Picom

Picom
Name	Picom
Developer	Leena Postnova; community contributors
Released	2018
Latest release	2024
Programming language	C (programming language), Xlib
Operating system	Linux, FreeBSD, OpenBSD
Genre	Compositor
License	MIT License

Picom Picom is a lightweight standalone compositor for the X Window System designed to provide window compositing, shadows, translucency, and other desktop visual effects for environments that use X.Org Server or related display servers. Picom originated as a fork of earlier compositors to address performance, configuration flexibility, and compatibility across a variety of Linux distributions and window managers such as i3 and Openbox. The project is maintained by a distributed set of contributors and is commonly packaged by maintainers of distributions like Arch Linux, Debian, and Fedora.

Overview

Picom implements compositing for X11-based sessions, integrating with display servers such as X.Org Server and running alongside window managers including i3, bspwm, awesome, and fluxbox. It provides effects similar to those offered by compositors in desktop environments like GNOME and KDE Plasma, while remaining usable with lightweight setups that prefer tools like xmonad, herbstluftwm, or ratpoison. Picom features options for drop shadows, fading, transparency, blur, and vsync, and exposes configuration through text files compatible with package managers used in Ubuntu, Arch Linux, and Gentoo Linux.

History and Development

Picom began as a fork intended to continue development after stagnation in predecessor projects derived from xcompmgr and compton. The lineage traces from xcompmgr to compton, with community-driven efforts leading to forks and patches maintained by contributors associated with projects hosted on platforms like GitHub and GitLab. Key milestones include adoption of backends supporting Xrender and OpenGL through GLX, integration of experimental blur algorithms, and fixes for issues reported by users of desktop stacks such as LXQt and MATE. Development has been driven by bug reports from distributions like Arch Linux and collaboration with maintainers of window managers including dwm and Xfce.

Features and Architecture

Picom supports multiple backends including the Xrender backend and hardware-accelerated backends using GLX and OpenGL extensions. It offers configurable features: adjustable shadows, window fading, opacity rules, blur via techniques such as kernel convolution, and compositor-managed vsync to mitigate tearing with display servers like X.Org Server. Picom’s architecture separates configuration parsing from compositing loops and uses event handling from Xlib to respond to window mapping, unmapping, and damage events emitted by compositing managers and window managers like i3 or Openbox. Optional modules allow support for natively accelerated blur that can interact with GPU drivers such as Mesa and proprietary drivers from NVIDIA.

Configuration and Usage

Picom is configured primarily via a text file often placed in user directories managed by standards from freedesktop.org, and distributions typically provide example configuration snippets for integration with window managers such as i3, bspwm, and herbstluftwm. Common command-line flags allow selection of the backend (e.g., --backend glx), toggle for experimental features, and control of parameters like shadow radius, blur strength, and frame-rate limiting to coordinate with compositors in GNOME or KDE Plasma. Users often launch Picom from session startup scripts used by display managers like LightDM or SDDM or from initialisation files managed by shells such as bash and zsh. Configuration includes rules keyed to window roles from toolkits like GTK and Qt, enabling tailored opacity for applications such as Firefox, Chromium, or GIMP.

Performance and Compatibility

Performance of Picom depends on the chosen backend, GPU driver stack, and interaction with window managers such as i3 and awesome. The GLX backend typically provides superior frame rates on systems with modern Mesa drivers or NVIDIA proprietary drivers, while the Xrender backend offers broader compatibility with legacy hardware found in systems running Debian stable. Picom includes tuning parameters to limit CPU usage, avoid compositing on fullscreen or video windows from applications like VLC media player or mpv, and reduce tearing in environments managed by display servers like X.Org Server.

Security and Bugs

As a userspace compositor interacting with X11 protocol events, Picom has historically been subject to issues reported via trackers hosted on GitHub and advisory mailing lists associated with distributions like Debian and Fedora. Notable classes of bugs include crashes triggered by malformed window properties from toolkits such as GTK or Qt, driver-specific rendering faults with NVIDIA or AMD stacks, and race conditions exposed by tiling window managers like i3. Security concerns are typically low-level and relate to robustness rather than privilege escalation; maintainers follow best practices for patch submissions via code review systems used by projects in the Free and Open Source Software ecosystem.

Adoption and Integration

Picom is widely adopted in the tiling and stacking window manager communities, with packages maintained for distributions including Arch Linux, Ubuntu, Debian, Fedora, Gentoo Linux, and openSUSE. It integrates with desktop utilities such as Nitrogen for wallpaper management and compton-conf-style configuration frontends, and is frequently recommended alongside compositing-aware utilities like xrandr and xprop. Picom’s lightweight footprint makes it popular for users of minimalist setups featuring window managers like i3, bspwm, dwm, and for those customizing environments on hardware ranging from laptops by Lenovo and Dell to single-board computers like the Raspberry Pi.

Category:Compositors