haalka হালকা

in bengali, haalka means "light" (e.g. not heavy) and can also be used to mean "easy"

haalka is an ergonomic reactive Bevy UI library powered by the incredible FRP signals of futures-signals and the convenient async ECS of bevy-async-ecs with API ported from web UI libraries MoonZoon and Dominator.

While haalka is primarily targeted at UI and provides high level UI abstractions as such, its core abstraction can be used to manage signals-powered reactivity for any entity, not just bevy_ui nodes.

considerations

If one is using the text_input feature (enabled by default) and using multiple cameras in the same world, they must enable the multicam feature AND add the bevy_cosmic_edit::CosmicPrimaryCamera marker component to the primary camera.

feature flags

examples

use bevy::prelude::*;
use haalka::prelude::*;

fn main() {
    App::new()
        .add_plugins((DefaultPlugins, HaalkaPlugin))
        .add_systems(
            Startup,
            (
                |world: &mut World| {
                    ui_root().spawn(world);
                },
                camera,
            ),
        )
        .run();
}

#[derive(Component)]
struct Counter(Mutable<i32>);

fn ui_root() -> impl Element {
    let counter = Mutable::new(0);
    El::<NodeBundle>::new()
        .height(Val::Percent(100.))
        .width(Val::Percent(100.))
        .align_content(Align::center())
        .child(
            Row::<NodeBundle>::new()
                .with_style(|mut style| style.column_gap = Val::Px(15.0))
                .item(counter_button(counter.clone(), "-", -1))
                .item(El::<TextBundle>::new().text_signal(counter.signal().map(text)))
                .item(counter_button(counter.clone(), "+", 1))
                .update_raw_el(move |raw_el| raw_el.insert(Counter(counter))),
        )
}

fn counter_button(counter: Mutable<i32>, label: &str, step: i32) -> impl Element {
    let hovered = Mutable::new(false);
    El::<NodeBundle>::new()
        .width(Val::Px(45.0))
        .align_content(Align::center())
        .background_color_signal(
            hovered
                .signal()
                .map_bool(|| Color::hsl(300., 0.75, 0.85), || Color::hsl(300., 0.75, 0.75))
                .map(BackgroundColor),
        )
        .hovered_sync(hovered)
        .on_click(move || *counter.lock_mut() += step)
        .child(El::<TextBundle>::new().text(text(label)))
}

fn text(text: impl ToString) -> Text {
    Text::from_section(
        text.to_string(),
        TextStyle {
            font_size: 30.0,
            ..default()
        },
    )
}

fn camera(mut commands: Commands) {
    commands.spawn(Camera2dBundle::default());
}

cargo run --example counter  # the example above
cargo run --example button  # port of https://github.com/bevyengine/bevy/blob/main/examples/ui/button.rs
cargo run --example align  # alignment API demo, port of https://github.com/MoonZoon/MoonZoon/tree/main/examples/align and https://github.com/MoonZoon/MoonZoon/tree/main/examples/align_content
cargo run --example scroll  # scrollability API demo, inspired by https://github.com/mintlu8/bevy-rectray/blob/main/examples/scroll_discrete.rs
cargo run --example scroll_grid  # i can't believe it's not scrolling !
cargo run --example snake  # with adjustable grid size and tick rate
cargo run --example ecs_ui_sync  # forward ecs changes to the ui
cargo run --example key_values_sorted  # text inputs, scrolling/viewport control, and reactive lists; promises made promises kept ! https://discord.com/channels/691052431525675048/1192585689460658348/1193431789465776198 (yes i take requests)
cargo run --example calculator  # simple calculator, spurred by https://discord.com/channels/691052431525675048/885021580353237032/1263661461364932639

# ui challenges from https://github.com/bevyengine/bevy/discussions/11100
cargo run --example main_menu  # sub menus, sliders, dropdowns, reusable composable widgets, gamepad navigation
cargo run --example inventory  # grid, icons, drag and drop, tooltips
cargo run --example healthbar  # 3d character anchor, customizable widgets
cargo run --example responsive_menu  # nine-patch buttons, screen size reactivity
cargo run --example character_editor  # scrollable buttons, mutable viewport, text input reactivity

One can also run the examples with just, e.g. just example snake -r.

Bevy compatibility

development

1. include submodules when fetching the repo

   git clone --recurse-submodules https://github.com/databasedav/haalka.git
   

2. install just
3. install nickel for modifying CI configuration (nickel must be in your PATH)
4. install File Watcher for automatically syncing nickels

license

All code in this repository is dual-licensed under either:

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

at your option.

Assets used in examples may be licensed under different terms, see the examples README.

your contributions

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.