WASM asset loading (#559)

wasm assets

Cargo.toml

@@ -94,6 +94,7 @@ log = "0.4"
 #wasm
 console_error_panic_hook = "0.1.6"
 console_log = { version = "0.2", features = ["color"] }
+anyhow = "1.0"
 
 [[example]]
 name = "hello_world"
@@ -281,3 +282,8 @@ required-features = []
 name = "winit_wasm"
 path = "examples/wasm/winit_wasm.rs"
 required-features = ["bevy_winit"]
+
+[[example]]
+name = "assets_wasm"
+path = "examples/wasm/assets_wasm.rs"
+required-features = ["bevy_winit"]

crates/bevy_asset/Cargo.toml

@@ -34,3 +34,10 @@ thiserror = "1.0"
 log = { version = "0.4", features = ["release_max_level_info"] }
 notify = { version = "5.0.0-pre.2", optional = true }
 parking_lot = "0.11.0"
+async-trait = "0.1.40"
+
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+wasm-bindgen = { version = "0.2" }
+web-sys = { version = "0.3", features = ["Request", "Window", "Response"]}
+wasm-bindgen-futures = "0.4"
+js-sys = "0.3"

crates/bevy_asset/src/asset_server.rs

@@ -9,11 +9,10 @@ use bevy_utils::{HashMap, HashSet};
 use crossbeam_channel::TryRecvError;
 use parking_lot::RwLock;
 use std::{
-    env, fs, io,
+    fs, io,
     path::{Path, PathBuf},
     sync::Arc,
 };
-
 use thiserror::Error;
 
 /// The type used for asset versioning
@@ -67,8 +66,7 @@ impl LoadState {
 /// Loads assets from the filesystem on background threads
 pub struct AssetServer {
     asset_folders: RwLock<Vec<PathBuf>>,
-    asset_handlers: Arc<RwLock<Vec<Box<dyn AssetLoadRequestHandler>>>>,
-    // TODO: this is a hack to enable retrieving generic AssetLoader<T>s. there must be a better way!
+    asset_handlers: RwLock<Vec<Arc<dyn AssetLoadRequestHandler>>>,
     loaders: Vec<Resources>,
     task_pool: TaskPool,
     extension_to_handler_index: HashMap<String, usize>,
@@ -106,7 +104,7 @@ impl AssetServer {
                 .insert(extension.to_string(), handler_index);
         }
 
-        asset_handlers.push(Box::new(asset_handler));
+        asset_handlers.push(Arc::new(asset_handler));
     }
 
     pub fn add_loader<TLoader, TAsset>(&mut self, loader: TLoader)
@@ -173,11 +171,12 @@ impl AssetServer {
         Ok(())
     }
 
+    #[cfg(not(target_arch = "wasm32"))]
     fn get_root_path(&self) -> Result<PathBuf, AssetServerError> {
-        if let Ok(manifest_dir) = env::var("CARGO_MANIFEST_DIR") {
+        if let Ok(manifest_dir) = std::env::var("CARGO_MANIFEST_DIR") {
             Ok(PathBuf::from(manifest_dir))
         } else {
-            match env::current_exe() {
+            match std::env::current_exe() {
                 Ok(exe_path) => exe_path
                     .parent()
                     .ok_or(AssetServerError::InvalidRootPath)
@@ -187,6 +186,11 @@ impl AssetServer {
         }
     }
 
+    #[cfg(target_arch = "wasm32")]
+    fn get_root_path(&self) -> Result<PathBuf, AssetServerError> {
+        Ok(PathBuf::from("/"))
+    }
+
     // TODO: add type checking here. people shouldn't be able to request a Handle<Texture> for a Mesh asset
     pub fn load<T, P: AsRef<Path>>(&self, path: P) -> Result<Handle<T>, AssetServerError> {
         self.load_untyped(self.get_root_path()?.join(path))
@@ -272,19 +276,22 @@ impl AssetServer {
                     version: new_version,
                 };
 
-                let asset_handlers = self.asset_handlers.clone();
+                let handlers = self.asset_handlers.read();
+                let request_handler = handlers[load_request.handler_index].clone();
+
                 self.task_pool
                     .spawn(async move {
-                        let handlers = asset_handlers.read();
-                        let request_handler = &handlers[load_request.handler_index];
-                        request_handler.handle_request(&load_request);
+                        request_handler.handle_request(&load_request).await;
                     })
                     .detach();
 
