Picom — Lightweight X11 Compositor with Animation Support

Introduction

Picom is a standalone compositor for X11, forked from Compton. It adds visual effects like transparency, shadows, blur, and rounded corners to windows managed by any window manager. Picom is the go-to compositor for tiling WM users who want a polished desktop without switching to a full compositing WM.

What Picom Does

• Composites X11 windows with true transparency and opacity control
• Renders drop shadows behind windows with configurable radius and offset
• Applies background blur (Gaussian or dual-Kawase) behind transparent windows
• Draws rounded corners on window frames
• Supports window animations for open, close, and workspace transitions

Architecture Overview

Picom uses the X Composite extension to redirect window rendering into offscreen pixmaps, then composites them onto the root window. It supports multiple backends: xrender (CPU-based), GLX (OpenGL), and the newer EGL backend. The animation system interpolates window geometry and opacity between states using configurable curves.

Self-Hosting & Configuration

• Config file at ~/.config/picom/picom.conf using a simple key-value format
• Set shadow = true, shadow-radius, and shadow-offset-x/y for shadows
• Configure blur with blur-method = "dual_kawase" and blur-strength
• Use corner-radius for rounded window corners
• Define window rules with opacity-rule and shadow-exclude using WM class matching

Key Features

• Multiple backends: xrender, GLX, and EGL for different hardware profiles
• Dual-Kawase blur: efficient real-time background blur algorithm
• Animation support: smooth transitions for window open/close/move
• Per-window rules: set opacity, shadow, and blur exceptions by window class
• VSync: tear-free rendering with configurable sync strategies

Comparison with Similar Tools

• Compiz — older compositing WM with many effects; heavier and less maintained
• xcompmgr — minimal X11 compositor; no blur, rounded corners, or animations
• KWin — KDE compositor; full desktop integration, not standalone
• Mutter — GNOME compositor; tied to the GNOME desktop
• Hyprland — Wayland compositor with built-in effects; not X11

FAQ

Q: Does Picom work on Wayland? A: No. Picom is X11-only. On Wayland, compositing is handled by the compositor itself (Sway, Hyprland).

Q: How do I fix screen tearing with Picom? A: Enable VSync with vsync = true and try the GLX or EGL backend for best results.

Q: Can I disable effects for specific applications? A: Yes. Use shadow-exclude, opacity-rule, and blur-background-exclude with window class or name matching.

Q: What is the difference between GLX and EGL backends? A: EGL is the newer, preferred backend with better Wayland compatibility foundations. GLX is the legacy OpenGL path, still useful on older drivers.

Sources

• https://github.com/yshui/picom
• https://wiki.archlinux.org/title/Picom