widget: Add gtk_widget_get_size()

A little bit of convenience.

docs/reference/gtk/gtk4-sections.txt

@@ -4858,6 +4858,7 @@ gtk_widget_get_allocation
 gtk_widget_get_allocated_baseline
 gtk_widget_get_width
 gtk_widget_get_height
+gtk_widget_get_size
 gtk_widget_compute_bounds
 gtk_widget_compute_transform
 gtk_widget_compute_point

gtk/gtkwidget.c

@@ -13364,6 +13364,31 @@ gtk_widget_get_height (GtkWidget *widget)
   return priv->height;
 }
 
+/**
+ * gtk_widget_get_size:
+ * @widget: a #GtkWidget
+ * @orientation: the orientation to query
+ *
+ * Returns the content width or height of the widget, depending on @orientation.
+ * This is equivalent to calling gtk_widget_get_width() for %GTK_ORIENTATION_HORIZONTAL
+ * or gtk_widget_get_height() for %GTK_ORIENTATION_VERTICAL, but can be used when
+ * writing orientation-independent code, such as when implementing #GtkOrientable
+ * widgets.
+ *
+ * Returns: The size of @widget in @orientation.
+ */
+int
+gtk_widget_get_size (GtkWidget      *widget,
+                     GtkOrientation  orientation)
+{
+  g_return_val_if_fail (GTK_IS_WIDGET (widget), 0);
+
+  if (orientation == GTK_ORIENTATION_HORIZONTAL)
+    return gtk_widget_get_width (widget);
+  else
+    return gtk_widget_get_height (widget);
+}
+
 /**
  * gtk_widget_class_set_layout_manager_type:
  * @widget_class: class to set the layout manager type for

gtk/gtkwidget.h

@@ -576,6 +576,9 @@ GDK_AVAILABLE_IN_ALL
 int                   gtk_widget_get_width              (GtkWidget     *widget);
 GDK_AVAILABLE_IN_ALL
 int                   gtk_widget_get_height             (GtkWidget     *widget);
+GDK_AVAILABLE_IN_ALL
+int                   gtk_widget_get_size               (GtkWidget     *widget,
+                                                         GtkOrientation orientation);
 
 GDK_AVAILABLE_IN_ALL
 gboolean   gtk_widget_child_focus         (GtkWidget           *widget,