Paint menu scrollers, tear off on top of QWidgetAction items

The menu scrollers and the tear off items are painted in the layer
 of QMenu. In a case that QMenu contains QWidgetAction items, the items
are painted under QWidgetAction items. They are visually hidden unless
QWidgetAction items' background is transparent. The tear off doesn't work
since QWidgetAction item on top of it grabs mouse events. To fix the issue,
add two child widgets in QMenu, paint the scroll up and the tear off items
in one child widget and the scroll down item in the other one. Both child
widgets are painted on top of overlapping sibling menu item widgets.

Change-Id: I7eaef21b667b388fbb78b60664f4a4bd91215309
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@qt.io>

2 files changed, 130 insertions, 30 deletions

diff --git a/src/widgets/widgets/qmenu.cpp b/src/widgets/widgets/qmenu.cpp
index b0c9512344..36a8a96b79 100644
--- a/src/widgets/widgets/qmenu.cpp
+++ b/src/widgets/widgets/qmenu.cpp
@@ -816,6 +816,93 @@ void QMenuPrivate::updateLayoutDirection()
     }
 }
 
+void QMenuPrivate::drawScroller(QPainter *painter, QMenuPrivate::ScrollerTearOffItem::Type type, const QRect &rect)
+{
+    if (!painter || rect.isEmpty())
+        return;
+
+    if (!scroll || !(scroll->scrollFlags & (QMenuPrivate::QMenuScroller::ScrollUp
+                                         | QMenuPrivate::QMenuScroller::ScrollDown)))
+        return;
+
+    Q_Q(QMenu);
+    QStyleOptionMenuItem menuOpt;
+    menuOpt.initFrom(q);
+    menuOpt.state = QStyle::State_None;
+    menuOpt.checkType = QStyleOptionMenuItem::NotCheckable;
+    menuOpt.maxIconWidth = 0;
+    menuOpt.tabWidth = 0;
+    menuOpt.rect = rect;
+    menuOpt.menuItemType = QStyleOptionMenuItem::Scroller;
+    menuOpt.state |= QStyle::State_Enabled;
+    if (type == QMenuPrivate::ScrollerTearOffItem::ScrollDown)
+        menuOpt.state |= QStyle::State_DownArrow;
+
+    painter->setClipRect(menuOpt.rect);
+    q->style()->drawControl(QStyle::CE_MenuScroller, &menuOpt, painter, q);
+}
+
+void QMenuPrivate::drawTearOff(QPainter *painter, const QRect &rect)
+{
+    if (!painter || rect.isEmpty())
+        return;
+
+    if (!tearoff)
+        return;
+
+    Q_Q(QMenu);
+    QStyleOptionMenuItem menuOpt;
+    menuOpt.initFrom(q);
+    menuOpt.state = QStyle::State_None;
+    menuOpt.checkType = QStyleOptionMenuItem::NotCheckable;
+    menuOpt.maxIconWidth = 0;
+    menuOpt.tabWidth = 0;
+    menuOpt.rect = rect;
+    menuOpt.menuItemType = QStyleOptionMenuItem::TearOff;
+    if (tearoffHighlighted)
+        menuOpt.state |= QStyle::State_Selected;
+
+    painter->setClipRect(menuOpt.rect);
+    q->style()->drawControl(QStyle::CE_MenuTearoff, &menuOpt, painter, q);
+}
+
+QMenuPrivate::ScrollerTearOffItem::ScrollerTearOffItem(QMenuPrivate::ScrollerTearOffItem::Type type, QMenuPrivate *mPrivate, QWidget *parent, Qt::WindowFlags f)
+    : QWidget(parent, f), menuPrivate(mPrivate), scrollType(type)
+{
+    if (parent)
+        setMouseTracking(parent->style()->styleHint(QStyle::SH_Menu_MouseTracking, 0, parent));
+}
+
+void QMenuPrivate::ScrollerTearOffItem::paintEvent(QPaintEvent *e)
+{
+    if (!e->rect().intersects(rect()))
+        return;
+
+    QPainter p(this);
+    QWidget *parent = parentWidget();
+
+    //paint scroll up / down arrows
+    menuPrivate->drawScroller(&p, scrollType, QRect(0, 0, width(), menuPrivate->scrollerHeight()));
+    //paint the tear off
+    if (scrollType == QMenuPrivate::ScrollerTearOffItem::ScrollUp) {
+        QRect rect(0, 0, width(), parent->style()->pixelMetric(QStyle::PM_MenuTearoffHeight, 0, parent));
+        if (menuPrivate->scroll && menuPrivate->scroll->scrollFlags & QMenuPrivate::QMenuScroller::ScrollUp)
+            rect.translate(0, menuPrivate->scrollerHeight());
+        menuPrivate->drawTearOff(&p, rect);
+    }
+}
+
+void QMenuPrivate::ScrollerTearOffItem::updateScrollerRects(const QRect &rect)
+{
+    if (rect.isEmpty())
+        setVisible(false);
+    else {
+        setGeometry(rect);
+        raise();
+        setVisible(true);
+    }
+}
+
 
 /*!
     Returns the action associated with this menu.
@@ -2595,35 +2682,20 @@ void QMenu::paintEvent(QPaintEvent *e)
         style()->drawControl(QStyle::CE_MenuItem, &opt, &p, this);
     }
 
