scene: Track stack position in WindowItem

If the WindowItem tracks the stack position, it will automagically
schedule repaints when a window is raised or lowered.

src/scene/windowitem.cpp

@@ -50,6 +50,9 @@ WindowItem::WindowItem(Window *window, Scene *scene, Item *parent)
     connect(window, &Window::opacityChanged, this, &WindowItem::updateOpacity);
     updateOpacity();
 
+    connect(window, &Window::stackingOrderChanged, this, &WindowItem::updateStackingOrder);
+    updateStackingOrder();
+
     connect(window, &Window::windowClosed, this, &WindowItem::handleWindowClosed);
 }
 
@@ -252,6 +255,11 @@ void WindowItem::updateOpacity()
     setOpacity(m_window->opacity());
 }
 
+void WindowItem::updateStackingOrder()
+{
+    setZ(m_window->stackingOrder());
+}
+
 void WindowItem::markDamaged()
 {
     Q_EMIT m_window->damaged(m_window);

src/scene/windowitem.h

@@ -64,6 +64,7 @@ private Q_SLOTS:
     void updateSurfaceVisibility();
     void updatePosition();
     void updateOpacity();
+    void updateStackingOrder();
 
 private:
     bool computeVisibility() const;

src/scene/workspacescene.cpp

@@ -85,6 +85,7 @@ namespace KWin
 
 WorkspaceScene::WorkspaceScene(std::unique_ptr<ItemRenderer> renderer)
     : Scene(std::move(renderer))
+    , m_containerItem(std::make_unique<Item>(this))
 {
 }
 
@@ -94,8 +95,6 @@ WorkspaceScene::~WorkspaceScene()
 
 void WorkspaceScene::initialize()
 {
-    connect(workspace(), &Workspace::stackingOrderChanged, this, &WorkspaceScene::addRepaintFull);
-
     setGeometry(workspace()->geometry());
     connect(workspace(), &Workspace::geometryChanged, this, [this]() {
         setGeometry(workspace()->geometry());
@@ -132,6 +131,11 @@ void WorkspaceScene::destroyDndIconItem()
     m_dndIcon.reset();
 }
 
+Item *WorkspaceScene::containerItem() const
+{
+    return m_containerItem.get();
+}
+
 QRegion WorkspaceScene::damage() const
 {
     return m_paintContext.damage;
@@ -426,14 +430,14 @@ void WorkspaceScene::paintSimpleScreen(int, const QRegion &region)
 void WorkspaceScene::createStackingOrder()
 {
     // Create a list of all windows in the stacking order
-    QList<Window *> windows = workspace()->stackingOrder();
+    QList<Item *> items = m_containerItem->sortedChildItems();
 
     // Move elevated windows to the top of the stacking order
     const QList<EffectWindow *> elevatedList = static_cast<EffectsHandlerImpl *>(effects)->elevatedWindows();
     for (EffectWindow *c : elevatedList) {
-        Window *t = static_cast<EffectWindowImpl *>(c)->window();
-        windows.removeAll(t);
-        windows.append(t);
+        WindowItem *item = static_cast<EffectWindowImpl *>(c)->windowItem();
+        items.removeAll(item);
+        items.append(item);
     }
 
     // Skip windows that are not yet ready for being painted and if screen is locked skip windows
@@ -442,9 +446,10 @@ void WorkspaceScene::createStackingOrder()
     // TODO? This cannot be used so carelessly - needs protections against broken clients, the
     // window should not get focus before it's displayed, handle unredirected windows properly and
     // so on.
-    for (Window *window : std::as_const(windows)) {
-        if (window->windowItem()->isVisible()) {
-            stacking_order.append(window->windowItem());
+    for (Item *item : std::as_const(items)) {
+        WindowItem *windowItem = static_cast<WindowItem *>(item);
+        if (windowItem->isVisible()) {
+            stacking_order.append(windowItem);
         }
     }
 }

src/scene/workspacescene.h

@@ -52,6 +52,8 @@ public:
 
     void initialize();
 
+    Item *containerItem() const;
+
     QRegion damage() const override;
     SurfaceItem *scanoutCandidate() const override;
     void prePaint(SceneDelegate *delegate) override;
@@ -133,6 +135,7 @@ private:
     // how many times finalPaintScreen() has been called
     int m_paintScreenCount = 0;
     PaintContext m_paintContext;
+    std::unique_ptr<Item> m_containerItem;
     std::unique_ptr<DragAndDropIconItem> m_dndIcon;
 };
 

src/window.cpp

@@ -348,6 +348,7 @@ bool Window::setupCompositing()
     updateShadow();
 
     m_windowItem = createItem(scene);
+    m_windowItem->setParentItem(scene->containerItem());
     m_effectWindow->setWindowItem(m_windowItem.get());
 
     connect(windowItem(), &WindowItem::positionChanged, this, &Window::visibleGeometryChanged);