scene: Move item preprocessing to scene

We no longer use window pixmaps to get the shape and the opaque regions,
so preprocess() can be called now only if we are about to paint the item.

src/item.h

@@ -100,6 +100,7 @@ public:
     void resetRepaints(int screen);
 
     WindowQuadList quads() const;
+    virtual void preprocess();
 
 Q_SIGNALS:
     /**
@@ -126,7 +127,6 @@ Q_SIGNALS:
     void boundingRectChanged();
 
 protected:
-    virtual void preprocess();
     virtual WindowQuadList buildQuads() const;
     void discardQuads();
 
@@ -153,8 +153,6 @@ private:
     QVector<QRegion> m_repaints;
     mutable WindowQuadList m_quads;
     mutable bool m_quadsValid = false;
-
-    friend class Scene::Window;
 };
 
 } // namespace KWin

src/plugins/scenes/opengl/scene_opengl.cpp

@@ -1217,6 +1217,8 @@ static WindowQuadList clipQuads(const Item *item, const OpenGLWindow::RenderCont
 
 void OpenGLWindow::createRenderNode(Item *item, RenderContext *context)
 {
+    item->preprocess();
+
     if (auto shadowItem = qobject_cast<ShadowItem *>(item)) {
         WindowQuadList quads = clipQuads(item, context);
         if (!quads.isEmpty()) {

src/plugins/scenes/qpainter/scene_qpainter.cpp

@@ -245,6 +245,7 @@ void SceneQPainter::Window::performPaint(int mask, const QRegion &_region, const
 
 void SceneQPainter::Window::renderItem(QPainter *painter, Item *item) const
 {
+    item->preprocess();
     painter->save();
     painter->translate(item->position());
 

src/scene.cpp

@@ -239,9 +239,6 @@ void Scene::paintGenericScreen(int orig_mask, const ScreenPaintData &)
     QVector<Phase2Data> phase2;
     phase2.reserve(stacking_order.size());
     Q_FOREACH (Window * w, stacking_order) { // bottom to top
-        // Let the scene window update the window pixmap tree.
-        w->preprocess(w->windowItem());
-
         // Reset the repaint_region.
         // This has to be done here because many effects schedule a repaint for
         // the next frame within Effects::prePaintWindow.
@@ -311,9 +308,6 @@ void Scene::paintSimpleScreen(int orig_mask, const QRegion &region)
         data.paint = region;
         accumulateRepaints(window->windowItem(), painted_screen, &data.paint);
 
-        // Let the scene window update the window pixmap tree.
-        window->preprocess(window->windowItem());
-
         // Clip out the decoration for opaque windows; the decoration is drawn in the second pass
         opaqueFullscreen = false; // TODO: do we care about unmanged windows here (maybe input windows?)
         AbstractClient *client = dynamic_cast<AbstractClient *>(toplevel);
@@ -859,16 +853,6 @@ void Scene::Window::disablePainting(int reason)
     disable_painting |= reason;
 }
 
-void Scene::Window::preprocess(Item *item)
-{
-    item->preprocess();
-
-    const QList<Item *> children = item->childItems();
-    for (Item *child : children) {
-        preprocess(child);
-    }
-}
-
 WindowItem *Scene::Window::windowItem() const
 {
     return m_windowItem.data();

src/scene.h

@@ -340,7 +340,6 @@ public:
     void updateToplevel(Deleted *deleted);
     void referencePreviousPixmap();
     void unreferencePreviousPixmap();
-    void preprocess(Item *item);
     WindowItem *windowItem() const;
     SurfaceItem *surfaceItem() const;
     ShadowItem *shadowItem() const;