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 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.

examples

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

fn main() {
    App::new()
        .add_plugins((DefaultPlugins, HaalkaPlugin))
        .add_systems(Startup, (ui_root, camera))
        .run();
}

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

fn ui_root(world: &mut World) {
    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))),
        )
        .spawn(world);
}

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 challenge01  # game menu
cargo run --example challenge02  # inventory
cargo run --example challenge03  # health bar
cargo run --example challenge04  # responsive menu
cargo run --example challenge05  # character editor

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

Bevy compatibility

development

Remember to include submodules when fetching the repo git clone --recurse-submodules https://github.com/databasedav/haalka.git.

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.