Commit graph

17 commits

Author SHA1 Message Date
Joseph
5876352206
Optimize common usages of AssetReader (#14082)
# 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 {}
```
2024-07-01 19:59:42 +00:00
Ricky Taylor
efcb6d6c11
Make LoadContext use the builder pattern for loading dependent assets (#13465)
# Objective
- Fixes #13445.

## Solution
- Removes all `load_` methods from `LoadContext`.
- Introduces `fn loader()` which returns a builder.

## Testing
- I've tested with `cargo test --package=bevy_asset` and run the two
relevant examples (`asset_processing` & `asset_decompression`).

---

## Changelog
- Replaced all `load_` methods on `LoadContext` with the new `loader()`
pattern.

## Migration Guide
- Several LoadContext method calls will need to be updated:
- `load_context.load_with_settings(path, settings)` =>
`load_context.loader().with_settings(settings).load(path)`
- `load_context.load_untyped(path)` =>
`load_context.loader().untyped().load(path)`
- `load_context.load_direct(path)` =>
`load_context.loader().direct().load(path)`
- `load_context.load_direct_untyped(path)` =>
`load_context.loader().direct().untyped().load(path)`
- `load_context.load_direct_with_settings(path, settings)` =>
`load_context.loader().with_settings(settings).direct().load(path)`
- `load_context.load_direct_with_reader(reader, path)` =>
`load_context.loader().direct().with_reader(reader).load(path)`
- `load_context.load_direct_with_reader_and_settings(reader, path,
settings)` =>
`load_context.loader().with_settings(settings).direct().with_reader(reader).load(path)`
- `load_context.load_direct_untyped_with_reader(reader, path)` =>
`load_context.loader().direct().with_reader(reader).untyped().load(path)`

---

CC @alice-i-cecile / @bushrat011899 

Examples:
```rust
load_context.loader()
    .with_asset_type::<A>()
    .with_asset_type_id(TypeId::of::<A>())
    .with_settings(|mut settings| { settings.key = value; })
    // Then, for a Handle<A>:
    .load::<A>()
    // Or, for a Handle<LoadedUntypedAsset>:
    .untyped()
    .load()
    // Or, to load an `A` directly:
    .direct()
    .load::<A>()
    .await
    // Or, to load an `ErasedLoadedAsset` directly:
    .direct()
    .untyped()
    .load()
    .await
```
2024-05-22 23:35:41 +00:00
Ricky Taylor
26df1c1179
Add more load_direct implementations (#13415)
# Objective
- Introduce variants of `LoadContext::load_direct` which allow picking
asset type & configuring settings.
- Fixes #12963.

## Solution
- Implements `ErasedLoadedAsset::downcast` and adds some accessors to
`LoadedAsset<A>`.
- Changes `load_direct`/`load_direct_with_reader` to be typed, and
introduces `load_direct_untyped`/`load_direct_untyped_with_reader`.
- Introduces `load_direct_with_settings` and
`load_direct_with_reader_and_settings`.

## Testing
- I've run cargo test and played with the examples which use
`load_direct`.
- I also extended the `asset_processing` example to use the new typed
version of `load_direct` and use `load_direct_with_settings`.

---

## Changelog
- Introduced new `load_direct` methods in `LoadContext` to allow
specifying type & settings

## Migration Guide
- `LoadContext::load_direct` has been renamed to
`LoadContext::load_direct_untyped`. You may find the new `load_direct`
is more appropriate for your use case (and the migration may only be
moving one type parameter).
- `LoadContext::load_direct_with_reader` has been renamed to
`LoadContext::load_direct_untyped_with_reader`.

---

This might not be an obvious win as a solution because it introduces
quite a few new `load_direct` alternatives - but it does follow the
existing pattern pretty well. I'm very open to alternatives.
😅
2024-05-21 18:32:00 +00:00
BD103
7b8d502083
Fix beta lints (#12980)
# Objective

- Fixes #12976

## Solution

This one is a doozy.

- Run `cargo +beta clippy --workspace --all-targets --all-features` and
fix all issues
- This includes:
- Moving inner attributes to be outer attributes, when the item in
question has both inner and outer attributes
  - Use `ptr::from_ref` in more scenarios
- Extend the valid idents list used by `clippy:doc_markdown` with more
names
  - Use `Clone::clone_from` when possible
  - Remove redundant `ron` import
  - Add backticks to **so many** identifiers and items
    - I'm sorry whoever has to review this

---

## Changelog

- Added links to more identifiers in documentation.
2024-04-16 02:46:46 +00:00
Ame
0256dacba4
Fix some doc warnings (#12961)
# Objective

- Fix some doc warnings 
- Add doc-scrape-examples to all examples

Moved from #12692 

I run `cargo +nightly doc --workspace --all-features --no-deps
-Zunstable-options -Zrustdoc-scrape-examples`

<details>

```
warning: public documentation for `GzAssetLoaderError` links to private item `GzAssetLoader`
  --> examples/asset/asset_decompression.rs:24:47
   |
24 | /// Possible errors that can be produced by [`GzAssetLoader`]
   |                                               ^^^^^^^^^^^^^ this item is private
   |
   = note: this link will resolve properly if you pass `--document-private-items`
   = note: `#[warn(rustdoc::private_intra_doc_links)]` on by default

warning: `bevy` (example "asset_decompression") generated 1 warning
warning: unresolved link to `shape::Quad`
 --> examples/2d/mesh2d.rs:3:15
  |
3 | //! [`Quad`]: shape::Quad
  |               ^^^^^^^^^^^ no item named `shape` in scope
  |
  = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default

warning: `bevy` (example "mesh2d") generated 1 warning
warning: unresolved link to `WorldQuery`
 --> examples/ecs/custom_query_param.rs:1:49
  |
1 | //! This example illustrates the usage of the [`WorldQuery`] derive macro, which allows
  |                                                 ^^^^^^^^^^ no item named `WorldQuery` in scope
  |
  = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
  = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default

warning: `bevy` (example "custom_query_param") generated 1 warning
warning: unresolved link to `shape::Quad`
 --> examples/2d/mesh2d_vertex_color_texture.rs:4:15
  |
4 | //! [`Quad`]: shape::Quad
  |               ^^^^^^^^^^^ no item named `shape` in scope
  |
  = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default

warning: `bevy` (example "mesh2d_vertex_color_texture") generated 1 warning
warning: public documentation for `TextPlugin` links to private item `CoolText`
  --> examples/asset/processing/asset_processing.rs:48:9
   |
48 | /// * [`CoolText`]: a custom RON text format that supports dependencies and embedded dependencies
   |         ^^^^^^^^ this item is private
   |
   = note: this link will resolve properly if you pass `--document-private-items`
   = note: `#[warn(rustdoc::private_intra_doc_links)]` on by default

warning: public documentation for `TextPlugin` links to private item `Text`
  --> examples/asset/processing/asset_processing.rs:49:9
   |
49 | /// * [`Text`]: a "normal" plain text file
   |         ^^^^ this item is private
   |
   = note: this link will resolve properly if you pass `--document-private-items`

warning: public documentation for `TextPlugin` links to private item `CoolText`
  --> examples/asset/processing/asset_processing.rs:51:57
   |
51 | /// It also defines an asset processor that will load [`CoolText`], resolve embedded dependenc...
   |                                                         ^^^^^^^^ this item is private
   |
   = note: this link will resolve properly if you pass `--document-private-items`

warning: `bevy` (example "asset_processing") generated 3 warnings
warning: public documentation for `CustomAssetLoaderError` links to private item `CustomAssetLoader`
  --> examples/asset/custom_asset.rs:20:47
   |
20 | /// Possible errors that can be produced by [`CustomAssetLoader`]
   |                                               ^^^^^^^^^^^^^^^^^ this item is private
   |
   = note: this link will resolve properly if you pass `--document-private-items`
   = note: `#[warn(rustdoc::private_intra_doc_links)]` on by default

warning: public documentation for `BlobAssetLoaderError` links to private item `CustomAssetLoader`
  --> examples/asset/custom_asset.rs:61:47
   |
61 | /// Possible errors that can be produced by [`CustomAssetLoader`]
   |                                               ^^^^^^^^^^^^^^^^^ this item is private
   |
   = note: this link will resolve properly if you pass `--document-private-items`
```

