JXL-UI

A cross-platform JPEG XL image viewer built with egui and jxl-rs.

Download • Features • Installation • Mobile • Shortcuts

Features

• Progressive decoding -- See images appear tile-by-tile and sharpen pass-by-pass using jxl-rs flush_pixels(). LF preview shows a blurry version almost instantly, then detail fills in progressively.
• Cross-platform -- Native apps for macOS (Intel + Apple Silicon), Windows, and Linux
• SIMD optimized -- Full SIMD support (SSE4.2, AVX, AVX512, NEON) via jxl-rs
• Animation support -- Smooth playback of animated JXL files with play/pause controls
• Multi-tab interface -- Open multiple images with tab navigation
• Decoder settings -- Configure output color format (RGB, RGBA, BGR, Grayscale, ...), data type (F32, F16, U16, U8), premultiplied alpha, and high precision mode
• Slow Loading Demo -- Simulate slow network loading with configurable chunk size (% of file) and delay (ms per chunk) to visualize progressive rendering
• Drag & drop -- Drop JXL files directly onto the window
• Image info panel -- Dimensions, decode time, speed (MP/s), animation frame info

Keyboard Shortcuts

Mouse wheel zooms, click and drag to pan when zoomed in.

Installation

From GitHub Releases

Download the latest release for your platform from the releases page.

• macOS: Download the .dmg file (available for both Intel and Apple Silicon)
• Windows: Download the .zip file
• Linux: Download the .tar.gz file

From Source

Requires Rust nightly (jxl-rs uses unstable features).

# Clone the repository
git clone https://github.com/hjanuschka/jxl-ui.git
cd jxl-ui

# Build and run
cargo +nightly run --release -- path/to/image.jxl

Mobile Apps (Local Build)

JXL-UI also includes native mobile apps in mobile/:

• Android app (mobile/android) built with Kotlin + Jetpack Compose
• iOS app (mobile/ios) built with Swift + SwiftUI
• Shared Rust decoder core in mobile/jxl-core

Android

cd mobile/android

# Build Rust JNI libraries (.so)
./build-rust.sh

# Build APK
./gradlew assembleDebug

# APK output
# app/build/outputs/apk/debug/app-debug.apk

Optional install to device/emulator:

adb install -r app/build/outputs/apk/debug/app-debug.apk

iOS

cd mobile/ios

# Build Rust XCFramework used by Swift app
./build-rust.sh

# Generate Xcode project
xcodegen generate

# Open in Xcode
open JxlUI.xcodeproj

Then pick simulator/device in Xcode and run.

For more mobile details, see mobile/README.md.

Requirements

• macOS: 10.13+ (High Sierra or later)
• Windows: Windows 10+
• Linux: X11 or Wayland with OpenGL support
• Rust nightly (for building from source)

Usage

# Open a single image
jxl-ui image.jxl

Or launch the app and use Cmd+O to open a file, or drag and drop a .jxl file onto the window.

Progressive Decoding

JXL-UI uses the jxl-rs progressive decoding API to show images as they decode:

1. LF preview -- A blurry low-frequency preview appears almost immediately
2. Tile fill-in -- Image groups/tiles fill in progressively within each pass
3. Pass sharpening -- Each completed pass sharpens the entire image

To visualize this on fast local files, open Settings (S) and enable Slow Loading Demo -- e.g. set 1% chunk size and 100ms delay for ~10% per second.

Built With

• jxl-rs -- Pure Rust JPEG XL decoder with progressive decoding and SIMD support
• egui -- Immediate mode GUI framework
• eframe -- egui framework for native apps

License

BSD-3-Clause License -- see LICENSE for details.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.