Dual monitor setup with BSPWM and Polybar

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A few months ago, I provided a detailed guide on how to set up BSPWM on Debian Sid. Several things have changed since then. Most notable among them is that I got hand of a second monitor that I promptly incorporated in my workflow. Here I document the adaptations I had to make, while concluding with my first impressions of what I got (plus a screen shot).

The code samples presented herein are representative of my setup as of 2018-09-21. If you are reading this at a future date, chances are I have introduced changes. In such a case, you might want to browse through my dotfiles, and/or contact me.

Let X know about the monitors

The display server needs to be configured in a way that mirrors the physical layout of the monitors. My primary monitor is the one that is built into my laptop, the Lenovo X220. The external monitor connects via a VGA port and is positioned to the right of the laptop.

The xrandr utility helps us identify the available connected monitors, or “outputs”, with the command xrandr -q.

What I get from that:

xrandr -q

Screen 0: minimum 8 x 8, current 3286 x 1080, maximum 32767 x 32767
LVDS1 connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 280mm x 160mm
   1366x768      60.00*+
   1360x768      59.96
   1280x720      59.86    60.00    59.74
   1024x768      60.00
   1024x576      60.00    59.90    59.82
   960x540       60.00    59.63    59.82
   800x600       60.32    56.25
   864x486       60.00    59.92    59.57
   640x480       59.94
   720x405       59.51    60.00    58.99
   680x384       60.00
   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)
DP3 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)
HDMI3 disconnected (normal left inverted right x axis y axis)
VGA1 connected 1920x1080+1366+0 (normal left inverted right x axis y axis) 480mm x 270mm
   1920x1080     60.00*+
   1680x1050     59.95
   1600x900      60.00
   1280x1024     75.02    60.02
   1440x900      59.89
   1280x800      59.81
   1152x864      75.00
   1280x720      60.00
   1024x768      75.03    70.07    60.00
   832x624       74.55
   800x600       72.19    75.00    60.32    56.25
   640x480       75.00    72.81    66.67    59.94
   720x400       70.08
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

And by including only the ones that are connected, I have:

xrandr -q | grep -w connected

LVDS1 connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 280mm x 160mm
VGA1 connected 1920x1080+1366+0 (normal left inverted right x axis y axis) 480mm x 270mm

As such, my two monitors are named LVDS1, which is the primary one on the laptop, and VGA1 for the external one.

What I want to do with this piece of information is tell the X display server to configure my monitors appropriately whenever I launch a BSPWM session. Here is the xrandr command:

xrandr --output LVDS1 --primary --mode 1366x768 --rotate normal --output VGA1 --mode 1920x1080 --rotate normal --right-of LVDS1

Auto starting inside BSPWM

Now I want to have some basic shell scripting in place, to check whether the external monitor is actually connected to the laptop.

First, this snippet is included in my bspwmrc:

# run the xrandr command if an external monitor is connected to the
# laptop.  This must be executed before the polybar command, so that
# polybar can set the two separate bars properly.
if [ -x $HOME/bin/own_script_bspwm_laptop_dual_monitor ];then
    own_script_bspwm_laptop_dual_monitor
fi

And here is the content of that command:

#!/bin/bash

# set up the two monitors for bspwm
# NOTE This is a simplistic approach because I already know the settings I
# want to apply.
my_laptop_external_monitor=$(xrandr --query | grep 'VGA1')
if [[ $my_laptop_external_monitor = *connected* ]]; then
    xrandr --output LVDS1 --primary --mode 1366x768 --rotate normal --output VGA1 --mode 1920x1080 --rotate normal --right-of LVDS1
fi

Maybe there are some things that could be done more efficiently, but this seems to work for the time being.

Per monitor workspaces

In BSPWM each monitor contains desktops, or else workspaces. While each workspace indicates a binary tree with nodes—basically windows in their given arrangement.

To have specific workspaces on each monitor, add this to bspwmrc:

bspc monitor LVDS1 -d 1 2 3 4 5
bspc monitor VGA1 -d 6 7 8 9 0

Note the names of the monitors, as where recognised by xrandr.

Now, when switching to desktops 1…5 the focus is on the primary monitor, while 6…0 on the second one.

Almost done.

