SurfaceView创建Surface的过程

在分析SurfaceView如何创建Surface之前需要先了解下SurfaceFlinger的知识，
几篇好文章

SurfaceView在显示时，会调用onWindowVisibilityChanged方法，详细流程请参考

//frameworks\base\core\java\android\view\SurfaceView.java
   @Override
   protected void onWindowVisibilityChanged(int visibility) {
       super.onWindowVisibilityChanged(visibility);
       mWindowVisibility = visibility == VISIBLE;
       updateRequestedVisibility();
       //创建surface入口
       updateSurface();
   }

接着分析下updateSurface

    /** @hide */
    protected void updateSurface() {
        if (!mHaveFrame) {
            return;
        }
        //获取宿主窗口
        ViewRootImpl viewRoot = getViewRootImpl();
        if (viewRoot == null || viewRoot.mSurface == null || !viewRoot.mSurface.isValid()) {
            return;
        }

        mTranslator = viewRoot.mTranslator;
        if (mTranslator != null) {
            mSurface.setCompatibilityTranslator(mTranslator);
        }

        int myWidth = mRequestedWidth;
        if (myWidth <= 0) myWidth = getWidth();
        int myHeight = mRequestedHeight;
        if (myHeight <= 0) myHeight = getHeight();

        final boolean formatChanged = mFormat != mRequestedFormat;
        final boolean visibleChanged = mVisible != mRequestedVisible;
        final boolean creating = (mSurfaceControl == null || formatChanged || visibleChanged)
                && mRequestedVisible;
        final boolean sizeChanged = mSurfaceWidth != myWidth || mSurfaceHeight != myHeight;
        final boolean windowVisibleChanged = mWindowVisibility != mLastWindowVisibility;
        boolean redrawNeeded = false;
       //检查surfaceview是否存在变化
        if (creating || formatChanged || sizeChanged || visibleChanged || windowVisibleChanged) {
            getLocationInWindow(mLocation);

            if (DEBUG) Log.i(TAG, System.identityHashCode(this) + " "
                    + "Changes: creating=" + creating
                    + " format=" + formatChanged + " size=" + sizeChanged
                    + " visible=" + visibleChanged
                    + " left=" + (mWindowSpaceLeft != mLocation[0])
                    + " top=" + (mWindowSpaceTop != mLocation[1]));

            try {
                final boolean visible = mVisible = mRequestedVisible;
                mWindowSpaceLeft = mLocation[0];
                mWindowSpaceTop = mLocation[1];
                mSurfaceWidth = myWidth;
                mSurfaceHeight = myHeight;
                mFormat = mRequestedFormat;
                mLastWindowVisibility = mWindowVisibility;

                mScreenRect.left = mWindowSpaceLeft;
                mScreenRect.top = mWindowSpaceTop;
                mScreenRect.right = mWindowSpaceLeft + getWidth();
                mScreenRect.bottom = mWindowSpaceTop + getHeight();
                if (mTranslator != null) {
                    mTranslator.translateRectInAppWindowToScreen(mScreenRect);
                }

                final Rect surfaceInsets = getParentSurfaceInsets();
                mScreenRect.offset(surfaceInsets.left, surfaceInsets.top);

                if (creating) {
                    //创建SurfaceSession，该类会连接surfaceFlinger
                    mSurfaceSession = new SurfaceSession(viewRoot.mSurface);
                    mDeferredDestroySurfaceControl = mSurfaceControl;

                    updateOpaqueFlag();
                    //创建SurfaceControl，对象会向surfaceFlinger发启创建surface的申请。
                    mSurfaceControl = new SurfaceControlWithBackground(mSurfaceSession,
                            "SurfaceView - " + viewRoot.getTitle().toString(),
                            mSurfaceWidth, mSurfaceHeight, mFormat,
                            mSurfaceFlags);
                } else if (mSurfaceControl == null) {
                    return;
                }

                boolean realSizeChanged = false;

                mSurfaceLock.lock();
                try {
                    mDrawingStopped = !visible;

                    if (DEBUG) Log.i(TAG, System.identityHashCode(this) + " "
                            + "Cur surface: " + mSurface);

