wayland: Setup compositing when window is mapped ready for painting

This prevents creating a WindowItem until we know that the window is
actually going to be visible on the screen.

src/composite.cpp

@@ -384,7 +384,8 @@ void Compositor::startupWithWorkspace()
 
     m_state = State::On;
 
-    for (X11Window *window : Workspace::self()->clientList()) {
+    const auto windows = workspace()->allClientList();
+    for (Window *window : windows) {
         window->setupCompositing();
     }
     for (Unmanaged *window : Workspace::self()->unmanagedList()) {
@@ -394,13 +395,6 @@ void Compositor::startupWithWorkspace()
         window->setupCompositing();
     }
 
-    if (auto *server = waylandServer()) {
-        const auto windows = server->windows();
-        for (Window *window : windows) {
-            window->setupCompositing();
-        }
-    }
-
     // Sets also the 'effects' pointer.
     kwinApp()->createEffectsHandler(this, m_scene.get());
 
@@ -515,7 +509,8 @@ void Compositor::stop()
     effects = nullptr;
 
     if (Workspace::self()) {
-        for (X11Window *window : Workspace::self()->clientList()) {
+        const auto windows = workspace()->allClientList();
+        for (Window *window : windows) {
             window->finishCompositing();
         }
         for (Unmanaged *window : Workspace::self()->unmanagedList()) {
@@ -536,13 +531,6 @@ void Compositor::stop()
         disconnect(workspace(), &Workspace::outputRemoved, this, &Compositor::removeOutput);
     }
 
-    if (waylandServer()) {
-        const QList<Window *> toFinishCompositing = waylandServer()->windows();
-        for (Window *window : toFinishCompositing) {
-            window->finishCompositing();
-        }
-    }
-
     const auto superlayers = m_superlayers;
     for (auto it = superlayers.begin(); it != superlayers.end(); ++it) {
         removeSuperLayer(*it);

src/inputpanelv1window.cpp

@@ -189,7 +189,7 @@ void InputPanelV1Window::maybeShow()
 {
     const bool shouldShow = m_mode == Mode::Overlay || (m_mode == Mode::VirtualKeyboard && m_allowed && m_virtualKeyboardShouldBeShown);
     if (shouldShow && !isZombie() && surface()->isMapped()) {
-        setReadyForPainting();
+        markAsMapped();
         reposition();
         showClient();
     }

src/layershellv1window.cpp

@@ -250,7 +250,7 @@ void LayerShellV1Window::handleUnmapped()
 void LayerShellV1Window::handleCommitted()
 {
     if (surface()->buffer()) {
-        setReadyForPainting();
+        markAsMapped();
     }
 }
 

src/waylandwindow.cpp

@@ -38,7 +38,6 @@ WaylandWindow::WaylandWindow(SurfaceInterface *surface)
 {
     setSurface(surface);
     setDepth(32);
-    setupCompositing();
 
     connect(surface, &SurfaceInterface::shadowChanged,
             this, &WaylandWindow::updateShadow);
@@ -323,4 +322,12 @@ void WaylandWindow::updateGeometry(const QRectF &rect)
     Q_EMIT geometryShapeChanged(oldFrameGeometry);
 }
 
+void WaylandWindow::markAsMapped()
+{
+    if (Q_UNLIKELY(!ready_for_painting)) {
+        setupCompositing();
+        setReadyForPainting();
+    }
+}
+
 } // namespace KWin

src/waylandwindow.h

@@ -47,6 +47,7 @@ protected:
 
     void cleanGrouping();
     void updateGeometry(const QRectF &rect);
+    void markAsMapped();
 
 private:
     void updateClientOutputs();

src/xdgshellwindow.cpp

@@ -52,10 +52,6 @@ XdgSurfaceWindow::XdgSurfaceWindow(XdgSurfaceInterface *shellSurface)
             this, &XdgSurfaceWindow::destroyWindow);
     connect(shellSurface->surface(), &SurfaceInterface::committed,
             this, &XdgSurfaceWindow::handleCommit);
-#if 0 // TODO: Refactor kwin core in order to uncomment this code.
-    connect(shellSurface->surface(), &SurfaceInterface::mapped,
-            this, &XdgSurfaceWindow::setReadyForPainting);
-#endif
     connect(shellSurface, &XdgSurfaceInterface::aboutToBeDestroyed,
             this, &XdgSurfaceWindow::destroyWindow);
     connect(shellSurface->surface(), &SurfaceInterface::aboutToBeDestroyed,
@@ -174,7 +170,7 @@ void XdgSurfaceWindow::handleCommit()
     m_lastAcknowledgedConfigure.reset();
     m_lastAcknowledgedConfigureSerial.reset();
 
-    setReadyForPainting();
+    markAsMapped();
 }
 
 void XdgSurfaceWindow::handleRolePrecommit()