egui

Immediate-mode GUIs in Rust with egui and eframe - fast iteration for tools, inspectors, and utilities.

Recipe

eframe::run_native(
    "My Tool",
    eframe::NativeOptions::default(),
    Box::new(|cc| {
        egui_extras::install_image_loaders(&cc.egui_ctx);
        Ok(Box::new(MyApp::default()))
    }),
)?;

When to reach for this:

• Internal dev tools and live data visualizers
• Game engine debug UI (pairs with Bevy bevy_egui)
• Prototyping layouts without CSS/HTML
• Apps prioritizing developer speed over native look

Working Example

struct MyApp {
    name: String,
    age: u32,
}
 
impl Default for MyApp {
    fn default() -> Self {
        Self {
            name: "Alice".into(),
            age: 30,
        }
    }
}
 
impl eframe::App for MyApp {
    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
        egui::CentralPanel::default().show(ctx, |ui| {
            ui.heading("Profile");
            ui.text_edit_singleline(&mut self.name);
            ui.add(egui::Slider::new(&mut self.age, 0..=120));
            if ui.button("Greet").clicked() {
                println!("Hello {}, age {}", self.name, self.age);
            }
        });
    }
}

What this demonstrates:

• Mutable app state on self each frame
• Standard widgets: text edit, slider, button
• Central panel layout baseline

Deep Dive

How It Works

• Each frame: input events -> update -> layout widgets -> paint.
• Widget IDs derived from memory locations and labels - stable IDs matter for focus.
• Context requests repaint when animations or async data arrive.
• Textures and fonts managed by egui atlas.

Immediate vs Retained

Gotchas

• Heavy work in update - drops frames. Fix: compute in background thread, poll results via channel.
• Unstable widget IDs - focus jumps. Fix: ui.push_id for dynamic lists.
• Not accessibility-first - screen reader support limited vs native toolkits. Fix: choose iced/Tauri for a11y-critical apps.
• High DPI scaling - verify on retina displays; set pixels_per_point appropriately.
• Default fonts and CJK - load custom font bytes for non-Latin scripts.

Alternatives

FAQs

Related

• GUI Basics - egui intro example
• State & Architecture - scaling state
• iced - retained alternative
• Packaging & Distribution - ship binary

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.