QWidgetBackingStore: clean up around dirtyOnScreenWidgets

The QVector dirtyOnScreenWidgets was aggregated by pointer, which
makes no sense, as a QVector is just as large as a pointer (and even
in Qt 6, when it will be larger, it's not going to be horrible). But
this complicated the code quite a bit.

Aggregate by value instead (it's just one of three such vectors now).

Drive-by fixes:

- use QVector::removeAll() instead of rolling your own

- port two indexed loops to ranged ones. In the first case, it's safe,
  as the loop body clearly doesn't touch the iteratee (it's just a
  std::accumulate). In the second, the question no longer applies, as
  we're now using a consume loop.

Change-Id: Icd4ac13bb4a6f9a783f0adf2fb6a5bdfacd1f91a
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/widgets/kernel/qwidgetbackingstore.cpp

@@ -397,15 +397,12 @@ QRegion QWidgetBackingStore::dirtyRegion(QWidget *widget) const
     // Append the region that needs flush.
     r += dirtyOnScreen;
 
-    if (dirtyOnScreenWidgets) { // Only in use with native child widgets.
+    for (QWidget *w : dirtyOnScreenWidgets) {
-        for (int i = 0; i < dirtyOnScreenWidgets->size(); ++i) {
+        if (widgetDirty && w != widget && !widget->isAncestorOf(w))
-            QWidget *w = dirtyOnScreenWidgets->at(i);
+            continue;
-            if (widgetDirty && w != widget && !widget->isAncestorOf(w))
+        QWidgetPrivate *wd = w->d_func();
-                continue;
+        Q_ASSERT(wd->needsFlush);
-            QWidgetPrivate *wd = w->d_func();
+        r += wd->needsFlush->translated(w->mapTo(tlw, QPoint()));
-            Q_ASSERT(wd->needsFlush);
-            r += wd->needsFlush->translated(w->mapTo(tlw, QPoint()));
-        }
     }
 
     if (widgetDirty) {
@@ -686,8 +683,8 @@ void QWidgetBackingStore::removeDirtyWidget(QWidget *w)
     if (!w)
         return;
 
-    dirtyWidgetsRemoveAll(w);
+    dirtyWidgets.removeAll(w);
-    dirtyOnScreenWidgetsRemoveAll(w);
+    dirtyOnScreenWidgets.removeAll(w);
     dirtyRenderToTextureWidgets.removeAll(w);
     resetWidget(w);
 
@@ -719,7 +716,6 @@ void QWidgetBackingStore::updateLists(QWidget *cur)
 
 QWidgetBackingStore::QWidgetBackingStore(QWidget *topLevel)
     : tlw(topLevel),
-      dirtyOnScreenWidgets(0),
       updateRequestSent(0),
       textureListWatcher(0),
       perfFrames(0)
@@ -737,8 +733,6 @@ QWidgetBackingStore::~QWidgetBackingStore()
         resetWidget(dirtyWidgets.at(c));
     for (int c = 0; c < dirtyRenderToTextureWidgets.size(); ++c)
         resetWidget(dirtyRenderToTextureWidgets.at(c));
-
-    delete dirtyOnScreenWidgets;
 }
 
 static QVector<QRect> getSortedRectsToScroll(const QRegion &region, int dx, int dy)
@@ -1373,7 +1367,7 @@ void QWidgetBackingStore::doSync()
 */
 void QWidgetBackingStore::flush(QWidget *widget)
 {
-    const bool hasDirtyOnScreenWidgets = dirtyOnScreenWidgets && !dirtyOnScreenWidgets->isEmpty();
+    const bool hasDirtyOnScreenWidgets = !dirtyOnScreenWidgets.isEmpty();
     bool flushed = false;
 
     // Flush the region in dirtyOnScreen.
@@ -1400,15 +1394,13 @@ void QWidgetBackingStore::flush(QWidget *widget)
     if (!hasDirtyOnScreenWidgets)
         return;
 
-    for (int i = 0; i < dirtyOnScreenWidgets->size(); ++i) {
+    for (QWidget *w : qExchange(dirtyOnScreenWidgets, {})) {
-        QWidget *w = dirtyOnScreenWidgets->at(i);
         QWidgetPrivate *wd = w->d_func();
         Q_ASSERT(wd->needsFlush);
         QPlatformTextureList *widgetTexturesForNative = wd->textureChildSeen ? widgetTexturesFor(tlw, w) : 0;
         qt_flush(w, *wd->needsFlush, store, tlw, widgetTexturesForNative, this);
         *wd->needsFlush = QRegion();
     }
-    dirtyOnScreenWidgets->clear();
 }
 
 /*!

src/widgets/kernel/qwidgetbackingstore_p.h

@@ -129,7 +129,7 @@ private:
     QRegion dirtyFromPreviousSync;
     QVector<QWidget *> dirtyWidgets;
     QVector<QWidget *> dirtyRenderToTextureWidgets;
-    QVector<QWidget *> *dirtyOnScreenWidgets;
+    QVector<QWidget *> dirtyOnScreenWidgets;
     QList<QWidget *> staticWidgets;
     QBackingStore *store;
     uint updateRequestSent : 1;
@@ -190,17 +190,6 @@ private:
         }
     }
 
-    inline void dirtyWidgetsRemoveAll(QWidget *widget)
-    {
-        int i = 0;
-        while (i < dirtyWidgets.size()) {
-            if (dirtyWidgets.at(i) == widget)
-                dirtyWidgets.remove(i);
-            else
-                ++i;
-        }
-    }
-
     inline void addStaticWidget(QWidget *widget)
     {
         if (!widget)
@@ -246,26 +235,8 @@ private:
         if (!widget)
             return;
 
-        if (!dirtyOnScreenWidgets) {
+        if (!dirtyOnScreenWidgets.contains(widget))
-            dirtyOnScreenWidgets = new QVector<QWidget *>;
+            dirtyOnScreenWidgets.append(widget);
-            dirtyOnScreenWidgets->append(widget);
-        } else if (!dirtyOnScreenWidgets->contains(widget)) {
-            dirtyOnScreenWidgets->append(widget);
-        }
-    }
-
-    inline void dirtyOnScreenWidgetsRemoveAll(QWidget *widget)
-    {
-        if (!widget || !dirtyOnScreenWidgets)
-            return;
-
-        int i = 0;
-        while (i < dirtyOnScreenWidgets->size()) {
-            if (dirtyOnScreenWidgets->at(i) == widget)
-                dirtyOnScreenWidgets->remove(i);
-            else
-                ++i;
-        }
     }
 
     inline void resetWidget(QWidget *widget)