```
warning: `bevy` (example "mesh2d") generated 1 warning
warning: public documentation for `log_layers_ecs` links to private item `update_subscriber`
 --> examples/app/log_layers_ecs.rs:6:18
  |
6 | //! Inside the [`update_subscriber`] function we will create a [`mpsc::Sender`] and a [`mpsc::R...
  |                  ^^^^^^^^^^^^^^^^^ this item is private
  |
  = note: this link will resolve properly if you pass `--document-private-items`
  = note: `#[warn(rustdoc::private_intra_doc_links)]` on by default

warning: unresolved link to `AdvancedLayer`
 --> examples/app/log_layers_ecs.rs:7:72
  |
7 | ... will go into the [`AdvancedLayer`] and the [`Receiver`](mpsc::Receiver) will
  |                        ^^^^^^^^^^^^^ no item named `AdvancedLayer` in scope
  |
  = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
  = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default

warning: unresolved link to `LogEvents`
 --> examples/app/log_layers_ecs.rs:8:42
  |
8 | //! go into a non-send resource called [`LogEvents`] (It has to be non-send because [`Receiver`...
  |                                          ^^^^^^^^^ no item named `LogEvents` in scope
  |
  = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`

warning: public documentation for `log_layers_ecs` links to private item `transfer_log_events`
 --> examples/app/log_layers_ecs.rs:9:30
  |
9 | //! From there we will use [`transfer_log_events`] to transfer log events from [`LogEvents`] to...
  |                              ^^^^^^^^^^^^^^^^^^^ this item is private
  |
  = note: this link will resolve properly if you pass `--document-private-items`

warning: unresolved link to `LogEvents`
 --> examples/app/log_layers_ecs.rs:9:82
  |
9 | ...nsfer log events from [`LogEvents`] to an ECS event called [`LogEvent`].
  |                            ^^^^^^^^^ no item named `LogEvents` in scope
  |
  = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`

warning: public documentation for `log_layers_ecs` links to private item `LogEvent`
 --> examples/app/log_layers_ecs.rs:9:119
  |
9 | ...nts`] to an ECS event called [`LogEvent`].
  |                                   ^^^^^^^^ this item is private
  |
  = note: this link will resolve properly if you pass `--document-private-items`

warning: public documentation for `log_layers_ecs` links to private item `LogEvent`
  --> examples/app/log_layers_ecs.rs:11:49
   |
11 | //! Finally, after all that we can access the [`LogEvent`] event from our systems and use it.
   |                                                 ^^^^^^^^ this item is private
   |
   = note: this link will resolve properly if you pass `--document-private-items`
```

<details/>
2024-04-14 15:23:44 +00:00
Arthur Brussee
ac49dce4ca
Use async-fn in traits rather than BoxedFuture (#12550)
# Objective

Simplify implementing some asset traits without Box::pin(async move{})
shenanigans.
Fixes (in part) https://github.com/bevyengine/bevy/issues/11308

## Solution
Use async-fn in traits when possible in all traits. Traits with return
position impl trait are not object safe however, and as AssetReader and
AssetWriter are both used with dynamic dispatch, you need a Boxed
version of these futures anyway.

In the future, Rust is [adding
](https://blog.rust-lang.org/2023/12/21/async-fn-rpit-in-traits.html)proc
macros to generate these traits automatically, and at some point in the
future dyn traits should 'just work'. Until then.... this seemed liked
the right approach given more ErasedXXX already exist, but, no clue if
there's plans here! Especially since these are public now, it's a bit of
an unfortunate API, and means this is a breaking change.

In theory this saves some performance when these traits are used with
static dispatch, but, seems like most code paths go through dynamic
dispatch, which boxes anyway.

I also suspect a bunch of the lifetime annotations on these function
could be simplified now as the BoxedFuture was often the only thing
returned which needed a lifetime annotation, but I'm not touching that
for now as traits + lifetimes can be so tricky.

This is a revival of
[pull/11362](https://github.com/bevyengine/bevy/pull/11362) after a
spectacular merge f*ckup, with updates to the latest Bevy. Just to recap
some discussion:
- Overall this seems like a win for code quality, especially when
implementing these traits, but a loss for having to deal with ErasedXXX
variants.
- `ConditionalSend` was the preferred name for the trait that might be
Send, to deal with wasm platforms.
- When reviewing be sure to disable whitespace difference, as that's 95%
of the PR.


## Changelog
- AssetReader, AssetWriter, AssetLoader, AssetSaver and Process now use
async-fn in traits rather than boxed futures.

## Migration Guide
- Custom implementations of AssetReader, AssetWriter, AssetLoader,
AssetSaver and Process should switch to async fn rather than returning a
bevy_utils::BoxedFuture.
- Simultaniously, to use dynamic dispatch on these traits you should
instead use dyn ErasedXXX.
2024-03-18 17:56:57 +00:00
James Liu
512b7463a3
Disentangle bevy_utils/bevy_core's reexported dependencies (#12313)
# Objective
Make bevy_utils less of a compilation bottleneck. Tackle #11478.

## Solution
* Move all of the directly reexported dependencies and move them to
where they're actually used.
* Remove the UUID utilities that have gone unused since `TypePath` took
over for `TypeUuid`.
* There was also a extraneous bytemuck dependency on `bevy_core` that
has not been used for a long time (since `encase` became the primary way
to prepare GPU buffers).
* Remove the `all_tuples` macro reexport from bevy_ecs since it's
accessible from `bevy_utils`.

---

## Changelog
Removed: Many of the reexports from bevy_utils (petgraph, uuid, nonmax,
smallvec, and thiserror).
Removed: bevy_core's reexports of bytemuck.

## Migration Guide
bevy_utils' reexports of petgraph, uuid, nonmax, smallvec, and thiserror
have been removed.

bevy_core' reexports of bytemuck's types has been removed. 

Add them as dependencies in your own crate instead.
2024-03-07 02:30:15 +00:00
Ame
9d67edc3a6
fix some typos (#12038)
# Objective

Split - containing only the fixed typos

-
https://github.com/bevyengine/bevy/pull/12036#pullrequestreview-1894738751


# Migration Guide
In `crates/bevy_mikktspace/src/generated.rs` 

```rs
// before
pub struct SGroup {
    pub iVertexRepresentitive: i32,
    ..
}

// after
pub struct SGroup {
    pub iVertexRepresentative: i32,
    ..
}
```

In `crates/bevy_core_pipeline/src/core_2d/mod.rs`

```rs
// before
Node2D::ConstrastAdaptiveSharpening

// after
Node2D::ContrastAdaptiveSharpening
```

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: James Liu <contact@jamessliu.com>
Co-authored-by: François <mockersf@gmail.com>
2024-02-22 18:55:22 +00:00
Tristan Guichaoua
694c06f3d0
Inverse missing_docs logic (#11676)
# Objective

Currently the `missing_docs` lint is allowed-by-default and enabled at
crate level when their documentations is complete (see #3492).
This PR proposes to inverse this logic by making `missing_docs`
warn-by-default and mark crates with imcomplete docs allowed.

## Solution

Makes `missing_docs` warn at workspace level and allowed at crate level
when the docs is imcomplete.
2024-02-03 21:40:55 +00:00
CowSociety
8866c61161
Fix AssetTransformer breaking LabeledAssets (#11626)
# Objective

- `AssetTransformer` provides an input asset, and output an asset, but
provides no access to the `LabeledAsset`'s created by the `AssetLoader`.
Labeled sub assets are an extremely important piece of many assets, Gltf
in particular, and without them the amount of transformation on an asset
is limited. In order for `AssetTransformer`'s to be useful, they need to
have access to these sub assets.
- LabeledAsset's loaded by `AssetLoader`s are provided to `AssetSaver`s
in the `LoadAndSave` process, but the `LoadTransformAndSave` process
drops these values in the transform stage, and so `AssetSaver` is given
none.
- Fixes #11606

Ideally the AssetTransformer should not ignore labeled sub assets, and
they should be kept at least for the AssetSaver

## Solution

- I created a new struct similar to `SavedAsset` named
`TransformedAsset` which holds the input asset, and the HashMap of
`LabeledAsset`s. The transform function now takes as input a
`TransformedAsset`, and returns a `TransformedAsset::<AssetOutput>`.
This gives the transform function access to the labeled sub assets
created by the `AssetLoader`.
- I also created `TransformedSubAsset` which holds mutable references to
a sub asset and that sub assets HashMap of `LabeledAsset`s. This allows
you to travers the Tree of `LabeledAsset`s by reference relatively
easily.
- The `LoadTransformAndSave` processor was then reworked to use the new
structs, stopping the `LabeledAsset`s from being dropped.

---

## Changelog

- Created TransformedAsset struct and TransformedSubAsset struct.
- Changed `get_untyped_handle` to return a `UntypedHandle` directly
rather than a reference and added `get_handle` as a typed variant in
SavedAsset and TransformedAsset
- Added `SavedAsset::from_transformed` as a constructor from a
`TransformedAsset`
- Switched LoadTransformAndSave process code to work with new
`TransformedAsset` type
- Added a `ProcessError` for `AssetTransformer` in process.rs
- Switched `AssetTransformer::transform` to use `TransformedAsset` as
input and output.
- Switched `AssetTransformer` to use a `BoxedFuture` like `AssetLoader`
and `AssetSaver` to allow for async transformation code.
- Updated AssetTransformer example to use new structure.
2024-02-02 14:57:31 +00:00
thepackett
76682fdcb7
AssetSaver and AssetTransformer split (#11260)
# Objective
One of a few Bevy Asset improvements I would like to make: #11216.

Currently asset processing and asset saving are handled by the same
trait, `AssetSaver`. This makes it difficult to reuse saving
implementations and impossible to have a single "universal" saver for a
given asset type.

## Solution
This PR splits off the processing portion of `AssetSaver` into
`AssetTransformer`, which is responsible for transforming assets. This
change involves adding the `LoadTransformAndSave` processor, which
utilizes the new API. The `LoadAndSave` still exists since it remains
useful in situations where no "transformation" of the asset is done,
such as when compressing assets.

## Notes:
As an aside, Bikeshedding is welcome on the names. I'm not entirely
convinced by `AssetTransformer`, which was chosen mostly because
`AssetProcessor` is taken. Additionally, `LoadTransformSave` may be
sufficient instead of `LoadTransformAndSave`.


---

## Changelog
### Added 
- `AssetTransformer` which is responsible for transforming Assets.
- `LoadTransformAndSave`, a `Process` implementation.
### Changed
- Changed `AssetSaver`'s responsibilities from processing and saving to
just saving.
- Updated `asset_processing` example to use new API.
- Old asset .meta files regenerated with new processor.
2024-01-26 20:20:58 +00:00
Joseph
dcfae72386
Re-export ron in bevy_scene (#10529)
# Objective

Close #10504. Improve the development experience for working with scenes
by not requiring the user to specify a matching version of `ron` in
their `Cargo.toml`

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2023-11-15 14:45:54 +00:00
Niklas Eicker
317903f42a
Reduce noise in asset processing example (#10262)
# Objective

- Reduce noise to allow users to see previous asset changes and other
logs like from asset reloading
- The example file is named differently than the example

## Solution

- Only print the asset content if there are asset events
- Rename the example file to `asset_processing`
2023-10-25 19:37:03 +00:00
Carter Anderson
6f27e0e35f
Add asset_processor feature and remove AssetMode::ProcessedDev (#10194)
# Objective

Users shouldn't need to change their source code between "development
workflows" and "releasing". Currently, Bevy Asset V2 has two "processed"
asset modes `Processed` (assumes assets are already processed) and
`ProcessedDev` (starts an asset processor and processes assets). This
means that the mode must be changed _in code_ when switching from "app
dev" to "release". Very suboptimal.

We have already removed "runtime opt-in" for hot-reloading. Enabling the
`file_watcher` feature _automatically_ enables file watching in code.
This means deploying a game (without hot reloading enabled) just means
calling `cargo build --release` instead of `cargo run --features
bevy/file_watcher`.

We should adopt this pattern for asset processing.

## Solution

This adds the `asset_processor` feature, which will start the
`AssetProcessor` when an `AssetPlugin` runs in `AssetMode::Processed`.

The "asset processing workflow" is now:
1. Enable `AssetMode::Processed` on `AssetPlugin`
2. When developing, run with the `asset_processor` and `file_watcher`
features
3. When releasing, build without these features.

The `AssetMode::ProcessedDev` mode has been removed.
2023-10-20 20:50:26 +00:00
Carter Anderson
35073cf7aa
Multiple Asset Sources (#9885)
This adds support for **Multiple Asset Sources**. You can now register a
named `AssetSource`, which you can load assets from like you normally
would:

