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

[Ivan Krylov]

On Mon, 22 Mar 2021 16:57:48 -0500
Dirk Eddelbuettel <edd using debian.org> wrote:

> Do you want to send a proper patch to bugzilla?

Would be glad to, especially if we manage to solve that problem you
uncovered while I was asleep.

On Mon, 22 Mar 2021 22:23:47 -0500
Dirk Eddelbuettel <edd using debian.org> wrote:

> Close, close, close but no cigar yet: For a given R process, x11()
> windows group for a that process. But we often run multiple R
> processes.  Have you seen anything for grouping under the
> "program" (in some sense) but not the concrete process from it?

Do windows from different Emacs processes group together the way you
want them to group? What other applications group together for you
despite running from different processes? Do they have the same window
id # of group leader in `xprop WM_HINTS`? I checked Firefox, but its
windows all seem to have the same _NET_WM_PID.

I decided to copy the way GVim sets its group leader ID (because I know
the windows are different processes _and_ that they group in Xfce) and
spent a while chasing this red herring before realising that (1) on my
PC, different x11() windows are still grouped together, even from
different R processes, even without the patch (I never used the "group
windows" option in xfce4-panel before) and (2) different GVim windows
actually have different group leader XIDs in their WM_HINTS properties.
Oops.

Apparently Xfce uses libwnck [*] which groups windows by WM_CLASS in
addition to WM_HINTS (as far as understand the code).

Here is what GNOME Shell does [**] besides looking at
WM_HINTS.window_group:

 - looks up the window's WM_CLASS in .desktop files known to it
 - looks up the window's _NET_WM_PID among running applications (?)
 - looks for an XDG startup notification matching the window
 - checks other things not likely applicable to R, such as sandbox IDs
   and GApplication IDs

Adding StartupWMClass=R_x11 to R.desktop (not part of R sources, but
part of the .deb package, I believe) should help GNOME Shell match all
x11() windows to a single application without any changes to devX11.c,
but I don't have GNOME installed to check it.

Alternatively, we can also add a _NET_WM_PID property to x11() windows
(in the hope that GNOME Shell matches the PIDs to the same binary), but
then we'd have to add the WM_CLIENT_MACHINE property too [***], which
is way more hacky than I would prefer it to be:

-----------------------------------8<-----------------------------------
Index: src/modules/X11/devX11.c
===================================================================
--- src/modules/X11/devX11.c	(revision 80104)
+++ src/modules/X11/devX11.c	(working copy)
@@ -52,6 +52,8 @@
 #endif
 #include <X11/keysymdef.h>
 
+#include <sys/utsname.h> /* for uname -> WM_CLIENT_MACHINE -> _NET_WM_PID */
+#include <unistd.h> /* getpid -> _NET_WM_PID */
 
 #define R_USE_PROTOTYPES 1
 #include <R_ext/GraphicsEngine.h>
@@ -105,7 +107,7 @@
 static Display *display;			/* Display */
 static char dspname[101]="";
 static int screen;				/* Screen */
-static Window rootwin;				/* Root Window */
+static Window rootwin, group_leader;		/* Root Window */
 static Visual *visual;				/* Visual */
 static int depth;				/* Pixmap depth */
 static int Vclass;				/* Visual class */
@@ -1617,6 +1619,39 @@
                             PropModeReplace,
                             (const unsigned char*) rlogo_icon, 2 + 99*77);
 
+	    /* set the window group leader */
+	    XWMHints * hints;
+	    hints = XAllocWMHints();
+	    if (hints) {
+		hints->window_group = group_leader;
+		hints->flags |= WindowGroupHint;
+		XSetWMHints(display, xd->window, hints);
+		XFree(hints);
+	    }
+
+	    /* Provide WM_CLIENT_MACHINE to set a valid _NET_WM_PID */
+	    struct utsname unm;
+	    if (uname(&unm)) goto no_wm_pid;
+	    char * nodename = &unm.nodename[0];
+	    XTextProperty hostname = {0}; /* initialise the value pointer */
+	    if (Success != XmbTextListToTextProperty(
+		display, &nodename, 1, XStringStyle, &hostname
+	    )) {
+		if (hostname.value) XFree(hostname.value);
+		goto no_wm_pid;
+	    }
+	    XSetWMClientMachine(display, xd->window, &hostname);
+	    XFree(hostname.value);
+
+	    /* set _NET_WM_PID */
+	    uint32_t mypid = (uint32_t)getpid(); /* must be CARDINAL(32) */
+            XChangeProperty(display, xd->window,
+                            XInternAtom(display, "_NET_WM_PID", False),
+                            XInternAtom(display, "CARDINAL", False), 32,
+                            PropModeReplace,
+                            (const unsigned char*) &mypid, 1);
+	    no_wm_pid:
+
 	    /* set up protocols so that window manager sends */
 	    /* me an event when user "destroys" window */
 	    _XA_WM_PROTOCOLS = XInternAtom(display, "WM_PROTOCOLS", 0);
@@ -2109,6 +2144,7 @@
     if (numX11Devices == 0)  {
 	int fd = ConnectionNumber(display);
 	/* Free Resources Here */
+	XDestroyWindow(display, group_leader);
 	while (nfonts--)
 	      R_XFreeFont(display, fontcache[nfonts].font);
 	nfonts = 0;
@@ -3133,6 +3169,9 @@
 #endif
     screen = DefaultScreen(display);
     rootwin = DefaultRootWindow(display);
+    group_leader = XCreateSimpleWindow(
+	display, rootwin, 0, 0, 1, 1, 0, 0, 0
+    );
     depth = DefaultDepth(display, screen);
     visual = DefaultVisual(display, screen);
     colormap = DefaultColormap(display, screen);
-----------------------------------8<-----------------------------------

-- 
Best regards,
Ivan

[*] 
https://gitlab.gnome.org/GNOME/libwnck/-/blob/master/libwnck/class-group.c
https://gitlab.gnome.org/GNOME/libwnck/-/blob/master/libwnck/window.c

[**]
https://gitlab.gnome.org/GNOME/gnome-shell/-/blob/4dfc53ca/src/shell-window-tracker.c#L371

[***]
https://specifications.freedesktop.org/wm-spec/1.3/ar01s05.html#idm45225103239616