Android 渲染机制小结

surface

源码定义:

class Surface
    : public ANativeObjectBase<ANativeWindow, Surface, RefBase>
{
public:

    /*
     * creates a Surface from the given IGraphicBufferProducer (which concrete
     * implementation is a BufferQueue).
     *
     * Surface is mainly state-less while it's disconnected, it can be
     * viewed as a glorified IGraphicBufferProducer holder. It's therefore
     * safe to create other Surfaces from the same IGraphicBufferProducer.
     *
     * However, once a Surface is connected, it'll prevent other Surfaces
     * referring to the same IGraphicBufferProducer to become connected and
     * therefore prevent them to be used as actual producers of buffers.
     *
     * the controlledByApp flag indicates that this Surface (producer) is
     * controlled by the application. This flag is used at connect time.
     */
    //sp 智能引用
    explicit Surface(const sp<IGraphicBufferProducer>& bufferProducer,
            bool controlledByApp = false);
            ...

** IGraphicBufferProducer**

• dequeueBuffer : 返回一个新的buffer 供客户端调用
• queueBuffer: 客户端完成buffer 填充后进行提交

SurfaceControl 和 Layer 创建绑定

• ViewRootImp:
  • performTraversals -> relayoutWindow -> mWindowSession.relayout
• WindowManagerService:
  • relayoutWindow -> createSurfaceControl -> winAnimator.createSurfaceLocked
• WindowStateAnimator
  • createSurfaceLocked -> mSurfaceController = new WindowSurfaceController(xxxx)
• WindowSurfaceController:
  • win.makeSurface() .... .build
• SurfaceControl
  • init(xxx) -> nativeCreate(xxxxx)
• android_view_SurfaceControl.cpp
  • sp client;
  • client->createSurfaceChecked(xxx)
• SurfaceComposerClient.cpp
  • sp SurfaceComposerClient::connection() const {\ return IInterface::asBinder(mClient);\ }
  • createSurfaceChecked-> mClient.createSurface(xxx) // binder 调用 ,服务端在 SurfaceFlinger 进程
  • *outSurface = new SurfaceControl(this, handle, gbp, transformHint);
• Client.cpp // surfacefinger进程
  • class BnSurfaceComposerClient : public SafeBnInterface
  • class Client : public BnSurfaceComposerClient
  • sp mFlinger;
  • createSurface -> mFlinger->createLayer(xxx)/
• SurfaceFlinger.cpp
  • sp layer;
  • createBufferStateLayer(xxx) // switch (ISurfaceComposerClient::eFXSurfaceBufferState) -> getFactory().createBufferStateLayer(args)

status_t SurfaceFlinger::createBufferStateLayer(const sp<Client>& client, std::string name,
                                                uint32_t w, uint32_t h, uint32_t flags,
                                                LayerMetadata metadata, sp<IBinder>* handle,
                                                sp<Layer>* outLayer) {
    LayerCreationArgs args(this, client, std::move(name), w, h, flags, std::move(metadata));
    args.textureName = getNewTexture();
    sp<BufferStateLayer> layer = getFactory().createBufferStateLayer(args);
    // 绑定 handler 与 layer
    *handle = layer->getHandle();
    *outLayer = layer;

    return NO_ERROR;
}

• SurfaceFlingerDefaultFactory.cpp
  • new BufferStateLayer(args);
    小结

// SurfaceComposerClient.cpp
status_t SurfaceComposerClient::createSurfaceChecked(const String8& name, uint32_t w, uint32_t h,
                                                     PixelFormat format,
                                                     sp<SurfaceControl>* outSurface, uint32_t flags,
                                                     SurfaceControl* parent, LayerMetadata metadata,
                                                     uint32_t* outTransformHint) {
    sp<SurfaceControl> sur;
    status_t err = mStatus;

    if (mStatus == NO_ERROR) {
        sp<IBinder> handle;
        sp<IBinder> parentHandle;
        sp<IGraphicBufferProducer> gbp;

        if (parent != nullptr) {
            parentHandle = parent->getHandle();
        }

        uint32_t transformHint = 0;
        //  最终会在 SurfaceFlinger 这边创建一块 Layer 对象
        // handle 作为参数一路传递下去 完成与layer的绑定()
        err = mClient->createSurface(name, w, h, format, flags, parentHandle, std::move(metadata),
                                     &handle, &gbp, &transformHint);
        if (outTransformHint) {
            *outTransformHint = transformHint;
        }
        ALOGE_IF(err, "SurfaceComposerClient::createSurface error %s", strerror(-err));
        if (err == NO_ERROR) {
            // 最终会作为 SurfaceControl 构造函数的参数传递给 SurfaceControl
            *outSurface = new SurfaceControl(this, handle, gbp, transformHint);
        }
    }
    return err;
}

