From 3beb2e88ecf0687831eb97a25da789f225d25fad Mon Sep 17 00:00:00 2001
From: Alx Sa <cmyk.student@gmail.com>
Date: Thu, 21 Sep 2023 05:30:48 +0000
Subject: [PATCH] widgets: Restore GTK2 tab scrolling behavior

In GTK2 and GIMP 2.10, you can use the mouse scroller to
switch between dockable tabs if you hover over the bar.
This behavior was removed from GtkNotebook in GTK3.
This patch follows other GTK3 applications in re-implementing
the behavior with a scroll-event callback.
---
 app/widgets/gimpdockbook.c | 44 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/app/widgets/gimpdockbook.c b/app/widgets/gimpdockbook.c
index acaabaee816..4572fe9eb38 100644
--- a/app/widgets/gimpdockbook.c
+++ b/app/widgets/gimpdockbook.c
@@ -126,6 +126,9 @@ static void         gimp_dockbook_page_reordered    (GtkNotebook    *notebook,
                                                      GtkWidget      *child,
                                                      guint           page_num);
 
+static gboolean     gimp_dockbook_tab_scroll_cb     (GtkWidget      *widget,
+                                                     GdkEventScroll *event);
+
 static gboolean     gimp_dockbook_menu_button_press (GimpDockbook   *dockbook,
                                                      GdkEventButton *bevent,
                                                      GtkWidget      *button);
@@ -222,6 +225,12 @@ gimp_dockbook_init (GimpDockbook *dockbook)
   gtk_notebook_set_show_tabs (notebook, TRUE);
   gtk_notebook_set_group_name (notebook, "gimp-dockbook");
 
+  gtk_widget_add_events (GTK_WIDGET (notebook),
+                         GDK_SCROLL_MASK);
+  g_signal_connect (GTK_WIDGET (notebook), "scroll-event",
+                    G_CALLBACK (gimp_dockbook_tab_scroll_cb),
+                    NULL);
+
   gtk_drag_dest_set (GTK_WIDGET (dockbook),
                      0,
                      dialog_target_table, G_N_ELEMENTS (dialog_target_table),
@@ -522,6 +531,41 @@ gimp_dockbook_page_removed (GtkNotebook *notebook,
     }
 }
 
+/* Restore GTK2 behavior of mouse-scrolling to switch between
+ * notebook tabs. References Geany's notebook_tab_bar_click_cb ()
+ * at https://github.com/geany/geany/blob/master/src/notebook.c
+ */
+static gboolean
+gimp_dockbook_tab_scroll_cb (GtkWidget      *widget,
+                             GdkEventScroll *event)
+{
+  GtkNotebook *notebook = GTK_NOTEBOOK (widget);
+  GtkWidget   *page     = NULL;
+
+  page = gtk_notebook_get_nth_page (notebook,
+                                    gtk_notebook_get_current_page (notebook));
+  if (! page)
+    return FALSE;
+
+  switch (event->direction)
+    {
+    case GDK_SCROLL_RIGHT:
+    case GDK_SCROLL_DOWN:
+      gtk_notebook_next_page (notebook);
+      break;
+
+    case GDK_SCROLL_LEFT:
+    case GDK_SCROLL_UP:
+      gtk_notebook_prev_page (notebook);
+      break;
+
+    default:
+      break;
+    }
+
+  return TRUE;
+}
+
 static void
 gimp_dockbook_page_reordered (GtkNotebook *notebook,
                               GtkWidget   *child,
-- 
GitLab