StyleSheet: use item background rule when filling row backround

QTreeView draws the different sub-rects of an item's background over
multiple calls to drawPrimitive(PE_PanelItemViewRow). The item row is
not separately stylable, but the item might have a styled background
property. To get a consistent background, we must use the item's
background rule when filling the item's row background.

To fix that, delegate the filling of the branch background to
drawPrimitive(PE_PanelItemViewRow), and implement PE_PanelItemViewRow
handling to render the rule for the ViewItem pseudo element if there is
a background rule defined for it.

Add a baseline test stylesheet for this scenario. Note that the selection
in an item view is better styled via the selection-background-color
qss property.

Task-number: QTBUG-73251
Task-number: QTBUG-106227
Change-Id: I5d0c170f78009fe5015dd749975e6df27485b3b8
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
(cherry picked from commit 483ae6c448ff95354c22e7d6e71117a9f9c40421)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 22 insertions, 4 deletions

diff --git a/src/widgets/styles/qstylesheetstyle.cpp b/src/widgets/styles/qstylesheetstyle.cpp
index 6eb7f477d2..5ebe6c491b 100644
--- a/src/widgets/styles/qstylesheetstyle.cpp
+++ b/src/widgets/styles/qstylesheetstyle.cpp
@@ -4734,10 +4734,7 @@ void QStyleSheetStyle::drawPrimitive(PrimitiveElement pe, const QStyleOption *op
         if (const QStyleOptionViewItem *vopt = qstyleoption_cast<const QStyleOptionViewItem *>(opt)) {
             QRenderRule subRule = renderRule(w, opt, PseudoElement_TreeViewBranch);
             if (subRule.hasDrawable()) {
-                if ((vopt->state & QStyle::State_Selected) && vopt->showDecorationSelected)
-                    p->fillRect(vopt->rect, vopt->palette.highlight());
-                else if (vopt->features & QStyleOptionViewItem::Alternate)
-                    p->fillRect(vopt->rect, vopt->palette.alternateBase());
+                proxy()->drawPrimitive(PE_PanelItemViewRow, vopt, p, w);
                 subRule.drawRule(p, opt->rect);
             } else {
                 baseStyle()->drawPrimitive(pe, vopt, p, w);
@@ -4805,6 +4802,17 @@ void QStyleSheetStyle::drawPrimitive(PrimitiveElement pe, const QStyleOption *op
         pseudoElement = PseudoElement_DockWidgetSeparator;
         break;
 
+    case PE_PanelItemViewRow:
+        // For compatibility reasons, QTreeView draws different parts of
+        // the background of an item row separately, before calling the
+        // delegate to draw the item. The row background of an item is
+        // however not separately styleable through a style sheet, but
+        // only indirectly through the background of the item. To get the
+        // same background for all parts drawn by QTreeView, we have to
+        // use the background rule for the item here.
+        if (renderRule(w, opt, PseudoElement_ViewItem).hasBackground())
+            pseudoElement = PseudoElement_ViewItem;
+        break;
     case PE_PanelItemViewItem:
         pseudoElement = PseudoElement_ViewItem;
         break;
diff --git a/tests/baseline/stylesheet/qss/qtreeview/styledSelection.qss b/tests/baseline/stylesheet/qss/qtreeview/styledSelection.qss
new file mode 100644
index 0000000000..7d54a74fe5
--- /dev/null
+++ b/tests/baseline/stylesheet/qss/qtreeview/styledSelection.qss
@@ -0,0 +1,10 @@
+QTreeView {
+    alternate-background-color: yellow;
+    show-decoration-selected: 1;
+}
+QTreeView::item:selected:active {
+    background: qlineargradient(x1:0, y1:0 x2: 0, y2: 1, stop: 0 #fea1f1 stop: 1 #567dbc)
+}
+QTreeView::branch {
+    border: 2px
+}