# Objective
`bevy_reflect` can be a moderately complex crate to try and understand. It has many moving parts, a handful of gotchas, and a few subtle contracts that aren't immediately obvious to users and even other contributors.
The current README does an okay job demonstrating how the crate can be used. However, the crate's actual documentation should give a better overview of the crate, its inner-workings, and show some of its own examples.
## Solution
Added crate-level documentation that attempts to summarize the main parts of `bevy_reflect` into small sections.
This PR also updates the documentation for:
- `Reflect`
- `FromReflect`
- The reflection subtraits
- Other important types and traits
- The reflection macros (including the derive macros)
- Crate features
### Open Questions
1. ~~Should I update the docs for the Dynamic types? I was originally going to, but I'm getting a little concerned about the size of this PR 😅~~ Decided to not do this in this PR. It'll be better served from its own PR.
2. Should derive macro documentation be moved to the trait itself? This could improve visibility and allow for better doc links, but could also clutter up the trait's documentation (as well as not being on the actual derive macro's documentation).
### TODO
- [ ] ~~Document Dynamic types (?)~~ I think this should be done in a separate PR.
- [x] Document crate features
- [x] Update docs for `GetTypeRegistration`
- [x] Update docs for `TypeRegistration`
- [x] Update docs for `derive_from_reflect`
- [x] Document `reflect_trait`
- [x] Document `impl_reflect_value`
- [x] Document `impl_from_reflect_value`
---
## Changelog
- Updated documentation across the `bevy_reflect` crate
- Removed `#[module]` helper attribute for `Reflect` derives (this is not currently used)
## Migration Guide
- Removed `#[module]` helper attribute for `Reflect` derives. If your code is relying on this attribute, please replace it with either `#[reflect]` or `#[reflect_value]` (dependent on use-case).
Co-authored-by: Gino Valente <49806985+MrGVSV@users.noreply.github.com>
# Objective
Fixes#7704
## Solution
Added a small section that describes the meaning of each letter prefix for issue labels.
Co-authored-by: Adam <59033400+adam-shih@users.noreply.github.com>
follow-up to https://github.com/bevyengine/bevy/pull/7716
# Objective
System access is only populated in `System::initialize`, so without calling `initialize` it's actually impossible to see most ambiguities.
## Solution
- make `initialize` public. The method is idempotent, so calling it multiple times doesn't hurt
# Objective
Continuation of https://github.com/bevyengine/bevy/pull/5719
Now that we have a definable type for the iterator.
---
## Changelog
- Implemented IntoIterator for EventReader so you can now do `&mut reader` instead of `reader.iter()` for events.
# Objective
- bevy_ggrs uses `reflect_hash` in order to produce checksums for its world snapshots. These checksums are sent between clients in order to detect desyncronization.
- However, since we currently use `async::AHasher` with the `std` feature, this means that hashes will always be different for different peers, even if the state is identical.
- This means bevy_ggrs needs a way to get a deterministic (fixed) hash.
## Solution
- ~~Add a feature to use `bevy_utils::FixedState` for the hasher used by bevy_reflect.~~
- Always use `bevy_utils::FixedState` for initializing the bevy_reflect hasher.
---
## Changelog
- bevy_reflect now uses a fixed state for its hasher, which means the output of `Reflect::reflect_hash` is now deterministic across processes.
# Objective
Fix#7440. Fix#7441.
## Solution
* Remove builder functions on `ScheduleBuildSettings` in favor of public fields, move docs to the fields.
* Add `use_shortnames` and use it in `get_node_name` to feed it through `bevy_utils::get_short_name`.
# Objective
Allow for creating pipelines that use push constants. To be able to use push constants. Fixes#4825
As of right now, trying to call `RenderPass::set_push_constants` will trigger the following error:
```
thread 'main' panicked at 'wgpu error: Validation Error
Caused by:
In a RenderPass
note: encoder = `<CommandBuffer-(0, 59, Vulkan)>`
In a set_push_constant command
provided push constant is for stage(s) VERTEX | FRAGMENT | VERTEX_FRAGMENT, however the pipeline layout has no push constant range for the stage(s) VERTEX | FRAGMENT | VERTEX_FRAGMENT
```
## Solution
Add a field push_constant_ranges to` RenderPipelineDescriptor` and `ComputePipelineDescriptor`.
This PR supersedes #4908 which now contains merge conflicts due to significant changes to `bevy_render`.
