Bad drawing of styled viewports within QAbstractScrollArea

This patch includes lots of refactoring, but the real problem was that
in QWidgetPrivate::paintBackground we call drawPrimitive(PE_Widget) with
a potentialy translated painter,   but the opt.rect is not translated.

When having a scroll area the calling function used to translated the
painter and then pass the offset around to rectify. but drawPrimitive
cannot rectify it.

The solution is not to translate the painter but use other way to
rectify the brush

Task-number: 257517
Reviewed-by: bnilsen

4 files changed, 35 insertions, 46 deletions

diff --git a/src/gui/kernel/qcocoaview_mac.mm b/src/gui/kernel/qcocoaview_mac.mm
index 52685ca..3e5bfb6 100644
--- a/src/gui/kernel/qcocoaview_mac.mm
+++ b/src/gui/kernel/qcocoaview_mac.mm
@@ -550,15 +550,7 @@ extern "C" {
                        qwidget->objectName().local8Bit().data());
 #endif
             QPainter p(qwidget);
-            QAbstractScrollArea *scrollArea = qobject_cast<QAbstractScrollArea *>(qwidget->parent());
-            QPoint scrollAreaOffset;
-            if (scrollArea && scrollArea->viewport() == qwidget) {
-                QAbstractScrollAreaPrivate *priv
-                        = static_cast<QAbstractScrollAreaPrivate *>(qt_widget_private(scrollArea));
-                scrollAreaOffset = priv->contentsOffset();
-                p.translate(-scrollAreaOffset);
-            }
-            qwidgetprivate->paintBackground(&p, qrgn, scrollAreaOffset,
+            qwidgetprivate->paintBackground(&p, qrgn,
                                             qwidget->isWindow() ? QWidgetPrivate::DrawAsRoot : 0);
             p.end();
         }
diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index 5f076ff..7026525 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -1966,10 +1966,9 @@ void QPixmap::fill( const QWidget *widget, const QPoint &off )
     QPainter p(this);
     p.translate(-off);
     widget->d_func()->paintBackground(&p, QRect(off, size()));
-
 }
 
-static inline void fillRegion(QPainter *painter, const QRegion &rgn, const QPoint &offset, const QBrush &brush)
+static inline void fillRegion(QPainter *painter, const QRegion &rgn, const QBrush &brush)
 {
     Q_ASSERT(painter);
 
@@ -1978,26 +1977,39 @@ static inline void fillRegion(QPainter *painter, const QRegion &rgn, const QPoin
         // Optimize pattern filling on mac by using HITheme directly
         // when filling with the standard widget background.
         // Defined in qmacstyle_mac.cpp
-        extern void qt_mac_fill_background(QPainter *painter, const QRegion &rgn, const QPoint &offset, const QBrush &brush);
-        qt_mac_fill_background(painter, rgn, offset, brush);
+        extern void qt_mac_fill_background(QPainter *painter, const QRegion &rgn, const QBrush &brush);
+        qt_mac_fill_background(painter, rgn, brush);
 #else
-        const QRegion translated = rgn.translated(offset);
-        const QRect rect(translated.boundingRect());
-        painter->setClipRegion(translated);
+        const QRect rect(rgn.boundingRect());
+        painter->setClipRegion(rgn);
         painter->drawTiledPixmap(rect, brush.texture(), rect.topLeft());
 #endif
     } else {
         const QVector<QRect> &rects = rgn.rects();
         for (int i = 0; i < rects.size(); ++i)
-            painter->fillRect(rects.at(i).translated(offset), brush);
+            painter->fillRect(rects.at(i), brush);
     }
 }
 
-
-void QWidgetPrivate::paintBackground(QPainter *painter, const QRegion &rgn, const QPoint &offset, int flags) const
+void QWidgetPrivate::paintBackground(QPainter *painter, const QRegion &rgn, int flags) const
 {
     Q_Q(const QWidget);
 
+#ifndef QT_NO_SCROLLAREA
+    bool resetBrushOrigin = false;
+    QPointF oldBrushOrigin;
+    //If we are painting the viewport of a scrollarea, we must apply an offset to the brush in case we are drawing a texture
+    QAbstractScrollArea *scrollArea = qobject_cast<QAbstractScrollArea *>(parent);
+    if (scrollArea && scrollArea->viewport() == q) {
+        QObjectData *scrollPrivate = static_cast<QWidget *>(scrollArea)->d_ptr;
+        QAbstractScrollAreaPrivate *priv = static_cast<QAbstractScrollAreaPrivate *>(scrollPrivate);
+        oldBrushOrigin = painter->brushOrigin();
+        resetBrushOrigin = true;
+        painter->setBrushOrigin(-priv->contentsOffset());
+
+    }
+#endif // QT_NO_SCROLLAREA
+
     const QBrush autoFillBrush = q->palette().brush(q->backgroundRole());
 