                 // TODO: watching each asset explicitly is a simpler implementation, its possible it would be more efficient to watch
                 // folders instead (when possible)
                 #[cfg(feature = "filesystem_watcher")]
-                Self::watch_path_for_changes(&mut self.filesystem_watcher.write(), path)?;
+                Self::watch_path_for_changes(
+                    &mut self.filesystem_watcher.write(),
+                    path.to_owned(),
+                )?;
                 Ok(handle_id)
             } else {
                 Err(AssetServerError::MissingAssetHandler)

crates/bevy_asset/src/load_request/mod.rs

@@ -0,0 +1,31 @@
+use crate::{AssetLoader, AssetResult, AssetVersion, HandleId};
+use crossbeam_channel::Sender;
+use std::path::PathBuf;
+
+#[cfg(not(target_arch = "wasm32"))]
+#[path = "platform_default.rs"]
+mod platform_specific;
+
+#[cfg(target_arch = "wasm32")]
+#[path = "platform_wasm.rs"]
+mod platform_specific;
+
+pub use platform_specific::*;
+
+/// A request from an [AssetServer](crate::AssetServer) to load an asset.
+#[derive(Debug)]
+pub struct LoadRequest {
+    pub path: PathBuf,
+    pub handle_id: HandleId,
+    pub handler_index: usize,
+    pub version: AssetVersion,
+}
+
+pub(crate) struct ChannelAssetHandler<TLoader, TAsset>
+where
+    TLoader: AssetLoader<TAsset>,
+    TAsset: 'static,
+{
+    sender: Sender<AssetResult<TAsset>>,
+    loader: TLoader,
+}

crates/bevy_asset/src/load_request/platform_default.rs

@@ -1,32 +1,16 @@
-use crate::{AssetLoadError, AssetLoader, AssetResult, AssetVersion, Handle, HandleId};
+use super::{ChannelAssetHandler, LoadRequest};
+use crate::{AssetLoadError, AssetLoader, AssetResult, Handle};
 use anyhow::Result;
+use async_trait::async_trait;
 use crossbeam_channel::Sender;
-use fs::File;
-use io::Read;
-use std::{fs, io, path::PathBuf};
-
-/// A request from an [AssetServer](crate::AssetServer) to load an asset.
-#[derive(Debug)]
-pub struct LoadRequest {
-    pub path: PathBuf,
-    pub handle_id: HandleId,
-    pub handler_index: usize,
-    pub version: AssetVersion,
-}
+use std::{fs::File, io::Read};
 
 /// Handles load requests from an AssetServer
-pub trait AssetLoadRequestHandler: Send + Sync + 'static {
-    fn handle_request(&self, load_request: &LoadRequest);
-    fn extensions(&self) -> &[&str];
-}
 
-pub(crate) struct ChannelAssetHandler<TLoader, TAsset>
-where
-    TLoader: AssetLoader<TAsset>,
-    TAsset: 'static,
-{
-    sender: Sender<AssetResult<TAsset>>,
-    loader: TLoader,
+#[async_trait]
+pub trait AssetLoadRequestHandler: Send + Sync + 'static {
+    async fn handle_request(&self, load_request: &LoadRequest);
+    fn extensions(&self) -> &[&str];
 }
 
 impl<TLoader, TAsset> ChannelAssetHandler<TLoader, TAsset>
@@ -53,12 +37,13 @@ where
     }
 }
 
+#[async_trait]
 impl<TLoader, TAsset> AssetLoadRequestHandler for ChannelAssetHandler<TLoader, TAsset>
 where
     TLoader: AssetLoader<TAsset> + 'static,
     TAsset: Send + 'static,
 {
-    fn handle_request(&self, load_request: &LoadRequest) {
+    async fn handle_request(&self, load_request: &LoadRequest) {
         let result = self.load_asset(load_request);
         let asset_result = AssetResult {
             handle: Handle::from(load_request.handle_id),

crates/bevy_asset/src/load_request/platform_wasm.rs

@@ -0,0 +1,62 @@
+use super::{ChannelAssetHandler, LoadRequest};
+use crate::{AssetLoadError, AssetLoader, AssetResult, Handle};
+use anyhow::Result;
+use async_trait::async_trait;
+use crossbeam_channel::Sender;
+
+use js_sys::Uint8Array;
+use wasm_bindgen::JsCast;
+use wasm_bindgen_futures::JsFuture;
+use web_sys::Response;
+
+#[async_trait(?Send)]
+pub trait AssetLoadRequestHandler: Send + Sync + 'static {
+    async fn handle_request(&self, load_request: &LoadRequest);
+    fn extensions(&self) -> &[&str];
+}
+
+impl<TLoader, TAsset> ChannelAssetHandler<TLoader, TAsset>
+where
+    TLoader: AssetLoader<TAsset>,
+{
+    pub fn new(loader: TLoader, sender: Sender<AssetResult<TAsset>>) -> Self {
+        ChannelAssetHandler { sender, loader }
+    }
+
+    async fn load_asset(&self, load_request: &LoadRequest) -> Result<TAsset, AssetLoadError> {
+        // TODO - get rid of some unwraps below (do some retrying maybe?)
+        let window = web_sys::window().unwrap();
+        let resp_value = JsFuture::from(window.fetch_with_str(load_request.path.to_str().unwrap()))
+            .await
+            .unwrap();
+        let resp: Response = resp_value.dyn_into().unwrap();
+        let data = JsFuture::from(resp.array_buffer().unwrap()).await.unwrap();
+        let bytes = Uint8Array::new(&data).to_vec();
+        let asset = self.loader.from_bytes(&load_request.path, bytes).unwrap();
+        Ok(asset)
+    }
+}
+
+#[async_trait(?Send)]
+impl<TLoader, TAsset> AssetLoadRequestHandler for ChannelAssetHandler<TLoader, TAsset>
+where
+    TLoader: AssetLoader<TAsset> + 'static,
+    TAsset: Send + 'static,
+{
+    async fn handle_request(&self, load_request: &LoadRequest) {
+        let asset = self.load_asset(load_request).await;
+        let asset_result = AssetResult {
+            handle: Handle::from(load_request.handle_id),
+            result: asset,
+            path: load_request.path.clone(),
+            version: load_request.version,
+        };
+        self.sender
+            .send(asset_result)
+            .expect("loaded asset should have been sent");
+    }
+
+    fn extensions(&self) -> &[&str] {
+        self.loader.extensions()
+    }
+}