Meanwhile, this PR also made the `layout` field of `RenderPipelineDescriptor` and `ComputePipelineDescriptor` non-optional. If the user do not need to specify the bind group layouts, they can simply supply an empty vector here. No need for it to be optional.
---
## Changelog
- Add a field push_constant_ranges to RenderPipelineDescriptor and ComputePipelineDescriptor
- Made the `layout` field of RenderPipelineDescriptor and ComputePipelineDescriptor non-optional.
## Migration Guide
- Add push_constant_ranges: Vec::new() to every `RenderPipelineDescriptor` and `ComputePipelineDescriptor`
- Unwrap the optional values on the `layout` field of `RenderPipelineDescriptor` and `ComputePipelineDescriptor`. If the descriptor has no layout, supply an empty vector.
Co-authored-by: Zhixing Zhang <me@neoto.xin>
# Objective
Fixes#7295
Should we maybe default to 4x if 2x/8x is selected but not supported?
---
## Changelog
- Added 2x and 8x sample counts for MSAA.
# Objective
- Environment maps use these formats, and in the future rendering LUTs will need textures loaded by default in the engine
## Solution
- Make ktx2 and zstd part of the default feature
- Let examples assume these features are enabled
---
## Changelog
- `ktx2` and `zstd` are now party of bevy's default enabled features
## Migration Guide
- If you used the `ktx2` or `zstd` features, you no longer need to explicitly enable them, as they are now part of bevy's default enabled features
# Objective
The type `SyncCell<T>` (added in #5483) is used to force any wrapped type to be `Sync`, by only allowing exclusive access to the wrapped value. This restriction is unnecessary for types which are already `Sync`.
---
## Changelog
+ Added the method `read` to `SyncCell`, which allows shared access to values that already implement the `Sync` trait.
# Objective
Web builds do not support running on multiple threads right now. Defaulting to the multi-threaded executor has significant overhead without any benefit.
## Solution
Default to the single threaded executor on wasm32 builds.
# Objective
- other tools (bevy_mod_debugdump) would like to have access to the ambiguities so that they can do their own reporting/visualization
## Solution
- store `conflicting_systems` in `ScheduleGraph` after calling `build_schedule`
The solution isn't very pretty and as pointed out it https://github.com/bevyengine/bevy/pull/7522, there may be a better way of exposing this, but this is the quick and dirty way if we want to have this functionality exposed in 0.10.
# Objective
- RemovedComponents is just a thin wrapper around Events/ManualEventReader which is the same as an EventReader, so most usecases that of an EventReader will probably be useful for RemovedComponents too.
I was thinking of making a trait for this but I don't think it is worth the overhead currently.
## Solution
- Mirror the api surface of EventReader
# Objective
Motivated by #7469.
`EventReader` iterators use the default implementations for `.nth()` and `.last()`, which includes iterating over and throwing out all events before the desired one.
## Solution
Add specialized implementations for these methods that directly updates the unread event counter and returns a reference to the desired event.
TODO:
- [x] Add a unit test.
- [x] ~~Add a benchmark, to see if the compiler was doing this automatically already.~~ *On second thought, this doesn't feel like a very useful thing to include in the benchmark suite.*
# Objective
- it would be nice to be able to associate a `NodeId` of a system type set to the `NodeId` of the actual system (used in bevy_mod_debugdump)
## Solution
- make `system_type` return the type id of the system
- that way you can check if a `dyn SystemSet` is the system type set of a `dyn System`
- I don't know if this information is already present somewhere else in the scheduler or if there is a better way to expose it
# Objective
Fixes#7702.
## Solution
- Added an test that ensures that no error is returned if a system or set is inside two different sets that share the same base set.
- Added an check to only return an error if the two base sets are not equal.
# Objective
The `ScheduleGraph` should be expose so that crates like [bevy_mod_debugdump](https://github.com/jakobhellermann/bevy_mod_debugdump/blob/stageless/docs/README.md) can access useful information.
## Solution
- expose `ScheduleGraph`, `NodeId`, `BaseSetMembership`, `Dag`
- add accessor functions for sets and systems
## Changelog
- expose `ScheduleGraph` for use in third party tools
This does expose our use of `petgraph` as a graph library, so we can only change that as a breaking change.
# Objective
- Fixes#5432
- Fixes#6680
## Solution
- move code responsible for generating the `impl TypeUuid` from `type_uuid_derive` into a new function, `gen_impl_type_uuid`.
