Assets / Custom Asset

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This example is running in WebGL2 and should work in most browsers. You can check the WebGPU examples here.

//! Implements loader for a custom asset type.

use bevy::{
    asset::{AssetLoader, LoadContext, LoadedAsset},
    reflect::{TypePath, TypeUuid},
use serde::Deserialize;

#[derive(Debug, Deserialize, TypeUuid, TypePath)]
#[uuid = "39cadc56-aa9c-4543-8640-a018b74b5052"]
pub struct CustomAsset {
    pub value: i32,

pub struct CustomAssetLoader;

impl AssetLoader for CustomAssetLoader {
    fn load<'a>(
        &'a self,
        bytes: &'a [u8],
        load_context: &'a mut LoadContext,
    ) -> BoxedFuture<'a, Result<(), bevy::asset::Error>> {
        Box::pin(async move {
            let custom_asset = ron::de::from_bytes::<CustomAsset>(bytes)?;

    fn extensions(&self) -> &[&str] {

fn main() {
        .add_systems(Startup, setup)
        .add_systems(Update, print_on_load)

#[derive(Resource, Default)]
struct State {
    handle: Handle<CustomAsset>,
    printed: bool,

fn setup(mut state: ResMut<State>, asset_server: Res<AssetServer>) {
    state.handle = asset_server.load("data/asset.custom");

fn print_on_load(mut state: ResMut<State>, custom_assets: ResMut<Assets<CustomAsset>>) {
    let custom_asset = custom_assets.get(&state.handle);
    if state.printed || custom_asset.is_none() {

    info!("Custom asset loaded: {:?}", custom_asset.unwrap());
    state.printed = true;