OMG, thank you so much Subbu, that did it!   :-D

The xprop command did already return that exact output, but it wasn't until
adding that line you said to my .desktop file that it worked.

99%, anyway.  I'd hoped I'd be able to have a .desktop file for a specific
image (so it can have its own icon, instead of the Squeak icon).

    # standard Squeak icon for launching any image
    Name=Squeak
    Exec=/usr/local/bin/spur %f
    Icon=/home/cmm/my/icons/Squeak-logo-white-background-68x51.png
    StartupWMClass=squeak
    ...

the other, for MyApp,

    # for launching MyApp's image.
    Name=MyApp
    Exec=/path/for/apps/vm/squeak.sh /path/for/apps/image/app.image
    Icon=/home/cmm/my/icons/My-App-logo.png
    StartupWMClass=squeak
    ...

I put both of the above into separate .desktop files at
~/.local/share/applications.  After an afternoon of tinkering, what I found
was a little strange -- for the icon, Ubuntu 18.04 seems to use whichever
desktop file was launched first.  However, even though it gets the icon
wrong, it at least uses the right Exec= vm specification.   I tried
changing the StartupWMClass on one of them, but it didn't work.  But, I can
at least work again..  :)

Thanks,
  Chris


On Sat, Jul 4, 2020 at 2:37 AM K K Subbu <kksubbu.ml at gmail.com> wrote:

> On 04/07/20 2:34 am, Chris Muller wrote:
> > But the problem is not actually Gnome's window manager -- it works
> > beautifully with _every other app_ *except* Squeak.
>
> Perhaps those apps come with properly configured .desktop file. Squeak
> does not ship with one.
>
> Could you please report Squeak app window has the right class?
>
> $ xprop WM_CLASS
> WM_CLASS(STRING) = "squeak", "Squeak"
>
> If this does not appear, then you will have to add one to your .desktop
> launcher file:
>
> StartupWMClass=squeak
>
> HTH .. Subbu
>
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