                    SurfaceControl.openTransaction();
                    try {
                       //设置Layer属性
                        mSurfaceControl.setLayer(mSubLayer);
                        if (mViewVisibility) {
                            mSurfaceControl.show();
                        } else {
                            mSurfaceControl.hide();
                        }

                        // While creating the surface, we will set it's initial
                        // geometry. Outside of that though, we should generally
                        // leave it to the RenderThread.
                        //
                        // There is one more case when the buffer size changes we aren't yet
                        // prepared to sync (as even following the transaction applying
                        // we still need to latch a buffer).
                        // b/28866173
                        if (sizeChanged || creating || !mRtHandlingPositionUpdates) {
                            mSurfaceControl.setPosition(mScreenRect.left, mScreenRect.top);
                            mSurfaceControl.setMatrix(mScreenRect.width() / (float) mSurfaceWidth,
                                    0.0f, 0.0f,
                                    mScreenRect.height() / (float) mSurfaceHeight);
                        }
                        if (sizeChanged) {
                            mSurfaceControl.setSize(mSurfaceWidth, mSurfaceHeight);
                        }
                    } finally {
                        SurfaceControl.closeTransaction();
                    }

                    if (sizeChanged || creating) {
                        redrawNeeded = true;
                    }

                    mSurfaceFrame.left = 0;
                    mSurfaceFrame.top = 0;
                    if (mTranslator == null) {
                        mSurfaceFrame.right = mSurfaceWidth;
                        mSurfaceFrame.bottom = mSurfaceHeight;
                    } else {
                        float appInvertedScale = mTranslator.applicationInvertedScale;
                        mSurfaceFrame.right = (int) (mSurfaceWidth * appInvertedScale + 0.5f);
                        mSurfaceFrame.bottom = (int) (mSurfaceHeight * appInvertedScale + 0.5f);
                    }

                    final int surfaceWidth = mSurfaceFrame.right;
                    final int surfaceHeight = mSurfaceFrame.bottom;
                    realSizeChanged = mLastSurfaceWidth != surfaceWidth
                            || mLastSurfaceHeight != surfaceHeight;
                    mLastSurfaceWidth = surfaceWidth;
                    mLastSurfaceHeight = surfaceHeight;
                } finally {
                    mSurfaceLock.unlock();
                }

                try {
                    redrawNeeded |= visible && !mDrawFinished;

                    SurfaceHolder.Callback callbacks[] = null;

                    final boolean surfaceChanged = creating;
                    if (mSurfaceCreated && (surfaceChanged || (!visible && visibleChanged))) {
                        mSurfaceCreated = false;
                        if (mSurface.isValid()) {
                            if (DEBUG) Log.i(TAG, System.identityHashCode(this) + " "
                                    + "visibleChanged -- surfaceDestroyed");
                            callbacks = getSurfaceCallbacks();
                            for (SurfaceHolder.Callback c : callbacks) {
                                c.surfaceDestroyed(mSurfaceHolder);
                            }
                            // Since Android N the same surface may be reused and given to us
                            // again by the system server at a later point. However
                            // as we didn't do this in previous releases, clients weren't
                            // necessarily required to clean up properly in
                            // surfaceDestroyed. This leads to problems for example when
                            // clients don't destroy their EGL context, and try
                            // and create a new one on the same surface following reuse.
                            // Since there is no valid use of the surface in-between
                            // surfaceDestroyed and surfaceCreated, we force a disconnect,
                            // so the next connect will always work if we end up reusing
                            // the surface.
                            if (mSurface.isValid()) {
                                mSurface.forceScopedDisconnect();
                            }
                        }
                    }

                    if (creating) {
                    //将mSurfaceControl中创建的Native surface信息复制给mSurface
                        mSurface.copyFrom(mSurfaceControl);
                    }
                    //如果API小于O,在sizeChanged发生变化后，会重新从mSurfaceControl赋值surface信息给mSurface
                    if (sizeChanged && getContext().getApplicationInfo().targetSdkVersion
                            < Build.VERSION_CODES.O) {
                        // Some legacy applications use the underlying native {@link Surface} object
                        // as a key to whether anything has changed. In these cases, updates to the
                        // existing {@link Surface} will be ignored when the size changes.
                        // Therefore, we must explicitly recreate the {@link Surface} in these
                        // cases.
                        mSurface.createFrom(mSurfaceControl);
                    }

