcel&)>)+228) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#12 pc 00054779  /system/lib/libhidlbase.so (android::hardware::BHwBinder::transact(unsigned int, android::hardware::Parcel const&, android::hardware::Parcel*, unsigned int, std::__1::function<void (android::hardware::Parcel&)>)+96) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#13 pc 0004fc67  /system/lib/libhidlbase.so (android::hardware::IPCThreadState::transact(int, unsigned int, android::hardware::Parcel const&, android::hardware::Parcel*, unsigned int)+2174) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#14 pc 0004f2e5  /system/lib/libhidlbase.so (android::hardware::BpHwBinder::transact(unsigned int, android::hardware::Parcel const&, android::hardware::Parcel*, unsigned int, std::__1::function<void (android::hardware::Parcel&)>)+36) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#15 pc 0002bdf1  /system/lib/android.hardware.graphics.composer@2.4.so (android::hardware::graphics::composer::V2_4::BpHwComposerClient::_hidl_registerCallback_2_4(android::hardware::IInterface*, android::hardware::details::HidlInstrumentor*, android::sp<android::hardware::graphics::composer::V2_4::IComposerCallback> const&)+296) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#16 pc 0002ed8d  /system/lib/android.hardware.graphics.composer@2.4.so (android::hardware::graphics::composer::V2_4::BpHwComposerClient::registerCallback_2_4(android::sp<android::hardware::graphics::composer::V2_4::IComposerCallback> const&)+34) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#17 pc 00085627  /system/bin/surfaceflinger (android::Hwc2::impl::Composer::registerCallback(android::sp<android::hardware::graphics::composer::V2_4::IComposerCallback> const&)+98) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#18 pc 00092d63  /system/bin/surfaceflinger (android::impl::HWComposer::setCallback(android::HWC2::ComposerCallback*)+2206) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#19 pc 000cd35b  /system/bin/surfaceflinger (android::SurfaceFlinger::init()+438) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#20 pc 000feb03  /system/bin/surfaceflinger (main+862) 11-13 00:52:58.581   227   227 E BufferQueueProducer: stackdump:#21 pc 0003253b  /apex/com.android.runtime/lib/bionic/libc.so (__libc_init+54) 11-13 00:52:58.582   227   227 D BufferQueueProducer: connect[1307] /vendor/bin/hw/android.hardware.graphics.composer@2.4-service end

注意 本文作者@二的次方  2022-05-10 发布于博客园

注意 本文作者@二的次方  2022-05-10 发布于博客园

注意 本文作者@二的次方  2022-05-10 发布于博客园

这里有一个小细节要留意下,因为SurfaceFlinger::onComposerHalHotplug是HWC回调过来的,所以代码执行是在android.hardware.graphics.composer@2.4-service这个进程中的。

BufferQueueProducer::connect中记录的mConnectedPid就是composer service的PID

[ /frameworks/native/libs/gui/BufferQueueProducer.cpp] mCore->mConnectedPid = BufferQueueThreadState::getCallingPid();

在dump BufferQueue的信息时,根据PID获取的 producer name 也就是 android.hardware.graphics.composer@2.4-service

[/frameworks/native/libs/gui/BufferQueueCore.cpp] void BufferQueueCore::dumpState(const String8& prefix, String8* outResult) const {     ...     getProcessName(mConnectedPid, producerProcName);     getProcessName(pid, consumerProcName);     .... }

如下是我的平台dumpsys SurfaceFlinger的信息打印出来的Composition RenderSurface State的信息,看看是不是和代码的设置都有对应起来:

😅 mConsumerName=FramebufferSurface

🥳 producer=[342:/vendor/bin/hw/android.hardware.graphics.composer@2.4-service]

😏 consumer=[223:/system/bin/surfaceflinger])

🙄 format/size/usage也都可以对应到代码的设置

   Composition RenderSurface State:    size=[1920 1080] ANativeWindow=0xef2c3278 (format 1) flips=605    FramebufferSurface: dataspace: Default(0)    mAbandoned=0    - BufferQueue mMaxAcquiredBufferCount=2 mMaxDequeuedBufferCount=1      mDequeueBufferCannotBlock=0 mAsyncMode=0      mQueueBufferCanDrop=0 mLegacyBufferDrop=1      default-size=[1920x1080] default-format=1      transform-hint=00 frame-counter=580      mTransformHintInUse=00 mAutoPrerotation=0    FIFO(0):    (mConsumerName=FramebufferSurface, mConnectedApi=1, mConsumerUsageBits=6656, mId=df00000000, producer=[342:/vendor/bin/hw/android.hardware.graphics.composer@2.4-service], consumer=[223:/system/bin/surfaceflinger])    Slots:     >[01:0xeec82110] state=ACQUIRED 0xef4429c0 frame=2 [1920x1080:1920,  1]     >[02:0xeec806f0] state=ACQUIRED 0xef443100 frame=580 [1920x1080:1920,  1]      [00:0xeec81f00] state=FREE     0xef440580 frame=579 [1920x1080:1920,  1]

 

四、对上述分析的一个小结和猜想

上述内容中出现的一些字眼,不禁令人”瞎想连篇“

SurfaceFlinger创建了BufferQueue ==> Producer & Consumer

创建了RenderSurface作为生产者,它持有Producer

创建了FramebufferSurface作为消费者,它持有Consumer

 

前面分析BufferQueue的工作原理时,有讲过:

生产者不断的dequeueBuffer & queueBuffer ; 而消费者不断的acquireBuffer & releaseBuffer ,这样图像缓存就在 生产者 -- BufferQueue -- 消费者 间流转起来了。

 

看看作为生产者的RenderSurface中方法:

[/frameworks/native/services/surfaceflinger/CompositionEngine/include/compositionengine/RenderSurface.h] /**  * Encapsulates everything for composing to a render surface with RenderEngine  */ class RenderSurface {     ....     // Allocates a buffer as scratch space for GPU composition     virtual std::shared_ptr<renderengine::ExternalTexture> dequeueBuffer(             base::unique_fd* bufferFence) = 0;      // Queues the drawn buffer for consumption by HWC. readyFence is the fence     // which will fire when the buffer is ready for consumption.     virtual void queueBuffer(base::unique_fd readyFence) = 0;     ... };

熟悉的味道:

dequeueBuffer : 分配一个缓冲区作为GPU合成的暂存空间

queueBuffer :  入队列已绘制好的图形缓存供HWC使用

同样如果去查看作为消费者的FramebufferSurface也会看到acquireBuffer & releaseBuffer的调用,如下:

[/frameworks/native/services/surfaceflinger/DisplayHardware/FramebufferSurface.cpp] status_t FramebufferSurface::nextBuffer(uint32_t& outSlot,         sp<GraphicBuffer>& outBuffer, sp<Fence>& outFence,         Dataspace& outDataspace) {     Mutex::Autolock lock(mMutex);      BufferItem item;     status_t err = acquireBufferLocked(&item, 0); // 获取待显示的buffer      ...              status_t result = mHwc.setClientTarget(mDisplayId, outSlot, outFence, outBuffer, outDataspace); // 传递给HWC进一步处理显示      return NO_ERROR; }

 


 

大概会有这样一种逻辑处理流程:

当需要GPU合成时,会通过生产者RenderSurface::dequeueBuffer请求一块图形缓存,然后GPU就合成/绘图,把数据保存到这块图形缓存中,通过RenderSurface::queueBuffer提交这块缓存

调用mDisplaySurface->advanceFrame()通知消费者来消费:

FramebufferSurface::advanceFrame ==>FramebufferSurface::nextBuffer ==> acquireBufferLocked

去请求