bevy/examples/ui/text.rs

//! This example illustrates how to create UI text and update it in a system.
//!
//! It displays the current FPS in the top left corner, as well as text that changes color
//! in the bottom right. For text within a scene, please see the text2d example.

use bevy::{
    diagnostic::{Diagnostics, FrameTimeDiagnosticsPlugin},
    prelude::*,
};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugin(FrameTimeDiagnosticsPlugin::default())
        .add_startup_system(setup)
        .add_system(text_update_system)
        .add_system(text_color_system)
        .run();
}

// A unit struct to help identify the FPS UI component, since there may be many Text components
#[derive(Component)]
struct FpsText;

// A unit struct to help identify the color-changing Text component
#[derive(Component)]
struct ColorText;

fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
    // UI camera
    commands.spawn(Camera2dBundle::default());
    // Text with one section
    commands.spawn((
        // Create a TextBundle that has a Text with a single section.
        TextBundle::from_section(
            // Accepts a `String` or any type that converts into a `String`, such as `&str`
            "hello\nbevy!",
            TextStyle {
                font: asset_server.load("fonts/FiraSans-Bold.ttf"),
                font_size: 100.0,
                color: Color::WHITE,
            },
        ) // Set the alignment of the Text
        .with_text_alignment(TextAlignment::TOP_CENTER)
        // Set the style of the TextBundle itself.
        .with_style(Style {
            position_type: PositionType::Absolute,
            position: UiRect {
                bottom: Val::Px(5.0),
                right: Val::Px(15.0),
                ..default()
            },
            ..default()
        }),
        ColorText,
    ));
    // Text with multiple sections
    commands.spawn((
        // Create a TextBundle that has a Text with a list of sections.
        TextBundle::from_sections([
            TextSection::new(
                "FPS: ",
                TextStyle {
                    font: asset_server.load("fonts/FiraSans-Bold.ttf"),
                    font_size: 60.0,
                    color: Color::WHITE,
                },
            ),
            TextSection::from_style(TextStyle {
                font: asset_server.load("fonts/FiraMono-Medium.ttf"),
                font_size: 60.0,
                color: Color::GOLD,
            }),
        ]),
        FpsText,
    ));
}

fn text_color_system(time: Res<Time>, mut query: Query<&mut Text, With<ColorText>>) {
    for mut text in &mut query {
        let seconds = time.seconds_since_startup() as f32;

        // Update the color of the first and only section.
        text.sections[0].style.color = Color::Rgba {
            red: (1.25 * seconds).sin() / 2.0 + 0.5,
            green: (0.75 * seconds).sin() / 2.0 + 0.5,
            blue: (0.50 * seconds).sin() / 2.0 + 0.5,
            alpha: 1.0,
        };
    }
}

fn text_update_system(diagnostics: Res<Diagnostics>, mut query: Query<&mut Text, With<FpsText>>) {
    for mut text in &mut query {
        if let Some(fps) = diagnostics.get(FrameTimeDiagnosticsPlugin::FPS) {
            if let Some(average) = fps.average() {
                // Update the value of the second section
                text.sections[1].value = format!("{average:.2}");
            }
        }
    }
}