                    if (visible && mSurface.isValid()) {
                        if (!mSurfaceCreated && (surfaceChanged || visibleChanged)) {
                            mSurfaceCreated = true;
                            mIsCreating = true;
                            if (DEBUG) Log.i(TAG, System.identityHashCode(this) + " "
                                    + "visibleChanged -- surfaceCreated");
                            if (callbacks == null) {
                                callbacks = getSurfaceCallbacks();
                            }
                            //surfaceCreated回调
                            for (SurfaceHolder.Callback c : callbacks) {
                                c.surfaceCreated(mSurfaceHolder);
                            }
                        }
                        if (creating || formatChanged || sizeChanged
                                || visibleChanged || realSizeChanged) {
                            if (DEBUG) Log.i(TAG, System.identityHashCode(this) + " "
                                    + "surfaceChanged -- format=" + mFormat
                                    + " w=" + myWidth + " h=" + myHeight);
                            if (callbacks == null) {
                                callbacks = getSurfaceCallbacks();
                            }
                            //surfaceChanged回调
                            for (SurfaceHolder.Callback c : callbacks) {
                                c.surfaceChanged(mSurfaceHolder, mFormat, myWidth, myHeight);
                            }
                        }
                        if (redrawNeeded) {
                            if (DEBUG) Log.i(TAG, System.identityHashCode(this) + " "
                                    + "surfaceRedrawNeeded");
                            if (callbacks == null) {
                                callbacks = getSurfaceCallbacks();
                            }

                            mPendingReportDraws++;
                            viewRoot.drawPending();
                            SurfaceCallbackHelper sch =
                                    new SurfaceCallbackHelper(this::onDrawFinished);
                            sch.dispatchSurfaceRedrawNeededAsync(mSurfaceHolder, callbacks);
                        }
                    }
                } finally {
                    mIsCreating = false;
                    if (mSurfaceControl != null && !mSurfaceCreated) {
                        mSurface.release();
                        // If we are not in the stopped state, then the destruction of the Surface
                        // represents a visual change we need to display, and we should go ahead
                        // and destroy the SurfaceControl. However if we are in the stopped state,
                        // we can just leave the Surface around so it can be a part of animations,
                        // and we let the life-time be tied to the parent surface.
                        if (!mWindowStopped) {
                            mSurfaceControl.destroy();
                            mSurfaceControl = null;
                        }
                    }
                }
            } catch (Exception ex) {
                Log.e(TAG, "Exception configuring surface", ex);
            }
            if (DEBUG) Log.v(
                TAG, "Layout: x=" + mScreenRect.left + " y=" + mScreenRect.top
                + " w=" + mScreenRect.width() + " h=" + mScreenRect.height()
                + ", frame=" + mSurfaceFrame);
        } else {
            // Calculate the window position in case RT loses the window
            // and we need to fallback to a UI-thread driven position update
            getLocationInSurface(mLocation);
            final boolean positionChanged = mWindowSpaceLeft != mLocation[0]
                    || mWindowSpaceTop != mLocation[1];
            final boolean layoutSizeChanged = getWidth() != mScreenRect.width()
                    || getHeight() != mScreenRect.height();
            if (positionChanged || layoutSizeChanged) { // Only the position has changed
                mWindowSpaceLeft = mLocation[0];
                mWindowSpaceTop = mLocation[1];
                // For our size changed check, we keep mScreenRect.width() and mScreenRect.height()
                // in view local space.
                mLocation[0] = getWidth();
                mLocation[1] = getHeight();

                mScreenRect.set(mWindowSpaceLeft, mWindowSpaceTop,
                        mWindowSpaceLeft + mLocation[0], mWindowSpaceTop + mLocation[1]);