     if ((flags & DrawAsRoot) && !(q->autoFillBackground() && autoFillBrush.isOpaque())) {
@@ -2006,18 +2018,24 @@ void QWidgetPrivate::paintBackground(QPainter *painter, const QRegion &rgn, cons
         if (!(flags & DontSetCompositionMode) && painter->paintEngine()->hasFeature(QPaintEngine::PorterDuff))
             painter->setCompositionMode(QPainter::CompositionMode_Source); //copy alpha straight in
 #endif
-        fillRegion(painter, rgn, offset, bg);
+        fillRegion(painter, rgn, bg);
     }
 
     if (q->autoFillBackground())
-        fillRegion(painter, rgn, offset, autoFillBrush);
+        fillRegion(painter, rgn, autoFillBrush);
+
 
     if (q->testAttribute(Qt::WA_StyledBackground)) {
-        painter->setClipRegion(rgn.translated(offset));
+        painter->setClipRegion(rgn);
         QStyleOption opt;
         opt.initFrom(q);
         q->style()->drawPrimitive(QStyle::PE_Widget, &opt, painter, q);
     }
+
+#ifndef QT_NO_SCROLLAREA
+    if (resetBrushOrigin)
+        painter->setBrushOrigin(oldBrushOrigin);
+#endif // QT_NO_SCROLLAREA
 }
 
 /*
@@ -4998,19 +5016,7 @@ void QWidgetPrivate::drawWidget(QPaintDevice *pdev, const QRegion &rgn, const QP
                     && !q->testAttribute(Qt::WA_OpaquePaintEvent) && !q->testAttribute(Qt::WA_NoSystemBackground)) {
 
                     QPainter p(q);
-                    QPoint scrollAreaOffset;
-
-#ifndef QT_NO_SCROLLAREA
-                    QAbstractScrollArea *scrollArea = qobject_cast<QAbstractScrollArea *>(parent);
-                    if (scrollArea && scrollArea->viewport() == q) {
-                        QObjectData *scrollPrivate = static_cast<QWidget *>(scrollArea)->d_ptr;
-                        QAbstractScrollAreaPrivate *priv = static_cast<QAbstractScrollAreaPrivate *>(scrollPrivate);
-                        scrollAreaOffset = priv->contentsOffset();
-                        p.translate(-scrollAreaOffset);
-                    }
-#endif // QT_NO_SCROLLAREA
-
-                    paintBackground(&p, toBePainted, scrollAreaOffset, (asRoot || onScreen) ? flags | DrawAsRoot : 0);
+                    paintBackground(&p, toBePainted, (asRoot || onScreen) ? flags | DrawAsRoot : 0);
                 }
 
                 if (!sharedPainter)
diff --git a/src/gui/kernel/qwidget_mac.mm b/src/gui/kernel/qwidget_mac.mm
index 5577224..84c3def 100644
--- a/src/gui/kernel/qwidget_mac.mm
+++ b/src/gui/kernel/qwidget_mac.mm
@@ -1198,16 +1198,7 @@ OSStatus QWidgetPrivate::qt_widget_event(EventHandlerCallRef er, EventRef event,
                         p.setClipping(false);
                         if(was_unclipped)
                             widget->setAttribute(Qt::WA_PaintUnclipped);
-
-                        QAbstractScrollArea *scrollArea = qobject_cast<QAbstractScrollArea *>(widget->parent());
-                        QPoint scrollAreaOffset;
-                        if (scrollArea && scrollArea->viewport() == widget) {
-                            QAbstractScrollAreaPrivate *priv = static_cast<QAbstractScrollAreaPrivate *>(static_cast<QWidget *>(scrollArea)->d_ptr);
-                            scrollAreaOffset = priv->contentsOffset();
-                            p.translate(-scrollAreaOffset);
-                        }
-
-                        widget->d_func()->paintBackground(&p, qrgn, scrollAreaOffset, widget->isWindow() ? DrawAsRoot : 0);
+                        widget->d_func()->paintBackground(&p, qrgn, widget->isWindow() ? DrawAsRoot : 0);
                         if (widget->testAttribute(Qt::WA_TintedBackground)) {
                             QColor tint = widget->palette().window().color();
                             tint.setAlphaF(.6);
diff --git a/src/gui/kernel/qwidget_p.h b/src/gui/kernel/qwidget_p.h
index 626950e..998181e 100644
--- a/src/gui/kernel/qwidget_p.h
+++ b/src/gui/kernel/qwidget_p.h
@@ -295,7 +295,7 @@ public:
 
     void setUpdatesEnabled_helper(bool );
 
-    void paintBackground(QPainter *, const QRegion &, const QPoint & = QPoint(), int flags = DrawAsRoot) const;
+    void paintBackground(QPainter *, const QRegion &, int flags = DrawAsRoot) const;
     bool isAboutToShow() const;
     QRegion prepareToRender(const QRegion &region, QWidget::RenderFlags renderFlags);
     void render_helper(QPainter *painter, const QPoint &targetOffset, const QRegion &sourceRegion,