```rust
let shader: Handle<Shader> = asset_server.load("custom_source://path/to/shader.wgsl");
```

Notice that `AssetPath` now supports `some_source://` syntax. This can
now be accessed through the `asset_path.source()` accessor.

Asset source names _are not required_. If one is not specified, the
default asset source will be used:

```rust
let shader: Handle<Shader> = asset_server.load("path/to/shader.wgsl");
```

The behavior of the default asset source has not changed. Ex: the
`assets` folder is still the default.

As referenced in #9714

## Why?

**Multiple Asset Sources** enables a number of often-asked-for
scenarios:

* **Loading some assets from other locations on disk**: you could create
a `config` asset source that reads from the OS-default config folder
(not implemented in this PR)
* **Loading some assets from a remote server**: you could register a new
`remote` asset source that reads some assets from a remote http server
(not implemented in this PR)
* **Improved "Binary Embedded" Assets**: we can use this system for
"embedded-in-binary assets", which allows us to replace the old
`load_internal_asset!` approach, which couldn't support asset
processing, didn't support hot-reloading _well_, and didn't make
embedded assets accessible to the `AssetServer` (implemented in this pr)

## Adding New Asset Sources

An `AssetSource` is "just" a collection of `AssetReader`, `AssetWriter`,
and `AssetWatcher` entries. You can configure new asset sources like
this:

```rust
app.register_asset_source(
    "other",
    AssetSource::build()
        .with_reader(|| Box::new(FileAssetReader::new("other")))
    )
)
```

Note that `AssetSource` construction _must_ be repeatable, which is why
a closure is accepted.
`AssetSourceBuilder` supports `with_reader`, `with_writer`,
`with_watcher`, `with_processed_reader`, `with_processed_writer`, and
`with_processed_watcher`.

Note that the "asset source" system replaces the old "asset providers"
system.

## Processing Multiple Sources

The `AssetProcessor` now supports multiple asset sources! Processed
assets can refer to assets in other sources and everything "just works".
Each `AssetSource` defines an unprocessed and processed `AssetReader` /
`AssetWriter`.

Currently this is all or nothing for a given `AssetSource`. A given
source is either processed or it is not. Later we might want to add
support for "lazy asset processing", where an `AssetSource` (such as a
remote server) can be configured to only process assets that are
directly referenced by local assets (in order to save local disk space
and avoid doing extra work).

## A new `AssetSource`: `embedded`

One of the big features motivating **Multiple Asset Sources** was
improving our "embedded-in-binary" asset loading. To prove out the
**Multiple Asset Sources** implementation, I chose to build a new
`embedded` `AssetSource`, which replaces the old `load_interal_asset!`
system.

The old `load_internal_asset!` approach had a number of issues:

* The `AssetServer` was not aware of (or capable of loading) internal
assets.
* Because internal assets weren't visible to the `AssetServer`, they
could not be processed (or used by assets that are processed). This
would prevent things "preprocessing shaders that depend on built in Bevy
shaders", which is something we desperately need to start doing.
* Each "internal asset" needed a UUID to be defined in-code to reference
it. This was very manual and toilsome.

The new `embedded` `AssetSource` enables the following pattern:

```rust
// Called in `crates/bevy_pbr/src/render/mesh.rs`
embedded_asset!(app, "mesh.wgsl");

// later in the app
let shader: Handle<Shader> = asset_server.load("embedded://bevy_pbr/render/mesh.wgsl");
```

Notice that this always treats the crate name as the "root path", and it
trims out the `src` path for brevity. This is generally predictable, but
if you need to debug you can use the new `embedded_path!` macro to get a
`PathBuf` that matches the one used by `embedded_asset`.

You can also reference embedded assets in arbitrary assets, such as WGSL
shaders:

```rust
#import "embedded://bevy_pbr/render/mesh.wgsl"
```

This also makes `embedded` assets go through the "normal" asset
lifecycle. They are only loaded when they are actually used!

We are also discussing implicitly converting asset paths to/from shader
modules, so in the future (not in this PR) you might be able to load it
like this:

```rust
#import bevy_pbr::render::mesh::Vertex
```

Compare that to the old system!

```rust
pub const MESH_SHADER_HANDLE: Handle<Shader> = Handle::weak_from_u128(3252377289100772450);

load_internal_asset!(app, MESH_SHADER_HANDLE, "mesh.wgsl", Shader::from_wgsl);

// The mesh asset is the _only_ accessible via MESH_SHADER_HANDLE and _cannot_ be loaded via the AssetServer.
```

## Hot Reloading `embedded`

You can enable `embedded` hot reloading by enabling the
`embedded_watcher` cargo feature:

```
cargo run --features=embedded_watcher
```

## Improved Hot Reloading Workflow

First: the `filesystem_watcher` cargo feature has been renamed to
`file_watcher` for brevity (and to match the `FileAssetReader` naming
convention).

More importantly, hot asset reloading is no longer configured in-code by
default. If you enable any asset watcher feature (such as `file_watcher`
or `rust_source_watcher`), asset watching will be automatically enabled.

This removes the need to _also_ enable hot reloading in your app code.
That means you can replace this:

```rust
app.add_plugins(DefaultPlugins.set(AssetPlugin::default().watch_for_changes()))
```

with this:

```rust
app.add_plugins(DefaultPlugins)
```

If you want to hot reload assets in your app during development, just
run your app like this:

```
cargo run --features=file_watcher
```

This means you can use the same code for development and deployment! To
deploy an app, just don't include the watcher feature

```
cargo build --release
```

My intent is to move to this approach for pretty much all dev workflows.
In a future PR I would like to replace `AssetMode::ProcessedDev` with a
`runtime-processor` cargo feature. We could then group all common "dev"
cargo features under a single `dev` feature:

```sh
# this would enable file_watcher, embedded_watcher, runtime-processor, and more
cargo run --features=dev
```

## AssetMode

`AssetPlugin::Unprocessed`, `AssetPlugin::Processed`, and
`AssetPlugin::ProcessedDev` have been replaced with an `AssetMode` field
on `AssetPlugin`.

