(This is part of a larger series on finding your footing on Arch Linux.)
Last modified: 19 December 2022
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.
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
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" ];
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
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.
100) are opacity percentages; these are associated with a global X Window System class name
class_g and a focus state (
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
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...
xprop | grep "WM_CLASS"instead of
xpropto 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
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.conf is set up, I suggest launching
picom from the command line using the command
# Start picom as a daemon process picom -b
-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.
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
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
# 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 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…
You can set
picom’s rendering backend using the
backend setting in
picom.conf; your options are
xrender (the default) and
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
# 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
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
# 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