bug#27357: 26.0.50; Emacs starts fullscreen in Ubuntu 17.04

[Lars Ingebrigtsen <larsi@gnus.org>]

I found the place where the tooltips are positions, and that seemed like
an easy place to experiment, so I did.

If I divide root_x and root_y by 2, the positioning is exactly as it's
supposed to be.

So the wrong calculations here seem to be completely internal to gtk.
To verify, I did the following:

diff --git a/src/gtkutil.c b/src/gtkutil.c
index 2d4abefa96..050433d5c3 100644
--- a/src/gtkutil.c
+++ b/src/gtkutil.c
@@ -724,7 +724,10 @@ xg_show_tooltip (struct frame *f, int root_x, int root_y)
   if (x->ttip_window)
     {
       block_input ();
-      gtk_window_move (x->ttip_window, root_x, root_y);
+      printf("Input x %d, y %d\n", root_x, root_y);
+      gtk_window_move (x->ttip_window, root_x/2, root_y/2);
+      gtk_window_get_position (x->ttip_window, &root_x, &root_y);
+      printf("Output x %d, y %d\n", root_x, root_y);
       gtk_widget_show_all (GTK_WIDGET (x->ttip_window));
       unblock_input ();
     }

The output is:

Input x 725, y 464
Output x 362, y 232

So gtk seems to think that we're living in a world where the pixels
passed in are supposed to be doubled from what Emacs is passing it: That
is, that if you send in (2, 2), the physical pixel being addressed is
(4, 4).

Perhaps there's a way to tell gtk to stop doing that?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no