window: Improve how we tell the window to do layer-shell

Instead of telling it in the construction after forcing the window
creation, install an event handler that sets it when we get the
PlatformSurface event.

It has the advantage that it will also trigger in subsequent platform
surface events (e.g. after hide and show).

src/interfaces/window.cpp

@@ -186,27 +186,36 @@ Window::Window(QWindow *window)
     , d(new WindowPrivate(window))
 {
     s_map.insert(d->parentWindow, this);
+    window->installEventFilter(this);
+}
 
-    window->create();
+bool Window::eventFilter(QObject *watched, QEvent *event)
-
+{
-    auto waylandWindow = dynamic_cast<QtWaylandClient::QWaylandWindow *>(window->handle());
+    auto window = qobject_cast<QWindow *>(watched);
-    if (!waylandWindow) {
+    if (!window) {
-        qCWarning(LAYERSHELLQT) << window << "is not a wayland window. Not creating zwlr_layer_surface";
+        return false;
-        return;
     }
-
+    if (event->type() == QEvent::PlatformSurface) {
-    static QWaylandLayerShellIntegration *shellIntegration = nullptr;
+        auto waylandWindow = dynamic_cast<QtWaylandClient::QWaylandWindow *>(window->handle());
-    if (!shellIntegration) {
+        if (!waylandWindow) {
-        shellIntegration = new QWaylandLayerShellIntegration();
+            qCWarning(LAYERSHELLQT) << window << "is not a wayland window. Not creating zwlr_layer_surface";
-        if (!shellIntegration->initialize(waylandWindow->display())) {
+            return false;
-            delete shellIntegration;
-            shellIntegration = nullptr;
-            qCWarning(LAYERSHELLQT) << "Failed to initialize layer-shell integration, possibly because compositor does not support the layer-shell protocol";
-            return;
         }
-    }
 
-    waylandWindow->setShellIntegration(shellIntegration);
+        static QWaylandLayerShellIntegration *shellIntegration = nullptr;
+        if (!shellIntegration) {
+            shellIntegration = new QWaylandLayerShellIntegration();
+            if (!shellIntegration->initialize(waylandWindow->display())) {
+                delete shellIntegration;
+                shellIntegration = nullptr;
+                qCWarning(LAYERSHELLQT)
+                    << "Failed to initialize layer-shell integration, possibly because compositor does not support the layer-shell protocol";
+                return false;
+            }
+        }
+        waylandWindow->setShellIntegration(shellIntegration);
+    }
+    return false;
 }
 
 Window *Window::get(QWindow *window)

src/interfaces/window.h

@@ -138,6 +138,8 @@ public:
 
     static Window *qmlAttachedProperties(QObject *object);
 
+    bool eventFilter(QObject *watched, QEvent *event) override;
+
 Q_SIGNALS:
     void anchorsChanged();
     void exclusionZoneChanged();

tests/become-layershell.qml

@@ -0,0 +1,42 @@
+/*
+ *   SPDX-FileCopyrightText: 2025 Aleix Pol i Gonzalez <aleixpol@kde.org>
+ *
+ *   SPDX-License-Identifier: LGPL-3.0-or-later
+ */
+
+import QtQuick
+import QtQuick.Controls
+import org.kde.layershell 1.0 as LayerShell
+
+Item
+{
+    Button {
+        text: "Convert"
+        anchors.centerIn: parent
+
+        onClicked: {
+            win.close()
+            win.LayerShell.Window.anchors = LayerShell.Window.AnchorLeft;
+            win.LayerShell.Window.layer = LayerShell.Window.LayerTop;
+            win.LayerShell.Window.exclusionZone = -1;
+            win.show()
+        }
+    }
+
+    Window {
+        id: win
+
+        width: 100
+        height: 100
+        Rectangle {
+            anchors.fill: parent
+            color: "red"
+
+            Text {
+                anchors.centerIn: parent
+                text: "top"
+            }
+        }
+        visible: true
+    }
+}