```rust
// before 
app.add_plugins(DefaultPlugins.set(AssetPlugin::Processed { /* fields here */ })

// after 
app.add_plugins(DefaultPlugins.set(AssetPlugin { mode: AssetMode::Processed, ..default() })
```

This aligns `AssetPlugin` with our other struct-like plugins. The old
"source" and "destination" `AssetProvider` fields in the enum variants
have been replaced by the "asset source" system. You no longer need to
configure the AssetPlugin to "point" to custom asset providers.

## AssetServerMode

To improve the implementation of **Multiple Asset Sources**,
`AssetServer` was made aware of whether or not it is using "processed"
or "unprocessed" assets. You can check that like this:

```rust
if asset_server.mode() == AssetServerMode::Processed {
    /* do something */
}
```

Note that this refactor should also prepare the way for building "one to
many processed output files", as it makes the server aware of whether it
is loading from processed or unprocessed sources. Meaning we can store
and read processed and unprocessed assets differently!

## AssetPath can now refer to folders

The "file only" restriction has been removed from `AssetPath`. The
`AssetServer::load_folder` API now accepts an `AssetPath` instead of a
`Path`, meaning you can load folders from other asset sources!

## Improved AssetPath Parsing

AssetPath parsing was reworked to support sources, improve error
messages, and to enable parsing with a single pass over the string.
`AssetPath::new` was replaced by `AssetPath::parse` and
`AssetPath::try_parse`.

## AssetWatcher broken out from AssetReader

`AssetReader` is no longer responsible for constructing `AssetWatcher`.
This has been moved to `AssetSourceBuilder`.


## Duplicate Event Debouncing

Asset V2 already debounced duplicate filesystem events, but this was
_input_ events. Multiple input event types can produce the same _output_
`AssetSourceEvent`. Now that we have `embedded_watcher`, which does
expensive file io on events, it made sense to debounce output events
too, so I added that! This will also benefit the AssetProcessor by
preventing integrity checks for duplicate events (and helps keep the
noise down in trace logs).

## Next Steps

* **Port Built-in Shaders**: Currently the primary (and essentially
only) user of `load_interal_asset` in Bevy's source code is "built-in
shaders". I chose not to do that in this PR for a few reasons:
1. We need to add the ability to pass shader defs in to shaders via meta
files. Some shaders (such as MESH_VIEW_TYPES) need to pass shader def
values in that are defined in code.
2. We need to revisit the current shader module naming system. I think
we _probably_ want to imply modules from source structure (at least by
default). Ideally in a way that can losslessly convert asset paths
to/from shader modules (to enable the asset system to resolve modules
using the asset server).
  3. I want to keep this change set minimal / get this merged first.
* **Deprecate `load_internal_asset`**: we can't do that until we do (1)
and (2)
* **Relative Asset Paths**: This PR significantly increases the need for
relative asset paths (which was already pretty high). Currently when
loading dependencies, it is assumed to be an absolute path, which means
if in an `AssetLoader` you call `context.load("some/path/image.png")` it
will assume that is the "default" asset source, _even if the current
asset is in a different asset source_. This will cause breakage for
AssetLoaders that are not designed to add the current source to whatever
paths are being used. AssetLoaders should generally not need to be aware
of the name of their current asset source, or need to think about the
"current asset source" generally. We should build apis that support
relative asset paths and then encourage using relative paths as much as
possible (both via api design and docs). Relative paths are also
important because they will allow developers to move folders around
(even across providers) without reprocessing, provided there is no path
breakage.
2023-10-13 23:17:32 +00:00
Zachary Harrold
dd46fd3aee
Removed anyhow (#10003)
# Objective

- Fixes #8140

## Solution

- Added Explicit Error Typing for `AssetLoader` and `AssetSaver`, which
were the last instances of `anyhow` in use across Bevy.

---

## Changelog

- Added an associated type `Error` to `AssetLoader` and `AssetSaver` for
use with the `load` and `save` methods respectively.
- Changed `ErasedAssetLoader` and `ErasedAssetSaver` `load` and `save`
methods to use `Box<dyn Error + Send + Sync + 'static>` to allow for
arbitrary `Error` types from the non-erased trait variants. Note the
strict requirements match the pre-existing requirements around
`anyhow::Error`.

## Migration Guide

- `anyhow` is no longer exported by `bevy_asset`; Add it to your own
project (if required).
- `AssetLoader` and `AssetSaver` have an associated type `Error`; Define
an appropriate error type (e.g., using `thiserror`), or use a pre-made
error type (e.g., `anyhow::Error`). Note that using `anyhow::Error` is a
drop-in replacement.
- `AssetLoaderError` has been removed; Define a new error type, or use
an alternative (e.g., `anyhow::Error`)
- All the first-party `AssetLoader`'s and `AssetSaver`'s now return
relevant (and narrow) error types instead of a single ambiguous type;
Match over the specific error type, or encapsulate (`Box<dyn>`,
`thiserror`, `anyhow`, etc.)

## Notes

A simpler PR to resolve this issue would simply define a Bevy `Error`
type defined as `Box<dyn std::error::Error + Send + Sync + 'static>`,
but I think this type of error handling should be discouraged when
possible. Since only 2 traits required the use of `anyhow`, it isn't a
substantive body of work to solidify these error types, and remove
`anyhow` entirely. End users are still encouraged to use `anyhow` if
that is their preferred error handling style. Arguably, adding the
`Error` associated type gives more freedom to end-users to decide
whether they want more or less explicit error handling (`anyhow` vs
`thiserror`).

As an aside, I didn't perform any testing on Android or WASM. CI passed
locally, but there may be mistakes for those platforms I missed.
2023-10-06 07:20:13 +00:00
Carter Anderson
5eb292dc10
Bevy Asset V2 (#8624)
# Bevy Asset V2 Proposal

## Why Does Bevy Need A New Asset System?

Asset pipelines are a central part of the gamedev process. Bevy's
current asset system is missing a number of features that make it
non-viable for many classes of gamedev. After plenty of discussions and
[a long community feedback
period](https://github.com/bevyengine/bevy/discussions/3972), we've
identified a number missing features:

* **Asset Preprocessing**: it should be possible to "preprocess" /
"compile" / "crunch" assets at "development time" rather than when the
game starts up. This enables offloading expensive work from deployed
apps, faster asset loading, less runtime memory usage, etc.
* **Per-Asset Loader Settings**: Individual assets cannot define their
own loaders that override the defaults. Additionally, they cannot
provide per-asset settings to their loaders. This is a huge limitation,
as many asset types don't provide all information necessary for Bevy
_inside_ the asset. For example, a raw PNG image says nothing about how
it should be sampled (ex: linear vs nearest).
* **Asset `.meta` files**: assets should have configuration files stored
adjacent to the asset in question, which allows the user to configure
asset-type-specific settings. These settings should be accessible during
the pre-processing phase. Modifying a `.meta` file should trigger a
re-processing / re-load of the asset. It should be possible to configure
asset loaders from the meta file.
* **Processed Asset Hot Reloading**: Changes to processed assets (or
their dependencies) should result in re-processing them and re-loading
the results in live Bevy Apps.
* **Asset Dependency Tracking**: The current bevy_asset has no good way
to wait for asset dependencies to load. It punts this as an exercise for
consumers of the loader apis, which is unreasonable and error prone.
There should be easy, ergonomic ways to wait for assets to load and
block some logic on an asset's entire dependency tree loading.
* **Runtime Asset Loading**: it should be (optionally) possible to load
arbitrary assets dynamically at runtime. This necessitates being able to
deploy and run the asset server alongside Bevy Apps on _all platforms_.
For example, we should be able to invoke the shader compiler at runtime,
stream scenes from sources like the internet, etc. To keep deployed
binaries (and startup times) small, the runtime asset server
configuration should be configurable with different settings compared to
the "pre processor asset server".
* **Multiple Backends**: It should be possible to load assets from
arbitrary sources (filesystems, the internet, remote asset serves, etc).
* **Asset Packing**: It should be possible to deploy assets in
compressed "packs", which makes it easier and more efficient to
distribute assets with Bevy Apps.
* **Asset Handoff**: It should be possible to hold a "live" asset
handle, which correlates to runtime data, without actually holding the
asset in memory. Ex: it must be possible to hold a reference to a GPU
mesh generated from a "mesh asset" without keeping the mesh data in CPU
memory
* **Per-Platform Processed Assets**: Different platforms and app
distributions have different capabilities and requirements. Some
platforms need lower asset resolutions or different asset formats to
operate within the hardware constraints of the platform. It should be
possible to define per-platform asset processing profiles. And it should
be possible to deploy only the assets required for a given platform.

These features have architectural implications that are significant
enough to require a full rewrite. The current Bevy Asset implementation
got us this far, but it can take us no farther. This PR defines a brand
new asset system that implements most of these features, while laying
the foundations for the remaining features to be built.

## Bevy Asset V2

Here is a quick overview of the features introduced in this PR.
* **Asset Preprocessing**: Preprocess assets at development time into
more efficient (and configurable) representations
* **Dependency Aware**: Dependencies required to process an asset are
tracked. If an asset's processed dependency changes, it will be
reprocessed
* **Hot Reprocessing/Reloading**: detect changes to asset source files,
reprocess them if they have changed, and then hot-reload them in Bevy
Apps.
* **Only Process Changes**: Assets are only re-processed when their
source file (or meta file) has changed. This uses hashing and timestamps
to avoid processing assets that haven't changed.
* **Transactional and Reliable**: Uses write-ahead logging (a technique
commonly used by databases) to recover from crashes / forced-exits.
Whenever possible it avoids full-reprocessing / only uncompleted
transactions will be reprocessed. When the processor is running in
parallel with a Bevy App, processor asset writes block Bevy App asset
reads. Reading metadata + asset bytes is guaranteed to be transactional
/ correctly paired.
* **Portable / Run anywhere / Database-free**: The processor does not
rely on an in-memory database (although it uses some database techniques
for reliability). This is important because pretty much all in-memory
databases have unsupported platforms or build complications.
* **Configure Processor Defaults Per File Type**: You can say "use this
processor for all files of this type".
* **Custom Processors**: The `Processor` trait is flexible and
unopinionated. It can be implemented by downstream plugins.
* **LoadAndSave Processors**: Most asset processing scenarios can be
expressed as "run AssetLoader A, save the results using AssetSaver X,
and then load the result using AssetLoader B". For example, load this
png image using `PngImageLoader`, which produces an `Image` asset and
then save it using `CompressedImageSaver` (which also produces an
`Image` asset, but in a compressed format), which takes an `Image` asset
as input. This means if you have an `AssetLoader` for an asset, you are
already half way there! It also means that you can share AssetSavers
across multiple loaders. Because `CompressedImageSaver` accepts Bevy's
generic Image asset as input, it means you can also use it with some
future `JpegImageLoader`.
* **Loader and Saver Settings**: Asset Loaders and Savers can now define
their own settings types, which are passed in as input when an asset is
loaded / saved. Each asset can define its own settings.
* **Asset `.meta` files**: configure asset loaders, their settings,
enable/disable processing, and configure processor settings
* **Runtime Asset Dependency Tracking** Runtime asset dependencies (ex:
if an asset contains a `Handle<Image>`) are tracked by the asset server.
An event is emitted when an asset and all of its dependencies have been
loaded
* **Unprocessed Asset Loading**: Assets do not require preprocessing.
They can be loaded directly. A processed asset is just a "normal" asset
with some extra metadata. Asset Loaders don't need to know or care about
whether or not an asset was processed.
* **Async Asset IO**: Asset readers/writers use async non-blocking
interfaces. Note that because Rust doesn't yet support async traits,
there is a bit of manual Boxing / Future boilerplate. This will
hopefully be removed in the near future when Rust gets async traits.
* **Pluggable Asset Readers and Writers**: Arbitrary asset source
readers/writers are supported, both by the processor and the asset
server.
* **Better Asset Handles**
* **Single Arc Tree**: Asset Handles now use a single arc tree that
represents the lifetime of the asset. This makes their implementation
simpler, more efficient, and allows us to cheaply attach metadata to
handles. Ex: the AssetPath of a handle is now directly accessible on the
handle itself!
* **Const Typed Handles**: typed handles can be constructed in a const
context. No more weird "const untyped converted to typed at runtime"
patterns!
* **Handles and Ids are Smaller / Faster To Hash / Compare**: Typed
`Handle<T>` is now much smaller in memory and `AssetId<T>` is even
smaller.
* **Weak Handle Usage Reduction**: In general Handles are now considered
to be "strong". Bevy features that previously used "weak `Handle<T>`"
have been ported to `AssetId<T>`, which makes it statically clear that
the features do not hold strong handles (while retaining strong type
information). Currently Handle::Weak still exists, but it is very
possible that we can remove that entirely.
* **Efficient / Dense Asset Ids**: Assets now have efficient dense
runtime asset ids, which means we can avoid expensive hash lookups.
Assets are stored in Vecs instead of HashMaps. There are now typed and
untyped ids, which means we no longer need to store dynamic type
information in the ID for typed handles. "AssetPathId" (which was a
nightmare from a performance and correctness standpoint) has been
entirely removed in favor of dense ids (which are retrieved for a path
on load)
* **Direct Asset Loading, with Dependency Tracking**: Assets that are
defined at runtime can still have their dependencies tracked by the
Asset Server (ex: if you create a material at runtime, you can still
wait for its textures to load). This is accomplished via the (currently
optional) "asset dependency visitor" trait. This system can also be used
to define a set of assets to load, then wait for those assets to load.
* **Async folder loading**: Folder loading also uses this system and
immediately returns a handle to the LoadedFolder asset, which means
folder loading no longer blocks on directory traversals.
* **Improved Loader Interface**: Loaders now have a specific "top level
asset type", which makes returning the top-level asset simpler and
statically typed.
* **Basic Image Settings and Processing**: Image assets can now be
processed into the gpu-friendly Basic Universal format. The ImageLoader
now has a setting to define what format the image should be loaded as.
Note that this is just a minimal MVP ... plenty of additional work to do
here. To demo this, enable the `basis-universal` feature and turn on
asset processing.
* **Simpler Audio Play / AudioSink API**: Asset handle providers are
cloneable, which means the Audio resource can mint its own handles. This
means you can now do `let sink_handle = audio.play(music)` instead of
`let sink_handle = audio_sinks.get_handle(audio.play(music))`. Note that
this might still be replaced by
https://github.com/bevyengine/bevy/pull/8424.
**Removed Handle Casting From Engine Features**: Ex: FontAtlases no
longer use casting between handle types

## Using The New Asset System

### Normal Unprocessed Asset Loading

By default the `AssetPlugin` does not use processing. It behaves pretty
much the same way as the old system.

If you are defining a custom asset, first derive `Asset`:

```rust
#[derive(Asset)]
struct Thing {
    value: String,
}
```

Initialize the asset:
```rust
app.init_asset:<Thing>()
```

Implement a new `AssetLoader` for it:

```rust
#[derive(Default)]
struct ThingLoader;

#[derive(Serialize, Deserialize, Default)]
pub struct ThingSettings {
    some_setting: bool,
}

impl AssetLoader for ThingLoader {
    type Asset = Thing;
    type Settings = ThingSettings;

    fn load<'a>(
        &'a self,
        reader: &'a mut Reader,
        settings: &'a ThingSettings,
        load_context: &'a mut LoadContext,
    ) -> BoxedFuture<'a, Result<Thing, anyhow::Error>> {
        Box::pin(async move {
            let mut bytes = Vec::new();
            reader.read_to_end(&mut bytes).await?;
            // convert bytes to value somehow
            Ok(Thing {
                value 
            })
        })
    }

    fn extensions(&self) -> &[&str] {
        &["thing"]
    }
}
```

Note that this interface will get much cleaner once Rust gets support
for async traits. `Reader` is an async futures_io::AsyncRead. You can
stream bytes as they come in or read them all into a `Vec<u8>`,
depending on the context. You can use `let handle =
load_context.load(path)` to kick off a dependency load, retrieve a
handle, and register the dependency for the asset.

Then just register the loader in your Bevy app:

```rust
app.init_asset_loader::<ThingLoader>()
```

Now just add your `Thing` asset files into the `assets` folder and load
them like this:

```rust
fn system(asset_server: Res<AssetServer>) {
    let handle = Handle<Thing> = asset_server.load("cool.thing");
}
```

You can check load states directly via the asset server:

```rust
if asset_server.load_state(&handle) == LoadState::Loaded { }
```

You can also listen for events:

```rust
fn system(mut events: EventReader<AssetEvent<Thing>>, handle: Res<SomeThingHandle>) {
    for event in events.iter() {
        if event.is_loaded_with_dependencies(&handle) {
        }
    }
}
```

Note the new `AssetEvent::LoadedWithDependencies`, which only fires when
the asset is loaded _and_ all dependencies (and their dependencies) have
loaded.

Unlike the old asset system, for a given asset path all `Handle<T>`
values point to the same underlying Arc. This means Handles can cheaply
hold more asset information, such as the AssetPath:

```rust
// prints the AssetPath of the handle
info!("{:?}", handle.path())
```

### Processed Assets

Asset processing can be enabled via the `AssetPlugin`. When developing
Bevy Apps with processed assets, do this:

```rust
app.add_plugins(DefaultPlugins.set(AssetPlugin::processed_dev()))
```

This runs the `AssetProcessor` in the background with hot-reloading. It
reads assets from the `assets` folder, processes them, and writes them
to the `.imported_assets` folder. Asset loads in the Bevy App will wait
for a processed version of the asset to become available. If an asset in
the `assets` folder changes, it will be reprocessed and hot-reloaded in
the Bevy App.

When deploying processed Bevy apps, do this:

```rust
app.add_plugins(DefaultPlugins.set(AssetPlugin::processed()))
```

This does not run the `AssetProcessor` in the background. It behaves
like `AssetPlugin::unprocessed()`, but reads assets from
`.imported_assets`.

When the `AssetProcessor` is running, it will populate sibling `.meta`
files for assets in the `assets` folder. Meta files for assets that do
not have a processor configured look like this:

```rust
(
    meta_format_version: "1.0",
    asset: Load(
        loader: "bevy_render::texture::image_loader::ImageLoader",
        settings: (
            format: FromExtension,
        ),
    ),
)
```

This is metadata for an image asset. For example, if you have
`assets/my_sprite.png`, this could be the metadata stored at
`assets/my_sprite.png.meta`. Meta files are totally optional. If no
metadata exists, the default settings will be used.

In short, this file says "load this asset with the ImageLoader and use
the file extension to determine the image type". This type of meta file
is supported in all AssetPlugin modes. If in `Unprocessed` mode, the
asset (with the meta settings) will be loaded directly. If in
`ProcessedDev` mode, the asset file will be copied directly to the
`.imported_assets` folder. The meta will also be copied directly to the
`.imported_assets` folder, but with one addition:

```rust
(
    meta_format_version: "1.0",
    processed_info: Some((
        hash: 12415480888597742505,
        full_hash: 14344495437905856884,
        process_dependencies: [],
    )),
    asset: Load(
        loader: "bevy_render::texture::image_loader::ImageLoader",
        settings: (
            format: FromExtension,
        ),
    ),
)
```

`processed_info` contains `hash` (a direct hash of the asset and meta
bytes), `full_hash` (a hash of `hash` and the hashes of all
`process_dependencies`), and `process_dependencies` (the `path` and
`full_hash` of every process_dependency). A "process dependency" is an
asset dependency that is _directly_ used when processing the asset.
Images do not have process dependencies, so this is empty.

When the processor is enabled, you can use the `Process` metadata
config:

