QHeaderView: create virutal initStyleOptionForIndex function

The paintSection was very long and thus difficult to override.
This change makes it far more easy to do custom section painting
or styling in the headerview.

[ChangeLog][QtWidgets][QHeaderView] Introduced QHeaderView::initStyleOptionForIndex
to make it easier to reimplement custom styling and painting of sections.

Change-Id: I99e5fe8d70485a4650ab33e3d3eb4a46d6468326
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

2 files changed, 50 insertions, 19 deletions

diff --git a/src/widgets/itemviews/qheaderview.cpp b/src/widgets/itemviews/qheaderview.cpp
index fcb74370c7..dd6dbab0c3 100644
--- a/src/widgets/itemviews/qheaderview.cpp
+++ b/src/widgets/itemviews/qheaderview.cpp
@@ -2833,23 +2833,25 @@ bool QHeaderView::viewportEvent(QEvent *e)
 }
 
 /*!
-    Paints the section specified by the given \a logicalIndex, using the given
-    \a painter and \a rect.
+    \fn void QHeaderView::initStyleOptionForIndex(QStyleOptionHeader *option, int logicalIndex)
+    \since 6.0
 
-    Normally, you do not have to call this function.
+    Initializes the style \a option from the specified \a logicalIndex.
+    This function is called by the default implementation of paintSection after
+    initStyleOption has been called.
+
+    \sa paintSection(), initStyleOption()
 */
 
-void QHeaderView::paintSection(QPainter *painter, const QRect &rect, int logicalIndex) const
+void QHeaderView::initStyleOptionForIndex(QStyleOptionHeader *option, int logicalIndex) const
 {
     Q_D(const QHeaderView);
-    if (!rect.isValid())
+
+    if (!option)
         return;
-    // get the state of the section
-    QStyleOptionHeader opt;
-    initStyleOption(&opt);
+    QStyleOptionHeader &opt = *option;
+
     QStyle::State state = QStyle::State_None;
-    if (isEnabled())
-        state |= QStyle::State_Enabled;
     if (window()->isActiveWindow())
         state |= QStyle::State_Active;
     if (d->clickableSections) {
@@ -2863,7 +2865,6 @@ void QHeaderView::paintSection(QPainter *painter, const QRect &rect, int logical
             if (d->isSectionSelected(logicalIndex))
                 state |= QStyle::State_Sunken;
         }
-
     }
     if (isSortIndicatorShown() && sortIndicatorSection() == logicalIndex)
         opt.sortIndicator = (sortIndicatorOrder() == Qt::AscendingOrder)
@@ -2872,7 +2873,6 @@ void QHeaderView::paintSection(QPainter *painter, const QRect &rect, int logical
     // setup the style options structure
     QVariant textAlignment = d->model->headerData(logicalIndex, d->orientation,
                                                   Qt::TextAlignmentRole);
-    opt.rect = rect;
     opt.section = logicalIndex;
     opt.state |= state;
     opt.textAlignment = Qt::Alignment(textAlignment.isValid()
@@ -2909,13 +2909,11 @@ void QHeaderView::paintSection(QPainter *painter, const QRect &rect, int logical
     if (foregroundBrush.canConvert<QBrush>())
         opt.palette.setBrush(QPalette::ButtonText, qvariant_cast<QBrush>(foregroundBrush));
 
-    QPointF oldBO = painter->brushOrigin();
     QVariant backgroundBrush = d->model->headerData(logicalIndex, d->orientation,
                                                     Qt::BackgroundRole);
     if (backgroundBrush.canConvert<QBrush>()) {
         opt.palette.setBrush(QPalette::Button, qvariant_cast<QBrush>(backgroundBrush));
         opt.palette.setBrush(QPalette::Window, qvariant_cast<QBrush>(backgroundBrush));
-        painter->setBrushOrigin(opt.rect.topLeft());
     }
 
     // the section position
@@ -2943,9 +2941,42 @@ void QHeaderView::paintSection(QPainter *painter, const QRect &rect, int logical
         opt.selectedPosition = QStyleOptionHeader::NextIsSelected;
     else
         opt.selectedPosition = QStyleOptionHeader::NotAdjacent;
-    // draw the section
-    style()->drawControl(QStyle::CE_Header, &opt, painter, this);
+}
+
+/*!
+    Paints the section specified by the given \a logicalIndex, using the given
+    \a painter and \a rect.
 
+    Normally, you do not have to call this function.
+*/
+
+void QHeaderView::paintSection(QPainter *painter, const QRect &rect, int logicalIndex) const
+{
+    if (!rect.isValid())
+        return;
+
+    QStyleOptionHeader opt;
+    QPointF oldBO = painter->brushOrigin();
+
+    initStyleOption(&opt);
+
+    QBrush oBrushButton = opt.palette.brush(QPalette::Button);
+    QBrush oBrushWindow = opt.palette.brush(QPalette::Window);
+
+    initStyleOptionForIndex(&opt, logicalIndex);
+    // We set rect here. If it needs to be changed it can be changed by overriding this function
+    opt.rect = rect;
+
+    QBrush nBrushButton = opt.palette.brush(QPalette::Button);
+    QBrush nBrushWindow = opt.palette.brush(QPalette::Window);
+
+    // If relevant brushes are not the same as from the regular widgets we set the brush origin
+    if (oBrushButton != nBrushButton || oBrushWindow != nBrushWindow) {
+        painter->setBrushOrigin(opt.rect.topLeft());
+    }
+
+    // draw the section.
+    style()->drawControl(QStyle::CE_Header, &opt, painter, this);
     painter->setBrushOrigin(oldBO);
 }
 
@@ -3370,7 +3401,7 @@ void QHeaderViewPrivate::updateSectionIndicator(int section, int position)
     useful for subclasses when they need a QStyleOptionHeader, but do not want
     to fill in all the information themselves.
 
-    \sa QStyleOption::initFrom()
+    \sa QStyleOption::initFrom(), initStyleOptionForIndex()
 */
 void QHeaderView::initStyleOption(QStyleOptionHeader *option) const
 {
@@ -3388,8 +3419,7 @@ void QHeaderView::initStyleOption(QStyleOptionHeader *option) const
 void QHeaderView::initStyleOption(QStyleOptionFrame *option) const
 {
     // The QFrame version is only here to avoid compiler warnings.
-    // If invoked (it can be invoked with QFrame *f = headerview; f->initStyleOption()),
-    // and here we just pass it on to the frame version.
+    // If invoked we just pass it on to the base class.
     QFrame::initStyleOption(option);
 }
 
diff --git a/src/widgets/itemviews/qheaderview.h b/src/widgets/itemviews/qheaderview.h
index 6bbfb8449c..a836f4a50a 100644
--- a/src/widgets/itemviews/qheaderview.h
+++ b/src/widgets/itemviews/qheaderview.h
@@ -230,6 +230,7 @@ protected:
     QModelIndex moveCursor(CursorAction, Qt::KeyboardModifiers) override;
     void setSelection(const QRect& rect, QItemSelectionModel::SelectionFlags flags) override;
     QRegion visualRegionForSelection(const QItemSelection &selection) const override;
+    virtual void initStyleOptionForIndex(QStyleOptionHeader *option, int logicalIndex) const;
     virtual void initStyleOption(QStyleOptionHeader *option) const;
 
     friend class QTableView;