Android窗口顯示流程淺析(三)

上回說到，ViewRootImpl.setView與WMS和SurfaceFlinger建立完鏈接後，接着會執行SurfaceControl和Surface的申請，因爲沒有Surface，APP端就無法進行view的繪製。好的，我們看下requestLayout()裏面發生了什麼。

本篇代碼基於原生Android Q

一.顯示過程概覽

老規矩，先上圖：

二.核心代碼流程

1.checkThread

void checkThread() {
        if (mThread != Thread.currentThread()) { //檢查是否是同一線程訪問
            throw new CalledFromWrongThreadException(
                    "Only the original thread that created a view hierarchy can touch its views.");
        }
    }

2.relayoutWindow

private int relayoutWindow(WindowManager.LayoutParams params, int viewVisibility,
            boolean insetsPending) throws RemoteException {

       //......

       //通過session進行IPC調用
        int relayoutResult = mWindowSession.relayout(mWindow, mSeq, params,
                (int) (mView.getMeasuredWidth() * appScale + 0.5f),
                (int) (mView.getMeasuredHeight() * appScale + 0.5f), viewVisibility,
                insetsPending ? WindowManagerGlobal.RELAYOUT_INSETS_PENDING : 0, frameNumber,
                mTmpFrame, mPendingOverscanInsets, mPendingContentInsets, mPendingVisibleInsets,
                mPendingStableInsets, mPendingOutsets, mPendingBackDropFrame, mPendingDisplayCutout,
                mPendingMergedConfiguration, mSurfaceControl, mTempInsets);
        if (mSurfaceControl.isValid()) {
            mSurface.copyFrom(mSurfaceControl);
        } else {
            destroySurface();
        }

        mPendingAlwaysConsumeSystemBars =
                (relayoutResult & WindowManagerGlobal.RELAYOUT_RES_CONSUME_ALWAYS_SYSTEM_BARS) != 0;

        if (restore) {
            params.restore();
        }

        if (mTranslator != null) {
            mTranslator.translateRectInScreenToAppWinFrame(mTmpFrame);
            mTranslator.translateRectInScreenToAppWindow(mPendingOverscanInsets);
            mTranslator.translateRectInScreenToAppWindow(mPendingContentInsets);
            mTranslator.translateRectInScreenToAppWindow(mPendingVisibleInsets);
            mTranslator.translateRectInScreenToAppWindow(mPendingStableInsets);
        }
        setFrame(mTmpFrame);
        mInsetsController.onStateChanged(mTempInsets);
        return relayoutResult;
    }

3.這裏會調用WMS的relayoutWindow

public int relayout(IWindow window, int seq, WindowManager.LayoutParams attrs,
            int requestedWidth, int requestedHeight, int viewFlags, int flags, long frameNumber,
            Rect outFrame, Rect outOverscanInsets, Rect outContentInsets, Rect outVisibleInsets,
            Rect outStableInsets, Rect outsets, Rect outBackdropFrame,
            DisplayCutout.ParcelableWrapper cutout, MergedConfiguration mergedConfiguration,
            SurfaceControl outSurfaceControl, InsetsState outInsetsState) {
        if (false) Slog.d(TAG_WM, ">>>>>> ENTERED relayout from "
                + Binder.getCallingPid());
        Trace.traceBegin(TRACE_TAG_WINDOW_MANAGER, mRelayoutTag);
        int res = mService.relayoutWindow(this, window, seq, attrs,  //調用WMS的方法
                requestedWidth, requestedHeight, viewFlags, flags, frameNumber,
                outFrame, outOverscanInsets, outContentInsets, outVisibleInsets,
                outStableInsets, outsets, outBackdropFrame, cutout,
                mergedConfiguration, outSurfaceControl, outInsetsState);
        Trace.traceEnd(TRACE_TAG_WINDOW_MANAGER);
        if (false) Slog.d(TAG_WM, "<<<<<< EXITING relayout to "
                + Binder.getCallingPid());
        return res;
    }

4.這裏是WMS的方法：

public int relayoutWindow(Session session, IWindow client, int seq, LayoutParams attrs,
            int requestedWidth, int requestedHeight, int viewVisibility, int flags,
            long frameNumber, Rect outFrame, Rect outOverscanInsets, Rect outContentInsets,
            Rect outVisibleInsets, Rect outStableInsets, Rect outOutsets, Rect outBackdropFrame,
            DisplayCutout.ParcelableWrapper outCutout, MergedConfiguration mergedConfiguration,
            SurfaceControl outSurfaceControl, InsetsState outInsetsState) {
        
//......

                try {
                 //創建WMS的SurfaceControl，注意這裏的outSurfaceControl是viewRootImpl傳來的
                    result = createSurfaceControl(outSurfaceControl, result, win, winAnimator);
                } catch (Exception e) {
                    displayContent.getInputMonitor().updateInputWindowsLw(true /*force*/);

