bevy-input-handling

Bevy input handling

When to use

Load this when a system should read keyboard, mouse, or gamepad state. The bevy::input module on Bevy 0.20 is the source for the names below.

ECS shape

• Plugin: InputPlugin adds input from keyboard, mouse, gamepad, and touch. It ships inside the usual app plugins. InputSystems labels the systems that refresh that data.
• Keyboard resource: Res<ButtonInput<KeyCode>>. KeyCode is the physical key (layout-stable). Res<ButtonInput<Key>> is the logical key. The keyboard example uses pressed, just_pressed, and just_released.
• Mouse: mouse_button_input_system writes ButtonInput<MouseButton> from MouseButtonInput. AccumulatedMouseMotion and AccumulatedMouseScroll are resources reset every frame. MouseMotion and MouseWheel are the underlying events.
• Gamepad: Gamepad stores a connected pad's metadata (GamepadButton, GamepadAxis). Connection and axis changes arrive as GamepadConnectionEvent, GamepadAxisChangedEvent, and GamepadButtonChangedEvent. GamepadRumbleRequest is the force-feedback event.
• Schedule: read these resources from a system on Update (or a schedule you already chain). Do not invent an input-map resource.

Coming from Godot

Godot idea	Bevy idiom
Action just pressed	ButtonInput::just_pressed on KeyCode or MouseButton
Action held	ButtonInput::pressed
Physical WASD vs symbol keys	KeyCode for location, Key for the character
Mouse look delta	AccumulatedMouseMotion (reset each frame)
Controller	Gamepad plus the gamepad events listed above

Scope

Keyboard, mouse, and gamepad state live on ButtonInput and Gamepad. Named actions, a jump buffer, a radial stick deadzone, and the last active device are resources you define. Glyph art is a UI concern once that device flag is set.

Examples

[dependencies]
bevy = "0.20"

Read edges in Update. FixedUpdate can run zero or several times per frame, so a press sampled there is dropped or repeated. Store the edge on an intent component and let the fixed step consume it.

#[derive(Component, Default)]
struct MoveIntent {
    axis: Vec2,
    jump: bool,
}

fn read_keys(keys: Res<ButtonInput<KeyCode>>, mut intents: Query<&mut MoveIntent>) {
    let mut axis = Vec2::ZERO;
    if keys.pressed(KeyCode::KeyA) || keys.pressed(KeyCode::ArrowLeft) {
        axis.x -= 1.0;
    }
    if keys.pressed(KeyCode::KeyD) || keys.pressed(KeyCode::ArrowRight) {
        axis.x += 1.0;
    }
    if keys.pressed(KeyCode::KeyW) || keys.pressed(KeyCode::ArrowUp) {
        axis.y += 1.0;
    }
    if keys.pressed(KeyCode::KeyS) || keys.pressed(KeyCode::ArrowDown) {
        axis.y -= 1.0;
    }
    let jump = keys.just_pressed(KeyCode::Space);
    for mut intent in &mut intents {
        intent.axis = axis;
        if jump {
            intent.jump = true;
        }
    }
}

use bevy::input::mouse::AccumulatedMouseMotion;

fn look(motion: Res<AccumulatedMouseMotion>, mut cameras: Query<&mut Transform, With<LookCam>>) {
    for mut tf in &mut cameras {
        tf.rotate_y(-motion.delta.x * 0.002);
        tf.rotate_local_x(-motion.delta.y * 0.002);
    }
}

#[derive(Component)]
struct LookCam;

A radial deadzone drops stick drift, then rescales the remaining range so full deflection still reaches length 1. The jump buffer keeps a press that landed a few frames early.

#[derive(Component, Default)]
struct MoveIntent {
    axis: Vec2,
    jump: bool,
}

fn radial_deadzone(stick: Vec2, deadzone: f32) -> Vec2 {
    let mag = stick.length();
    if mag <= deadzone || mag == 0.0 {
        return Vec2::ZERO;
    }
    let scaled = ((mag - deadzone) / (1.0 - deadzone)).clamp(0.0, 1.0);
    stick / mag * scaled
}

fn read_pad(pads: Query<&Gamepad>, mut intents: Query<&mut MoveIntent>) {
    let Some(pad) = pads.iter().next() else {
        return;
    };
    let stick = Vec2::new(
        pad.get(GamepadAxis::LeftStickX).unwrap_or(0.0),
        pad.get(GamepadAxis::LeftStickY).unwrap_or(0.0),
    );
    let axis = radial_deadzone(stick, 0.15);
    let jump = pad.just_pressed(GamepadButton::South);
    for mut intent in &mut intents {
        if axis.length_squared() > 0.0 {
            intent.axis = axis;
        }
        if jump {
            intent.jump = true;
        }
    }
}

#[derive(Resource)]
struct JumpBuffer {
    remaining: f32,
    window: f32,
}

fn arm_jump_buffer(time: Res<Time>, mut intents: Query<&mut MoveIntent>, mut buffer: ResMut<JumpBuffer>) {
    let dt = time.delta_secs();
    buffer.remaining = (buffer.remaining - dt).max(0.0);
    for mut intent in &mut intents {
        if intent.jump {
            buffer.remaining = buffer.window;
            intent.jump = false;
        }
    }
}

#[derive(Clone, Copy, PartialEq, Eq, Default)]
enum DeviceKind {
    #[default]
    Keyboard,
    Gamepad,
}

#[derive(Resource, Default)]
struct LastDevice(DeviceKind);

fn track_device(
    keys: Res<ButtonInput<KeyCode>>,
    mouse: Res<ButtonInput<MouseButton>>,
    pads: Query<&Gamepad>,
    mut last: ResMut<LastDevice>,
) {
    if keys.get_pressed().next().is_some() || mouse.get_pressed().next().is_some() {
        last.0 = DeviceKind::Keyboard;
    }
    for pad in &pads {
        if pad.get_pressed().next().is_some() {
            last.0 = DeviceKind::Gamepad;
        }
    }
}

pub struct InputHandlingPlugin;

impl Plugin for InputHandlingPlugin {
    fn build(&self, app: &mut App) {
        app.insert_resource(JumpBuffer {
            remaining: 0.0,
            window: 0.12,
        })
        .init_resource::<LastDevice>()
        .add_systems(Update, (read_pad, track_device, arm_jump_buffer).chain());
    }
}

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 Godot node script
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
An API outside the documented set	Check the official docs first	A made-up crate or API

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 input-map, event, or device types. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No APIs this file did not open (pressed, just_pressed, just_released are the button methods cited). WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No third-party input crates. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

Reference

The library pin on bevy-master stays 0.20.0.

Official Documentation

• bevy crate - API index for this skill's types.
• bevy::input - ButtonInput, InputPlugin, and the device modules.
• ButtonInput - pressed, just_pressed, just_released, KeyCode, and Key.
• bevy::input::mouse - MouseButton, motion, and scroll resources.
• bevy::input::gamepad - Gamepad and connection events.
• Examples - Example tree on the latest branch.

Related Skills

Prerequisites

• bevy-master - Who owns which piece of state.
• bevy-ecs-composition - Systems and Query.

Complements

• bevy-character-movement - Motion that consumes this input on the fixed timestep.
• bevy-camera-systems - Viewpoint that may read mouse motion.
• godot-input-handling - Equivalent Godot skill.

Downstream / consumers

• bevy-audio-systems - The audio control example reads ButtonInput<KeyCode> to pause and mute.

Master

• bevy-master - Bevy router.