Fixed painting issues with draggable tabs

This fixes a few of the remaining glitches tabbar animations have:
* We no longer grab tabs but paint them through QStyle. This makes tabs
work and animate correctly when they are outside the visible region.
* Buttons now correctly follow tabs when dropped
* Gtkstyle recieved some polish to make it look more native.

Task-number: 247694, 251166
Reviewed-by: nrc

3 files changed, 57 insertions, 75 deletions

diff --git a/src/gui/styles/qgtkstyle.cpp b/src/gui/styles/qgtkstyle.cpp
index 519fed7..541415f 100644
--- a/src/gui/styles/qgtkstyle.cpp
+++ b/src/gui/styles/qgtkstyle.cpp
@@ -2760,10 +2760,13 @@ void QGtkStyle::drawControl(ControlElement element,
             if (tab->state & State_Selected)
                 state = GTK_STATE_NORMAL;
 
-            bool first = tab->position == QStyleOptionTab::Beginning || tab->position == QStyleOptionTab::OnlyOneTab;
-            bool last = tab->position == QStyleOptionTab::End || tab->position == QStyleOptionTab::OnlyOneTab;
             bool selected = (tab->state & State_Selected);
-            if (option->direction == Qt::RightToLeft) {
+            bool first = false, last = false;
+            if (widget) {
+                // This is most accurate and avoids resizing tabs while moving
+                first = tab->rect.left() == widget->rect().left();
+                last = tab->rect.right() == widget->rect().right();
+            } else if (option->direction == Qt::RightToLeft) {
                 bool tmp = first;
                 first = last;
                 last = tmp;
diff --git a/src/gui/widgets/qtabbar.cpp b/src/gui/widgets/qtabbar.cpp
index 7d970ad..b6e6b6d 100644
--- a/src/gui/widgets/qtabbar.cpp
+++ b/src/gui/widgets/qtabbar.cpp
@@ -131,7 +131,7 @@ void QTabBar::initStyleOption(QStyleOptionTab *option, int tabIndex) const
         option->state &= ~QStyle::State_Enabled;
     if (isActiveWindow())
         option->state |= QStyle::State_Active;
-    if (option->rect == d->hoverRect)
+    if (!d->dragInProgress && option->rect == d->hoverRect)
         option->state |= QStyle::State_MouseOver;
     option->shape = d->shape;
     option->text = tab.text;
@@ -454,9 +454,6 @@ void QTabBarPrivate::layoutTabs()
         maxExtent = maxWidth;
     }
 
-    if (pressedIndex != -1 && movable)
-        grabCache(0, tabList.count(), true);
-
     Q_ASSERT(tabChainIndex == tabChain.count() - 1); // add an assert just to make sure.
     // Mirror our front item.
     tabChain[tabChainIndex].init();
@@ -1484,6 +1481,8 @@ void QTabBar::paintEvent(QPaintEvent *)
     bool vertical = verticalTabs(d->shape);
     QStyleOptionTab cutTab;
     selected = d->currentIndex;
+    if (d->dragInProgress)
+        selected = d->pressedIndex;
 
     for (int i = 0; i < d->tabList.count(); ++i)
          optTabBase.tabBarRect |= tabRect(i);
@@ -1522,11 +1521,7 @@ void QTabBar::paintEvent(QPaintEvent *)
         if (i == selected)
             continue;
 
-        if (!d->tabList[i].animatingCache.isNull() && d->paintWithOffsets) {
-            p.drawPixmap(tab.rect, d->tabList[i].animatingCache);
-        } else {
-            p.drawControl(QStyle::CE_TabBarTab, tab);
-        }
+        p.drawControl(QStyle::CE_TabBarTab, tab);
     }
 
     // Draw the selected tab last to get it "on top"
@@ -1539,7 +1534,11 @@ void QTabBar::paintEvent(QPaintEvent *)
             else
                 tab.rect.moveLeft(tab.rect.x() + d->tabList[selected].dragOffset);
         }
-        p.drawControl(QStyle::CE_TabBarTab, tab);
+        if (!d->dragInProgress)
+            p.drawControl(QStyle::CE_TabBarTab, tab);
+        else
+            d->movingTab->setGeometry(tab.rect);
+
     }
 
