outfly/src/main.rs

use bevy::{
    asset::LoadState,
    core_pipeline::Skybox,
    prelude::*,
    render::{
        render_resource::{TextureViewDescriptor, TextureViewDimension},
        renderer::RenderDevice,
        texture::CompressedImageFormats,
    },
};

fn main() {
    App::new()
        .add_systems(Startup, setup)
        .add_systems(Update, (
                asset_loaded.after(load_cubemap_asset),
                handle_input
        ))
        .add_plugins(DefaultPlugins.set(ImagePlugin::default_nearest()))
        .run();
}

#[derive(Resource)]
struct Cubemap {
    is_loaded: bool,
    index: usize,
    image_handle: Handle<Image>,
}

const CUBEMAPS: &[(&str, CompressedImageFormats)] = &[
    (
        "textures/stars_cubemap.png",
        CompressedImageFormats::NONE,
    ),
];

fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
    let skybox_handle = asset_server.load(CUBEMAPS[0].0);
    // camera
    commands.spawn((
        Camera3dBundle {
            transform: Transform::from_xyz(0.0, 0.0, 8.0).looking_at(Vec3::ZERO, Vec3::Y),
            ..default()
        },
        Skybox {
            image: skybox_handle.clone(),
            brightness: 150.0,
        },
    ));
    commands.insert_resource(Cubemap {
        is_loaded: false,
        index: 0,
        image_handle: skybox_handle,
    });
}

fn load_cubemap_asset(
    mut cubemap: ResMut<Cubemap>,
    asset_server: Res<AssetServer>,
    render_device: Res<RenderDevice>,
) {
    let supported_compressed_formats =
        CompressedImageFormats::from_features(render_device.features());

    let mut new_index = cubemap.index;
    for _ in 0..CUBEMAPS.len() {
        new_index = (new_index + 1) % CUBEMAPS.len();
        if supported_compressed_formats.contains(CUBEMAPS[new_index].1) {
            break;
        }
        info!("Skipping unsupported format: {:?}", CUBEMAPS[new_index]);
    }

    // Skip swapping to the same texture. Useful for when ktx2, zstd, or compressed texture support
    // is missing
    if new_index == cubemap.index {
        return;
    }

    cubemap.index = new_index;
    cubemap.image_handle = asset_server.load(CUBEMAPS[cubemap.index].0);
    cubemap.is_loaded = false;
}

fn asset_loaded(
    asset_server: Res<AssetServer>,
    mut images: ResMut<Assets<Image>>,
    mut cubemap: ResMut<Cubemap>,
    mut skyboxes: Query<&mut Skybox>,
) {
    if !cubemap.is_loaded && asset_server.load_state(&cubemap.image_handle) == LoadState::Loaded {
        info!("Swapping to {}...", CUBEMAPS[cubemap.index].0);
        let image = images.get_mut(&cubemap.image_handle).unwrap();
        // NOTE: PNGs do not have any metadata that could indicate they contain a cubemap texture,
        // so they appear as one texture. The following code reconfigures the texture as necessary.
        if image.texture_descriptor.array_layer_count() == 1 {
            image.reinterpret_stacked_2d_as_array(image.height() / image.width());
            image.texture_view_descriptor = Some(TextureViewDescriptor {
                dimension: Some(TextureViewDimension::Cube),
                ..default()
            });
        }

        for mut skybox in &mut skyboxes {
            skybox.image = cubemap.image_handle.clone();
        }

        cubemap.is_loaded = true;
    }
}

fn handle_input(
    keyboard_input: Res<ButtonInput<KeyCode>>,
    mut app_exit_events: ResMut<Events<bevy::app::AppExit>>
) {
    if keyboard_input.pressed(KeyCode::KeyQ) {
        app_exit_events.send(bevy::app::AppExit);
    }
}