                if (mTranslator != null) {
                    mTranslator.translateRectInAppWindowToScreen(mScreenRect);
                }

                if (mSurfaceControl == null) {
                    return;
                }

                if (!isHardwareAccelerated() || !mRtHandlingPositionUpdates) {
                    try {
                        if (DEBUG) Log.d(TAG, String.format("%d updateSurfacePosition UI, " +
                                "postion = [%d, %d, %d, %d]", System.identityHashCode(this),
                                mScreenRect.left, mScreenRect.top,
                                mScreenRect.right, mScreenRect.bottom));
                        setParentSpaceRectangle(mScreenRect, -1);
                    } catch (Exception ex) {
                        Log.e(TAG, "Exception configuring surface", ex);
                    }
                }
            }
        }
    }

重点分析下SurfaceSession创建及SurfaceControl的创建

首先创建SurfaceSession时，调用的是 new SurfaceSession(viewRoot.mSurface)，使用的是SurfaceSession的构造函数为：

//frameworks\base\core\java\android\view\SurfaceSession.java
//root是viewRoot中的surface
    public SurfaceSession(Surface root) {
    //root.mNativeObject 是Native层的Surface指针
        mNativeClient = nativeCreateScoped(root.mNativeObject);
    }

接着分析下nativeCreateScoped

//frameworks\base\core\java\android\view\SurfaceSession.java
    private static native long nativeCreateScoped(long surfacePtr);

对应的JNI实现为:

//frameworks\base\core\jni\android_view_SurfaceSession.cpp
static jlong nativeCreateScoped(JNIEnv* env, jclass clazz, jlong surfaceObject) {
    Surface *parent = reinterpret_cast<Surface*>(surfaceObject);
    //创建SurfaceComposerClient对象
    SurfaceComposerClient* client = new SurfaceComposerClient(parent->getIGraphicBufferProducer());
    //增加引用计数
    client->incStrong((void*)nativeCreate);
    return reinterpret_cast<jlong>(client);
}

从此可见SurfaceSession创建了一个SurfaceComposerClient对象，接着分析SurfaceComposerClient的创建过程。
其构造函数为：

//frameworks\native\libs\gui\SurfaceComposerClient.cpp
SurfaceComposerClient::SurfaceComposerClient(const sp<IGraphicBufferProducer>& root)
    : mStatus(NO_INIT), mComposer(Composer::getInstance()), mParent(root)
{
}

调用 client->incStrong((void*)nativeCreate);会触发onFirstRef方法

//frameworks\native\libs\gui\SurfaceComposerClient.cpp
void SurfaceComposerClient::onFirstRef() {
    sp<ISurfaceComposer> sm(ComposerService::getComposerService());
    if (sm != 0) {
      
        auto rootProducer = mParent.promote();
        sp<ISurfaceComposerClient> conn;
          //mParent.promote()不为空
        conn = (rootProducer != nullptr) ? sm->createScopedConnection(rootProducer) :
                sm->createConnection();
        if (conn != 0) {
            mClient = conn;
            mStatus = NO_ERROR;
        }
    }
}

首先获取ISurfaceComposer服务代理对象BpSurfaceComposer

ISurfaceComposer服务的获取在
Android4.4深入浅出之SurfaceFlinger与Client通信框架（一）讲的比较清楚了，
这里借用一下其流程图，方便理解。
在这里插入图片描述

现在直接进入SurfaceFlinger，分析下createScopedConnection

//frameworks\native\services\surfaceflinger\SurfaceFlinger.cpp
sp<ISurfaceComposerClient> SurfaceFlinger::createScopedConnection(
        const sp<IGraphicBufferProducer>& gbp) {
    if (authenticateSurfaceTexture(gbp) == false) {
        return nullptr;
    }
    const auto& layer = (static_cast<MonitoredProducer*>(gbp.get()))->getLayer();
    if (layer == nullptr) {
        return nullptr;
    }

   return initClient(new Client(this, layer));
}

创建一个Client对象，然后调用对象的initCheck并返回应用该client的代理。
先分析下Client的创建。其中Client继承实现了BnSurfaceComposerClient
代码如下：

