Rust bevy egui stamina.

main.rs

use bevy::prelude::*;

#[derive(Resource)]
pub struct Stamina {
    pub current: f32,
    pub max: f32,

    pub regen_rate: f32,     // stamina per second
    pub regen_delay: f32,    // seconds after last drain before regen
    pub time_since_drain: f32,
}

impl Stamina {
    pub fn new(max: f32) -> Self {
        Self {
            current: max,
            max,
            regen_rate: 80.0,
            regen_delay: 0.6,
            time_since_drain: 0.0,
        }
    }

    pub fn drain(&mut self, amount: f32) {
        self.current = (self.current - amount).max(0.0);
        self.time_since_drain = 0.0;
    }

    pub fn regen(&mut self, dt: f32) {
        if self.time_since_drain >= self.regen_delay {
            self.current = (self.current + self.regen_rate * dt)
                .min(self.max);
        } else {
            self.time_since_drain += dt;
        }
    }

    pub fn ratio(&self) -> f32 {
        self.current / self.max
    }
}

use bevy_egui::{EguiContexts, EguiPlugin};

pub struct StaminaPlugin;

impl Plugin for StaminaPlugin {
    fn build(&self, app: &mut App) {
        app
            .insert_resource(Stamina::new(360.0))
            .add_systems(Update, (
                stamina_input_system,
                stamina_regen_system,
                stamina_ui_system,
            ));
    }
}

fn stamina_input_system(
    mouse: Res<Input<MouseButton>>,
    mut stamina: ResMut<Stamina>,
) {
    if mouse.just_pressed(MouseButton::Left) {
        if stamina.current >= 40.0 {
            stamina.drain(40.0);
            // Trigger slash animation here
        }
    }
}

use bevy_egui::egui;
use std::f32::consts::TAU;

fn stamina_ui_system(
    mut contexts: EguiContexts,
    stamina: Res<Stamina>,
) {
    egui::Area::new("stamina_ui")
        .fixed_pos(egui::pos2(40.0, 40.0))
        .show(contexts.ctx_mut(), |ui| {
            let size = egui::vec2(90.0, 90.0);
            let (rect, _) = ui.allocate_exact_size(size, egui::Sense::hover());

            let painter = ui.painter();
            let center = rect.center();
            let radius = rect.width() * 0.45;

            let start_angle = -TAU / 4.0;
            let end_angle = start_angle + TAU * stamina.ratio();

            // Background ring
            painter.circle_stroke(
                center,
                radius,
                egui::Stroke::new(6.0, egui::Color32::DARK_GRAY),
            );

            // Stamina arc
            painter.arc(
                center,
                radius,
                start_angle,
                end_angle,
                egui::Stroke::new(6.0, egui::Color32::from_rgb(70, 220, 120)),
            );
        });
}

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugins(EguiPlugin)
        .add_plugins(StaminaPlugin)
        .run();
}