crates/bevy_tasks/Cargo.toml

@@ -16,3 +16,5 @@ event-listener = "2.4.0"
 async-executor = "1.3.0"
 async-channel = "1.4.2"
 num_cpus = "1"
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+wasm-bindgen-futures = "0.4"

crates/bevy_tasks/src/single_threaded_task_pool.rs

@@ -82,6 +82,32 @@ impl TaskPool {
             .map(|result| result.lock().unwrap().take().unwrap())
             .collect()
     }
+
+    // Spawns a static future onto the JS event loop. For now it is returning FakeTask
+    // instance with no-op detach method. Returning real Task is possible here, but tricky:
+    // future is running on JS event loop, Task is running on async_executor::LocalExecutor
+    // so some proxy future is needed. Moreover currently we don't have long-living
+    // LocalExecutor here (above `spawn` implementation creates temporary one)
+    // But for typical use cases it seems that current implementation should be sufficient:
+    // caller can spawn long-running future writing results to some channel / event queue
+    // and simply call detach on returned Task (like AssetServer does) - spawned future
+    // can write results to some channel / event queue.
+
+    pub fn spawn<T>(&self, future: impl Future<Output = T> + 'static) -> FakeTask
+    where
+        T: 'static,
+    {
+        wasm_bindgen_futures::spawn_local(async move {
+            future.await;
+        });
+        FakeTask
+    }
+}
+
+pub struct FakeTask;
+
+impl FakeTask {
+    pub fn detach(self) {}
 }
 
 pub struct Scope<'scope, T> {

examples/wasm/assets_wasm.rs

@@ -0,0 +1,65 @@
+extern crate console_error_panic_hook;
+use bevy::{asset::AssetLoader, prelude::*};
+use std::{panic, path::PathBuf};
+
+fn main() {
+    panic::set_hook(Box::new(console_error_panic_hook::hook));
+    console_log::init_with_level(log::Level::Debug).expect("cannot initialize console_log");
+
+    App::build()
+        .add_default_plugins()
+        .add_asset::<RustSourceCode>()
+        .add_asset_loader::<RustSourceCode, RustSourceCodeLoader>()
+        .add_startup_system(asset_system.system())
+        .add_system(asset_events.system())
+        .run();
+}
+
+fn asset_system(asset_server: Res<AssetServer>) {
+    asset_server
+        .load::<Handle<RustSourceCode>, _>(PathBuf::from("assets_wasm.rs"))
+        .unwrap();
+    log::info!("hello wasm");
+}
+
+#[derive(Debug)]
+pub struct RustSourceCode(pub String);
+
+#[derive(Default)]
+pub struct RustSourceCodeLoader;
+impl AssetLoader<RustSourceCode> for RustSourceCodeLoader {
+    fn from_bytes(
+        &self,
+        _asset_path: &std::path::Path,
+        bytes: Vec<u8>,
+    ) -> Result<RustSourceCode, anyhow::Error> {
+        Ok(RustSourceCode(String::from_utf8(bytes)?))
+    }
+
+    fn extensions(&self) -> &[&str] {
+        static EXT: &[&str] = &["rs"];
+        EXT
+    }
+}
+
+#[derive(Default)]
+pub struct AssetEventsState {
+    reader: EventReader<AssetEvent<RustSourceCode>>,
+}
+
+pub fn asset_events(
+    mut state: Local<AssetEventsState>,
+    rust_sources: Res<Assets<RustSourceCode>>,
+    events: Res<Events<AssetEvent<RustSourceCode>>>,
+) {
+    for event in state.reader.iter(&events) {
+        match event {
+            AssetEvent::Created { handle } => {
+                if let Some(code) = rust_sources.get(handle) {
+                    log::info!("code: {}", code.0);
+                }
+            }
+            _ => continue,
+        };
+    }
+}