About the top panel
The panel that appears at the uppermost side of the viewport is drawn by
lemonbar. This is a beautifully simple tool. On the face of it, all
it does is place an empty bar at either the top (default) or bottom of
the screen, while offering a syntax for formatting any output it may
display. It is up to the user to add content to it.
This is where my melonpanel comes into play. It is a shell script
that fetches and parses some useful information about the system and the
running session, and lays it on the bar. Each snippet of info is
internally referred to as a “module” and has its own dedicated logic
inside the script.
The modules are the following:
- BSPWM report about the workspaces, nodes, their flags and state (see next section about it).
- Battery status and current capacity.
- Speaker volume strength and status.
- Active keyboard layout.
- Date and time.
This is what a module looks like:
# Battery status: charging (c), discharging (d), full (f), unknown (?).
battery_status() {
local battery_path battery_status battery_label battery_output
battery_path='/sys/class/power_supply/BAT0'
battery_output=$(sed 1q $battery_path/capacity)
battery_status="$(sed 1q $battery_path/status)"
battery_label='Bat'
if [ -d "$battery_path" ]; then
case "$battery_status" in
'Charging')
echo "%{F$color14}$battery_label <c>%{F-} ${battery_output}%"
;;
'Discharging')
case "$battery_output" in
1[0-9])
echo "%{F$color1}$battery_label <d>%{F-} ${battery_output}%"
;;
[0-9])
echo "%{B$color1}%{F$background} $battery_label ${battery_output}% %{F-}%{B-}"
;;
*)
echo "%{F$color11}$battery_label <d>%{F-} ${battery_output}%"
;;
esac
;;
'Full')
echo "%{F$color2}$battery_label%{F-} Full"
;;
*)
echo "%{F$color3}$battery_label <?>%{F-} ${battery_output}%"
;;
esac
else
echo ''
fi
}
How the modules are placed on the panel
All modules will grab some piece of text and clean it up so that it
looks nice on the panel. However, each individual module does not
output directly to the named pipe where the data is read from.
Instead, all modules are called from my_modules(), which I need to
explain a bit:
my_modules() {
while true; do
echo "B" "$(battery_status)"
echo "D" "$(date +'%a %d %b %H:%M')"
echo "K" "$(keyboard_layout)"
echo "V" "$(volume_status)"
sleep 1s
done
}
You will notice that each individual item echoes a majuscule and then
the output of the module it references. These capital letters are
important because they demarcate each set of data in the named pipe,
making it possible to put the right thing in the right place. We see
this in practice at melonpanel(), specifically this part:
while read -r line ; do
case $line in
B*)
# battery status
bat="${line#?}"
;;
D*)
# current date and time
date="${line#?}"
;;
K*)
# keyboard layout (en or gr)
key="${line#?}"
;;
V*)
# volume level
vol="${line#?}"
;;
What this does is identify the part that contains the data of each module and assign a variable to it. The variables are then placed on the panel with the following:
panel_layout() {
echo "%{l}$wm%{r}$bat $vol $key $date "
}
Focus on the content of the echo. The syntax %{l} places things on
the left, while %{r} aligns them to the right (this notation is
provided by lemonbar—see its manpage).
I believe this pretty much covers the essentials of how melonpanel is
designed. As with all my scripts, this too is heavily documented. So
do read it. That granted, I admit that lemonbar is not the most
user-friendly program out there.
The BSPWM module
On the left side of the panel lies the set of indicators that report on
the status of the window manager (based on the output of the command
bspc subscribe report). This is what you see when starting the
session (note that I have taken care to use the appropriate spacing, so
that all typographic elements are evenly spread out):
[1] 2 3 4 5 6 *
The numbers correspond to the names of the available desktops. While
the desktop inside square brackets is the current one. As shown below,
the asterisk is a placeholder for the layout of the current desktop.
