Egui – An immediate mode GUI written in Rust

Original Article ↗ Hacker News Discussion ↗

Use cases and strengths

  • Used for a wide range of tools: data viewers, scientific sims, CAD-like tools, photo/glitch art editors, plasmid editors, embedded-device configuration UIs, and game overlays.
  • Integrates with game engines (e.g., via Bevy bindings) and is seen as especially suitable for in-game/2D overlays on 3D rendering.
  • Popular for “scrappy prototypes” and small cross‑platform utilities, including browser builds via WebAssembly.
  • Many commenters report using it daily and consider it their default choice for quick, functional desktop GUIs.

Immediate‑mode model, layout, and redraw behavior

  • Core model: UI code runs each frame; widgets are rebuilt from state instead of being retained.
  • Debate over whether it “redraws everything all the time”: some say that in native setups you can tie redraws to events; others point to cases where network or other external events require manually triggering redraws.
  • Single‑pass layout works well for straightforward top‑to‑bottom, left‑to‑right layouts; more complex dependent layouts can cause mispositioning or jitter across frames.
  • Two‑phase layout is approximated by discarding a frame and recomputing, which can work but leads to edge cases like briefly displaying out‑of‑bounds values.
  • Several reports of window resizing quirks and difficulty expressing proportional layouts (e.g., 60/25/15% width splits).

Performance and platform behavior

  • Some find demos extremely snappy on mobile; others see high CPU usage even when idle, slow text input on phones, and various mobile browser errors (missing WASM, runtime panics, blank page on iOS Safari).
  • Concerns about power usage if redrawing at high FPS for non‑game apps; others argue you can and should gate redraws.

Text, internationalization, and accessibility

  • Current internationalization is limited: Arabic text becomes tofu; text shaping work is in progress via Rust bindings to HarfBuzz‑style libraries.
  • Font rendering can look blurry on low‑DPI displays; canvas/WebGL UIs lack subpixel rendering that DOM text enjoys.
  • Inability to select/copy text on mobile (and in many canvas/native UIs generally) is a major complaint, especially versus HTML’s text‑first model.
  • This also raises accessibility and automation concerns; workarounds rely on OS‑level OCR features.

Developer experience and tooling

  • Rust compile/link times can make rapid UI iteration feel slow; suggestions include faster linkers and hot‑reloading, though the latter is described as immature.
  • Version lockstep between egui, winit, wgpu, etc., causes friction when APIs break.
  • Requests for higher‑level tooling: dialog/WYSIWYG builders, global font‑size and high‑contrast options, and easier “serious”/pixel‑perfect design support.
  • Some view egui as excellent for functional UIs and prototypes but not ideal for complex, highly polished visual design.