picom
(This is part of a larger series on finding your footing on Arch Linux.)
Last modified: 13 July 2024
Goal: Use the picom
compositor to make unfocused window backgrounds slightly transparent, so you can enjoy your background wallpaper.
Dependencies: This guide works on the X Window System. You should first set up X if you have not yet done so.
References:
man picom
Example: Here’s my own computer screen while writing this web page:
The window manager is i3-gaps; you can find the wallpaper on r/wallpaper at the time of writing.
You can set window transparency (and many other “eye candy” features like blurring, shadows, rounded corners, etc.) using a tool called a compositor.
This guide will use the popular picom
compositor and covers only transparency.
First install the picom
package, then make a copy of the default config file as a starting point for your own configuration:
sudo pacman -S picom
cp /etc/xdg/picom.conf ~/.config/picom/picom.conf
The default picom.conf
is quite verbose, with a lot of explanatory comments.
You can locate the transparency part by searching for Transparency
(this begins on line 100 at the time of writing); the relevant lines are
# Default opacity of active windows.
active-opacity = 1.0;
# Default opacity of inactive windows.
inactive-opacity = 1.0;
# Opacity of window titlebars and borders.
frame-opacity = 1.0;
# Application-specific settings; these override the default `active-opacity`
opacity-rule = [
"95:class_g = 'Alacritty' && focused",
"80:class_g = 'Alacritty' && !focused"
];
Note that picom
works in terms of opacity instead of transparency; 1.0
is complete opacity (and no transparency); 0.0
is zero opacity (and complete transparency).
Setting a global opacity for all windows is as simple as tweaking the values of active-opacity
, inactive-opacity
, and frame-opacity
to your liking.
You can try something close to 1.0
for active windows, and something more transparent, perhaps 0.5
, for inactive windows.
If you want more customizability, the next section shows how to set specific opacities for specific window classes (read: applications).
Use case: make your terminal emulator more transparent than your web browser (for example).
The application-specific opacity syntax in the picom.conf
file looks like this:
# Application-specific settings; these override the default `active-opacity`
opacity-rule = [
# Makes Alacritty 95% opaque when focused...
"95:class_g = 'Alacritty' && focused",
# ... and 40% opaque when not focused.
"40:class_g = 'Alacritty' && !focused",
];
The numbers (e.g. 95
, 40
, 100
) are opacity percentages; these are associated with a global X Window System class name class_g
and a focus state (focused
or !focused
).
You can find a window’s class name by running xprop
from the command line and clicking on clicking on target window (xprop
displays the window’s X properties);
then search the xprop
output for the WM_CLASS(STRING)
property, which will show the window class name you should use with picom
.
Here is an example xprop
output on my computer for Alacritty terminal windows:
$ xprop
# *clicks on an Alacritty terminal window*
WM_HINTS(WM_HINTS):
_NET_WM_DESKTOP(CARDINAL) = 1
# ...irrelevant output omitted...
_NET_WM_PID(CARDINAL) = 34016
WM_CLASS(STRING) = "Alacritty", "Alacritty"
# ...irrelevant output omitted...
Tips:
xprop | grep "WM_CLASS"
instead of xprop
to show only the window class name.WM_CLASS(STRING)
are different, use the second one.Once you know a window’s class name, you can then assign custom opacity settings using the opacity-rule
key in picom.conf
.
Here are some more examples:
# Application-specific settings; these override the default `active-opacity`
opacity-rule = [
"100:class_g = 'Zathura' && focused",
"80:class_g = 'Zathura' && !focused",
"100:class_g = 'firefox' && focused",
"80:class_g = 'firefox' && !focused",
];
For the transparency features to take effect, you just have to launch picom
.
picom
Once your picom.conf
is set up, I suggest launching picom
from the command line using the command
# Start picom as a daemon process
picom -b
Using the -b
flag starts picom
as a daemon process that forks to the background after initialization.
This has two practical benefits: the picom
process won’t freeze up the shell you ran it from, and the process will survive (i.e. picom
will continue running) even if you close the shell you started it from.
Tip: picom
performs live updates when you write changes to your picom.conf
file, so you can experiment with tweaks to your config without having to manually restart picom
.
You can use the same picom -b
command to autostart picom
when you launch a new X session (i.e. to avoid having to open up a terminal and typing picom -b
manually).
I recommend placing the autostart command in your window manager or desktop environment’s config file.
The details depend on your WM or DE; for the i3 window manager, for example, you would place the following line in your ~/.config/i3/config
file:
# Autostart picom when starting the i3 window manager
exec_always --no-startup-id picom -b
See ArchWiki: Autostarting for how to autostart processes on other WMs and DEs.
picom
featuresThe picom
compositor offers window background blurring, shadows, fading, and rounded corners in addition to opacity settings.
I have intentionally covered only opacity in this guide, but wanted to at least give some pointers to anyone interested in other features. For…
picom.conf
for “Background-Blurring”;picom.conf
for “Shadows”;picom.conf
for “Fading”;picom.conf
for “Corners”.You can set picom
’s rendering backend using the backend
setting in picom.conf
; your options are xrender
(the default) and glx
.
xrender
uses the X Render extension, which is built-in to the X Window System.
It is stable and reliable for transparency, but not suitable for rendering blurred windows.
glx
uses OpenGL.
It handles blur, color inversion, and other “fancy” compositing features much better than xrender
, but requires (quoting from man picom
) proper OpenGL 2.0 support from your driver and hardware.
I suggest sticking with the default backend = xrender
if you only need window transparency, and setting backend = glx
only if you have OpenGL set up and want blurred windows.
If you are using glx
and window blurring, here are some potentially useful picom.conf
settings:
# Search picom.conf for "General Settings"
backend = "glx";
glx-no-stencil = true;
# Search picom.conf for "Background-Blurring"
blur-background = true;
blur-method = "dual_kawase";
# Set blur-size, blur-strength, and other settings as needed.
Blur settings are documented in the BLUR
section of man picom
;
using glx-no-stencil
may increase performance; search man picom
for glx-no-stencil
for details.
For better performance and a more minimalistic setup you can disable all features except window opacity by placing the following in your picom.conf
:
# Disable background blur; search picom.conf for "Background-Blurring" for details
blur-background = false;
# Disable background blur; search picom.conf for "Shadows" for details
shadow = false
# Disable window fading; search picom.conf for "Fading" for details
fading = false
# Disable rounded window corners; search picom.conf for "Corners" for details
corner-radius = 0
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