EUI

EUI is a minimal retained‑mode UI built with the Ebiten game engine. It provides basic window management, flows and widgets built entirely with vector graphics. The project is currently in early development and APIs will likely change.

Live demo here

Currently the API is not complete!

Features

EUI aims to stay small and easy to use while still providing the essentials for building a game UI. Highlights include:

• Window management – draggable, resizable windows with optional pinning and fixed aspect ratios.
• Main portal windows – draw before other UI, black out the rest of the screen and leave the window background transparent for game content.
• Window transparency – set Transparent with an Alpha value to draw windows with partial opacity.
• Flow layouts – vertical or horizontal flows for composing widgets.
• Overlay items – keep controls always on screen.
• Palette and style themes – JSON files define colors and spacing. Switch them at runtime or reload automatically while iterating.
• UI scaling – call eui.SetUIScale() to adapt to any resolution or eui.UIScale() to read the current value. The scale is clamped between 1.0 and 2.5. Windows using AutoSize adjust their dimensions automatically when the scale changes, and all windows remain within the screen bounds.
• Image caching – widgets cache their drawing for better performance. Enable eui.DumpMode to write the cached images to disk for inspection.
• Tree dump – press Shift+</kbd> or run the demo with -tree` to save the window hierarchy as JSON.
• Event system – each widget returns an EventHandler that uses channels or callbacks so your code can react to clicks, slider movements and text input.
• Debug overlays – toggle with the -debug flag when running the demo.
• Cross platform – runs anywhere Ebiten does: desktop, web or mobile.
• Basic touch support – with two‑finger scrolling (drag up to scroll up). Mouse scrolling is clamped to +/-3 and rate-limited to 4 events per half-second on WebAssembly.
• Image labels – buttons, sliders, checkboxes, radios and dropdowns can combine image and text labels, with the image drawn before the text and optional custom sizing.
• Vertical sliders – sliders can be oriented vertically.
• Logarithmic sliders – sliders can map values on a logarithmic scale.
• Hidden inputs – text fields can mask their contents and reveal them while the eye icon is pressed.
• Tooltips – optional text hints appear when hovering over any item except flows.

Running the Demo

The demonstration application lives under cmd/demo. You can run it directly using go run or build a binary:

go run ./cmd/demo             # launches the showcase window
# or
go build -o demo ./cmd/demo
./demo -debug                 # optional debug overlays and disposal logs
# dump cached images to ./debug after one frame then exit
./demo -dump
# dump the window tree to ./debug/tree.json then exit
./demo -tree
# pass -debug with go run to enable overlays
go run ./cmd/demo -debug

The demo now calculates the initial window size using the monitor's device scale factor so the interface appears the same on standard and high‑DPI displays.

Building for WebAssembly

Compile the demo to wasm using the provided script. It passes size optimization flags to go build and also creates a Brotli compressed demo.wasm.br for the browser:

./scripts/build_wasm.sh

Open web/index.html in a browser to run it.

WCAG adjustments

The scripts/wcag_adjust.py helper rewrites all palette and style files so text and accents meet the WCAG 2 contrast recommendations. Run it whenever you tweak the theme JSON files:

python3 scripts/wcag_adjust.py

Customization

The library loads the built in AccentDark palette, RoundHybrid style and a default font automatically. Additional examples live under eui/themes. Use eui.ListThemes() and eui.ListStyles() to see the names that are available. To try a different look enable eui.AutoReload and load files explicitly:

// var ttf []byte
// _ = eui.EnsureFontSource(ttf)
// _ = eui.LoadTheme("MyTheme")
// _ = eui.LoadStyle("MyStyle")

See themes/README.md for a list of the bundled schemes and details on creating your own.

Project Layout

• eui – reusable library code containing windows, flows and widgets
• cmd/demo – standalone example program wiring the library together

For a generated listing of all library functions see the API reference.

Testing

Some tests depend on a build tag. Run them with:

go test -tags test ./...