                    Slog.w(TAG_WM, "Exception thrown when creating surface for client "
                             + client + " (" + win.mAttrs.getTitle() + ")",
                             e);
                    Binder.restoreCallingIdentity(origId);
                    return 0;
                }
               //......
                    winAnimator.mSurfaceController.getSurfaceControl(outSurfaceControl); //獲取surfaceControl
                    Trace.traceEnd(TRACE_TAG_WINDOW_MANAGER);
                } else {
                    if (DEBUG_VISIBILITY) Slog.i(TAG_WM, "Releasing surface in: " + win);

                    try {
                        Trace.traceBegin(TRACE_TAG_WINDOW_MANAGER, "wmReleaseOutSurface_"
                                + win.mAttrs.getTitle());
                        outSurfaceControl.release();
                    } finally {
                        Trace.traceEnd(TRACE_TAG_WINDOW_MANAGER);
                    }
                }

                Trace.traceEnd(TRACE_TAG_WINDOW_MANAGER);
            }

            //......
    }

5.直接到WindowSurfaceController

public WindowSurfaceController(SurfaceSession s, String name, int w, int h, int format,
            int flags, WindowStateAnimator animator, int windowType, int ownerUid) {
        mAnimator = animator;

        mSurfaceW = w;
        mSurfaceH = h;

        title = name;

        mService = animator.mService;
        final WindowState win = animator.mWin;
        mWindowType = windowType;
        mWindowSession = win.mSession;

        Trace.traceBegin(TRACE_TAG_WINDOW_MANAGER, "new SurfaceControl");
        final SurfaceControl.Builder b = win.makeSurface() //通過build模式構建surfaceControl
                .setParent(win.getSurfaceControl())
                .setName(name)
                .setBufferSize(w, h)
                .setFormat(format)
                .setFlags(flags)
                .setMetadata(METADATA_WINDOW_TYPE, windowType)
                .setMetadata(METADATA_OWNER_UID, ownerUid);
        mSurfaceControl = b.build();   //看一下最終的build方法
        Trace.traceEnd(TRACE_TAG_WINDOW_MANAGER);
    }

6.進入SurfaceControl的build方法：

public SurfaceControl build() {
            if (mWidth < 0 || mHeight < 0) {
                throw new IllegalStateException(
                        "width and height must be positive or unset");
            }
            if ((mWidth > 0 || mHeight > 0) && (isColorLayerSet() || isContainerLayerSet())) {
                throw new IllegalStateException(
                        "Only buffer layers can set a valid buffer size.");
            }
            return new SurfaceControl(
                    mSession, mName, mWidth, mHeight, mFormat, mFlags, mParent, mMetadata);
        }


//這是構造方法：
private SurfaceControl(SurfaceSession session, String name, int w, int h, int format, int flags,
            SurfaceControl parent, SparseIntArray metadata)
                    throws OutOfResourcesException, IllegalArgumentException {
        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;
        mWidth = w;
        mHeight = h;
        Parcel metaParcel = Parcel.obtain();
        try {
            if (metadata != null && metadata.size() > 0) {
                metaParcel.writeInt(metadata.size());
                for (int i = 0; i < metadata.size(); ++i) {
                    metaParcel.writeInt(metadata.keyAt(i));
                    metaParcel.writeByteArray(
                            ByteBuffer.allocate(4).order(ByteOrder.nativeOrder())
                                    .putInt(metadata.valueAt(i)).array());
                }
                metaParcel.setDataPosition(0);
            }
            //這裏會創建SurfaceControl的Native對象
            mNativeObject = nativeCreate(session, name, w, h, format, flags,
                    parent != null ? parent.mNativeObject : 0, metaParcel);
        } finally {
            metaParcel.recycle();
        }
        if (mNativeObject == 0) {
            throw new OutOfResourcesException(
                    "Couldn't allocate SurfaceControl native object");
        }

        mCloseGuard.open("release");
    }

7.進入SurfaceControl的JNI方法：

static jlong nativeCreate(JNIEnv* env, jclass clazz, jobject sessionObj,
        jstring nameStr, jint w, jint h, jint format, jint flags, jlong parentObject,
        jobject metadataParcel) {
    ScopedUtfChars name(env, nameStr);
    sp<SurfaceComposerClient> client;
    if (sessionObj != NULL) {
        client = android_view_SurfaceSession_getClient(env, sessionObj);//這裏通過SurfaceSession獲得了SurfaceComposerClient對象
    } else {
        client = SurfaceComposerClient::getDefault();
    }
   //......

    status_t err = client->createSurfaceChecked(  //調用Client進行創建
            String8(name.c_str()), w, h, format, &surface, flags, parent, std::move(metadata));
    if (err == NAME_NOT_FOUND) {
        jniThrowException(env, "java/lang/IllegalArgumentException", NULL);
        return 0;
    } else if (err != NO_ERROR) {
        jniThrowException(env, OutOfResourcesException, NULL);
        return 0;
    }

    surface->incStrong((void *)nativeCreate);
    return reinterpret_cast<jlong>(surface.get());
}

8.進入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) {
    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();
        }

