widgets: Mark widgets as needing flush during painting

Except for the case of syncing in response to an expose event,
where the platform asked us to flush a specific region, we
should strive to only flush parts that have been repainted.

And we should flush those parts to their nearest native child,
instead of unconditionally flushing the root/top level widget
as well.

By allowing drawWidget to schedule the flush we automatically
flush the minimal region, to the right widgets.

Change-Id: I73c143761d4a0da6991433b41dea0a0bc83a448a
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

2 files changed, 4 insertions, 15 deletions

diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index 45be132e59..cf5a81c204 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -5313,9 +5313,7 @@ void QWidgetPrivate::drawWidget(QPaintDevice *pdev, const QRegion &rgn, const QP
             }
             sourced->context = 0;
 
-            // Native widgets need to be marked dirty on screen so painting will be done in correct context
-            // Same check as in the no effects case below.
-            if (repaintManager && !asRoot && (q->internalWinId() || !q->nativeParentWidget()->isWindow()))
+            if (repaintManager)
                 repaintManager->markNeedsFlush(q, rgn, offset);
 
             return;
@@ -5422,8 +5420,7 @@ void QWidgetPrivate::drawWidget(QPaintDevice *pdev, const QRegion &rgn, const QP
                 sendPaintEvent(toBePainted);
             }
 
-            // Native widgets need to be marked dirty on screen so painting will be done in correct context
-            if (repaintManager && !asRoot && (q->internalWinId() || (q->nativeParentWidget() && !q->nativeParentWidget()->isWindow())))
+            if (repaintManager)
                 repaintManager->markNeedsFlush(q, toBePainted, offset);
 
             //restore
diff --git a/src/widgets/kernel/qwidgetrepaintmanager.cpp b/src/widgets/kernel/qwidgetrepaintmanager.cpp
index d1ebf7dc25..4eb298e108 100644
--- a/src/widgets/kernel/qwidgetrepaintmanager.cpp
+++ b/src/widgets/kernel/qwidgetrepaintmanager.cpp
@@ -979,12 +979,6 @@ void QWidgetRepaintManager::paintAndFlush()
     }
 #endif
 
-    // Always flush repainted areas. FIXME: We should mark individual widgets,
-    // not the top level widget unconditionally, as this results in always
-    // flushing the top level widget, even if the painted region is entirely
-    // within a native child.
-    markNeedsFlush(tlw, toClean, QPoint());
-
     store->beginPaint(toClean);
 
     // Must do this before sending any paint events because
@@ -1041,8 +1035,7 @@ void QWidgetRepaintManager::markNeedsFlush(QWidget *widget, const QRegion &regio
         // Top-level (native)
         qCInfo(lcWidgetPainting) << "Marking" << region << "of top level"
             << widget << "as needing flush";
-        if (!widget->testAttribute(Qt::WA_WState_InPaintEvent))
-            topLevelNeedsFlush += region;
+        topLevelNeedsFlush += region;
     } else if (!hasPlatformWindow(widget) && !widget->isWindow()) {
         QWidget *nativeParent = widget->nativeParentWidget();
         qCInfo(lcWidgetPainting) << "Marking" << region << "of"
@@ -1050,8 +1043,7 @@ void QWidgetRepaintManager::markNeedsFlush(QWidget *widget, const QRegion &regio
                 << "at offset" << topLevelOffset;
         if (nativeParent == tlw) {
             // Alien widgets with the top-level as the native parent (common case)
-            if (!widget->testAttribute(Qt::WA_WState_InPaintEvent))
-                topLevelNeedsFlush += region.translated(topLevelOffset);
+            topLevelNeedsFlush += region.translated(topLevelOffset);
         } else {
             // Alien widgets with native parent != tlw
             const QPoint nativeParentOffset = widget->mapTo(nativeParent, QPoint());