It displays the letter M when monocle is toggled on. The layout
cycles between tiled and monocle, but because the former is what we
normally use, I have opted to hide the T behind the asterisk and only
display the M.
[1] 2 3 4 5 6 M
If you open a window, another asterisk will be appended to the module.
This one is a placeholder for the active node’s flags. The flags
I define in my sxhkdrc are: Sticky, Private, Locked (see man bspc
for their meaning). When a flag for the current node is active, its
first letter is displayed on the panel. More than one flags can be
activated at once. Such as:
[1] 2 3 4 5 6 * SPL
Other indicators concern occupied and urgent desktops that are not already in focus. For example, the following means that desktop 2 holds nodes, while 1 is focused:
[1] 2^ 3 4 5 6 * *
While urgent and unfocused desktops are denoted thus and are coloured red:
[1] 2# 3 4 5 6 * *
On multi head setups, the BSPWM report will divide desktops and their corresponding indicators per monitor. Combined with the above, we get the following:
[1] 2^ 3 * L 4- 5# 6 M SP
Notice how the indicators that display the * (asterisk) are visible
for each set of desktops. Also look at the use of another indicator,
the - (hyphen), for showing the focused desktop on the unfocused
monitor: desktop 4. The letter M in this case concerns desktop 4.
Same with the node flags S and P. While L applies to the focused
node in desktop 1 and the asterisk next to it informs us that the layout
is the default, i.e. tiled.
I believe all this will become easier to grasp once you start using the
system. For the record, this design bears close resemblance to the
status line of my tmux setup.
Panel transparency
By default, the panel is opaque, though I have made it fairly trivial to
add a transparency effect to its background. The following is an
excerpt from the relevant melonpanel section:
melonpanel < "$melonpanel_fifo" | lemonbar -u 1 -p -g "x${melonpanel_height}" \
-F "$foreground" -B "#ff${background:1}" -f "$melonpanel_font" -n "Melonpanel" &
Taken a closer look at the segment of the command that controls the
background colour: -B "#ff${background:1}". I have designed so that
you can tweak its alpha value, which is governed by the ff part. This
is hexadecimal notation and means that the alpha channel is set to full,
which translates into complete opacity. 00 is the opposite.
Try replacing ff with aa to get some subtle transparency, or with
55 for a more pronounced effect. Possible values for each digit are:
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f.
As a rule of thumb, light themes will require a greater adjustment than dark themes to create a noticeable see-through style. The choice of wallpaper will also affect your perception of it.
For changes to be applied, reload the panel with the key chord chain
super + e ; p (as explained in the chapter about the basics of my
BSPWM). Otherwise, you can always just use tempusmenu to switch to
another Tempus theme (as discussed in the chapter about my themes), thus
forcing a panel reload.
Known issues
Sometimes, seemingly at random, the panel will not be hidden when
entering a window’s full screen view. The less-than-ideal workaround is
to reload melonpanel with the key chord chain super + e ; p. This
seems to be an upstream bug.
Another thing to bear in mind is that lemonbar does not support
proportional or outline fonts (e.g. the “DejaVu” family). It can only
display fixed-size, else bitmap, typefaces such as “Terminus”. If you
have followed the instructions in the chapter about installing the core
packages, you will have xfonts-terminus available on your system.
This is an optional dependency, as the panel will fall back to the
fixed typeface which comes pre-installed with Debian. I just think
that Terminus is more consistent and is better suited for such a UI
task.
Finally, I have noticed that pgrep melonpanel always lists two running
processes. I have not been able to troubleshoot this problem just yet,
assuming it is a “problem” to begin with, given that pgrep tmux gives
two results as well (any help is much appreciated).
At any rate, this is the load on my system while using my custom desktop
session (with compton and mate-settings-daemon active), with
a single terminal that runs tmux, plus mpd playing music:
~ $ free -mt
total used free shared buff/cache available
Mem: 3829 310 2990 59 528 3234
Swap: 3979 0 3979
Total: 7809 310 6970