QTabBar: draw text within moving tab

When a tab was moved by dragging, the tab's rectangle was drawn empty,
without the tab text. When a tab was moved by animated snap back to
its original position, the tab text was already drawn on the original
position, while the rectangle was still moving due to animation.

Adds the enum value QStyleOptionTab::TabPosition::Moving
When this option is set, QCommonStyle draws the tab text at the
current position instead of the original home position of the tab.

The QMacStyle switches over the TabPosition enum. As a moving tab
is laid out like the last tab in the given orientation, the enum value
Moving is treated like End.


Fixes: QTBUG-112277
Change-Id: I42a2d9c269dadfe9819c12dbc69e3ae995a45b09
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/plugins/styles/mac/qmacstyle_mac.mm

@@ -3915,6 +3915,7 @@ void QMacStyle::drawControl(ControlElement ce, const QStyleOption *opt, QPainter
                     frameRect = frameRect.adjusted(-1, 0, 1, 0);
                 }
                 break;
+            case QStyleOptionTab::Moving: // Moving tab treated like End
             case QStyleOptionTab::End:
                 // Pressed state hack: tweak adjustments in preparation for flip below
                 if (isSelected || tabDirection == QMacStylePrivate::West)

src/widgets/styles/qcommonstyle.cpp

@@ -2009,7 +2009,10 @@ void QCommonStyle::drawControl(ControlElement element, const QStyleOption *opt,
             }
             QRect iconRect;
             d->tabLayout(tab, widget, &tr, &iconRect);
-            tr = proxy()->subElementRect(SE_TabBarTabText, opt, widget); //we compute tr twice because the style may override subElementRect
+
+            // compute tr again, unless tab is moving, because the style may override subElementRect
+            if (tab->position != QStyleOptionTab::TabPosition::Moving)
+                tr = proxy()->subElementRect(SE_TabBarTabText, opt, widget);
 
             if (!tab->icon.isNull()) {
                 QPixmap tabIcon = tab->icon.pixmap(tab->iconSize, p->device()->devicePixelRatio(),

src/widgets/styles/qstyleoption.cpp

@@ -1314,6 +1314,8 @@ QStyleOptionTab::QStyleOptionTab(int version)
     \value Middle The tab is neither the first nor the last tab in the tab bar.
     \value End The tab is the last tab in the tab bar.
     \value OnlyOneTab The tab is both the first and the last tab in the tab bar.
+    \value Moving The tab is moving by mouse drag or animation.
+           This enum value was added in Qt 6.6.
 
     \sa position
 */

src/widgets/styles/qstyleoption.h

@@ -244,7 +244,7 @@ public:
     enum StyleOptionType { Type = SO_Tab };
     enum StyleOptionVersion { Version = 1 };
 
-    enum TabPosition { Beginning, Middle, End, OnlyOneTab };
+    enum TabPosition { Beginning, Middle, End, OnlyOneTab, Moving };
     enum SelectedPosition { NotAdjacent, NextIsSelected, PreviousIsSelected };
     enum CornerWidget { NoCornerWidgets = 0x00, LeftCornerWidget = 0x01,
                         RightCornerWidget = 0x02 };

src/widgets/widgets/qtabbar.cpp

@@ -1873,21 +1873,30 @@ void QTabBar::paintEvent(QPaintEvent *)
         QStyleOptionTab tabOption;
         const auto tab = d->tabList.at(selected);
         initStyleOption(&tabOption, selected);
+
         if (d->paintWithOffsets && tab->dragOffset != 0) {
+            // if the drag offset is != 0, a move is in progress (drag or animation)
+            // => set the tab position to Moving to preserve the rect
+            tabOption.position = QStyleOptionTab::TabPosition::Moving;
+
             if (vertical)
                 tabOption.rect.moveTop(tabOption.rect.y() + tab->dragOffset);
             else
                 tabOption.rect.moveLeft(tabOption.rect.x() + tab->dragOffset);
         }
-        if (!d->dragInProgress)
-            p.drawControl(QStyle::CE_TabBarTab, tabOption);
-        else {
-            int taboverlap = style()->pixelMetric(QStyle::PM_TabBarTabOverlap, nullptr, this);
-            if (verticalTabs(d->shape))
-                d->movingTab->setGeometry(tabOption.rect.adjusted(0, -taboverlap, 0, taboverlap));
-            else
-                d->movingTab->setGeometry(tabOption.rect.adjusted(-taboverlap, 0, taboverlap, 0));
-        }
+
+        // Calculate the rect of a moving tab
+        const int taboverlap = style()->pixelMetric(QStyle::PM_TabBarTabOverlap, nullptr, this);
+        const QRect &movingRect = verticalTabs(d->shape)
+                ? tabOption.rect.adjusted(0, -taboverlap, 0, taboverlap)
+                : tabOption.rect.adjusted(-taboverlap, 0, taboverlap, 0);
+
+        // If a drag is in process, set the moving tab's geometry here
+        // (in an animation, it is already set)
+        if (d->dragInProgress)
+            d->movingTab->setGeometry(movingRect);
+
+        p.drawControl(QStyle::CE_TabBarTab, tabOption);
     }
 
     // Only draw the tear indicator if necessary. Most of the time we don't need too.