//frameworks\native\services\surfaceflinger\Client.cpp
Client::Client(const sp<SurfaceFlinger>& flinger, const sp<Layer>& parentLayer)
    : mFlinger(flinger),
      mParentLayer(parentLayer)
{
}

status_t Client::initCheck() const {
    return NO_ERROR;
}

至此分析完成了SurfaceSession的创建过程，最终会在SurfaceFlinger中创建一个BnSurfaceComposerClient子类对象Client，然后将该BnSurfaceComposerClient的代理对象BpSurfaceComposerClient返回赋值给给应用进程SurfaceComposerClient的mClient。

接着分析下SurfaceControl的创建

//frameworks\base\core\java\android\view\SurfaceView.java
//mSurfaceSession是上一步创建session
  mSurfaceControl = new SurfaceControlWithBackground(mSurfaceSession,
           "SurfaceView - " + viewRoot.getTitle().toString(),
           mSurfaceWidth, mSurfaceHeight, mFormat,
           mSurfaceFlags);

其实现代码如下：

//frameworks\base\core\java\android\view\SurfaceView.java
    class SurfaceControlWithBackground extends SurfaceControl {
        private SurfaceControl mBackgroundControl;
        private boolean mOpaque = true;
        public boolean mVisible = false;
       //一起创建了两个SurfaceControl，还不明白其目的。
        public SurfaceControlWithBackground(SurfaceSession s,
                        String name, int w, int h, int format, int flags)
                       throws Exception {
            super(s, name, w, h, format, flags);
            mBackgroundControl = new SurfaceControl(s, "Background for - " + name, w, h,
                    PixelFormat.OPAQUE, flags | SurfaceControl.FX_SURFACE_DIM);
            mOpaque = (flags & SurfaceControl.OPAQUE) != 0;
        }

其代码如下：

//\frameworks\base\core\java\android\view\SurfaceControl.java
public SurfaceControl(SurfaceSession session,
            String name, int w, int h, int format, int flags)
                    throws OutOfResourcesException {
        this(session, name, w, h, format, flags, null, INVALID_WINDOW_TYPE, Binder.getCallingUid());
    }

    public SurfaceControl(SurfaceSession session, String name, int w, int h, int format, int flags,
            SurfaceControl parent, int windowType, int ownerUid)
                    throws OutOfResourcesException {
        if (session == null) {
            throw new IllegalArgumentException("session must not be null");
        }
        if (name == null) {
            throw new IllegalArgumentException("name must not be null");
        }

        if ((flags & SurfaceControl.HIDDEN) == 0) {
            Log.w(TAG, "Surfaces should always be created with the HIDDEN flag set "
                    + "to ensure that they are not made visible prematurely before "
                    + "all of the surface's properties have been configured.  "
                    + "Set the other properties and make the surface visible within "
                    + "a transaction.  New surface name: " + name,
                    new Throwable());
        }

        mName = name;
        //调用Native方法
        mNativeObject = nativeCreate(session, name, w, h, format, flags,
            parent != null ? parent.mNativeObject : 0, windowType, ownerUid);
        if (mNativeObject == 0) {
            throw new OutOfResourcesException(
                    "Couldn't allocate SurfaceControl native object");
        }

        mCloseGuard.open("release");
    }

接着分析下Native方法nativeCreate

//frameworks\base\core\java\android\view\SurfaceControl.java
    private static native long nativeCreate(SurfaceSession session, String name,
            int w, int h, int format, int flags, long parentObject, int windowType, int ownerUid)

