Bevy Input Handling Agent Skill

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.