keyboard_input.md

Keyboard Input

Our app can monitor if a key of the keyboard is pressed or not.

In the following example, we use the key left and the key right to control a circle. When left is pressed, the circle is moved toward left, and when right is pressed, the circle is moved toward right.

We create a resource MyCirclePositionX to hold the x position of the circle.

#[derive(Resource, Default)]
struct MyCirclePositionX(f32);

We add a Circle to our App.

fn setup(mut commands: Commands, mut meshes: ResMut<Assets<Mesh>>) {
    commands.spawn(Camera2dBundle::default());

    commands.spawn(ColorMesh2dBundle {
        mesh: meshes.add(Circle::new(50.).into()).into(),
        ..default()
    });
}

When the target keys are pressed, we change the Transform of the circle according to the x position stored in MyCirclePositionX.

fn handle_keys(
    keyboard_input: Res<Input<KeyCode>>,
    mut my_circle_pos_x: ResMut<MyCirclePositionX>,
    mut circles: Query<&mut Transform, With<Handle<ColorMaterial>>>,
) {
    let mut transform = circles.single_mut();

    if keyboard_input.pressed(KeyCode::Left) {
        my_circle_pos_x.0 -= 10.;
        *transform = Transform::from_xyz(my_circle_pos_x.0, 0., 0.);
    }

    if keyboard_input.pressed(KeyCode::Right) {
        my_circle_pos_x.0 += 10.;
        *transform = Transform::from_xyz(my_circle_pos_x.0, 0., 0.);
    }
}

We use the resource Input<KeyCode> to get the information of the keyboard. The method pressed of keyboard_input returns true if the corresponding key is pressed. Our system handle_keys will be executed for each frame update.

The full code is as follows:

use bevy::{
    app::{App, Startup, Update},
    asset::{Assets, Handle},
    core_pipeline::core_2d::Camera2dBundle,
    ecs::{
        query::With,
        system::{Commands, Query, Res, ResMut, Resource},
    },
    input::{keyboard::KeyCode, Input},
    render::mesh::{shape::Circle, Mesh},
    sprite::{ColorMaterial, ColorMesh2dBundle},
    transform::components::Transform,
    utils::default,
    DefaultPlugins,
};

#[derive(Resource, Default)]
struct MyCirclePositionX(f32);

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .init_resource::<MyCirclePositionX>()
        .add_systems(Startup, setup)
        .add_systems(Update, handle_keys)
        .run();
}

fn setup(mut commands: Commands, mut meshes: ResMut<Assets<Mesh>>) {
    commands.spawn(Camera2dBundle::default());

    commands.spawn(ColorMesh2dBundle {
        mesh: meshes.add(Circle::new(50.).into()).into(),
        ..default()
    });
}

fn handle_keys(
    keyboard_input: Res<Input<KeyCode>>,
    mut my_circle_pos_x: ResMut<MyCirclePositionX>,
    mut circles: Query<&mut Transform, With<Handle<ColorMaterial>>>,
) {
    let mut transform = circles.single_mut();

    if keyboard_input.pressed(KeyCode::Left) {
        my_circle_pos_x.0 -= 10.;
        *transform = Transform::from_xyz(my_circle_pos_x.0, 0., 0.);
    }

    if keyboard_input.pressed(KeyCode::Right) {
        my_circle_pos_x.0 += 10.;
        *transform = Transform::from_xyz(my_circle_pos_x.0, 0., 0.);
    }
}

When the app just starts:

After the key right pressed for a while:

The resource Input<KeyCode> also monitors modifier keys such as ShiftLeft, ShiftRight, ControlLeft, ControlRight, etc.

➡️ Next: Keyboard Just Input

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