其JNI实现方法：

//frameworks\base\core\jni\android_view_SurfaceControl.cpp
//sessionObj为之前创建的session
//parentObject为null
static jlong nativeCreate(JNIEnv* env, jclass clazz, jobject sessionObj,
        jstring nameStr, jint w, jint h, jint format, jint flags, jlong parentObject,
        jint windowType, jint ownerUid) {
    ScopedUtfChars name(env, nameStr);
     //由sessionObj获取其SurfaceComposerClient代理对象BpSurfaceComposerClient
    sp<SurfaceComposerClient> client(android_view_SurfaceSession_getClient(env, sessionObj));
    SurfaceControl *parent = reinterpret_cast<SurfaceControl*>(parentObject);
   //client为frameworks\native\libs\gui\SurfaceComposerClient.cpp的SurfaceComposerClient对象
    sp<SurfaceControl> surface = client->createSurface(
            String8(name.c_str()), w, h, format, flags, parent, windowType, ownerUid);
    if (surface == NULL) {
        jniThrowException(env, OutOfResourcesException, NULL);
        return 0;
    }
    //增加引用计数
    surface->incStrong((void *)nativeCreate);
    return reinterpret_cast<jlong>(surface.get());
}

接着分析下SurfaceComposerClient的createSurface

//frameworks\native\libs\gui\SurfaceComposerClient.cpp
sp<SurfaceControl> SurfaceComposerClient::createSurface(
        const String8& name,
        uint32_t w,
        uint32_t h,
        PixelFormat format,
        uint32_t flags,
        SurfaceControl* parent,
        uint32_t windowType,
        uint32_t ownerUid)
{
    sp<SurfaceControl> sur;
    if (mStatus == NO_ERROR) {
        sp<IBinder> handle;
        sp<IBinder> parentHandle;
        sp<IGraphicBufferProducer> gbp;

        if (parent != nullptr) {
            parentHandle = parent->getHandle();
        }
        //mClient为BpSurfaceComposerClient类对象，是创建SurfaceSession时创建的
        //向surfaceFlinger申请创建surface，并将创建的 sp<IBinder> handle及IGraphicBufferProducer gbp返回给当前进程，IGraphicBufferProducer其实是BpGraphicBufferProducer
        status_t err = mClient->createSurface(name, w, h, format, flags, parentHandle,
                windowType, ownerUid, &handle, &gbp);
        ALOGE_IF(err, "SurfaceComposerClient::createSurface error %s", strerror(-err));
        if (err == NO_ERROR) {
           //将返回的 handle, gbp封装为Native的SurfaceControl
            sur = new SurfaceControl(this, handle, gbp);
        }
    }
    return sur;
}

跨进程PRC通信，进入surfaceFlinger进程中创建的client

//frameworks\native\services\surfaceflinger\Client.cpp
status_t Client::createSurface(
        const String8& name,
        uint32_t w, uint32_t h, PixelFormat format, uint32_t flags,
        const sp<IBinder>& parentHandle, uint32_t windowType, uint32_t ownerUid,
        sp<IBinder>* handle,
        sp<IGraphicBufferProducer>* gbp)
{
//由之前的分析可知parentHandle为null，parent为null
    sp<Layer> parent = nullptr;
    if (parentHandle != nullptr) {
        parent = getLayerUser(parentHandle);
        if (parent == nullptr) {
            return NAME_NOT_FOUND;
        }
    }
    if (parent == nullptr) {
        bool parentDied;
        parent = getParentLayer(&parentDied);
        // If we had a parent, but it died, we've lost all
        // our capabilities.
        if (parentDied) {
            return NAME_NOT_FOUND;
        }
    }
    //给rendor thread 发消息
    /*
     * createSurface must be called from the GL thread so that it can
     * have access to the GL context.
     */
    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;
        sp<Layer>* parent;
        uint32_t windowType;
        uint32_t ownerUid;
    public:
        MessageCreateLayer(SurfaceFlinger* flinger,
                const String8& name, Client* client,
                uint32_t w, uint32_t h, PixelFormat format, uint32_t flags,
                sp<IBinder>* handle, uint32_t windowType, uint32_t ownerUid,
                sp<IGraphicBufferProducer>* gbp,
                sp<Layer>* parent)
            : flinger(flinger), client(client),
              handle(handle), gbp(gbp), result(NO_ERROR),
              name(name), w(w), h(h), format(format), flags(flags),
              parent(parent), windowType(windowType), ownerUid(ownerUid) {
        }
        status_t getResult() const { return result; }
        virtual bool handler() {
            //处理消息
            //
            result = flinger->createLayer(name, client, w, h, format, flags,
                    windowType, ownerUid, handle, gbp, parent);
            return true;
        }
    };

    sp<MessageBase> msg = new MessageCreateLayer(mFlinger.get(),
            name, this, w, h, format, flags, handle,
            windowType, ownerUid, gbp, &parent);
     //发送消息
    mFlinger->postMessageSync(msg);
    return static_cast<MessageCreateLayer*>( msg.get() )->getResult();
}

