Bevy survival

Vitals, a day clock, and crafting inputs live on components and resources. Stats, item stacks, gathering, and camps stay on the skills linked below.

When to use

Load this for vitals, crafting inputs, and a day clock you own.

ECS shape

• Components hold the genre's per-entity flags as plain data. This file does not name new engine types.
• Resources hold run-wide counters (score, wave index, seed) via bevy-data-resources.
• Systems read those components on Update or the fixed timestep from bevy-master. Order them with .chain() when a later system must see the result.
• Schedule: gameplay mode changes go through bevy-state-machines. Do not invent a genre plugin.

Ownership

Need	Bevy shape
Actors in the genre	Entities plus the domain skills linked below
Run-wide director	A resource
Loop notices	bevy-events-messaging

Routing

• bevy-rpg-stats - Vitals as stats.
• bevy-inventory-system - Items.
• bevy-game-loop-harvest - Gathering.
• bevy-3d-world-building - Camps.

Scope

• Hunger, warmth, and the day clock are data you own. Item stacks and camp layout stay on the linked skills.

Examples

[package]
name = "survival"
version = "0.1.0"
edition = "2021"

[dependencies]
bevy = "0.20"

Hunger and warmth drain on the fixed step. Cold hours drain warmth faster. A meal and a fire restore them.

#[derive(Component)]
struct Vitals {
    hunger: f32,
    warmth: f32,
}

#[derive(Resource)]
struct DayClock {
    hour: f32,
    hours_per_day: f32,
}

fn tick_day(time: Res<Time<Fixed>>, mut clock: ResMut<DayClock>) {
    let hours = time.delta_secs() * (24.0 / clock.hours_per_day);
    clock.hour = (clock.hour + hours) % 24.0;
}

fn drain_vitals(time: Res<Time<Fixed>>, clock: Res<DayClock>, mut people: Query<&mut Vitals>) {
    let dt = time.delta_secs();
    let night = clock.hour < 6.0 || clock.hour >= 20.0;
    let warmth_rate = if night { 2.5 } else { 0.4 };
    for mut vitals in &mut people {
        vitals.hunger = (vitals.hunger - 1.2 * dt).max(0.0);
        vitals.warmth = (vitals.warmth - warmth_rate * dt).max(0.0);
    }
}

#[derive(Message)]
struct Eat {
    who: Entity,
    amount: f32,
}

fn apply_meals(mut meals: MessageReader<Eat>, mut people: Query<&mut Vitals>) {
    for meal in meals.read() {
        let Ok(mut vitals) = people.get_mut(meal.who) else {
            continue;
        };
        vitals.hunger = (vitals.hunger + meal.amount).min(100.0);
    }
}

pub struct SurvivalPlugin;

impl Plugin for SurvivalPlugin {
    fn build(&self, app: &mut App) {
        app.insert_resource(DayClock {
            hour: 8.0,
            hours_per_day: 480.0,
        })
        .add_message::<Eat>()
        .add_systems(FixedUpdate, (tick_day, drain_vitals, apply_meals).chain());
    }
}

A recipe spends named counts from a bag, then writes a crafted stack. The bag is a component so each camp or player carries their own stores.

#[derive(Clone, Copy, PartialEq, Eq)]
enum ItemKind {
    Wood,
    Fiber,
    Bandage,
}

#[derive(Component, Default)]
struct Bag {
    stacks: Vec<(ItemKind, u32)>,
}

fn count_of(bag: &Bag, kind: ItemKind) -> u32 {
    bag.stacks
        .iter()
        .filter(|(k, _)| *k == kind)
        .map(|(_, n)| *n)
        .sum()
}

fn spend(bag: &mut Bag, kind: ItemKind, mut need: u32) -> bool {
    if count_of(bag, kind) < need {
        return false;
    }
    for (k, n) in &mut bag.stacks {
        if *k != kind || need == 0 {
            continue;
        }
        let take = (*n).min(need);
        *n -= take;
        need -= take;
    }
    bag.stacks.retain(|(_, n)| *n > 0);
    true
}

fn craft_bandage(mut bags: Query<&mut Bag>) {
    for mut bag in &mut bags {
        if spend(&mut bag, ItemKind::Fiber, 2) {
            bag.stacks.push((ItemKind::Bandage, 1));
        }
    }
}

Spawn a survivor at dawn with full vitals.

#[derive(Component)]
struct Vitals {
    hunger: f32,
    warmth: f32,
}

fn spawn_survivor(mut commands: Commands) {
    commands.spawn((
        Vitals {
            hunger: 100.0,
            warmth: 100.0,
        },
        Transform::from_xyz(0.0, 0.0, 0.0),
    ));
}

Expert Knowledge Delta

Target: Bevy 0.20+.

Core ECS types: Component, Resource, Query, Commands, Startup, Update, Fixed / FixedMain (bevy::time), .chain(), Plugin, DefaultPlugins, MinimalPlugins. Messages and observers are an ownership slot. See bevy-events-messaging for their APIs. Systems run in parallel unless .chain() orders the ones that conflict.

Who owns state

Piece	Owner	Who may mutate	Schedule
Data on one entity	Component	One system via Query	Update or FixedMain
One value for the whole app	Resource	One system	Startup to insert, then the schedule that reads it
Spawn	Commands	The spawning system	Startup for the initial world; later schedules for runtime spawn
Order that must not race	.chain()	The chained systems only	Same schedule
Plugin boundary	Plugin	build registers systems and resources	Before the app runs

Borrow rule: two systems that both mutably query the same component must be ordered (.chain()) or split so only one writes. Unrelated systems stay parallel. That is the ECS page rule, not a guess at a system-set API.

Decision

If you need	Do this	Do not
Per-entity data	Component + Query	A field stored outside a component
App-wide config or clock	Resource	Copy the value onto every entity
Stable simulation step	FixedMain and the Fixed clock	Tie simulation to raw frame Update
Startup spawn	Commands in Startup	Spawn from a render system
Cross-system notice that is not shared state	Message or observer slot in bevy-events-messaging	A new event type invented in this file
Hunger, warmth, clock, recipes	Components and resources in the examples	An engine survival module

Load references/ecs-ownership.md for the ownership table.

NEVER

• Do not pin /0.20.0/ in docs URLs. WHY: links stay on latest; the 0.20 target is stated once in prose.

• Do not mutably query the same component from two unordered systems. WHY: the schedule runs systems in parallel unless .chain() orders them.

• Do not invent a physics, navigation, networking, or XR crate here. WHY: this skill only names documented Bevy crates and modules.

• No types from another engine in Bevy code. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No invented genre APIs. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• Do not pick a physics or net crate here. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

Reference

Official links stay on bevy.org. The library pin on bevy-master stays 0.20.

Official Documentation

• Assets - Official asset catalog. No third-party crate was selected.
• Examples - Example tree on the latest branch.
• ECS - Component, systems, Query, Startup, Update, and .chain().
• Plugins - Plugin, DefaultPlugins, MinimalPlugins, and add_plugins.

Related Skills

Prerequisites

• bevy-master - ECS ownership and schedules.
• bevy-ecs-composition - Spawn and query shape.

Complements

• bevy-rpg-stats - Vitals as stats.
• bevy-inventory-system - Items.
• bevy-game-loop-harvest - Gathering.
• bevy-3d-world-building - Camps.

Downstream / consumers

• None. This router does not own a second implementation.

Master

• bevy-master - Bevy router.