```rust
(
    meta_format_version: "1.0",
    asset: Process(
        processor: "bevy_asset::processor::process::LoadAndSave<bevy_render::texture::image_loader::ImageLoader, bevy_render::texture::compressed_image_saver::CompressedImageSaver>",
        settings: (
            loader_settings: (
                format: FromExtension,
            ),
            saver_settings: (
                generate_mipmaps: true,
            ),
        ),
    ),
)
```

This configures the asset to use the `LoadAndSave` processor, which runs
an AssetLoader and feeds the result into an AssetSaver (which saves the
given Asset and defines a loader to load it with). (for terseness
LoadAndSave will likely get a shorter/friendlier type name when [Stable
Type Paths](#7184) lands). `LoadAndSave` is likely to be the most common
processor type, but arbitrary processors are supported.

`CompressedImageSaver` saves an `Image` in the Basis Universal format
and configures the ImageLoader to load it as basis universal. The
`AssetProcessor` will read this meta, run it through the LoadAndSave
processor, and write the basis-universal version of the image to
`.imported_assets`. The final metadata will look like this:

```rust
(
    meta_format_version: "1.0",
    processed_info: Some((
        hash: 905599590923828066,
        full_hash: 9948823010183819117,
        process_dependencies: [],
    )),
    asset: Load(
        loader: "bevy_render::texture::image_loader::ImageLoader",
        settings: (
            format: Format(Basis),
        ),
    ),
)
```

To try basis-universal processing out in Bevy examples, (for example
`sprite.rs`), change `add_plugins(DefaultPlugins)` to
`add_plugins(DefaultPlugins.set(AssetPlugin::processed_dev()))` and run
with the `basis-universal` feature enabled: `cargo run
--features=basis-universal --example sprite`.

To create a custom processor, there are two main paths:
1. Use the `LoadAndSave` processor with an existing `AssetLoader`.
Implement the `AssetSaver` trait, register the processor using
`asset_processor.register_processor::<LoadAndSave<ImageLoader,
CompressedImageSaver>>(image_saver.into())`.
2. Implement the `Process` trait directly and register it using:
`asset_processor.register_processor(thing_processor)`.

You can configure default processors for file extensions like this:

```rust
asset_processor.set_default_processor::<ThingProcessor>("thing")
```

There is one more metadata type to be aware of:

```rust
(
    meta_format_version: "1.0",
    asset: Ignore,
)
```

This will ignore the asset during processing / prevent it from being
written to `.imported_assets`.

The AssetProcessor stores a transaction log at `.imported_assets/log`
and uses it to gracefully recover from unexpected stops. This means you
can force-quit the processor (and Bevy Apps running the processor in
parallel) at arbitrary times!

`.imported_assets` is "local state". It should _not_ be checked into
source control. It should also be considered "read only". In practice,
you _can_ modify processed assets and processed metadata if you really
need to test something. But those modifications will not be represented
in the hashes of the assets, so the processed state will be "out of
sync" with the source assets. The processor _will not_ fix this for you.
Either revert the change after you have tested it, or delete the
processed files so they can be re-populated.

## Open Questions

There are a number of open questions to be discussed. We should decide
if they need to be addressed in this PR and if so, how we will address
them:

### Implied Dependencies vs Dependency Enumeration

There are currently two ways to populate asset dependencies:
* **Implied via AssetLoaders**: if an AssetLoader loads an asset (and
retrieves a handle), a dependency is added to the list.
* **Explicit via the optional Asset::visit_dependencies**: if
`server.load_asset(my_asset)` is called, it will call
`my_asset.visit_dependencies`, which will grab dependencies that have
been manually defined for the asset via the Asset trait impl (which can
be derived).

This means that defining explicit dependencies is optional for "loaded
assets". And the list of dependencies is always accurate because loaders
can only produce Handles if they register dependencies. If an asset was
loaded with an AssetLoader, it only uses the implied dependencies. If an
asset was created at runtime and added with
`asset_server.load_asset(MyAsset)`, it will use
`Asset::visit_dependencies`.

However this can create a behavior mismatch between loaded assets and
equivalent "created at runtime" assets if `Assets::visit_dependencies`
doesn't exactly match the dependencies produced by the AssetLoader. This
behavior mismatch can be resolved by completely removing "implied loader
dependencies" and requiring `Asset::visit_dependencies` to supply
dependency data. But this creates two problems:
* It makes defining loaded assets harder and more error prone: Devs must
remember to manually annotate asset dependencies with `#[dependency]`
when deriving `Asset`. For more complicated assets (such as scenes), the
derive likely wouldn't be sufficient and a manual `visit_dependencies`
impl would be required.
* Removes the ability to immediately kick off dependency loads: When
AssetLoaders retrieve a Handle, they also immediately kick off an asset
load for the handle, which means it can start loading in parallel
_before_ the asset finishes loading. For large assets, this could be
significant. (although this could be mitigated for processed assets if
we store dependencies in the processed meta file and load them ahead of
time)

### Eager ProcessorDev Asset Loading

I made a controversial call in the interest of fast startup times ("time
to first pixel") for the "processor dev mode configuration". When
initializing the AssetProcessor, current processed versions of unchanged
assets are yielded immediately, even if their dependencies haven't been
checked yet for reprocessing. This means that
non-current-state-of-filesystem-but-previously-valid assets might be
returned to the App first, then hot-reloaded if/when their dependencies
change and the asset is reprocessed.

Is this behavior desirable? There is largely one alternative: do not
yield an asset from the processor to the app until all of its
dependencies have been checked for changes. In some common cases (load
dependency has not changed since last run) this will increase startup
time. The main question is "by how much" and is that slower startup time
worth it in the interest of only yielding assets that are true to the
current state of the filesystem. Should this be configurable? I'm
starting to think we should only yield an asset after its (historical)
dependencies have been checked for changes + processed as necessary, but
I'm curious what you all think.

### Paths Are Currently The Only Canonical ID / Do We Want Asset UUIDs?

In this implementation AssetPaths are the only canonical asset
identifier (just like the previous Bevy Asset system and Godot). Moving
assets will result in re-scans (and currently reprocessing, although
reprocessing can easily be avoided with some changes). Asset
renames/moves will break code and assets that rely on specific paths,
unless those paths are fixed up.

Do we want / need "stable asset uuids"? Introducing them is very
possible:
1. Generate a UUID and include it in .meta files
2. Support UUID in AssetPath
3. Generate "asset indices" which are loaded on startup and map UUIDs to
paths.
4 (maybe). Consider only supporting UUIDs for processed assets so we can
generate quick-to-load indices instead of scanning meta files.

The main "pro" is that assets referencing UUIDs don't need to be
migrated when a path changes. The main "con" is that UUIDs cannot be
"lazily resolved" like paths. They need a full view of all assets to
answer the question "does this UUID exist". Which means UUIDs require
the AssetProcessor to fully finish startup scans before saying an asset
doesnt exist. And they essentially require asset pre-processing to use
in apps, because scanning all asset metadata files at runtime to resolve
a UUID is not viable for medium-to-large apps. It really requires a
pre-generated UUID index, which must be loaded before querying for
assets.

I personally think this should be investigated in a separate PR. Paths
aren't going anywhere ... _everyone_ uses filesystems (and
filesystem-like apis) to manage their asset source files. I consider
them permanent canonical asset information. Additionally, they behave
well for both processed and unprocessed asset modes. Given that Bevy is
supporting both, this feels like the right canonical ID to start with.
UUIDS (and maybe even other indexed-identifier types) can be added later
as necessary.

### Folder / File Naming Conventions

All asset processing config currently lives in the `.imported_assets`
folder. The processor transaction log is in `.imported_assets/log`.
Processed assets are added to `.imported_assets/Default`, which will
make migrating to processed asset profiles (ex: a
`.imported_assets/Mobile` profile) a non-breaking change. It also allows
us to create top-level files like `.imported_assets/log` without it
being interpreted as an asset. Meta files currently have a `.meta`
suffix. Do we like these names and conventions?

### Should the `AssetPlugin::processed_dev` configuration enable
`watch_for_changes` automatically?

Currently it does (which I think makes sense), but it does make it the
only configuration that enables watch_for_changes by default.

### Discuss on_loaded High Level Interface:

This PR includes a very rough "proof of concept" `on_loaded` system
adapter that uses the `LoadedWithDependencies` event in combination with
`asset_server.load_asset` dependency tracking to support this pattern

```rust
fn main() {
    App::new()
        .init_asset::<MyAssets>()
        .add_systems(Update, on_loaded(create_array_texture))
        .run();
}