     // Only draw the tear indicator if necessary. Most of the time we don't need too.
@@ -1680,6 +1679,7 @@ void QTabBarPrivate::_q_moveTab(int offset)
         if (!validIndex(index))
             return;
         tabList[index].dragOffset = offset;
+        layoutTab(index); // Make buttons follow tab
         q->update();
     }
 }
@@ -1727,8 +1727,7 @@ void QTabBar::mouseMoveEvent(QMouseEvent *event)
         if (!d->dragInProgress && d->pressedIndex != -1) {
             if ((event->pos() - d->dragStartPosition).manhattanLength() > QApplication::startDragDistance()) {
                 d->dragInProgress = true;
-                if (d->animations.isEmpty())
-                    d->grabCache(0, d->tabList.count(), false);
+                d->setupMovableTab();
             }
         }
 
@@ -1773,7 +1772,6 @@ void QTabBar::mouseMoveEvent(QMouseEvent *event)
                     if (dragDistance > needsToBeOver)
                         d->slide(i + offset, d->pressedIndex);
                 }
-
             }
             // Buttons needs to follow the dragged tab
             d->layoutTab(d->pressedIndex);
@@ -1801,32 +1799,41 @@ void QTabBarPrivate::_q_moveTabFinished()
     }
 }
 
-void QTabBarPrivate::grabCache(int start, int end, bool unhide)
+void QTabBarPrivate::setupMovableTab()
 {
     Q_Q(QTabBar);
-    paintWithOffsets = false;
-    bool showButtonsAgain = rightB->isVisible();
-    rightB->hide();
-    leftB->hide();
-
-    QWidget *topLevel = q->window();
-    QPoint topLevelOffset(q->mapTo(topLevel, QPoint()));
-    for (int i = start; i < end; ++i) {
-        QRect tabRect = q->tabRect(i);
-        tabRect.translate(topLevelOffset);
-        if (unhide) {
-            tabList[i].unHideWidgets();
-            layoutWidgets(i);
-        }
-        tabList[i].animatingCache = QPixmap::grabWidget(topLevel, tabRect);
-        if (i != pressedIndex)
-            tabList[i].hideWidgets();
-    }
-    if (showButtonsAgain) {
-        rightB->show();
-        leftB->show();
-    }
-    paintWithOffsets = true;
+    if (!movingTab)
+        movingTab = new QWidget(q);
+
+    QRect grabRect = q->tabRect(pressedIndex);
+
+    QPixmap grabImage(grabRect.size());
+    grabImage.fill(Qt::transparent);
+    QStylePainter p(&grabImage, q);
+
+    QStyleOptionTabV3 tab;
+    q->initStyleOption(&tab, pressedIndex);
+    tab.rect.moveTopLeft(QPoint(0, 0));
+    p.drawControl(QStyle::CE_TabBarTab, tab);
+    p.end();
+
+    QPalette pal;
+    pal.setBrush(QPalette::All, QPalette::Window, grabImage);
+    movingTab->setPalette(pal);
+    movingTab->setGeometry(grabRect);
+    movingTab->setAutoFillBackground(true);
+    movingTab->raise();
+
+    // Re-arrange widget order to avoid overlaps
+    if (tabList[pressedIndex].leftWidget)
+        tabList[pressedIndex].leftWidget->raise();
+    if (tabList[pressedIndex].rightWidget)
+        tabList[pressedIndex].rightWidget->raise();
+    if (leftB)
+        leftB->raise();
+    if (rightB)
+        rightB->raise();
+    movingTab->setVisible(true);
 }
 
 void QTabBarPrivate::_q_moveTabFinished(int index)
@@ -1834,10 +1841,9 @@ void QTabBarPrivate::_q_moveTabFinished(int index)
     Q_Q(QTabBar);
     bool cleanup = (pressedIndex == index) || (pressedIndex == -1) || !validIndex(index);
     if (animations.isEmpty() && cleanup) {
+        movingTab->setVisible(false); // We might not get a mouse release
         for (int i = 0; i < tabList.count(); ++i) {
             tabList[i].dragOffset = 0;
-            tabList[i].unHideWidgets();
-            tabList[i].animatingCache = QPixmap();
         }
         if (pressedIndex != -1 && movable) {
             pressedIndex = -1;
@@ -1881,6 +1887,7 @@ void QTabBar::mouseReleaseEvent(QMouseEvent *event)
             d->_q_moveTabFinished(d->pressedIndex);
         }
         d->dragInProgress = false;
+        d->movingTab->setVisible(false);
         d->dragStartPosition = QPoint();
     }
 