- this allows the new proc macro, `impl_type_uuid`, to call the code for generation.
- added struct `TypeUuidDef` and implemented `syn::Parse` to allow parsing of the input for the new macro.
- finally, used the new macro `impl_type_uuid` to implement `TypeUuid` for the standard library (in `crates/bevy_reflect/src/type_uuid_impl.rs`).
- fixes#6680 by doing a wrapping add of the param's index to its `TYPE_UUID`
Co-authored-by: dis-da-moe <84386186+dis-da-moe@users.noreply.github.com>
# Objective
The trait `Condition<>` is implemented for any type that can be converted into a `ReadOnlySystem` which takes no inputs and returns a bool. However, due to the current implementation, consumers of the trait cannot rely on the fact that `<T as Condition>::System` implements `ReadOnlySystem`. In cases such as the `not` combinator (added in #7559), we are required to add redundant `T::System: ReadOnlySystem` trait bounds, even though this should be implied by the `Condition<>` trait.
## Solution
Add a hidden associated type which allows the compiler to figure out that the `System` associated type implements `ReadOnlySystem`.
# Objective
Fixes#7654
## Solution
Add `windows v0.43` to the list of skipped dependencies checked by CI (until `gilrs` publishes a new release with `windows v0.44`)
…able like Table. Rename clear to clear_entities to clarify that metadata keeps, only value cleared
# Objective
- Provide some inspectability for SparseSets.
## Solution
- `Tables` has these three methods, len, is_empty and iter too. Add these methods to `SparseSets`, so user can print the shape of storage.
---
## Changelog
> This section is optional. If this was a trivial fix, or has no externally-visible impact, you can delete this section.
- Add `len`, `is_empty`, `iter` methods on SparseSets.
- Rename `clear` to `clear_entities` to clarify its purpose.
- Add `new_for_test` on `ComponentInfo` to make test code easy.
- Add test case covering new methods.
## Migration Guide
> This section is optional. If there are no breaking changes, you can delete this section.
- Simply adding new functionality is not a breaking change.
# Objective
This PR improves message that caused by duplicate components in bundle.
## Solution
Show names of duplicate components.
The solution is not very elegant, in my opinion, I will be happy to listen to suggestions for improving it
Co-authored-by: Саня Череп <41489405+SDesya74@users.noreply.github.com>
# Objective
While porting my crate `bevy_trait_query` to bevy 0.10, I ran into an issue with the `DetectChangesMut` trait. Due to the way that the `set_if_neq` method (added in #6853) is implemented, you are forced to write a nonsense implementation of it for dynamically sized types. This edge case shows up when implementing trait queries, since `DetectChangesMut` is implemented for `Mut<dyn Trait>`.
## Solution
Simplify the generics for `set_if_neq` and add the `where Self::Target: Sized` trait bound to it. Add a default implementation so implementers don't need to implement a method with nonsensical trait bounds.
# Objective
The `SystemParamFunction` (and `ExclusiveSystemParamFunction`) trait is very cumbersome to use, due to it requiring four generic type parameters. These are currently all used as marker parameters to satisfy rust's trait coherence rules.
### Example (before)
```rust
pub fn pipe<AIn, Shared, BOut, A, AParam, AMarker, B, BParam, BMarker>(
mut system_a: A,
mut system_b: B,
) -> impl FnMut(In<AIn>, ParamSet<(AParam, BParam)>) -> BOut
where
A: SystemParamFunction<AIn, Shared, AParam, AMarker>,
B: SystemParamFunction<Shared, BOut, BParam, BMarker>,
AParam: SystemParam,
BParam: SystemParam,
```
## Solution
Turn the `In`, `Out`, and `Param` generics into associated types. Merge the marker types together to retain coherence.
### Example (after)
```rust
pub fn pipe<A, B, AMarker, BMarker>(
mut system_a: A,
mut system_b: B,
) -> impl FnMut(In<A::In>, ParamSet<(A::Param, B::Param)>) -> B::Out
where
A: SystemParamFunction<AMarker>,
B: SystemParamFunction<BMarker, In = A::Out>,
```
---
## Changelog
+ Simplified the `SystemParamFunction` and `ExclusiveSystemParamFunction` traits.
## Migration Guide
For users of the `SystemParamFunction` trait, the generic type parameters `In`, `Out`, and `Param` have been turned into associated types. The same has been done with the `ExclusiveSystemParamFunction` trait.
