Presenter mode in LibreOffice Impress without an external display

I typically use LibreOffice Impress for my talks, much to some folks' surprise. Yes, you can make slides look okay with free software! But there's one annoying caveat that has bothered me for ages.

Impress makes it nearly impossible to enter presenter mode with a single display, while also displaying slides. I have never understood this limitation, but it's existed for a minimum of seven years.

I've tried all sorts of workarounds over the years, including a macro that forces LibreOffice into presenter mode, which I never was able to figure out how to reverse once I ran it...

This has previously been an annoyance but never posed a big problem, because when push came to shove I could leave my house and use an external monitor or screen when presenting at meetups. But now, everything's virtual, I'm in lockdown indefinitely, and I don't have another display available at home. And about 8 hours before speaking at a meetup today, I realized I didn't have a way to share my slides while seeing my speaker notes. Uh oh.

So I got this stupid idea.

...why don't I just placate LibreOffice with a FAKE display?

Virtual displays with xrandr

My GPU had this capability innately, it turns out, if I could just whisper the right incantations to unlock its secrets:

ehashman@red-dot:~$ cat /usr/share/X11/xorg.conf.d/20-intel.conf 
Section "Device"
    Identifier "intelgpu0"
    Driver "intel"
    Option "VirtualHeads" "1"

After restarting X to allow this newly created config to take effect, I now could see two new virtual displays available for use:

ehashman@red-dot:~$ xrandr
Screen 0: minimum 8 x 8, current 3840 x 1080, maximum 32767 x 32767
eDP1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 310mm x 170mm
   1920x1080     60.01*+  59.93  
   640x360       59.84    59.32    60.00  
DP1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)
VIRTUAL2 disconnected (normal left inverted right x axis y axis)

Nice. Now, to actually use it:

ehashman@red-dot:~$ xrandr --addmode VIRTUAL1 1920x1080
ehashman@red-dot:~$ xrandr --output VIRTUAL1 --mode 1920x1080 --right-of eDP1

And indeed, after running these commands, I found myself with a virtual display, very happy to black hole all my windows, available to the imaginary right of my laptop screen.

This allowed me to mash that "Present" button in LibreOffice and get my presenter notes on my laptop display, while putting my actual slides in a virtual time-out that I could still screenshare!

Wouldn't it be nice if LibreOffice just fixed the actual bug? 🤷

Well, actually...

I must forgive myself for my stage panic. The talk ended up going great, and the immediate problem was solved. But it turns out this bug has been addressed upstream! It's just... not well-documented.

A couple years ago, there was a forum post on that featured this exact question, and a solution was provided!

Yes, use Open Expert Configuration via Tools > Options > LibreOffice > Advanced. Search for StartAlways. You should get a node org.openoffice.Office.PresenterScreen with line Presenter. Double-click that line to toggle the boolean value to true.

I tested this out locally and... yeah that works. But it turns out the bug from 2013 had not been updated with this solution until just a few months ago.

There are very limited search results for this configuration property. I wish this was much better documented. But so it goes with free software; here's a hack and a real solution as we all try to improve things :)