Run two separate bars with polybar

The reason I want two bars is to display information about the workspaces that are occupied on a per monitor basis. Besides, this opens up the possibility for fine grained control where, say, the laptop’s bar shows the xbacklight powered brightness level of the screen, while the external monitor’s bar has no use of such a module (it does not use xbacklight).

There are two parts to tackling this:

Define the two bars in the polybar configuration file.
Launch the second bar, if the external monitor is connected.

Configs for the two bars

Here are only the relevant parts from the polybar config. Refer to my dotfiles, specifically the contents of the “bspwm” and “polybar” directories for my actual configuration files.

[bar/top]
bottom = false
monitor = LVDS1

modules-left = bspwm mpd
modules-right = keyboard battery backlight temperature volume datetime powermenu

[bar/top_external]
bottom = false
monitor = VGA1

modules-left = bspwm mpd
modules-right = keyboard volume datetime powermenu

The module that requires attention is the one about bspwm. The following makes sure that each bar displays only the workspaces assigned to the given monitor.

[module/bspwm]
type = internal/bspwm

pin-workspaces = true

Again, these are not the full configs. Just the absolutely necessary parts. With them in place, polybar will show information about the occupied workspaces of each monitor. As such, the top_external bar will only include workspaces 6…0, while top will have 1…5, as per the settings in bspwmrc.

Launch the two bars on startup

This is my current script for calling polybar:

#!/usr/bin/env sh

# Terminate already running bar instances
killall -q polybar

# Wait until the processes have been shut down
while pgrep -u $UID -x polybar >/dev/null; do sleep 1; done

# Launch bar
polybar top &

my_laptop_external_monitor=$(xrandr --query | grep 'VGA1')
if [[ $my_laptop_external_monitor = *connected* ]]; then
    polybar top_external &
fi

You will notice the same conditional statement at the end which I used above to run xrandr if necessary. This script is now auto started from within bspwmrc, after the script that configures the layout of the monitors. The sequence is absolutely critical, otherwise polybar is not made aware of the two monitors and fails to position them properly.

# NOTE the path to the polybar executable.  This is the default location
# when compiling from source.
if [ -x /usr/local/bin/polybar ]; then
	bash $HOME/.config/polybar/launch.sh
fi

Putting it all together, the “autostart” section of my bspwmrc looks like this:

# autostart
# ============================

sxhkd &
xrdb -merge $HOME/.Xresources

# run the xrandr command if an external monitor is connected to the
# laptop.  This must be executed before the polybar command, so that
# polybar can set the two separate bars properly.
if [ -x bin/own_script_bspwm_laptop_dual_monitor ];then
    own_script_bspwm_laptop_dual_monitor
fi

# NOTE the path to the polybar executable.  This is the default location
# when compiling from source.
if [ -x /usr/local/bin/polybar ]; then
    bash $HOME/.config/polybar/launch.sh
fi

First impressions

I had never used a dual monitor setup before. I had no notion of what to expect. As such, I cautiously started out with a GNOME session to see how a major Desktop Environment handles things. In GNOME, the second monitor is basically a continuation of the current workspace, with no apparent way of turning the two monitors into standalone environments. I do not like that. I much prefer BSPWM’s approach where monitors contain separate workspaces. Furthermore, GNOME does not show the activities overview and the top bar in both monitors, which introduces friction to the kind of workflow I envision.

Whereas a multiheaded BSPWM is a joy to work with. Apart from the above configurations, I did not have to change any of my key bindings to have everything function as required. Switching to a virtual desktop will shift the focus to the corresponding monitor. Great! And yet, while workspaces are divided between monitors, window switching still follows an intuitive scheme of treating the two monitors as a unified space. Put concretely, if I start from a focused window on the left of the primary display and keep shifting focus to the right, I eventually ‘cross over’ to the second monitor on whatever node is displayed there. Same with the commands that swap the position of two nodes. I guess this is the best of both worlds: actually separate, visually contiguous.

That granted, this is just my first day on this setup. Things are likely to change as I continue tinkering with the various options.

On a final note, running a bespoke environment such as my BSPWM-based setup admittedly has a higher barrier to entry than the likes of the major DEs, with the upside of a potentially superior experience.