mirror of
https://github.com/bevyengine/bevy
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5876352206
# Objective
The `AssetReader` trait allows customizing the behavior of fetching
bytes for an `AssetPath`, and expects implementors to return `dyn
AsyncRead + AsyncSeek`. This gives implementors of `AssetLoader` great
flexibility to tightly integrate their asset loading behavior with the
asynchronous task system.
However, almost all implementors of `AssetLoader` don't use the async
functionality at all, and just call `AsyncReadExt::read_to_end(&mut
Vec<u8>)`. This is incredibly inefficient, as this method repeatedly
calls `poll_read` on the trait object, filling the vector 32 bytes at a
time. At my work we have assets that are hundreds of megabytes which
makes this a meaningful overhead.
## Solution
Turn the `Reader` type alias into an actual trait, with a provided
method `read_to_end`. This provided method should be more efficient than
the existing extension method, as the compiler will know the underlying
type of `Reader` when generating this function, which removes the
repeated dynamic dispatches and allows the compiler to make further
optimizations after inlining. Individual implementors are able to
override the provided implementation -- for simple asset readers that
just copy bytes from one buffer to another, this allows removing a large
amount of overhead from the provided implementation.
Now that `Reader` is an actual trait, I also improved the ergonomics for
implementing `AssetReader`. Currently, implementors are expected to box
their reader and return it as a trait object, which adds unnecessary
boilerplate to implementations. This PR changes that trait method to
return a pseudo trait alias, which allows implementors to return `impl
Reader` instead of `Box<dyn Reader>`. Now, the boilerplate for boxing
occurs in `ErasedAssetReader`.
## Testing
I made identical changes to my company's fork of bevy. Our app, which
makes heavy use of `read_to_end` for asset loading, still worked
properly after this. I am not aware if we have a more systematic way of
testing asset loading for correctness.
---
## Migration Guide
The trait method `bevy_asset::io::AssetReader::read` (and `read_meta`)
now return an opaque type instead of a boxed trait object. Implementors
of these methods should change the type signatures appropriately
```rust
impl AssetReader for MyReader {
// Before
async fn read<'a>(&'a self, path: &'a Path) -> Result<Box<Reader<'a>>, AssetReaderError> {
let reader = // construct a reader
Box::new(reader) as Box<Reader<'a>>
}
// After
async fn read<'a>(&'a self, path: &'a Path) -> Result<impl Reader + 'a, AssetReaderError> {
// create a reader
}
}
```
`bevy::asset::io::Reader` is now a trait, rather than a type alias for a
trait object. Implementors of `AssetLoader::load` will need to adjust
the method signature accordingly
```rust
impl AssetLoader for MyLoader {
async fn load<'a>(
&'a self,
// Before:
reader: &'a mut bevy::asset::io::Reader,
// After:
reader: &'a mut dyn bevy::asset::io::Reader,
_: &'a Self::Settings,
load_context: &'a mut LoadContext<'_>,
) -> Result<Self::Asset, Self::Error> {
}
```
Additionally, implementors of `AssetReader` that return a type
implementing `futures_io::AsyncRead` and `AsyncSeek` might need to
explicitly implement `bevy::asset::io::Reader` for that type.
```rust
impl bevy::asset::io::Reader for MyAsyncReadAndSeek {}
```
71 lines
2 KiB
TOML
71 lines
2 KiB
TOML
[package]
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name = "bevy_asset"
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version = "0.14.0-dev"
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edition = "2021"
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description = "Provides asset functionality for Bevy Engine"
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homepage = "https://bevyengine.org"
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repository = "https://github.com/bevyengine/bevy"
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license = "MIT OR Apache-2.0"
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keywords = ["bevy"]
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# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
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[features]
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file_watcher = ["notify-debouncer-full", "watch"]
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embedded_watcher = ["file_watcher"]
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multi_threaded = ["bevy_tasks/multi_threaded"]
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asset_processor = []
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watch = []
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trace = []
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[dependencies]
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bevy_app = { path = "../bevy_app", version = "0.14.0-dev" }
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bevy_asset_macros = { path = "macros", version = "0.14.0-dev" }
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bevy_ecs = { path = "../bevy_ecs", version = "0.14.0-dev" }
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bevy_reflect = { path = "../bevy_reflect", version = "0.14.0-dev", features = [
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"uuid",
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] }
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bevy_tasks = { path = "../bevy_tasks", version = "0.14.0-dev" }
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bevy_utils = { path = "../bevy_utils", version = "0.14.0-dev" }
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stackfuture = "0.3"
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async-broadcast = "0.5"
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async-fs = "2.0"
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async-lock = "3.0"
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crossbeam-channel = "0.5"
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downcast-rs = "1.2"
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futures-io = "0.3"
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futures-lite = "2.0.1"
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blake3 = "1.5"
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parking_lot = { version = "0.12", features = ["arc_lock", "send_guard"] }
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ron = "0.8"
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serde = { version = "1", features = ["derive"] }
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thiserror = "1.0"
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uuid = { version = "1.0", features = ["v4"] }
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[target.'cfg(target_os = "android")'.dependencies]
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bevy_winit = { path = "../bevy_winit", version = "0.14.0-dev" }
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[target.'cfg(target_arch = "wasm32")'.dependencies]
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wasm-bindgen = { version = "0.2" }
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web-sys = { version = "0.3", features = [
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"Window",
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"Response",
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"WorkerGlobalScope",
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] }
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wasm-bindgen-futures = "0.4"
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js-sys = "0.3"
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[target.'cfg(not(target_arch = "wasm32"))'.dependencies]
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notify-debouncer-full = { version = "0.3.1", optional = true }
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[dev-dependencies]
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bevy_core = { path = "../bevy_core", version = "0.14.0-dev" }
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bevy_log = { path = "../bevy_log", version = "0.14.0-dev" }
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[lints]
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workspace = true
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[package.metadata.docs.rs]
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rustdoc-args = ["-Zunstable-options", "--cfg", "docsrs"]
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all-features = true
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