#[derive(Asset, Clone)]
struct MyAssets {
    #[dependency]
    picture_of_my_cat: Handle<Image>,
    #[dependency]
    picture_of_my_other_cat: Handle<Image>,
}

impl FromWorld for ArrayTexture {
    fn from_world(world: &mut World) -> Self {
        picture_of_my_cat: server.load("meow.png"),
        picture_of_my_other_cat: server.load("meeeeeeeow.png"),
    }
}

fn spawn_cat(In(my_assets): In<MyAssets>, mut commands: Commands) {
    commands.spawn(SpriteBundle {
        texture: my_assets.picture_of_my_cat.clone(),  
        ..default()
    });
    
    commands.spawn(SpriteBundle {
        texture: my_assets.picture_of_my_other_cat.clone(),  
        ..default()
    });
}

```

The implementation is _very_ rough. And it is currently unsafe because
`bevy_ecs` doesn't expose some internals to do this safely from inside
`bevy_asset`. There are plenty of unanswered questions like:
* "do we add a Loadable" derive? (effectively automate the FromWorld
implementation above)
* Should `MyAssets` even be an Asset? (largely implemented this way
because it elegantly builds on `server.load_asset(MyAsset { .. })`
dependency tracking).

We should think hard about what our ideal API looks like (and if this is
a pattern we want to support). Not necessarily something we need to
solve in this PR. The current `on_loaded` impl should probably be
removed from this PR before merging.

## Clarifying Questions

### What about Assets as Entities?

This Bevy Asset V2 proposal implementation initially stored Assets as
ECS Entities. Instead of `AssetId<T>` + the `Assets<T>` resource it used
`Entity` as the asset id and Asset values were just ECS components.
There are plenty of compelling reasons to do this:
1. Easier to inline assets in Bevy Scenes (as they are "just" normal
entities + components)
2. More flexible queries: use the power of the ECS to filter assets (ex:
`Query<Mesh, With<Tree>>`).
3. Extensible. Users can add arbitrary component data to assets.
4. Things like "component visualization tools" work out of the box to
visualize asset data.

However Assets as Entities has a ton of caveats right now:
* We need to be able to allocate entity ids without a direct World
reference (aka rework id allocator in Entities ... i worked around this
in my prototypes by just pre allocating big chunks of entities)
* We want asset change events in addition to ECS change tracking ... how
do we populate them when mutations can come from anywhere? Do we use
Changed queries? This would require iterating over the change data for
all assets every frame. Is this acceptable or should we implement a new
"event based" component change detection option?
* Reconciling manually created assets with asset-system managed assets
has some nuance (ex: are they "loaded" / do they also have that
component metadata?)
* "how do we handle "static" / default entity handles" (ties in to the
Entity Indices discussion:
https://github.com/bevyengine/bevy/discussions/8319). This is necessary
for things like "built in" assets and default handles in things like
SpriteBundle.
* Storing asset information as a component makes it easy to "invalidate"
asset state by removing the component (or forcing modifications).
Ideally we have ways to lock this down (some combination of Rust type
privacy and ECS validation)

In practice, how we store and identify assets is a reasonably
superficial change (porting off of Assets as Entities and implementing
dedicated storage + ids took less than a day). So once we sort out the
remaining challenges the flip should be straightforward. Additionally, I
do still have "Assets as Entities" in my commit history, so we can reuse
that work. I personally think "assets as entities" is a good endgame,
but it also doesn't provide _significant_ value at the moment and it
certainly isn't ready yet with the current state of things.

### Why not Distill?

[Distill](https://github.com/amethyst/distill) is a high quality fully
featured asset system built in Rust. It is very natural to ask "why not
just use Distill?".

It is also worth calling out that for awhile, [we planned on adopting
Distill / I signed off on
it](https://github.com/bevyengine/bevy/issues/708).

However I think Bevy has a number of constraints that make Distill
adoption suboptimal:
* **Architectural Simplicity:**
* Distill's processor requires an in-memory database (lmdb) and RPC
networked API (using Cap'n Proto). Each of these introduces API
complexity that increases maintenance burden and "code grokability".
Ignoring tests, documentation, and examples, Distill has 24,237 lines of
Rust code (including generated code for RPC + database interactions). If
you ignore generated code, it has 11,499 lines.
* Bevy builds the AssetProcessor and AssetServer using pluggable
AssetReader/AssetWriter Rust traits with simple io interfaces. They do
not necessitate databases or RPC interfaces (although Readers/Writers
could use them if that is desired). Bevy Asset V2 (at the time of
writing this PR) is 5,384 lines of Rust code (ignoring tests,
documentation, and examples). Grain of salt: Distill does have more
features currently (ex: Asset Packing, GUIDS, remote-out-of-process
asset processor). I do plan to implement these features in Bevy Asset V2
and I personally highly doubt they will meaningfully close the 6115
lines-of-code gap.
* This complexity gap (which while illustrated by lines of code, is much
bigger than just that) is noteworthy to me. Bevy should be hackable and
there are pillars of Distill that are very hard to understand and
extend. This is a matter of opinion (and Bevy Asset V2 also has
complicated areas), but I think Bevy Asset V2 is much more approachable
for the average developer.
* Necessary disclaimer: counting lines of code is an extremely rough
complexity metric. Read the code and form your own opinions.
* **Optional Asset Processing:** Not all Bevy Apps (or Bevy App
developers) need / want asset preprocessing. Processing increases the
complexity of the development environment by introducing things like
meta files, imported asset storage, running processors in the
background, waiting for processing to finish, etc. Distill _requires_
preprocessing to work. With Bevy Asset V2 processing is fully opt-in.
The AssetServer isn't directly aware of asset processors at all.
AssetLoaders only care about converting bytes to runtime Assets ... they
don't know or care if the bytes were pre-processed or not. Processing is
"elegantly" (forgive my self-congratulatory phrasing) layered on top and
builds on the existing Asset system primitives.
* **Direct Filesystem Access to Processed Asset State:** Distill stores
processed assets in a database. This makes debugging / inspecting the
processed outputs harder (either requires special tooling to query the
database or they need to be "deployed" to be inspected). Bevy Asset V2,
on the other hand, stores processed assets in the filesystem (by default
... this is configurable). This makes interacting with the processed
state more natural. Note that both Godot and Unity's new asset system
store processed assets in the filesystem.
* **Portability**: Because Distill's processor uses lmdb and RPC
networking, it cannot be run on certain platforms (ex: lmdb is a
non-rust dependency that cannot run on the web, some platforms don't
support running network servers). Bevy should be able to process assets
everywhere (ex: run the Bevy Editor on the web, compile + process
shaders on mobile, etc). Distill does partially mitigate this problem by
supporting "streaming" assets via the RPC protocol, but this is not a
full solve from my perspective. And Bevy Asset V2 can (in theory) also
stream assets (without requiring RPC, although this isn't implemented
yet)

Note that I _do_ still think Distill would be a solid asset system for
Bevy. But I think the approach in this PR is a better solve for Bevy's
specific "asset system requirements".

### Doesn't async-fs just shim requests to "sync" `std::fs`? What is the
point?

"True async file io" has limited / spotty platform support. async-fs
(and the rust async ecosystem generally ... ex Tokio) currently use
async wrappers over std::fs that offload blocking requests to separate
threads. This may feel unsatisfying, but it _does_ still provide value
because it prevents our task pools from blocking on file system
operations (which would prevent progress when there are many tasks to
do, but all threads in a pool are currently blocking on file system
ops).

Additionally, using async APIs for our AssetReaders and AssetWriters
also provides value because we can later add support for "true async
file io" for platforms that support it. _And_ we can implement other
"true async io" asset backends (such as networked asset io).

## Draft TODO

- [x] Fill in missing filesystem event APIs: file removed event (which
is expressed as dangling RenameFrom events in some cases), file/folder
renamed event
- [x] Assets without loaders are not moved to the processed folder. This
breaks things like referenced `.bin` files for GLTFs. This should be
configurable per-non-asset-type.
- [x] Initial implementation of Reflect and FromReflect for Handle. The
"deserialization" parity bar is low here as this only worked with static
UUIDs in the old impl ... this is a non-trivial problem. Either we add a
Handle::AssetPath variant that gets "upgraded" to a strong handle on
scene load or we use a separate AssetRef type for Bevy scenes (which is
converted to a runtime Handle on load). This deserves its own discussion
in a different pr.
- [x] Populate read_asset_bytes hash when run by the processor (a bit of
a special case .. when run by the processor the processed meta will
contain the hash so we don't need to compute it on the spot, but we
don't want/need to read the meta when run by the main AssetServer)
- [x] Delay hot reloading: currently filesystem events are handled
immediately, which creates timing issues in some cases. For example hot
reloading images can sometimes break because the image isn't finished
writing. We should add a delay, likely similar to the [implementation in
this PR](https://github.com/bevyengine/bevy/pull/8503).
- [x] Port old platform-specific AssetIo implementations to the new
AssetReader interface (currently missing Android and web)
- [x] Resolve on_loaded unsafety (either by removing the API entirely or
removing the unsafe)
- [x]  Runtime loader setting overrides
- [x] Remove remaining unwraps that should be error-handled. There are
number of TODOs here
- [x] Pretty AssetPath Display impl
- [x] Document more APIs
- [x] Resolve spurious "reloading because it has changed" events (to
repro run load_gltf with `processed_dev()`)
- [x] load_dependency hot reloading currently only works for processed
assets. If processing is disabled, load_dependency changes are not hot
reloaded.
- [x] Replace AssetInfo dependency load/fail counters with
`loading_dependencies: HashSet<UntypedAssetId>` to prevent reloads from
(potentially) breaking counters. Storing this will also enable
"dependency reloaded" events (see [Next Steps](#next-steps))
- [x] Re-add filesystem watcher cargo feature gate (currently it is not
optional)
- [ ] Migration Guide
- [ ] Changelog

## Followup TODO

- [ ] Replace "eager unchanged processed asset loading" behavior with
"don't returned unchanged processed asset until dependencies have been
checked".
