Gui: Display workbench icon in the middle for icon-only

It ensures that for icon-only style it is displayed in the middle and
empty text is not accounted while calculating tab size hint. Custom
styles may need to target `QTabBar[style="icon-only"]` to apply specific
fixes like disabling padding.

Fixes: #14282

src/Gui/WorkbenchSelector.cpp

@@ -102,7 +102,6 @@ void WorkbenchComboBox::refreshList(QList<QAction*> actionList)
     }
 }
 
-
 WorkbenchTabWidget::WorkbenchTabWidget(WorkbenchGroup* aGroup, QWidget* parent)
     : QWidget(parent)
     , wbActionGroup(aGroup)
@@ -112,7 +111,7 @@ WorkbenchTabWidget::WorkbenchTabWidget(WorkbenchGroup* aGroup, QWidget* parent)
     setWhatsThis(aGroup->action()->whatsThis());
     setObjectName(QString::fromLatin1("WbTabBar"));
 
-    tabBar = new QTabBar(this);
+    tabBar = new WbTabBar(this);
     moreButton = new QToolButton(this);
     layout = new QBoxLayout(QBoxLayout::LeftToRight, this);
 
@@ -205,6 +204,12 @@ int WorkbenchTabWidget::tabIndexForWorkbenchActivateAction(QAction* workbenchAct
     return actionToTabIndex.at(workbenchActivateAction);
 }
 
+WorkbenchItemStyle Gui::WorkbenchTabWidget::itemStyle() const
+{
+    ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Workbenches");
+    return static_cast<WorkbenchItemStyle>(hGrp->GetInt("WorkbenchSelectorItem", 0));
+}
+
 void WorkbenchTabWidget::updateLayout()
 {
     if (!parentWidget()) {
@@ -293,6 +298,8 @@ void WorkbenchTabWidget::updateWorkbenchList()
         return;
     }
 
+    tabBar->setItemStyle(itemStyle());
+
     // As clearing and adding tabs can cause changing current tab in QTabBar.
     // This in turn will cause workbench to change, so we need to prevent
     // processing of such events until the QTabBar is fully prepared.
@@ -320,8 +327,7 @@ void WorkbenchTabWidget::updateWorkbenchList()
 
 int WorkbenchTabWidget::addWorkbenchTab(QAction* action, int tabIndex)
 {
-    ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath("User parameter:BaseApp/Preferences/Workbenches");
-    auto itemStyle = static_cast<WorkbenchItemStyle>(hGrp->GetInt("WorkbenchSelectorItem", 0));
+    auto itemStyle = this->itemStyle();
 
     // if tabIndex is negative we assume that tab must be placed at the end of tabBar (default behavior)
     if (tabIndex < 0) {
@@ -422,5 +428,3 @@ void WorkbenchTabWidget::adjustSize()
 
     parentWidget()->adjustSize();
 }
-
-#include "moc_WorkbenchSelector.cpp"

src/Gui/WorkbenchSelector.h

@@ -64,13 +64,61 @@ class GuiExport WorkbenchTabWidget : public QWidget
     Q_OBJECT
     Q_PROPERTY(Qt::LayoutDirection direction READ direction WRITE setDirection NOTIFY directionChanged)
 
-    int addWorkbenchTab(QAction* workbenchActivateAction, int index = -1);
+    class WbTabBar : public QTabBar {
+    public:
+        explicit WbTabBar(QWidget* parent) : QTabBar(parent) {}
 
-    void setTemporaryWorkbenchTab(QAction* workbenchActivateAction);
-    int temporaryWorkbenchTabIndex() const;
+        QSize tabSizeHint(int index) const override {
+            auto sizeFromParent = QTabBar::tabSizeHint(index);
 
-    QAction* workbenchActivateActionByTabIndex(int tabIndex) const;
-    int tabIndexForWorkbenchActivateAction(QAction* workbenchActivateAction) const;
+            if (itemStyle() != IconOnly) {
+                return sizeFromParent;
+            }
+
+            QStyleOptionTab opt;
+
+            initStyleOption(&opt, index);
+
+            int padding = style()->pixelMetric(QStyle::PM_TabBarTabHSpace, &opt, this);
+
+            auto csz = iconSize();
+            auto isHorizontal = opt.shape == RoundedNorth || opt.shape == RoundedSouth;
+
+            if (isHorizontal) {
+                csz.setWidth(csz.width() + padding);
+            } else {
+                csz.setHeight(csz.height() + padding);
+            }
+
+            auto size = style()->sizeFromContents(QStyle::CT_TabBarTab, &opt, csz, this);
+
+            if (isHorizontal) {
+                size.setHeight(sizeFromParent.height());
+            } else {
+                size.setWidth(sizeFromParent.width());
+            }
+
+            return size;
+        }
+
+        WorkbenchItemStyle itemStyle() const { return _itemStyle; }
+        void setItemStyle(WorkbenchItemStyle itemStyle) {
+            _itemStyle = itemStyle;
+            setProperty("style", QString::fromUtf8(workbenchItemStyleToString(itemStyle)));
+        }
+
+    private:
+        WorkbenchItemStyle _itemStyle;
+
+        static const char* workbenchItemStyleToString(WorkbenchItemStyle style)
+        {
+            switch (style) {
+                case IconAndText: return "icon-and-text";
+                case IconOnly: return "icon-only";
+                case TextOnly: return "text-only";
+            }
+        }
+    };
 
 public:
     explicit WorkbenchTabWidget(WorkbenchGroup* aGroup, QWidget* parent = nullptr);
@@ -93,12 +141,23 @@ public Q_SLOTS:
 Q_SIGNALS:
     void directionChanged(const Qt::LayoutDirection&);
 
+protected:
+    int addWorkbenchTab(QAction* workbenchActivateAction, int index = -1);
+
+    void setTemporaryWorkbenchTab(QAction* workbenchActivateAction);
+    int temporaryWorkbenchTabIndex() const;
+
+    QAction* workbenchActivateActionByTabIndex(int tabIndex) const;
+    int tabIndexForWorkbenchActivateAction(QAction* workbenchActivateAction) const;
+
+    WorkbenchItemStyle itemStyle() const;
+
 private:
     bool isInitializing = false;
 
     WorkbenchGroup* wbActionGroup;
     QToolButton* moreButton;
-    QTabBar* tabBar;
+    WbTabBar* tabBar;
     QBoxLayout* layout;
 
     Qt::LayoutDirection _direction = Qt::LeftToRight;