[tex-k] Problem with "mf" online display in GNOME

Paul Vojta vojta at math.berkeley.edu
Tue May 23 10:41:37 CEST 2017

Hi Igor,

First, for your original question:  it's probably either
Build/source/texk/web2c/window/x11-Xlib.c or
Build/source/texk/web2c/window/x11-Xt.c .
Probably the former, given the short output of "ldd .../mf"

However, I don't think the problem is specific to GNOME.  I use fvwm as
my window manager, and the bug affects me.
In fact, I tried the test file on seven different Linux machines before
finding one in which the bug did *not* occur.  For the seventh machine, the
bug sometimes occurred and sometimes did not.

I think that the problem is that mf is not handling expose events correctly
(or at all?).  I suspect that because on the seventh machine, when the dot
appeared, I switched to a different virtual desktop and back, and the dot
disappeared.  So I think that the presence or absence of the bug could be
a timing thing, and that maybe it occurs with GNOME because GNOME is bigger
and slower, so mf issues the draw requests before the window is fully

Here are some additional tests you can do (even under GNOME).

1.  Without using a file test.mf, type mf, \relax at the ** prompt, and
    drawdot(35,70); showit; at the * prompt.  Then, try drawing other dots
    (for example drawdot(20,20); showit; ).  Do they appear?

2.  If you are able to draw additional dots, are they redrawn on the screen
    if you cover them with another window and then uncover them?

In my own tests (not done on machine #7 since it's a really old machine and
hard to use), I do get the additional dots in #1 above, and they are not
redrawn in #2 (so they disappear after covering and uncovering them).

Paul Vojta, vojta at math dot berkeley dot edu

On Tue, May 23, 2017 at 10:48:34AM +0700, Igor Liferenko wrote:
> Hi all,
> This example from MetaFont Book (page 31) does not work with online
> display (run as "mf test.mf"):
>     drawdot (35,70); showit;
> I traced down the problem to GNOME. On MATE desktop everything works properly.
> There is also a report that it works in MobaXterm (X-Server on Windows 10):
>     https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=862943#10
> The problem is not in TeX Live (I tested on official TeX Live ISO),
> because this example works everywhere except GNOME. Thus, the problem
> is with GNOME. Can you please point me to the code in TeX Live which
> interfaces with window system so that I could trace down the bug
> myself?
> Thanks,
> Igor

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