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Bevy_Lunex is a blazingly fast, path-based retained layout engine designed for creating UI within the Bevy game engine.

Centered around Bevy ECS, Bevy_Lunex allows developers to manage their UI elements with the same principles and tools used for other game entities.

  • Lunex is great for:

    • Making a game-like user interface
    • Enjoying hands on approach
    • Requiring custom widgets
    • Requiring worldspace (diegetic) UI

  • Lunex is not optimal for:

    • Making a dektop application
    • Wanting to make UI quickly
    • Complex editor-like UI

Syntax Example

This is an example of a clickable Button created from scratch using predefined components. As you can see, ECS modularity is the focus here. The library will also greatly benefit from upcoming BSN (Bevy Scene Notation) addition that Cart is working on.

#![allow(unused)]
fn main() {
commands.spawn((

	// #=== UI DEFINITION ===#

	// This specifies the name and hierarchy of the node
	UiLink::<MainUi>::path("Menu/Button"),

	// Here you can define the layout using the provided units (per state like Base, Hover, Selected, etc.)
	UiLayout::window().pos(Rl((50.0, 50.0))).size((Rh(45.0), Rl(60.0))).pack::<Base>(),


	// #=== CUSTOMIZATION ===#

	// Give it a background image
	UiImage2dBundle { texture: assets.load("images/button.png"), ..default() },

	// Make the background image resizable
	ImageScaleMode::Sliced(TextureSlicer { border: BorderRect::square(32.0), ..default() }),

	// This is required to control our hover animation
	UiAnimator::<Hover>::new().forward_speed(5.0).backward_speed(1.0),

	// This will set the base color to red
	UiColor<Base>::new(Color::RED),

	// This will set hover color to yellow
	UiColor<Hover>::new(Color::YELLOW),


	// #=== INTERACTIVITY ===#

	// This is required for hit detection (make it clickable)
	PickableBundle::default(),

	// This will change cursor icon on mouse hover
    OnHoverSetCursor::new(CursorIcon::Pointer),

	// If we click on this, it will emmit UiClick event we can listen to
	UiClickEmitter::SELF,
));
}

^^^ Source from Bevypunk repo

Key Features

  • Path-Based Hierarchy: Bevy_Lunex utilizes its own custom hierarchy alongside Bevy's default hierarchy. This approach circumvents the borrow checking rules enforced by Rust, which can obstruct the ability to access data fluidly. This is achieved by introducing an iterable, hashmap-like "god" struct (UiTree component) that contains all the UI data. Developers navigate this structure using a syntax reminiscent of Unix file systems, such as "foo/bar", to retrieve specific data or bind entities to it.

  • Retained UI: Most UI frameworks for Bevy operate on an immediate mode basis, recalculating every tick. In contrast, Bevy_Lunex employs a retained mode, meaning that the UI state is stored and only recomputed when changes occur. This results in improved performance and reduced energy consumption, making Bevy_Lunex an efficient choice for UI development.

  • ECS Friendly: Traditional UI frameworks often impose special rules on UI entities, isolating them from the rest of the application's logic. Bevy_Lunex adopts a different approach, treating UI entities as regular game entities. By leveraging the Transform component, any entity, including 3D models, can be integrated into the layout engine. This design ensures seamless interaction and uniform behavior across all entities in the application.

  • Resizable Layouts: As a game-first UI framework, Bevy_Lunex is designed to support all aspect ratios and resolutions out of the box. UI layouts automatically adapt to different window sizes without collapsing or requiring explicit instructions for various circumstances. For instance, a UI designed for a 1920x1080 pixel window will maintain its layout proportionally when scaled down to a 1280x720 pixel window, simply appearing smaller. This behavior is ideal for games, though it may differ from traditional HTML-based layouts. For regular applications requiring different behavior, the Div layout (currently a work in progress) is recommended.