# Objective
The current doc comment for `flex-basis` states that it is "The initial size of the item", which is a bit confusing since size in Bevy is mostly used to refer to two-dimensional extents but `flex-basis` is a one-dimensional value.
It also needs to explain that:
* `flex-basis` sets the initial length of the main axis.
* Overrides `size` on the main axis.
* Obeys the `min_size` and `max_size` constraints.
# Objective
- #6402 changed `World::fetch_table` (now `UnsafeWorldCell::fetch_table`) to access the archetype in order to get the `table_id` and `table_row` of the entity involved. However this is useless since those were already present in the `EntityLocation`
- Moreover it's useless for `UnsafeWorldCell::fetch_table` to return the `TableRow` too, since the caller must already have access to the `EntityLocation` which contains the `TableRow`.
- The result is that `UnsafeWorldCell::fetch_table` now only does 2 memory fetches instead of 4.
## Solution
- Revert the changes to the implementation of `UnsafeWorldCell::fetch_table` made in #6402
…u64, so hash safety is not a concern
# Objective
- While reading the code, just noticed the BundleInfo's HashMap is std::collections::HashMap, which uses a slow but safe hasher.
## Solution
- Use bevy_utils::HashMap instead
benchmark diff (I run several times in a linux box, the perf improvement is consistent, though numbers varies from time to time, I paste my last run result here):
``` bash
cargo bench -- spawn
Compiling bevy_ecs v0.9.0 (/home/lishuo/developer/pr/bevy/crates/bevy_ecs)
Compiling bevy_app v0.9.0 (/home/lishuo/developer/pr/bevy/crates/bevy_app)
Compiling benches v0.1.0 (/home/lishuo/developer/pr/bevy/benches)
Finished bench [optimized] target(s) in 1m 17s
Running benches/bevy_ecs/change_detection.rs (/home/lishuo/developer/pr/bevy/benches/target/release/deps/change_detection-86c5445d0dc34529)
Gnuplot not found, using plotters backend
Running benches/bevy_ecs/benches.rs (/home/lishuo/developer/pr/bevy/benches/target/release/deps/ecs-e49b3abe80bfd8c0)
Gnuplot not found, using plotters backend
spawn_commands/2000_entities
time: [153.94 µs 159.19 µs 164.37 µs]
change: [-14.706% -11.050% -6.9633%] (p = 0.00 < 0.05)
Performance has improved.
spawn_commands/4000_entities
time: [328.77 µs 339.11 µs 349.11 µs]
change: [-7.6331% -3.9932% +0.0487%] (p = 0.06 > 0.05)
No change in performance detected.
spawn_commands/6000_entities
time: [445.01 µs 461.29 µs 477.36 µs]
change: [-16.639% -13.358% -10.006%] (p = 0.00 < 0.05)
Performance has improved.
spawn_commands/8000_entities
time: [657.94 µs 677.71 µs 696.95 µs]
change: [-8.8708% -5.2591% -1.6847%] (p = 0.01 < 0.05)
Performance has improved.
get_or_spawn/individual time: [452.02 µs 466.70 µs 482.07 µs]
change: [-17.218% -14.041% -10.728%] (p = 0.00 < 0.05)
Performance has improved.
get_or_spawn/batched time: [291.12 µs 301.12 µs 311.31 µs]
change: [-12.281% -8.9163% -5.3660%] (p = 0.00 < 0.05)
Performance has improved.
spawn_world/1_entities time: [81.668 ns 84.284 ns 86.860 ns]
change: [-12.251% -6.7872% -1.5402%] (p = 0.02 < 0.05)
Performance has improved.
spawn_world/10_entities time: [789.78 ns 821.96 ns 851.95 ns]
change: [-19.738% -14.186% -8.0733%] (p = 0.00 < 0.05)
Performance has improved.
spawn_world/100_entities
time: [7.9906 µs 8.2449 µs 8.5013 µs]
change: [-12.417% -6.6837% -0.8766%] (p = 0.02 < 0.05)
Change within noise threshold.
spawn_world/1000_entities
time: [81.602 µs 84.161 µs 86.833 µs]
change: [-13.656% -8.6520% -3.0491%] (p = 0.00 < 0.05)
Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
1 (1.00%) high mild
Benchmarking spawn_world/10000_entities: Warming up for 500.00 ms
Warning: Unable to complete 100 samples in 4.0s. You may wish to increase target time to 4.0s, enable flat sampling, or reduce sample count to 70.
spawn_world/10000_entities
time: [813.02 µs 839.76 µs 865.41 µs]
change: [-12.133% -6.1970% -0.2302%] (p = 0.05 < 0.05)
Change within noise threshold.
