[Rd] [Solved] Possible x11 window manager window aggregation under one icon?

[Ivan Krylov]

On Fri, 26 Mar 2021 14:49:56 +0100
Martin Maechler <maechler using stat.math.ethz.ch> wrote:

> I concluded I liked the first [patch] because it would achieve
> what's considered "uniformly better" in the sense that it makes
> R graphics behave like "all other" desktop applications *and* it
> would do so for all possible window manager scheme without any
> need of some desktop setting (which a typical user would not
> know about, nor know that s?he should/could change).

Martin, here is some information on how X11 (and rgl) windows are
grouped on different platforms, depending on the presence of the first
patch and the .desktop file:

 - GNOME [1] needs a .desktop file to group windows by their WM_CLASS
   and otherwise groups windows by their WM_HINTS.window_group only,
   which makes different configurations possible:
   * no window_group, no .desktop file: no grouping
   * window_group patch, no .desktop file: plot windows grouped
     per-process, x11 and rgl separately
   * StartupWMClass in .desktop file: x11 and rgl windows from all R
     processes grouped together
 - the XQuartz window manager apparently uses WM_HINTS.window_group but
   not WM_CLASS to group windows [2] (patch is only relevant for
   rgl, .desktop files aren't relevant)
 - Xfce groups windows by WM_CLASS [3], so adding WM_HINTS.window_group
   or changing the .desktop file doesn't group them any more
 - KDE seems to follow the .desktop file (if StartupWMClass is
   present) and group by WM_CLASS otherwise [4], but I don't have it
   installed to check. On the other hand, KDE might be ignoring
   WM_HINTS.window_group, judging by the absence of "WM2GroupLeader" in
   the source code of Plasma Workspace. This implies no changes in
   window grouping from patching window_group or changing the .desktop
   file. [5]

To summarise, the patch to x11() leads to visible window grouping in
GNOME-based environments. My impression is that most environments group
windows by WM_CLASS (which had been happening without the patch), but
there are far too many window managers to check that impression.

-- 
Best regards,
Ivan

[1] Including Cinammon:
https://github.com/linuxmint/cinnamon/blob/72732da43e971b83d926af56998c83ee8d000394/src/cinnamon-window-tracker.c#L482

Likely Unity forks too.

[2] Judging by
https://stat.ethz.ch/pipermail/r-devel/2021-March/080571.html

[3] With minor inconsistencies regarding x11 vs rgl windows between
Win+Tab "switch between application windows" and the window buttons on
the task bar, but let's not focus on that.

[4]
https://invent.kde.org/plasma/plasma-workspace/-/blob/7c49a0ae/libtaskmanager/xwindowtasksmodel.cpp#L439

[5] Strictly speaking, StartupWMClass= in the .desktop file lets the
desktop environment associate the plot windows with the R launcher
button if it's also present on the task bar.