Introduction

Book version: 0.4.0  ·  Last updated: 2026-05-05  ·  tracks egui_mobius v0.4.0

The book is live — it evolves alongside the framework. Each chapter footer notes the date of its last substantive revision. When egui_mobius ships v0.5.0, this book becomes 0.5.0.

This book is the know-how for building solid, professional GUI applications in Rust on top of egui and the egui_mobius framework. The framework is a workspace of coordinated crates that together make modern dockable, threaded, reactive UI cheap to assemble.

Citizens are plug-ins

The single most important idea in this book is that citizens are plug-ins. Once a panel implements the Citizen trait, it drops into any host app with a four-line integration: cargo add the crate, declare one Dynamic<T> field, add a TabKind variant, render it from the TabViewer. No glue code. Real apps grow by accumulating citizens, not by extending a core — and the Dispatcher is the registry those citizens register with.

egui_lens and egui_quill are the shipped examples; the same shape applies to future citizens, and to any third-party citizen on crates.io. This is what makes the ecosystem composable rather than just architecturally tidy.

CopperForge — a real-world egui_citizen + egui_dock application for PCB gerber inspection. Each docked region is a citizen-panel; the panels share state through reactive cells, and the 3D rendering thread is coordinated through the dispatcher.

Three levels of mobius-citizen apps

A mobius-citizen application sits at one of three levels, each adding capability without throwing away what came before:

• Level 1 — shared Dynamic<T> between panels; the dispatcher manages panel state. Examples: getting_started, citizen_dock.
• Level 2 — the dispatcher is extended to handle synchronous backend processing — filter, parser, anything in-process. Examples: filter_plotter, citizen_fetch.
• Level 3 — egui_mobius signals and slots wire the dispatcher to async / multi-threaded backends. Example: citizen_signal_async.

Levels 1–2 use egui_citizen and egui_mobius_reactive; level 3 brings in egui_mobius itself.

Who this book is for

Familiarity with egui, with dockable widgets — Qt's Advanced Docking Widgets or egui_dock directly — and with shared-memory threading concepts. If those are comfortable, the rest is just learning the pattern.

How to read this book

Background covers Dynamic<T>, egui_dock, and the vocabulary. Concepts cover the Citizen trait, the dispatcher, messages, and coupling. The Tutorial is a worked example end-to-end — you can go straight there and refer back to Concepts as needed. The book closes with patterns, common pitfalls, and a reference sheet.