进入surfaceFlinger

//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,
        uint32_t windowType, uint32_t ownerUid, sp<IBinder>* handle,
        sp<IGraphicBufferProducer>* gbp, sp<Layer>* parent)
{
    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;

    String8 uniqueName = getUniqueLayerName(name);
   //在之前的分析时，发现surfaceView使用SurfaceControlWithBackground创建两个
   //SurfaceControl，
   //第一个应该时eFXSurfaceNormal，需要在确定下
   //第二个是createDimLayer
   
    switch (flags & ISurfaceComposerClient::eFXSurfaceMask) {
        case ISurfaceComposerClient::eFXSurfaceNormal:

            result = createNormalLayer(client,
                    uniqueName, w, h, flags, format,
                    handle, gbp, &layer);
            break;
            //
        case ISurfaceComposerClient::eFXSurfaceDim:
            result = createDimLayer(client,
                    uniqueName, w, h, flags,
                    handle, gbp, &layer);
            break;
        default:
            result = BAD_VALUE;
            break;
    }

    if (result != NO_ERROR) {
        return result;
    }

    // window type is WINDOW_TYPE_DONT_SCREENSHOT from SurfaceControl.java
    // TODO b/64227542
    if (windowType == 441731) {
        windowType = 2024; // TYPE_NAVIGATION_BAR_PANEL
        layer->setPrimaryDisplayOnly();
    }

    layer->setInfo(windowType, ownerUid);
    //这个layer和client相关联, 添加到Client的mLayers集合中。
    result = addClientLayer(client, *handle, *gbp, layer, *parent);
    if (result != NO_ERROR) {
        return result;
    }
    mInterceptor.saveSurfaceCreation(layer);

    setTransactionFlags(eTransactionNeeded);
    return result;
}

先分析下createNormalLayer

//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surface，并赋值给outLayer 返回
    *outLayer = DisplayUtils::getInstance()->getLayerInstance(this,
                            client, name, w, h, flags);
    //设置buffer的宽、高、格式、flags属性
    status_t err = (*outLayer)->setBuffers(w, h, format, flags);
    //返回handle
    //返回gbp
    if (err == NO_ERROR) {
        *handle = (*outLayer)->getHandle();
        *gbp = (*outLayer)->getProducer();
    }

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

接着分析下DisplayUtils::getInstance()->getLayerInstance(this, client, name, w, h, flags);

//frameworks\native\services\surfaceflinger\DisplayUtils.cpp
Layer* DisplayUtils::getLayerInstance(SurfaceFlinger* flinger,
                            const sp<Client>& client, const String8& name,
                            uint32_t w, uint32_t h, uint32_t flags) {
     //sUseExtendedImplsw为false
    if (sUseExtendedImpls) {
        return new ExLayer(flinger, client, name, w, h, flags);
    } else {
        return new Layer(flinger, client, name, w, h, flags);
    }
}

创建了一个新的Layer对象，代码如下：

//\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),
        mPendingStateMutex(),
        mPendingStates(),
        mQueuedFrames(0),
        mSidebandStreamChanged(false),
        mActiveBufferSlot(BufferQueue::INVALID_BUFFER_SLOT),
        mCurrentTransform(0),
        mCurrentScalingMode(NATIVE_WINDOW_SCALING_MODE_FREEZE),
        mOverrideScalingMode(-1),
        mCurrentOpacity(true),
        mBufferLatched(false),
        mCurrentFrameNumber(0),
        mPreviousFrameNumber(0),
        mRefreshPending(false),
        mFrameLatencyNeeded(false),
        mFiltering(false),
        mNeedsFiltering(false),
        mMesh(Mesh::TRIANGLE_FAN, 4, 2, 2),
#ifndef USE_HWC2
        mIsGlesComposition(false),
#endif
        mProtectedByApp(false),
        mHasSurface(false),
        mClientRef(client),
        mPotentialCursor(false),
        mQueueItemLock(),
        mQueueItemCondition(),
        mQueueItems(),
        mLastFrameNumberReceived(0),
        mUpdateTexImageFailed(false),
        mAutoRefresh(false),
        mFreezeGeometryUpdates(false)
{
#ifdef USE_HWC2
    ALOGV("Creating Layer %s", name.string());
#endif

