Bevy Horror (thin router)

Genre router. Domain work lives in the Bevy skills below.

When to use

Load this for sanity or detection as your components, plus lighting and audio.

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. This file registers only the sanity, suspicion, and light systems.

Routing

• bevy-3d-lighting - Darkness.
• bevy-audio-systems - Stingers.
• bevy-ai-navigation - Stalker policy.
• bevy-mechanic-secrets - Lore flags.

Scope

Sanity, suspicion, and light energy live on components. Darkness, stingers, and stalker paths stay in the skills linked above.

Call	Owner here	Leave to the linked skill
Fear falls while the player is vulnerable	Sanity on FixedUpdate	A light or audio crate
The stalker has line of sight	Stalker.sees_player and suspicion	Pathfinding in bevy-ai-navigation
A held light spends energy	LightCell.energy	Spotlights in bevy-3d-lighting

[dependencies]
bevy = "0.20"

#[derive(Component)]
#[require(Transform)]
struct Sanity {
    value: f32,
}

#[derive(Resource)]
struct SanityDrain(f32);

fn drain_sanity(time: Res<Time>, drain: Res<SanityDrain>, mut minds: Query<&mut Sanity>) {
    let step = drain.0 * time.delta_secs();
    for mut sanity in &mut minds {
        sanity.value = (sanity.value - step).max(0.0);
    }
}

pub struct SanityPlugin;

impl Plugin for SanityPlugin {
    fn build(&self, app: &mut App) {
        app.insert_resource(SanityDrain(4.0))
            .add_systems(FixedUpdate, drain_sanity);
    }
}

#[derive(Component)]
struct Stalker {
    suspicion: f32,
    sees_player: bool,
}

fn raise_suspicion(time: Res<Time>, mut stalkers: Query<&mut Stalker>) {
    for mut stalker in &mut stalkers {
        if stalker.sees_player {
            stalker.suspicion = (stalker.suspicion + time.delta_secs()).min(1.0);
        } else {
            stalker.suspicion = (stalker.suspicion - time.delta_secs() * 0.25).max(0.0);
        }
    }
}

pub struct StalkerPlugin;

impl Plugin for StalkerPlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(FixedUpdate, raise_suspicion);
    }
}

#[derive(Component)]
#[require(Transform)]
struct Sanity {
    value: f32,
}

#[derive(Component)]
struct LightCell {
    energy: f32,
}

fn spend_light(time: Res<Time>, mut lights: Query<&mut LightCell>) {
    for mut light in &mut lights {
        light.energy = (light.energy - time.delta_secs() * 2.0).max(0.0);
    }
}

fn spawn_player(mut commands: Commands) {
    commands.spawn((Sanity { value: 100.0 }, LightCell { energy: 40.0 }));
}

pub struct HorrorSetupPlugin;

impl Plugin for HorrorSetupPlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(Startup, spawn_player)
            .add_systems(FixedUpdate, spend_light);
    }
}

fn main() {
    App::new()
        .add_plugins(MinimalPlugins)
        .add_plugins(HorrorSetupPlugin)
        .run();
}

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	One mutable blob shared by every entity
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
Behavior a linked domain skill already owns	Keep this router to components and resources	A second implementation in this file

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.

• Do not drain sanity on raw Update. WHY: fear and light energy are simulation and belong on FixedUpdate.

• 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

The library pin on bevy-master stays 0.20.0. Official pages stay on the unversioned site.

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-3d-lighting - Darkness.
• bevy-audio-systems - Stingers.
• bevy-ai-navigation - Stalker policy.
• bevy-mechanic-secrets - Lore flags.

Downstream / consumers

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

Master

• bevy-master - Bevy router.