Android SurfaceFlinger layer层级

壁纸作为显示的最底层窗口它是怎么显示的

1. SurfaceFlinger layer层级

 锁屏状态dump SurfaceFlinger ，adb shell dumpsys SurfaceFlinger

Display 0 (active) HWC layers:
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 Layer name
           Z |  Window Type |  Layer Type |  Comp Type |  Transform |   Disp Frame (LTRB) |          Source Crop (LTRB) |     Frame Rate (Explicit) (Seamlessness) [Focused]
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 Wallpaper BBQ wrapper#58
  rel      0 |            0 |            0 |     CLIENT |          0 |    0    0 1080 2408 |    0.0    0.0 1080.0 2408.0 |                                              [ ]
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 StatusBar#105
  rel      0 |         2000 |           21 |     CLIENT |          0 |    0    0 1080   76 |    0.0    0.0 1080.0   76.0 |                                              [ ]
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 NotificationShade#656
  rel      0 |         2040 |           17 |     CLIENT |          0 |    0    0 1080 2408 |    0.0    0.0 1080.0 2408.0 |                                              [*]
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 NavigationBar0#101
  rel      0 |         2019 |           21 |     CLIENT |          0 |    0 2364 1080 2408 |    0.0    0.0 1080.0   44.0 |                                              [ ]

 可以看到壁纸layer显示在最底层，其上依次是状态栏layer，锁屏layer，导航栏窗口layer。

void SurfaceFlinger::dumpHwcLayersMinidumpLockedLegacy(std::string& result) const {
    for (const auto& [token, display] : mDisplays) {
        const auto displayId = HalDisplayId::tryCast(display->getId());
        if (!displayId) {
            continue;
        }

        StringAppendF(&result, "Display %s (%s) HWC layers:\n", to_string(*displayId).c_str(),
                      displayId == mActiveDisplayId ? "active" : "inactive");
        Layer::miniDumpHeader(result);

        const DisplayDevice& ref = *display;
        mDrawingState.traverseInZOrder([&](Layer* layer) { layer->miniDumpLegacy(result, ref); });
        result.append("\n");
    }
}

mDrawingState是按照Layer.z属性排序的

frameworks/native/services/surfaceflinger/LayerVector.cpp

int LayerVector::do_compare(const void* lhs, const void* rhs) const
{
    // sort layers per layer-stack, then by z-order and finally by sequence
    const auto& l = *reinterpret_cast<const sp<Layer>*>(lhs);
    const auto& r = *reinterpret_cast<const sp<Layer>*>(rhs);

    const auto& lState = l->getDrawingState();
    const auto& rState = r->getDrawingState();

    const auto ls = lState.layerStack;
    const auto rs = rState.layerStack;
    if (ls != rs)
        return (ls > rs) ? 1 : -1;

    int32_t lz = lState.z;
    int32_t rz = rState.z;
    if (lz != rz)
        return (lz > rz) ? 1 : -1;
}

 2. system_server窗口层级

  通常我们看到的窗口层级如下

frameworks/base/services/core/java/com/android/server/policy/WindowManagerPolicy.java 

default int getWindowLayerFromTypeLw(int type, boolean canAddInternalSystemWindow,
            boolean roundedCornerOverlay) {
        // Always put the rounded corner layer to the top most.
        if (roundedCornerOverlay && canAddInternalSystemWindow) {
            return getMaxWindowLayer();
        }
        if (type >= FIRST_APPLICATION_WINDOW && type <= LAST_APPLICATION_WINDOW) {
            return APPLICATION_LAYER;
        }

        switch (type) {
            case TYPE_WALLPAPER:
                // wallpaper is at the bottom, though the window manager may move it.
                return  1;
}

/frameworks/base/services/core/java/com/android/server/wm/WindowState.java 

mBaseLayer = mPolicy.getWindowLayerLw(this)
                    * TYPE_LAYER_MULTIPLIER + TYPE_LAYER_OFFSET;

 大概层级

DisplayArea添加到DisplayContent

frameworks/base/services/core/java/com/android/server/wm/DisplayAreaPolicyBuilder.java

void instantiateChildren(DisplayArea<DisplayArea> parent, DisplayArea.Tokens[] areaForLayer,
                int level, Map<Feature, List<DisplayArea<WindowContainer>>> areas) {
            mChildren.sort(Comparator.comparingInt(pendingArea -> pendingArea.mMinLayer));
            for (int i = 0; i < mChildren.size(); i++) {
                final PendingArea child = mChildren.get(i);
                final DisplayArea area = child.createArea(parent, areaForLayer);
                if (area == null) {
                    // TaskDisplayArea and ImeContainer can be set at different hierarchy, so it can
                    // be null.
                    continue;
                }
                parent.addChild(area, WindowContainer.POSITION_TOP);
                if (child.mFeature != null) {
                    areas.get(child.mFeature).add(area);
                }
                child.instantiateChildren(area, areaForLayer, level + 1, areas);
            }
}

 创建37个layer并添加进displayContent中

frameworks/base/services/core/java/com/android/server/policy/WindowManagerPolicy.java
    
default int getMaxWindowLayer() {
        return 36;
}


frameworks/base/services/core/java/com/android/server/wm/DisplayAreaPolicyBuilder.java

private void build(@Nullable List<HierarchyBuilder> displayAreaGroupHierarchyBuilders) {
            final WindowManagerPolicy policy = mRoot.mWmService.mPolicy;
            final int maxWindowLayerCount = policy.getMaxWindowLayer() + 1;
            final DisplayArea.Tokens[] displayAreaForLayer =
                    new DisplayArea.Tokens[maxWindowLayerCount];


            .
            .
            .
            root.instantiateChildren(mRoot, displayAreaForLayer, 0, featureAreas);

            // Notify the root that we have finished attaching all the DisplayAreas. Cache all the
            // feature related collections there for fast access.
            mRoot.onHierarchyBuilt(mFeatures, displayAreaForLayer, featureAreas);

}

 通过assignLayer来设置surfacecontrol的layer属性及（LayerState的z属性）

frameworks/base/services/core/java/com/android/server/wm/WindowContainer.java

void assignChildLayers(Transaction t) {
        int layer = 0;

        // We use two passes as a way to promote children which
        // need Z-boosting to the end of the list.
        for (int j = 0; j < mChildren.size(); ++j) {
            final WindowContainer wc = mChildren.get(j);
            wc.assignChildLayers(t);
            if (!wc.needsZBoost()) {
                wc.assignLayer(t, layer++);
            }
        }
        for (int j = 0; j < mChildren.size(); ++j) {
            final WindowContainer wc = mChildren.get(j);
            if (wc.needsZBoost()) {
                wc.assignLayer(t, layer++);
            }
        }
        if (mOverlayHost != null) {
            mOverlayHost.setLayer(t, layer++);
        }
    }

 3. 通过SurfaceComposerClient 传递到SurfaceFlinger （ sf->setTransactionState）

frameworks/native/libs/gui/SurfaceComposerClient.cpp


SurfaceComposerClient::Transaction& SurfaceComposerClient::Transaction::setLayer(
        const sp<SurfaceControl>& sc, int32_t z) {
    layer_state_t* s = getLayerState(sc);
    if (!s) {
        mStatus = BAD_INDEX;
        return *this;
    }
    s->what |= layer_state_t::eLayerChanged;
    s->what &= ~layer_state_t::eRelativeLayerChanged;
    s->z = z;

    registerSurfaceControlForCallback(sc);
    return *this;
}