-    if (!scrollUpRect.isEmpty()) {
-        menuOpt.menuItemType = QStyleOptionMenuItem::Scroller;
-        menuOpt.state |= QStyle::State_Enabled;
-        menuOpt.rect = scrollUpRect;
-        emptyArea -= QRegion(menuOpt.rect);
-        p.setClipRect(menuOpt.rect);
-        style()->drawControl(QStyle::CE_MenuScroller, &menuOpt, &p, this);
-    }
-
-    if (!scrollDownRect.isEmpty()) {
-        menuOpt.menuItemType = QStyleOptionMenuItem::Scroller;
-        menuOpt.state |= QStyle::State_Enabled;
-        menuOpt.state |= QStyle::State_DownArrow;
-        menuOpt.rect = scrollDownRect;
-        emptyArea -= QRegion(menuOpt.rect);
-        p.setClipRect(menuOpt.rect);
-        style()->drawControl(QStyle::CE_MenuScroller, &menuOpt, &p, this);
-    }
+    emptyArea -= QRegion(scrollUpTearOffRect);
+    emptyArea -= QRegion(scrollDownRect);
 
-    //paint the tear off..
-    if (!tearOffRect.isEmpty()) {
-        menuOpt.menuItemType = QStyleOptionMenuItem::TearOff;
-        menuOpt.rect = tearOffRect;
-        emptyArea -= QRegion(menuOpt.rect);
-        p.setClipRect(menuOpt.rect);
-        menuOpt.state = QStyle::State_None;
-        if (d->tearoffHighlighted)
-            menuOpt.state |= QStyle::State_Selected;
-        style()->drawControl(QStyle::CE_MenuTearoff, &menuOpt, &p, this);
+    if (d->scrollUpTearOffItem || d->scrollDownItem) {
+        if (d->scrollUpTearOffItem)
+            d->scrollUpTearOffItem->updateScrollerRects(scrollUpTearOffRect);
+        if (d->scrollDownItem)
+            d->scrollDownItem->updateScrollerRects(scrollDownRect);
+    } else {
+        //paint scroll up /down
+        d->drawScroller(&p, QMenuPrivate::ScrollerTearOffItem::ScrollUp, scrollUpRect);
+        d->drawScroller(&p, QMenuPrivate::ScrollerTearOffItem::ScrollDown, scrollDownRect);
+        //paint the tear off..
+        d->drawTearOff(&p, tearOffRect);
     }
 
     //draw border
@@ -3356,8 +3428,17 @@ void QMenu::actionEvent(QActionEvent *e)
         }
         if (QWidgetAction *wa = qobject_cast<QWidgetAction *>(e->action())) {
             QWidget *widget = wa->requestWidget(this);
-            if (widget)
+            if (widget) {
                 d->widgetItems.insert(wa, widget);
+                if (d->scroll) {
+                    if (!d->scrollUpTearOffItem)
+                        d->scrollUpTearOffItem =
+                                new QMenuPrivate::ScrollerTearOffItem(QMenuPrivate::ScrollerTearOffItem::ScrollUp, d, this);
+                    if (!d->scrollDownItem)
+                        d->scrollDownItem =
+                                new QMenuPrivate::ScrollerTearOffItem(QMenuPrivate::ScrollerTearOffItem::ScrollDown, d, this);
+                }
+            }
         }
     } else if (e->type() == QEvent::ActionRemoved) {
         e->action()->disconnect(this);
diff --git a/src/widgets/widgets/qmenu_p.h b/src/widgets/widgets/qmenu_p.h
index 3166e6f6cd..64291e842f 100644
--- a/src/widgets/widgets/qmenu_p.h
+++ b/src/widgets/widgets/qmenu_p.h
@@ -276,7 +276,8 @@ public:
                       cancelAction(0),
 #endif
                       scroll(0), eventLoop(0), tearoff(0), tornoff(0), tearoffHighlighted(0),
-                      hasCheckableItems(0), doChildEffects(false), platformMenu(0)
+                      hasCheckableItems(0), doChildEffects(false), platformMenu(0),
+                      scrollUpTearOffItem(nullptr), scrollDownItem(nullptr)
     { }
 
     ~QMenuPrivate()
@@ -445,6 +446,24 @@ public:
     QPointer<QAction> actionAboutToTrigger;
 
     QPointer<QWidget> noReplayFor;
+
+    class ScrollerTearOffItem : public QWidget {
+    public:
+        enum Type { ScrollUp, ScrollDown };
+        ScrollerTearOffItem(Type type, QMenuPrivate *mPrivate,
+                            QWidget *parent = Q_NULLPTR, Qt::WindowFlags f = Qt::WindowFlags());
+        void paintEvent(QPaintEvent *e) Q_DECL_OVERRIDE;
+        void updateScrollerRects(const QRect &rect);
+
+    private:
+        QMenuPrivate *menuPrivate;
+        Type scrollType;
+    };
+    ScrollerTearOffItem *scrollUpTearOffItem;
+    ScrollerTearOffItem *scrollDownItem;
+
+    void drawScroller(QPainter *painter, ScrollerTearOffItem::Type type, const QRect &rect);
+    void drawTearOff(QPainter *painter, const QRect &rect);
 };
 
 #endif // QT_NO_MENU