Bevy Visual novel (thin router)

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

When to use

Load this for dialogue, portraits, and choice flags.

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.

Routing

• bevy-dialogue-system - Lines.
• bevy-ui-text - Body text.
• bevy-ui-layout - Choice buttons.
• bevy-save-load - Route flags.

Scope

Lines, the visible character index, and route flags are resources. Choice rows are entities. A full script parser stays data you load into those resources.

Examples

[package]
name = "visual-novel"
version = "0.1.0"
edition = "2021"

[dependencies]
bevy = "0.20"

One resource owns the script index and the flags later scenes read.

#[derive(Clone)]
struct Line {
    speaker: String,
    body: String,
}

#[derive(Resource)]
struct Script {
    lines: Vec<Line>,
    index: usize,
    flags: Vec<String>,
}

fn current_line(script: &Script) -> Option<&Line> {
    script.lines.get(script.index)
}

fn advance(script: &mut Script) {
    if script.index + 1 < script.lines.len() {
        script.index += 1;
    }
}

fn set_flag(script: &mut Script, flag: &str) {
    if !script.flags.iter().any(|f| f == flag) {
        script.flags.push(flag.to_string());
    }
}

Space advances. Number keys pick a choice and write its flag.

#[derive(Component)]
struct Choice {
    key: KeyCode,
    flag: String,
    next_index: usize,
}

#[derive(Clone)]
struct Line {
    speaker: String,
    body: String,
}

#[derive(Resource)]
struct Script {
    lines: Vec<Line>,
    index: usize,
    flags: Vec<String>,
}

fn advance(script: &mut Script) {
    if script.index + 1 < script.lines.len() {
        script.index += 1;
    }
}

fn set_flag(script: &mut Script, flag: &str) {
    if !script.flags.iter().any(|f| f == flag) {
        script.flags.push(flag.to_string());
    }
}

fn read_advance(keys: Res<ButtonInput<KeyCode>>, mut script: ResMut<Script>) {
    if keys.just_pressed(KeyCode::Space) {
        advance(&mut script);
    }
}

fn read_choice(
    keys: Res<ButtonInput<KeyCode>>,
    choices: Query<&Choice>,
    mut script: ResMut<Script>,
) {
    for choice in &choices {
        if keys.just_pressed(choice.key) {
            set_flag(&mut script, &choice.flag);
            script.index = choice.next_index.min(script.lines.len().saturating_sub(1));
        }
    }
}

pub struct NovelPlugin;

impl Plugin for NovelPlugin {
    fn build(&self, app: &mut App) {
        app.insert_resource(Script {
            lines: vec![Line {
                speaker: "Guide".to_string(),
                body: "The gate is shut.".to_string(),
            }],
            index: 0,
            flags: Vec::new(),
        })
        .add_systems(Update, (read_advance, read_choice).chain());
    }
}

Startup spawns two choices. The portrait name is a component on its own entity.

#[derive(Component)]
struct Portrait {
    name: String,
}

#[derive(Component)]
struct Choice {
    key: KeyCode,
    flag: String,
    next_index: usize,
}

#[derive(Resource)]
struct Script {
    lines: Vec<Line>,
    index: usize,
    flags: Vec<String>,
}

#[derive(Resource, Default)]
struct ShownLine {
    speaker: String,
    portrait: String,
    body: String,
}

#[derive(Clone)]
struct Line {
    speaker: String,
    body: String,
}

fn current_line(script: &Script) -> Option<&Line> {
    script.lines.get(script.index)
}

fn spawn_scene(mut commands: Commands) {
    commands.spawn(Portrait {
        name: "guide".to_string(),
    });
    commands.spawn(Choice {
        key: KeyCode::Digit1,
        flag: "opened_gate".to_string(),
        next_index: 1,
    });
    commands.spawn(Choice {
        key: KeyCode::Digit2,
        flag: "walked_away".to_string(),
        next_index: 2,
    });
}

fn show_portrait(
    portraits: Query<&Portrait>,
    script: Res<Script>,
    mut shown: ResMut<ShownLine>,
) {
    let Some(line) = current_line(&script) else {
        return;
    };
    let Some(portrait) = portraits.iter().next() else {
        return;
    };
    shown.speaker = line.speaker.clone();
    shown.portrait = portrait.name.clone();
    shown.body = line.body.clone();
}

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

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

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 Godot types 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

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

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

• godot-genre-visual-novel - Visual novel on the Godot engine, same depth.
• bevy-dialogue-system - Lines.
• bevy-ui-text - Body text.
• bevy-ui-layout - Choice buttons.
• bevy-save-load - Route flags.

Downstream / consumers

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

Master

• bevy-master - Bevy router.