trying to fix

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+
+         
+         <p>I have been running a dual monitor setup on my laptop for about a month
+or so.  This is a Lenovo ThinkPad X220 with a display resolution of
+1366x768.  I connect to it a 1920x1080 monitor via the VGA port.  It
+enables me to configure <a href="https://gitlab.com/protesilaos/dotfiles">my custom working
+environment</a> to have separate
+virtual desktops per display, which I consider a major productivity
+boost to an already efficient workflow.</p>
+
+<p>All was good. The one annoyance I had since the very beginning was the
+display manager (<code>lightdm</code>) not adapting to my hardware automagically
+(the display manager basically is the program that runs the login screen
+and handles user sessions).  I could not find a way to instruct it to
+use my monitors in the way I had laid them out, with the appropriate
+settings for each.</p>
+
+<p>This is no more.  Today I discovered a solution which, in hindsight, is
+obvious.  LightDM can execute a script at startup.  The exact same
+command I use to configure dual monitors on <code>bspwm</code> can be used by
+<code>lightdm</code>.</p>
+
+<h2>Script to set the correct Xrandr output</h2>
+
+<p>Here is the gist of my admittedly simplistic script in its current iteration.</p>
+
+<p class="warn">I might modify it further, so if you are reading this at a future date, better
+consult <a href="https://gitlab.com/protesilaos/dotfiles">my dotfiles</a>, specifically
+the items inside the “bin” directory.</p>
+
+<pre><code>#!/bin/bash
+
+# ... text goes here (see actual file)...
+
+# set variable with the command we need to evaluate
+my_laptop_external_monitor=$(xrandr --query | grep 'VGA1 connected')
+
+# If the VGA1 port connects to a monitor, the output of the variable
+# will not be empty.  In which case it is assumed that I am using my
+# secondary display, whose resolution I know in advance.  If the
+# variable is empty, then no external monitor is connected.
+#
+# This is a simplistic approach which will not work if the external
+# monitor has another resolution.  It will also fail if executed from
+# another machine, say, another laptop that uses an HDMI connection
+# instead.
+if [ -n "$my_laptop_external_monitor" ]; then
+	xrandr --output LVDS1 --primary --mode 1366x768 --rotate normal \
+	--output VGA1 --mode 1920x1080 --rotate normal --right-of LVDS1
+else
+	xrandr --output LVDS1 --mode 1366x768
+fi
+</code></pre>
+
+<p>I put this in a file inside my local “bin” directory, which I then make
+executable with <code>chmod +x</code> (my <code>~/bin</code> is included in the <code>$PATH</code>—see my
+dotfiles).</p>
+
+<h2>Edit the LightDM configuration file</h2>
+
+<p>On Debian we need to edit <code>/etc/lightdm/lightdm.conf</code>, which requires
+root privileges.  But first, make a backup of that file in case things
+go awry.</p>
+
+<p>Now search for <code>display-setup-script=</code>.  It should be commented out
+(preceded by a <code>#</code>) and should have nothing following the equal sign.
+This option is found under the settings heading for <code>[Seat:*]</code>.
+Uncomment it by removing the column sign at the beginning of the line.
+Then add the absolute path to the aforementioned script.</p>
+
+<p>For example:</p>
+
+<pre><code>[Seat:*]
+# other
+# options
+display-setup-script=/home/prot/bin/own_script_laptop_dual_monitor
+# more
+# options
+</code></pre>
+
+<p>Done!  LightDM now works the way I like it.  It presents the login
+window and top panel on the monitor where the mouse cursor is on.  If
+the cursor moves to the other monitor, so does the interface.  The
+inactive screen only displays the wallpaper.</p>
+
+<h2>An opportunity to simplify and refine my setup</h2>
+
+<p>Figuring out this fix provided a unique opportunity to revisit the
+scripts I had initially developed.  I found some errors and duplication
+of work, which I promptly addressed.</p>
+
+<p>If you have come across a similar problem, please make sure you do not
+copy-paste without understanding the meaning of these commands.  Also
+note that the script presented herein is not designed to work in a
+variety of multihead setups with arbitrary resolutions and a wide range
+of possible combinations.  I know my hardware: this only caters to my
+specific use case.</p>
+
+<p>That granted, feel free to <a href="https://protesilaos.com/contact/">contact me</a> in case you think I
+can help you adapt this to your system.</p>
+        
+