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 nameZ | Window Type | Layer Type | Comp Type | Transform | Disp Frame (LTRB) | Source Crop (LTRB) | Frame Rate (Explicit) (Seamlessness) [Focused]
---------------------------------------------------------------------------------------------------------------------------------------------------------------Wallpaper BBQ wrapper#58rel 0 | 0 | 0 | CLIENT | 0 | 0 0 1080 2408 | 0.0 0.0 1080.0 2408.0 | [ ]
---------------------------------------------------------------------------------------------------------------------------------------------------------------StatusBar#105rel 0 | 2000 | 21 | CLIENT | 0 | 0 0 1080 76 | 0.0 0.0 1080.0 76.0 | [ ]
---------------------------------------------------------------------------------------------------------------------------------------------------------------NotificationShade#656rel 0 | 2040 | 17 | CLIENT | 0 | 0 0 1080 2408 | 0.0 0.0 1080.0 2408.0 | [*]
---------------------------------------------------------------------------------------------------------------------------------------------------------------NavigationBar0#101rel 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.cppint LayerVector::do_compare(const void* lhs, const void* rhs) const
{// sort layers per layer-stack, then by z-order and finally by sequenceconst 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.javavoid 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.javadefault int getMaxWindowLayer() {return 36;
}frameworks/base/services/core/java/com/android/server/wm/DisplayAreaPolicyBuilder.javaprivate 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.javavoid 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.cppSurfaceComposerClient::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;
}
