Hot-Reloading Assets

Relevant official examples: hot_asset_reloading.

At runtime, if you modify the file of an asset that is loaded into the game (via the AssetServer), Bevy can detect that and reload the asset automatically. This is very useful for quick iteration. You can edit your assets while the game is running and see the changes instantly in-game.

Not all file formats and use cases are supported equally well. Typical asset types like textures / images should work without issues, but complex GLTF or scene files, or assets involving custom logic, might not.

If you need to run custom logic as part of your hot-reloading workflow, you could implement it in a system, using AssetEvent (learn more).

Hot reloading is opt-in and has to be enabled in order to work:

fn main() {
    App::new()
        .add_plugins(DefaultPlugins.set(AssetPlugin {
            watch_for_changes: true,
            ..Default::default()
        }))
        .run();
}

Note that this requires the filesystem_watcher Bevy cargo feature. It is enabled by default, but if you have disabled default features to customize Bevy, be sure to include it if you need it.

Shaders

Bevy also supports hot-reloading for shaders. You can edit your custom shader code and see the changes immediately.

This works for any shader loaded from a file path, such as shaders specified in your Materials definitions, or shaders loaded via the AssetServer.

Shader code that does not come from asset files, such as if you include it as a static string in your source code, cannot be hot-reloaded (for obvious reasons).