load a skybox with stars

src/main.rs

@@ -1,12 +1,114 @@
-use bevy::prelude::*;
+use bevy::{
+    asset::LoadState,
+    core_pipeline::Skybox,
+    prelude::*,
+    render::{
+        render_resource::{TextureViewDescriptor, TextureViewDimension},
+        renderer::RenderDevice,
+        texture::CompressedImageFormats,
+    },
+};
 
 fn main() {
     App::new()
-        .add_systems(Update, handle_input)
+        .add_systems(Startup, setup)
+        .add_systems(Update, (
+                asset_loaded.after(load_cubemap_asset),
+                handle_input
+        ))
         .add_plugins((DefaultPlugins, ))
         .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>>