GtkTooltip: Scale the cursor size on X11

GtkSettings/X11 takes the values as provided by
XSettings. Unlike other backends, the values of
XSettings are in physical size (that's because
X11 doesn't support mixed-DPI setups anyway).

Take that in account when retrieving the cursor
size in gtk_tooltip_position ().

Note that this discrepancy between the X11 and
other backends has been fixed in GTK4.

Fixes https://gitlab.gnome.org/GNOME/gtk/-/issues/5223

gtk/gtktooltip.c

@@ -42,6 +42,9 @@
 #ifdef GDK_WINDOWING_WAYLAND
 #include "wayland/gdkwayland.h"
 #endif
+#ifdef GDK_WINDOWING_X11
+#include "x11/gdkx.h"
+#endif
 
 
 /**
@@ -898,6 +901,16 @@ gtk_tooltip_position (GtkTooltip *tooltip,
   if (cursor_size == 0)
     cursor_size = gdk_display_get_default_cursor_size (display);
 
+#ifdef GDK_WINDOWING_X11
+  if (GDK_IS_X11_SCREEN (screen))
+    {
+      /* Cursor size on X11 comes directly from XSettings which
+       * report physical sizes, unlike on other backends. So in
+       * that case we have to scale the retrieved cursor_size */
+       cursor_size /= gtk_widget_get_scale_factor (new_tooltip_widget);
+    }
+#endif
+
   if (device)
     anchor_rect_padding = MAX (4, cursor_size - 32);
   else