yakui

yakui is a declarative Rust UI library for games.

 

yakui is a work in progress. Feedback is welcome, but mind the dragons, sharp edges, and exposed nails!

yakui combines a layout model inspired by Flutter with the ease-of-use of an immediate mode UI library like Dear Imgui or egui.

yakui has the following priorities:

1. Flexibility — yakui must be able to represent any widget
2. Ergonomics — yakui must be terse, but must enable the user to go outside the box
3. Performance — yakui must be fast enough to use in a shipping game

yakui being used in the editor for MS80

Table of Contents

• Getting Started
• Examples
• Rationale
• Architecture
• Crates
• Games Using yakui
• Name
• Minimum Supported Rust Version (MSRV)
• License

Getting Started

Add the yakui crate to your project:

[dependencies]
yakui = { git = "https://github.com/SecondHalfGames/yakui" }

Create a yakui::Yakui when your game starts:

let mut yak = yakui::Yakui::new();

Call start(), create your UI, then call finish():

yak.start();

yakui::center(|| {
    yakui::text(32.0, "Hello, world!");
});

yak.finish();

Finally, call paint() and feed the result to your renderer:

your_renderer.draw(yak.paint());

To see your UI, you'll need a renderer crate. You can also write your own integration for your game. Here are the officially supported renderer crates:

• yakui-wgpu — wgpu renderer
• yakui-vulkan — Vulkan renderer

You'll also need to send window and input events to yakui. These are the officially supported windowing library crates:

• yakui-winit — Winit integration

Examples

Example setup code for yakui is available in crates/bootstrap.

You can run examples with cargo run --example <example name>. Check out crates/yakui/examples to get a list of available examples.

Many of the examples look like this:

fn app() {
    yakui::column(|| {
        yakui::text(32.0, "Hello, world!");

        if yakui::button("Click me!").clicked {
            println!("Button clicked.");
        }
    })
}

In these examples, the app function is run every frame, processing input and updating the UI. This replicates how games tend to work.

Rationale

yakui exists to fill two roles in the Rust game UI ecosystem:

1. A library for prototype, development, or debug game UI
2. A library for building polished, custom game UI

Most importantly, yakui provides a smooth transition from #1 to #2. When you reach the phase of your game's development where custom UI makes sense, you shouldn't need to throw out your existing UI code or technology. You should be able to incrementally improve the look, fit, and feel of your UI.

While Rust has multiple libraries aimed at debug or development UI, they do not place an emphasis on being capable for building good custom game UI. None of them provide a gradual path for converting from UI suitable for a game prototype into polished UI for a quality shipping game. All of yakui's built-in widgets are created using public APIs and are easy to compose, extend, or fork.

Many Rust UI libraries have expanded their scope to become desktop application toolkits. This leaves their core proficiency half-baked. yakui will always be focused on practical problems encountered building game UI.

Most attempts at building UI libraries have limited layout capabilities, making some kinds of widgets impossible to express. yakui is built upon Flutter's layout protocol, which can efficiently handle both bottom-up and top-down sizing when appropriate.

Architecture

yakui stands on the shoulders of giants.

It takes heavy inspiration from:

• React — Declarative UI as a mainstream paradigm
• Flutter — Single pass layout model, composable layout widgets
• Moxie — Constructing UI as a tree of topologically-aware functions

A frame in yakui is divided up into distinct phases:

1. Event Phase
   • Events are piped from the application into yakui and tested against the current DOM.
   • Widgets can sink or bubble events. Events bubble by default, and any events that bubble are given back to the application.
2. Update Phase
   • This phase is started when Yakui::start is called. This binds the DOM to the current thread.
   • Functions are called that declare widgets and their current state.
   • Widgets that existed last frame are updated with new props, the input to a widget.
   • Widgets that didn't exist are created from props.
3. Layout Phase
   • This phase is started when Yakui::finish is called. This unbinds the DOM from the current thread.
   • Each widget has its layout function run once, depth first.
   • Each widget is asked what events it is interested in receiving, like mouse or keyboard events.
4. Paint Phase
   • This phase is started when Yakui::paint is called.
   • Each widget has its paint function run once, depth first.
   • Paint information is stored in the Paint DOM, which a renderer can use to draw the current set of widgets.

Crates

yakui is modular to support different kinds of users.

yakui

The yakui crate bundles together yakui-core with yakui-widgets to provide a pleasant out of the box experience.

If you're writing a game and want to use yakui, this is the crate to start with.

yakui-core

The yakui-core crate defines the DOM, layout, painting, and input, but provides no built-in widgets nor bindings to other libraries.

If you're working on a library that depends on yakui like a renderer or platform crate, this is the crate to use.

yakui-widgets

The yakui-widgets crate is a collection of built-in widgets for yakui. This includes layout primitives, text rendering, and basic form controls.

You should usually not depend on yakui-widgets directly. Instead, depend on yakui if you want to use these widgets, or yakui-core if you don't need widgets.

yakui-winit

The yakui-winit crate contains bindings for use with winit.

yakui-wgpu

The yakui-wgpu crate is a yakui renderer that uses wgpu.

yakui-vulkan

The yakui-vulkan crate is a yakui renderer that uses Vulkan via ash

yakui-app

The yakui-app crate is a wrapper around yakui-winit and yakui-wgpu intended to make getting started with yakui easier.

If you are writing your own integration for yakui, this crate is a good learning resource to reference.

Games Using yakui

There are a handful of games already using yakui for their UI. Here are a couple:

• MEANWHILE IN SECTOR 80
• Zombie Demo Game
• CyberGate

Name

yakui is all lowercase.

yakui is pronounced however you want to pronounce it. Here are some suggestions:

• ya-KOO-ee (like a sneeze)
• yak-yew-eye (like a marketing executive)
• ya-kwee (like a funny French word)

Minimum Supported Rust Version (MSRV)

yakui currently supports the latest stable version of Rust. Once yakui has matured, the MSRV will be pinned and updated only when it provides a large improvement.

License

Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.