    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;
    mTransactionName = String8("TX - ") + mName;

    mCurrentState.active.w = w;
    mCurrentState.active.h = h;
    mCurrentState.active.transform.set(0, 0);
    mCurrentState.crop.makeInvalid();
    mCurrentState.finalCrop.makeInvalid();
    mCurrentState.requestedFinalCrop = mCurrentState.finalCrop;
    mCurrentState.requestedCrop = mCurrentState.crop;
    mCurrentState.z = 0;
#ifdef USE_HWC2
    mCurrentState.alpha = 1.0f;
#else
    mCurrentState.alpha = 0xFF;
#endif
    mCurrentState.layerStack = 0;
    mCurrentState.flags = layerFlags;
    mCurrentState.sequence = 0;
    mCurrentState.requested = mCurrentState.active;
    mCurrentState.dataSpace = HAL_DATASPACE_UNKNOWN;
    mCurrentState.appId = 0;
    mCurrentState.type = 0;

    // drawing state & current state are identical
    mDrawingState = mCurrentState;

#ifdef USE_HWC2
    const auto& hwc = flinger->getHwComposer();
    const auto& activeConfig = hwc.getActiveConfig(HWC_DISPLAY_PRIMARY);
    nsecs_t displayPeriod = activeConfig->getVsyncPeriod();
#else
    nsecs_t displayPeriod =
            flinger->getHwComposer().getRefreshPeriod(HWC_DISPLAY_PRIMARY);
#endif
    mFrameTracker.setDisplayRefreshPeriod(displayPeriod);

    CompositorTiming compositorTiming;
    flinger->getCompositorTiming(&compositorTiming);
    mFrameEventHistory.initializeCompositorTiming(compositorTiming);
}

在将该对象赋值给outLayer时，会触发Layer的onFirstRef

//frameworks\native\services\surfaceflinger\Layer.cpp
void Layer::onFirstRef() {
   //创建producer及consumer及
    // Creates a custom BufferQueue for SurfaceFlingerConsumer to use
    sp<IGraphicBufferProducer> producer;
    sp<IGraphicBufferConsumer> consumer;
    BufferQueue::createBufferQueue(&producer, &consumer, true);
    //封装producer为MonitoredProducer
    mProducer = new MonitoredProducer(producer, mFlinger, this);
    //封装consumer为SurfaceFlingerConsumer
    mSurfaceFlingerConsumer = new SurfaceFlingerConsumer(consumer, mTextureName, this);
    mSurfaceFlingerConsumer->setConsumerUsageBits(getEffectiveUsage(0));
    //这个帧回调函数
    //有onFrameAvailable
    //onFrameReplaced
    mSurfaceFlingerConsumer->setContentsChangedListener(this);
    //设置consumer的name
    mSurfaceFlingerConsumer->setName(mName);
    //如果没有打开3buffer功能
    if (mFlinger->isLayerTripleBufferingDisabled()) {
      //在这个可以看到，mProducer能够申请到到的最大buffer数量时2
        mProducer->setMaxDequeuedBufferCount(2);
    }
    //不知道这句话的作用
    const sp<const DisplayDevice> hw(mFlinger->getDefaultDisplayDevice());
    updateTransformHint(hw);
}

所以构造一个SurfaceControl所做的工作就是创建了一个SurfaceControl,并让SurfaceFlinger创建了一个对应的Layer，Layer中有一个IGraphicBufferProducer,它的实例是BufferQueueProducer。
可以用下面这个图来描述SurfaceControl的创建过程¹:

在这里插入图片描述