Android GPU合成

1 FramebufferSurface 概述

   FramebufferSurface 根据名字解析：

  1： Surface 说明它是一个Surface， 那么它就会拥有一个 BufferQuere, 用于显示。

  2： FrameBuffer 这和 Linux 的 framebuffer 是完全不同的。 但是作用有些类似， SurfaceFlinger 在上面作画， 并把它交给HWC， 最终由HWC负责真正的显示。

1.1 FrameBufferSurface创建

SurfaceFlinger启动时会在SurfaceFlinger::init()中通过processDisplayHotplugEventsLocked()->processDisplayChangesLocked()->processDisplayAdded(displayToken, curr[i])中：

900  void SurfaceFlinger::init() {
.....
924      mCompositionEngine->setHwComposer(getFactory().createHWComposer(getBE().mHwcServiceName));
925      mCompositionEngine->getHwComposer().setConfiguration(this, getBE().mComposerSequenceId);
926      // Process any initial hotplug and resulting display changes.
927      processDisplayHotplugEventsLocked();
928      const auto display = getDefaultDisplayDeviceLocked();

        processDisplayAdded()方法如下，其创建了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合成图层时，可以向这个BufferQueue索要GraphicBuffer来存储合成后的数据，再呈现到屏幕上去。

3209  void SurfaceFlinger::processDisplayAdded(const wp<IBinder>& displayToken,
3210                                           const DisplayDeviceState& state) {
        .....
3265      sp<compositionengine::DisplaySurface> displaySurface;
3266      sp<IGraphicBufferProducer> producer;
       //创建BufferQueue,获取到生产者和消费者，而且消费者不是SurfaceFlinger。
3267      sp<IGraphicBufferProducer> bqProducer;
3268      sp<IGraphicBufferConsumer> bqConsumer;
3269      getFactory().createBufferQueue(&bqProducer, &bqConsumer, /*consumerIsSurfaceFlinger =*/false);
3270  
3271      std::optional<DisplayId> displayId = compositionDisplay->getId();
3272  
3273      if (state.isVirtual()) {//虚拟屏幕
3274          sp<VirtualDisplaySurface> vds =
3275                  new VirtualDisplaySurface(getHwComposer(), displayId, state.surface,
3276                                            bqProducer, bqConsumer, state.displayName,
3277                                            state.isSecure);
3278  
3279          displaySurface = vds;
3280          producer = vds;
3281      } else {
3282          ALOGE_IF(state.surface != nullptr,
3283                   "adding a supported display, but rendering "
3284                   "surface is provided (%p), ignoring it",
3285                   state.surface.get());
3286  
3287          LOG_ALWAYS_FATAL_IF(!displayId);
        //创建了FrameBufferSurface对象，及继承自compositionengine::DisplaySurface
        //FrameBufferSurface作为消费者的角色工作，消费SF GPU合成后的数据
3288          displaySurface = new FramebufferSurface(getHwComposer(), *displayId, bqConsumer,
3289                                                  maxGraphicsWidth, maxGraphicsHeight);
3290          producer = bqProducer;
3291      }
3292  
3293      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
3294      const auto display = setupNewDisplayDeviceInternal(displayToken, compositionDisplay, state,
3295                                                         displaySurface, producer);
3296      mDisplays.emplace(displayToken, display);
        .....

然后FrameBufferSurface的构造函数，只是一些设置，初始化一些成员：

59  FramebufferSurface::FramebufferSurface(HWComposer& hwc, DisplayId displayId,
60                                         const sp<IGraphicBufferConsumer>& consumer,
61                                         uint32_t maxWidth, uint32_t maxHeight)
62        : ConsumerBase(consumer),
63          mDisplayId(displayId),
64          mMaxWidth(maxWidth),
65          mMaxHeight(maxHeight),
66          mCurrentBufferSlot(-1),
67          mCurrentBuffer(),
68          mCurrentFence(Fence::NO_FENCE),
69          mHwc(hwc),
70          mHasPendingRelease(false),
71          mPreviousBufferSlot(BufferQueue::INVALID_BUFFER_SLOT),
72          mPreviousBuffer() {
73      ALOGV("Creating for display %s", to_string(displayId).c_str());
74  
75      mName = "FramebufferSurface";
76      mConsumer->setConsumerName(mName);
77      mConsumer->setConsumerUsageBits(GRALLOC_USAGE_HW_FB |
78                                         GRALLOC_USAGE_HW_RENDER |
79                                         GRALLOC_USAGE_HW_COMPOSER);
80      const auto& activeConfig = mHwc.getActiveConfig(displayId);
81      ui::Size limitedSize =
82              limitFramebufferSize(activeConfig->getWidth(), activeConfig->getHeight());
83      mConsumer->setDefaultBufferSize(limitedSize.width, limitedSize.height);
84      mConsumer->setMaxAcquiredBufferCount(
85              SurfaceFlinger::maxFrameBufferAcquiredBuffers - 1);
86  }

再进到surfaceflinger::setupNewDisplayDeviceInternal（）中：

3123  sp<DisplayDevice> SurfaceFlinger::setupNewDisplayDeviceInternal(
3124          const wp<IBinder>& displayToken,
3125          std::shared_ptr<compositionengine::Display> compositionDisplay,
3126          const DisplayDeviceState& state,
3127          const sp<compositionengine::DisplaySurface>& displaySurface,
3128          const sp<IGraphicBufferProducer>& producer) {
    .....
3133      creationArgs.displaySurface = displaySurface;
    .....
     //创建对应的surface
31