kwinquickeffect: Use an asynchronous incubator for view creation

Creating views is the main thing blocking quick effect activation.
Rather than blocking until everything is created, we can use
QQmlIncubator so we create views asynchronously. This allows KWin to do
other things while views are being created. This is mostly relevant for
multiscreen setups where we create a view per screen.

src/libkwineffects/kwinquickeffect.cpp

@@ -6,9 +6,11 @@
 
 #include "kwinquickeffect.h"
 
+#include "logging_p.h"
 #include "sharedqmlengine.h"
 
 #include <QQmlEngine>
+#include <QQmlIncubator>
 #include <QQuickItem>
 #include <QQuickWindow>
 #include <QWindow>
@@ -16,6 +18,24 @@
 namespace KWin
 {
 
+class QuickSceneViewIncubator : public QQmlIncubator
+{
+public:
+    QuickSceneViewIncubator(const std::function<void(QuickSceneViewIncubator *)> &statusChangedCallback)
+        : QQmlIncubator(QQmlIncubator::Asynchronous)
+        , m_statusChangedCallback(statusChangedCallback)
+    {
+    }
+
+    void statusChanged(QQmlIncubator::Status status) override
+    {
+        m_statusChangedCallback(this);
+    }
+
+private:
+    std::function<void(QuickSceneViewIncubator *)> m_statusChangedCallback;
+};
+
 class QuickSceneEffectPrivate
 {
 public:
@@ -28,6 +48,7 @@ public:
     SharedQmlEngine::Ptr qmlEngine;
     std::unique_ptr<QQmlComponent> qmlComponent;
     QUrl source;
+    std::map<EffectScreen *, std::unique_ptr<QQmlIncubator>> incubators;
     std::map<EffectScreen *, std::unique_ptr<QuickSceneView>> views;
     QPointer<QuickSceneView> mouseImplicitGrab;
     bool running = false;
@@ -336,29 +357,39 @@ void QuickSceneEffect::handleScreenAdded(EffectScreen *screen)
 void QuickSceneEffect::handleScreenRemoved(EffectScreen *screen)
 {
     d->views.erase(screen);
+    d->incubators.erase(screen);
 }
 
 void QuickSceneEffect::addScreen(EffectScreen *screen)
 {
-    QuickSceneView *view = new QuickSceneView(this, screen);
     auto properties = initialProperties(screen);
-    properties["width"] = view->geometry().width();
+    properties["width"] = screen->geometry().width();
-    properties["height"] = view->geometry().height();
+    properties["height"] = screen->geometry().height();
-    view->setRootItem(qobject_cast<QQuickItem *>(d->qmlComponent->createWithInitialProperties(properties)));
-    // we need the focus always set to the view of activescreen at first, and changed only upon user interaction
-    if (view->contentItem()) {
-        view->contentItem()->setFocus(false);
-    }
-    view->setAutomaticRepaint(false);
 
-    connect(view, &QuickSceneView::repaintNeeded, this, [view]() {
+    auto incubator = new QuickSceneViewIncubator([this, screen](QuickSceneViewIncubator *incubator) {
-        effects->addRepaint(view->geometry());
+        if (incubator->isReady()) {
+            auto view = new QuickSceneView(this, screen);
+            view->setRootItem(qobject_cast<QQuickItem *>(incubator->object()));
+            if (view->contentItem()) {
+                view->contentItem()->setFocus(false);
+            }
+            view->setAutomaticRepaint(false);
+            connect(view, &QuickSceneView::repaintNeeded, this, [view]() {
+                effects->addRepaint(view->geometry());
+            });
+            connect(view, &QuickSceneView::renderRequested, view, &QuickSceneView::scheduleRepaint);
+            connect(view, &QuickSceneView::sceneChanged, view, &QuickSceneView::scheduleRepaint);
+            view->scheduleRepaint();
+            d->views[screen].reset(view);
+        } else if (incubator->isError()) {
+            qCWarning(LIBKWINEFFECTS) << "Could not create a view for QML file" << d->qmlComponent->url();
+            qCWarning(LIBKWINEFFECTS) << incubator->errors();
+        }
     });
-    connect(view, &QuickSceneView::renderRequested, view, &QuickSceneView::scheduleRepaint);
-    connect(view, &QuickSceneView::sceneChanged, view, &QuickSceneView::scheduleRepaint);
 
-    view->scheduleRepaint();
+    incubator->setInitialProperties(properties);
-    d->views[screen].reset(view);
+    d->incubators[screen].reset(incubator);
+    d->qmlComponent->create(*incubator);
 }
 
 void QuickSceneEffect::startInternal()
@@ -423,6 +454,7 @@ void QuickSceneEffect::stopInternal()
     disconnect(effects, &EffectsHandler::screenAdded, this, &QuickSceneEffect::handleScreenAdded);
     disconnect(effects, &EffectsHandler::screenRemoved, this, &QuickSceneEffect::handleScreenRemoved);
 
+    d->incubators.clear();
     d->views.clear();
     d->dummyWindow.reset();
     d->running = false;