@@ -2203,19 +2210,16 @@ void QTabBar::setTabButton(int index, ButtonPosition position, QWidget *widget)
         widget->setParent(this);
         // make sure our left and right widgets stay on top
         widget->lower();
+        widget->show();
     }
     if (position == LeftSide) {
         if (d->tabList[index].leftWidget)
             d->tabList[index].leftWidget->hide();
         d->tabList[index].leftWidget = widget;
-        if(!d->tabList[index].hidLeft && widget)
-            widget->show();
     } else {
         if (d->tabList[index].rightWidget)
             d->tabList[index].rightWidget->hide();
         d->tabList[index].rightWidget = widget;
-        if(!d->tabList[index].hidRight && widget)
-            widget->show();
     }
     d->layoutTabs();
     update();
diff --git a/src/gui/widgets/qtabbar_p.h b/src/gui/widgets/qtabbar_p.h
index a117aa3..cb1a15b 100644
--- a/src/gui/widgets/qtabbar_p.h
+++ b/src/gui/widgets/qtabbar_p.h
@@ -70,7 +70,6 @@
 
 QT_BEGIN_NAMESPACE
 
-
 class QTabBarPrivate  : public QWidgetPrivate
 {
     Q_DECLARE_PUBLIC(QTabBar)
@@ -78,7 +77,7 @@ public:
     QTabBarPrivate()
         :currentIndex(-1), pressedIndex(-1),
          shape(QTabBar::RoundedNorth),
-         layoutDirty(false), drawBase(true), scrollOffset(0), expanding(true), closeButtonOnTabs(false), selectionBehaviorOnRemove(QTabBar::SelectRightTab), paintWithOffsets(true), movable(false), dragInProgress(false), documentMode(false) {}
+         layoutDirty(false), drawBase(true), scrollOffset(0), expanding(true), closeButtonOnTabs(false), selectionBehaviorOnRemove(QTabBar::SelectRightTab), paintWithOffsets(true), movable(false), dragInProgress(false), documentMode(false), movingTab(0) {}
 
     int currentIndex;
     int pressedIndex;
@@ -98,8 +97,6 @@ public:
             , lastTab(-1)
             , timeLine(0)
             , dragOffset(0)
-            , hidLeft(false)
-            , hidRight(false)
         {}
         bool enabled;
         int shortcutId;
@@ -123,9 +120,6 @@ public:
 
         QTimeLine *timeLine;
         int dragOffset;
-        QPixmap animatingCache;
-        bool hidLeft;
-        bool hidRight;
 
         void makeTimeLine(QWidget *q) {
             if (timeLine)
@@ -135,27 +129,6 @@ public:
             q->connect(timeLine, SIGNAL(finished()), q, SLOT(_q_moveTabFinished()));
         }
 
-        void hideWidgets() {
-            if (!hidRight && rightWidget) {
-                hidRight = rightWidget->isVisible();
-                rightWidget->hide();
-            }
-
-            if (!hidLeft && leftWidget) {
-                hidLeft = leftWidget->isVisible();
-                leftWidget->hide();
-            }
-        }
-
-        void unHideWidgets() {
-            if (leftWidget && hidLeft)
-                leftWidget->show();
-            hidLeft = false;
-            if (rightWidget && hidRight)
-                rightWidget->show();
-            hidRight = false;
-        }
-
     };
     QList<Tab> tabList;
     QHash<QTimeLine*, int> animations;
@@ -184,12 +157,12 @@ public:
     void _q_moveTabFinished(int offset);
     QRect hoverRect;
 
-    void grabCache(int start, int end, bool unhide);
     void refresh();
     void layoutTabs();
     void layoutWidgets(int index = -1);
     void layoutTab(int index);
     void updateMacBorderMetrics();
+    void setupMovableTab();
 
     void makeVisible(int index);
     QSize iconSize;
@@ -206,6 +179,8 @@ public:
     bool dragInProgress;
     bool documentMode;
 
+    QWidget *movingTab;
+
     // shared by tabwidget and qtabbar
     static void initStyleBaseOption(QStyleOptionTabBarBaseV2 *optTabBase, QTabBar *tabbar, QSize size)
     {