Add option to display tabs on the right and bottom (#3847)

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/widgets/Notebook.hpp

@@ -17,7 +17,7 @@ class NotebookButton;
 class NotebookTab;
 class SplitContainer;
 
-enum NotebookTabDirection { Horizontal = 0, Vertical = 1 };
+enum NotebookTabLocation { Top = 0, Left = 1, Right = 2, Bottom = 3 };
 
 class Notebook : public BaseWidget
 {
@@ -58,7 +58,7 @@ public:
 
     void performLayout(bool animate = false);
 
-    void setTabDirection(NotebookTabDirection direction);
+    void setTabLocation(NotebookTabLocation location);
 
     bool isNotebookLayoutLocked() const;
     void setLockNotebookLayout(bool value);
@@ -86,12 +86,17 @@ protected:
     }
 
 private:
+    void resizeAddButton();
+
     bool containsPage(QWidget *page);
     Item &findItem(QWidget *page);
 
     static bool containsChild(const QObject *obj, const QObject *child);
     NotebookTab *getTabFromPage(QWidget *page);
 
+    // Returns the number of buttons in `customButtons_` that are visible
+    size_t visibleButtonCount() const;
+
     QList<Item> items_;
     QMenu menu_;
     QWidget *selectedPage_ = nullptr;
@@ -104,7 +109,7 @@ private:
     bool showAddButton_ = false;
     int lineOffset_ = 20;
     bool lockNotebookLayout_ = false;
-    NotebookTabDirection tabDirection_ = NotebookTabDirection::Horizontal;
+    NotebookTabLocation tabLocation_ = NotebookTabLocation::Top;
     QAction *lockNotebookLayoutAction_;
 };