- [ ] Add true `Ignore` AssetAction that does not copy the asset to the
imported_assets folder.
- [ ] Finish "live asset unloading" (ex: free up CPU asset memory after
uploading an image to the GPU), rethink RenderAssets, and port renderer
features. The `Assets` collection uses `Option<T>` for asset storage to
support its removal. (1) the Option might not actually be necessary ...
might be able to just remove from the collection entirely (2) need to
finalize removal apis
- [ ] Try replacing the "channel based" asset id recycling with
something a bit more efficient (ex: we might be able to use raw atomic
ints with some cleverness)
- [ ] Consider adding UUIDs to processed assets (scoped just to helping
identify moved assets ... not exposed to load queries ... see [Next
Steps](#next-steps))
- [ ] Store "last modified" source asset and meta timestamps in
processed meta files to enable skipping expensive hashing when the file
wasn't changed
- [ ] Fix "slow loop" handle drop fix 
- [ ] Migrate to TypeName
- [x] Handle "loader preregistration". See #9429

## Next Steps

* **Configurable per-type defaults for AssetMeta**: It should be
possible to add configuration like "all png image meta should default to
using nearest sampling" (currently this hard-coded per-loader/processor
Settings::default() impls). Also see the "Folder Meta" bullet point.
* **Avoid Reprocessing on Asset Renames / Moves**: See the "canonical
asset ids" discussion in [Open Questions](#open-questions) and the
relevant bullet point in [Draft TODO](#draft-todo). Even without
canonical ids, folder renames could avoid reprocessing in some cases.
* **Multiple Asset Sources**: Expand AssetPath to support "asset source
names" and support multiple AssetReaders in the asset server (ex:
`webserver://some_path/image.png` backed by an Http webserver
AssetReader). The "default" asset reader would use normal
`some_path/image.png` paths. Ideally this works in combination with
multiple AssetWatchers for hot-reloading
* **Stable Type Names**: this pr removes the TypeUuid requirement from
assets in favor of `std::any::type_name`. This makes defining assets
easier (no need to generate a new uuid / use weird proc macro syntax).
It also makes reading meta files easier (because things have "friendly
names"). We also use type names for components in scene files. If they
are good enough for components, they are good enough for assets. And
consistency across Bevy pillars is desirable. However,
`std::any::type_name` is not guaranteed to be stable (although in
practice it is). We've developed a [stable type
path](https://github.com/bevyengine/bevy/pull/7184) to resolve this,
which should be adopted when it is ready.
* **Command Line Interface**: It should be possible to run the asset
processor in a separate process from the command line. This will also
require building a network-server-backed AssetReader to communicate
between the app and the processor. We've been planning to build a "bevy
cli" for awhile. This seems like a good excuse to build it.
* **Asset Packing**: This is largely an additive feature, so it made
sense to me to punt this until we've laid the foundations in this PR.
* **Per-Platform Processed Assets**: It should be possible to generate
assets for multiple platforms by supporting multiple "processor
profiles" per asset (ex: compress with format X on PC and Y on iOS). I
think there should probably be arbitrary "profiles" (which can be
separate from actual platforms), which are then assigned to a given
platform when generating the final asset distribution for that platform.
Ex: maybe devs want a "Mobile" profile that is shared between iOS and
Android. Or a "LowEnd" profile shared between web and mobile.
* **Versioning and Migrations**: Assets, Loaders, Savers, and Processors
need to have versions to determine if their schema is valid. If an asset
/ loader version is incompatible with the current version expected at
runtime, the processor should be able to migrate them. I think we should
try using Bevy Reflect for this, as it would allow us to load the old
version as a dynamic Reflect type without actually having the old Rust
type. It would also allow us to define "patches" to migrate between
versions (Bevy Reflect devs are currently working on patching). The
`.meta` file already has its own format version. Migrating that to new
versions should also be possible.
* **Real Copy-on-write AssetPaths**: Rust's actual Cow (clone-on-write
type) currently used by AssetPath can still result in String clones that
aren't actually necessary (cloning an Owned Cow clones the contents).
Bevy's asset system requires cloning AssetPaths in a number of places,
which result in actual clones of the internal Strings. This is not
efficient. AssetPath internals should be reworked to exhibit truer
cow-like-behavior that reduces String clones to the absolute minimum.
* **Consider processor-less processing**: In theory the AssetServer
could run processors "inline" even if the background AssetProcessor is
disabled. If we decide this is actually desirable, we could add this.
But I don't think its a priority in the short or medium term.
* **Pre-emptive dependency loading**: We could encode dependencies in
processed meta files, which could then be used by the Asset Server to
kick of dependency loads as early as possible (prior to starting the
actual asset load). Is this desirable? How much time would this save in
practice?
* **Optimize Processor With UntypedAssetIds**: The processor exclusively
uses AssetPath to identify assets currently. It might be possible to
swap these out for UntypedAssetIds in some places, which are smaller /
cheaper to hash and compare.
* **One to Many Asset Processing**: An asset source file that produces
many assets currently must be processed into a single "processed" asset
source. If labeled assets can be written separately they can each have
their own configured savers _and_ they could be loaded more granularly.
Definitely worth exploring!
* **Automatically Track "Runtime-only" Asset Dependencies**: Right now,
tracking "created at runtime" asset dependencies requires adding them
via `asset_server.load_asset(StandardMaterial::default())`. I think with
some cleverness we could also do this for
`materials.add(StandardMaterial::default())`, making tracking work
"everywhere". There are challenges here relating to change detection /
ensuring the server is made aware of dependency changes. This could be
expensive in some cases.
* **"Dependency Changed" events**: Some assets have runtime artifacts
that need to be re-generated when one of their dependencies change (ex:
regenerate a material's bind group when a Texture needs to change). We
are generating the dependency graph so we can definitely produce these
events. Buuuuut generating these events will have a cost / they could be
high frequency for some assets, so we might want this to be opt-in for
specific cases.
* **Investigate Storing More Information In Handles**: Handles can now
store arbitrary information, which makes it cheaper and easier to
access. How much should we move into them? Canonical asset load states
(via atomics)? (`handle.is_loaded()` would be very cool). Should we
store the entire asset and remove the `Assets<T>` collection?
(`Arc<RwLock<Option<Image>>>`?)
* **Support processing and loading files without extensions**: This is a
pretty arbitrary restriction and could be supported with very minimal
changes.
* **Folder Meta**: It would be nice if we could define per folder
processor configuration defaults (likely in a `.meta` or `.folder_meta`
file). Things like "default to linear filtering for all Images in this
folder".
* **Replace async_broadcast with event-listener?** This might be
approximately drop-in for some uses and it feels more light weight
* **Support Running the AssetProcessor on the Web**: Most of the hard
work is done here, but there are some easy straggling TODOs (make the
transaction log an interface instead of a direct file writer so we can
write a web storage backend, implement an AssetReader/AssetWriter that
reads/writes to something like LocalStorage).
* **Consider identifying and preventing circular dependencies**: This is
especially important for "processor dependencies", as processing will
silently never finish in these cases.
* **Built-in/Inlined Asset Hot Reloading**: This PR regresses
"built-in/inlined" asset hot reloading (previously provided by the
DebugAssetServer). I'm intentionally punting this because I think it can
be cleanly implemented with "multiple asset sources" by registering a
"debug asset source" (ex: `debug://bevy_pbr/src/render/pbr.wgsl` asset
paths) in combination with an AssetWatcher for that asset source and
support for "manually loading pats with asset bytes instead of
AssetReaders". The old DebugAssetServer was quite nasty and I'd love to
avoid that hackery going forward.
* **Investigate ways to remove double-parsing meta files**: Parsing meta
files currently involves parsing once with "minimal" versions of the
meta file to extract the type name of the loader/processor config, then
parsing again to parse the "full" meta. This is suboptimal. We should be
able to define custom deserializers that (1) assume the loader/processor
type name comes first (2) dynamically looks up the loader/processor
registrations to deserialize settings in-line (similar to components in
the bevy scene format). Another alternative: deserialize as dynamic
Reflect objects and then convert.
* **More runtime loading configuration**: Support using the Handle type
as a hint to select an asset loader (instead of relying on AssetPath
extensions)
* **More high level Processor trait implementations**: For example, it
might be worth adding support for arbitrary chains of "asset transforms"
that modify an in-memory asset representation between loading and
saving. (ex: load a Mesh, run a `subdivide_mesh` transform, followed by
a `flip_normals` transform, then save the mesh to an efficient
compressed format).
* **Bevy Scene Handle Deserialization**: (see the relevant [Draft TODO
item](#draft-todo) for context)
* **Explore High Level Load Interfaces**: See [this
discussion](#discuss-on_loaded-high-level-interface) for one prototype.
* **Asset Streaming**: It would be great if we could stream Assets (ex:
stream a long video file piece by piece)
* **ID Exchanging**: In this PR Asset Handles/AssetIds are bigger than
they need to be because they have a Uuid enum variant. If we implement
an "id exchanging" system that trades Uuids for "efficient runtime ids",
we can cut down on the size of AssetIds, making them more efficient.
This has some open design questions, such as how to spawn entities with
"default" handle values (as these wouldn't have access to the exchange
api in the current system).
* **Asset Path Fixup Tooling**: Assets that inline asset paths inside
them will break when an asset moves. The asset system provides the
functionality to detect when paths break. We should build a framework
that enables formats to define "path migrations". This is especially
important for scene files. For editor-generated files, we should also
consider using UUIDs (see other bullet point) to avoid the need to
migrate in these cases.

---------

Co-authored-by: BeastLe9enD <beastle9end@outlook.de>
Co-authored-by: Mike <mike.hsu@gmail.com>
Co-authored-by: Nicola Papale <nicopap@users.noreply.github.com>
2023-09-07 02:07:27 +00:00