[X2Go-User] Windows x2go client displays at incorrect resolution

[Davis, Jean-Paul]

> > Session Type = MATE (automatically changes to "Custom desktop" with
> > command "MATE") Display = Fullscreen Set display DPI = 192
> >
> > The session starts just fine, filling the screen with the MATE
> > desktop, except that the display resolution is incorrect... with
> > following information obtained inside a MATE terminal:
> >
> > jpdavis: xdpyinfo | grep dots
> >
> >   resolution:    192x193 dots per inch
> >
> > jpdavis: ps -waux | grep $DISPLAY | grep x2goagent
> >
> > jpdavis  28204  0.2  0.3 217268 57696 ?        S    10:05   0:08
> > /usr/lib64/nx/../x2go/bin/x2goagent -nolisten tcp -nolisten tcp -dpi
> > 192 -D -auth /home/jpdavis/.Xauthority -name
> > X2GO-jpdavis-50-1491062721_stDMATE_dp32 :50
> >
> > jpdavis: xrandr --prop
> >
> > xrandr: Failed to get size of gamma for output default Screen 0:
> > minimum 320 x 240, current 1280 x 720, maximum 1920 x 1200 default
> > connected 1280x720+0+0 0mm x 0mm
> >
> > Thus the actual dpi being used by the display is 192*1280/2560 = 96,
> > not the 192 sent to x2goagent and reported by xdpyinfo.
> 
> Your x2goagent is running using the correct (forced) 192 dpi as specified via the
> command line. But your x2go window is much smaller than your native
> desktop.
> 
> I am not really sure what to do here. Maybe we should try to calculate the
> window size in mm, pass that to x2goagent and let it recalculate the dpi itself.

I didn't see any options to x2goagent for passing window size.  I actually get something much more reasonable when I DON'T specify a DPI (see attachments); then xdpyinfo reports dpi of 75x75 and size 1280x720, but xrandr still says maximum resolution is 1920x1200.

> 
> > attempting to change the resolution from inside the session...
> >
> > xrandr --size 1920x1200 works but keeps same actual dpi of 96 (so
> > desktop is larger than my screen)
> 
> I don't get that. How can the desktop become larger than the screen?
> The window size of your x2go session is the size of the xserver the MATE
> desktop sees. The dpi setting should - from my understanding - influence the
> selected fonts and maybe scaling, but not the overall size of the desktop.
> 
> Can you please provide some screen shots to minimize miunderstandings?

By "screen" I mean the physical laptop display panel.  I have attached three fullscreen (2560x1440) images (taken on the laptop using Windows Snipping Tool) to this e-mail, I don't know if they will show up in the mail list (if not, well unfortunately I don't have anywhere I can put them publicly to link to), but at least you should receive them.

Capture_x2go_default_setdpi192.PNG = case with client "set display dpi" turned on and equal to 192, in which the X session thinks the display is 1280x720 at 96 dpi.

Capture_x2go_1920x1200setdpi192.PNG = what I see after issuing the command "xrandr --size 1920x1200" in the session; this is what I meant by desktop larger than the physical screen.

Capture_x2go_default_nosetdpi.PNG = case with client "set display dpi" turned off, in which the X session still thinks the display is 1280x720 but at 75 dpi.  This is better than the forced-dpi=192 cases, but still doesn't look like it's actually using the full resolution of the laptop.

So with some more research I have learned that the apparent 96 dpi I'm seeing is actually forced by gdm via gnome-settings-daemon for all X sessions, as explained in the comments at https://git.gnome.org/browse/gnome-settings-daemon/tree/plugins/xsettings/gsd-xsettings-manager.c#n70.  On the server, Xorg.0.log shows that Xorg correctly finds resolution (3840x2160) and dpi (139x137) of the attached monitor; but xdpyinfo shows dpi=96.  Perhaps the remote X session generated by the x2go login is using the physical size of the laptop screen but with dpi=96 to arrive at 1280x720.  I believe that when I force dpi=192, gdm automatically applies a scaling of 2, which would explain why everything is so huge in that case.

One thing I don't understand very well is the relationship between X running on the x2go server machine and X (in this case VcXsrv) running on the x2go client machine.  I have toyed with the idea of putting an xrandr command in a display-specific script under /etc/gdm/ to set up the screen for my remote sessions (I only ever have one running, and it's always display :10), but I haven't actually tried this yet.

> Also, can you please retry using the current developer version of nx-libs as
> described here:
> http://wiki.x2go.org/doku.php/doc:howto:nx-libs-betatesting

I made an attempt at this using the instructions in the README file (https://github.com/ArcticaProject/nx-libs) to create rhel/centos/fedora rpms, but I got an error from the mock --buildsrpm command; I think I was supposed to actually build the libraries first (using make all), so I'll try that and report back.

Jean-Paul

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