       //調用BnBinder對象的方法
        err = mClient->createSurface(name, w, h, format, flags, parentHandle,  std::move(metadata),
                                     &handle, &gbp);
        ALOGE_IF(err, "SurfaceComposerClient::createSurface error %s", strerror(-err));
        if (err == NO_ERROR) {
            *outSurface = new SurfaceControl(this, handle, gbp, true /* owned */);
        }
    }
    return err;
}

9.進入Client.cpp

status_t Client::createSurface(const String8& name, uint32_t w, uint32_t h, PixelFormat format,
                               uint32_t flags, const sp<IBinder>& parentHandle,
                               LayerMetadata metadata, sp<IBinder>* handle,
                               sp<IGraphicBufferProducer>* gbp) {
    // We rely on createLayer to check permissions.
    //surfaceFlinger終於來了，進行layer的創建
    return mFlinger->createLayer(name, this, w, h, format, flags, std::move(metadata), handle, gbp,
                                 parentHandle);
}

10.進入SurfaceFlinger.cpp

status_t SurfaceFlinger::createLayer(const String8& name, const sp<Client>& client, uint32_t w,
                                     uint32_t h, PixelFormat format, uint32_t flags,
                                     LayerMetadata metadata, sp<IBinder>* handle,
                                     sp<IGraphicBufferProducer>* gbp,
                                     const sp<IBinder>& parentHandle,
                                     const sp<Layer>& parentLayer) {
    //......
    status_t result = NO_ERROR;

    sp<Layer> layer;

    String8 uniqueName = getUniqueLayerName(name);

    bool primaryDisplayOnly = false;

    // window type is WINDOW_TYPE_DONT_SCREENSHOT from SurfaceControl.java
    // TODO b/64227542
    if (metadata.has(METADATA_WINDOW_TYPE)) {
        int32_t windowType = metadata.getInt32(METADATA_WINDOW_TYPE, 0);
        if (windowType == 441731) {
            metadata.setInt32(METADATA_WINDOW_TYPE, InputWindowInfo::TYPE_NAVIGATION_BAR_PANEL);
            primaryDisplayOnly = true;
        }
    }

    switch (flags & ISurfaceComposerClient::eFXSurfaceMask) { //根據window屬性創建不同的layer
        case ISurfaceComposerClient::eFXSurfaceBufferQueue:
            //以創建BufferQueueLayer爲例
            result = createBufferQueueLayer(client, uniqueName, w, h, flags, std::move(metadata),
                                            format, handle, gbp, &layer);

            break;
        //......
        default:
            result = BAD_VALUE;
            break;
    }

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

    if (primaryDisplayOnly) {
        layer->setPrimaryDisplayOnly();
    }

    bool addToCurrentState = callingThreadHasUnscopedSurfaceFlingerAccess();
    result = addClientLayer(client, *handle, *gbp, layer, parentHandle, parentLayer,
                            addToCurrentState);
    if (result != NO_ERROR) {
        return result;
    }
    mInterceptor->saveSurfaceCreation(layer);

    setTransactionFlags(eTransactionNeeded);
    return result;
}




//這裏是創建：

status_t SurfaceFlinger::createBufferQueueLayer(const sp<Client>& client, const String8& name,
                                                uint32_t w, uint32_t h, uint32_t flags,
                                                LayerMetadata metadata, 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;
    }

    //這裏會調用SurfaceFlingerFactory進行創建，會直接new一個：return new BufferQueueLayer
    sp<BufferQueueLayer> layer = getFactory().createBufferQueueLayer(
            LayerCreationArgs(this, client, name, w, h, flags, std::move(metadata)));
    status_t err = layer->setDefaultBufferProperties(w, h, format);
    if (err == NO_ERROR) {
        *handle = layer->getHandle(); //重要的handle和gbp會一併帶出，layer創建完成
        *gbp = layer->getProducer();
        *outLayer = layer;
    }

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

11.回到WindowSurfaceController，調用SurfaceControl.copyFrom

void getSurfaceControl(SurfaceControl outSurfaceControl) {
        outSurfaceControl.copyFrom(mSurfaceControl);
    }


 public void copyFrom(SurfaceControl other) {
        mName = other.mName;    //複製基本屬性
        mWidth = other.mWidth;
        mHeight = other.mHeight;
        assignNativeObject(nativeCopyFromSurfaceControl(other.mNativeObject)); //複製了一份SurfaceControl的Native對象
    }

至此，App端的surfaceControl得到了。

12.接着ViewRootImpl的surface對象也通過copy的方式獲得了，同時也賦值了gbp對象。

三.總結

1.本篇過程主要是APP端請求SurfaceControl和Surface，WMS端新建SurfaceControl，SurfaceFlinger創建layer，返回gbp對象，這樣後面APP端就能通過surface的gbp對象申請內存，然後進行view的繪製了，繪製完後交由SurfaceFlinger進行圖層排序和硬件顯示了。

2.重點關注SurfaceControl和surface對象的創建和傳遞過程。