BLASTBufferQueue

- ViewRootImpl
    - relayoutWindow - final Surface blastSurface = getOrCreateBLASTSurface(mSurfaceSize.x,
                    mSurfaceSize.y); -> mBlastBufferQueue = new BLASTBufferQueue()
                    -> mBlastBufferQueue.getSurface(); //获取Surface
- BLASTBufferQueue
    - init -> nativeCreate(sc.mNativeObject, width, height, tripleBufferingEnabled);
    - getSurface -> nativeGetSurface(mNativeObject);
- android_graphics_BLASTBufferQueue.cpp
    - sp<BLASTBufferQueue> queue = new BLASTBufferQueue(
            reinterpret_cast<SurfaceControl*>(surfaceControl), width, height, enableTripleBuffering);
    - nativeGetSurface -> android_view_Surface_createFromIGraphicBufferProducer(env, queue->getIGraphicBufferProducer()); -> sp<Surface> surface(new Surface(bufferProducer, true)); //android_view_Surface.cpp
- BLASTBufferQueue.cpp
    - sp<IGraphicBufferConsumer> mConsumer;
    - sp<IGraphicBufferProducer> mProducer;
    -  init -> BufferQueue::createBufferQueue(&mProducer, &mConsumer); // 创建 BufferQueueCore，mProducer 和 mConsumer 
    -  init -> mBufferItemConsumer =
        new BLASTBufferItemConsumer(mConsumer, GraphicBuffer::USAGE_HW_COMPOSER, 1, true); // 创建 mBufferItemConsumer
    - mBufferItemConsumer->setFrameAvailableListener(this); //把 FrameAvailableListener 的回调设置成自己, 也就是 BLASTBufferQueue
- BufferQueueCore.h
    -  BufferQueueDefs::SlotsType mSlots; //struct BufferSlot{...sp<GraphicBuffer> mGraphicBuffer; BufferState mBufferState;...}
    -  Fifo mQueue; // typedef Vector<BufferItem> Fifo; //class BufferItem{...sp<GraphicBuffer> mGraphicBuffer;...}
    

void BufferQueue::createBufferQueue(sp<IGraphicBufferProducer>* outProducer,
        sp<IGraphicBufferConsumer>* outConsumer,
        bool consumerIsSurfaceFlinger) {
    LOG_ALWAYS_FATAL_IF(outProducer == nullptr,
            "BufferQueue: outProducer must not be NULL");
    LOG_ALWAYS_FATAL_IF(outConsumer == nullptr,
            "BufferQueue: outConsumer must not be NULL");
    // 
    sp<BufferQueueCore> core(new BufferQueueCore());
    LOG_ALWAYS_FATAL_IF(core == nullptr,
            "BufferQueue: failed to create BufferQueueCore");

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

    sp<IGraphicBufferConsumer> consumer(new BufferQueueConsumer(core));
    LOG_ALWAYS_FATAL_IF(consumer == nullptr,
            "BufferQueue: failed to create BufferQueueConsumer");
    
    *outProducer = producer;
    *outConsumer = consumer;
}

流程

• Producer 从 mSlots 中拿到一块 BufferSlot // queueBuffer
• BufferSlot 转换成 BufferItem 插入 mQueue
• Comsumer 从 mQueue 中取出 BufferItem // acquireBuffer ,releaseBuffer
• BufferItem 转换成 BufferSlot 提交给 SurfaceFlinger
• mQueue 的主要作用是 "控制 Buffer 的出队顺序"

BufferQueueProducer

APP 侧

• SurfaceFlinger 收到 Vsync 分发给 Choreographer
• Choreographer -> doFrame ->
• ViewRootImpl.doTarversal -> ViewRootImpl.performTraversals
  • performTraversals ->
    ->performMeasure
    ->performLayout
    ->perforDraw
    -> Draw -> drawSoftware ->

draw

• canvas = mSurface.lockCanvas(dirty); //初始化 Canvas,从 BLASTBufferQueue 中申请一块 GraphicBuffer
• ...->Surface.cpp -> lock -> dequeueBuffer(&out, &fenceFd); -> mGraphicBufferProducer->dequeueBuffer(....)
• mView.draw(canvas); //绘制 ,使用绘制引擎 api 进行绘制 Skia / OpenGL
• surface.unlockCanvasAndPost(canvas); //绘制完成,提交到 BLASTBufferQueue
• ...->Surface.cpp ->unlockAndPost-> queueBuffer(mLockedBuffer.get(), fd); -> mGraphicBufferProducer->queueBuffer(i, input, &output);

GraphicBuffer

//GraphicBuffer.h
class GraphicBuffer
    : public ANativeObjectBase<ANativeWindowBuffer, GraphicBuffer, RefBase>,
      public Flattenable<GraphicBuffer> //支持序列化, 支持Binder 跨进程传递

//ANativeObjectBase.h
// 模版类
template <typename NATIVE_TYPE, typename TYPE, typename REF,
        typename NATIVE_BASE = android_native_base_t>
class ANativeObjectBase : public NATIVE_TYPE, public REF

//nativebase.h
typedef struct ANativeWindowBuffer{
    ...
    //底层 Buffer 内存 句柄
    const native_handle_t* handle;
}
typedef struct ANativeWindowBuffer ANativeWindowBuffer;

创建

BufferQueueProducer.cpp

• dequeueBuffer -> 查找可用buffer,复用 ,没有的话 创建 GraphicBuffer()
  GraphicBuffer.cpp
• init->initWithSize -> allocator.allocate(inWidth, inHeight, inFormat, inLayerCount,
  inUsage, &handle, &outStride, mId,
  std::move(requestorName)); // 通过 Binder Server 分配一块内存，并且返回这块内存的地址由 handle 持有
  GraphicBufferAllocator.cpp
• allocate -> allocateHelper -> mAllocator->allocate(....)