bevy 0.8.0

//! 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_bundle(Camera2dBundle::default());
    // Text with one section
    commands
        .spawn_bundle(
            // 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 {
                align_self: AlignSelf::FlexEnd,
                position_type: PositionType::Absolute,
                position: UiRect {
                    bottom: Val::Px(5.0),
                    right: Val::Px(15.0),
                    ..default()
                },
                ..default()
            }),
        )
        .insert(ColorText);
    // Text with multiple sections
    commands
        .spawn_bundle(
            // 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,
                }),
            ])
            .with_style(Style {
                align_self: AlignSelf::FlexEnd,
                ..default()
            }),
        )
        .insert(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}");
            }
        }
    }
}