```
---
## Changelog
> This section is optional. If this was a trivial fix, or has no externally-visible impact, you can delete this section.
- use bevy_utils::HashMap for Bundles::bundle_ids
## Migration Guide
> This section is optional. If there are no breaking changes, you can delete this section.
- Not a breaking change, hashmap is internal impl.
# Objective
We have a few old system labels that are now system sets but are still named or documented as labels. Documentation also generally mentioned system labels in some places.
## Solution
- Clean up naming and documentation regarding system sets
## Migration Guide
`PrepareAssetLabel` is now called `PrepareAssetSet`
# Objective
- Improve readability of the run condition for systems only running in a certain state
## Solution
- Rename `state_equals` to `in_state` (see [comment by cart](https://github.com/bevyengine/bevy/pull/7634#issuecomment-1428740311) in #7634 )
- `.run_if(state_equals(variant))` now is `.run_if(in_state(variant))`
This breaks the naming pattern a bit with the related conditions `state_exists` and `state_exists_and_equals` but I could not think of better names for those and think the improved readability of `in_state` is worth it.
# Objective
- Fixes#7612
- Since #7493, windows started as unfocused
## Solution
- Creating the window at the end of the event loop after the resume event instead of at the beginning of the loop of the next event fixes the focus
# Objective
The text contained by a text node is only recomputed when its `Style` or `Text` components change, or when the scale factor changes. Not when the geometry of the text node is modified.
Make it so that any change in text node size triggers a text recomputation.
## Solution
Change `text_system` so that it queries for text nodes with changed `Node` components and recomputes their text.
---
Most users won't notice any difference but it should fix some confusing edge cases in more complicated and interactive layouts.
## Changelog
* Added `Changed<Node>` to the change detection query of `text_system`. This ensures that any change in the size of a text node will cause any text it contains to be recomputed.
# Objective
Standard material defaults are currently strange, and the docs are wrong re: metallic.
## Solution
Change the defaults to be similar to [Godot](https://github.com/godotengine/godot/pull/62756).
---
## Changelog
#### Changed
- `StandardMaterial` now defaults to a dielectric material (0.0 `metallic`) with 0.5 `perceptual_roughness`.
## Migration Guide
`StandardMaterial`'s default have now changed to be a fully dielectric material with medium roughness. If you want to use the old defaults, you can set `perceptual_roughness = 0.089` and `metallic = 0.01` (though metallic should generally only be set to 0.0 or 1.0).
# Objective
Fixes#7632.
As discussed in #7634, it can be quite challenging for users to intuit the mental model of how states now work.
## Solution
Rather than change the behavior of the `OnUpdate` system set, instead work on making sure it's easy to understand what's going on.
Two things have been done:
1. Remove the `.on_update` method from our bevy of system building traits. This was special-cased and made states feel much more magical than they need to.
2. Improve the docs for the `OnUpdate` system set.
# Objective
Resolves#7121
## Solution
Decouples `List` and `Array` by removing `Array` as a supertrait of `List`. Additionally, similar methods from `Array` have been added to `List` so that their usages can remain largely unchanged.
#### Possible Alternatives
##### `Sequence`
My guess for why we originally made `List` a subtrait of `Array` is that they share a lot of common operations. We could potentially move these overlapping methods to a `Sequence` (name taken from #7059) trait and make that a supertrait of both. This would allow functions to contain logic that simply operates on a sequence rather than "list vs array".
However, this means that we'd need to add methods for converting to a `dyn Sequence`. It also might be confusing since we wouldn't add a `ReflectRef::Sequence` or anything like that. Is such a trait worth adding (either in this PR or a followup one)?
---
## Changelog
- Removed `Array` as supertrait of `List`
- Added methods to `List` that were previously provided by `Array`
## Migration Guide
The `List` trait is no longer dependent on `Array`. Implementors of `List` can remove the `Array` impl and move its methods into the `List` impl (with only a couple tweaks).
```rust
// BEFORE
impl Array for Foo {
fn get(&self, index: usize) -> Option<&dyn Reflect> {/* ... */}
fn get_mut(&mut self, index: usize) -> Option<&mut dyn Reflect> {/* ... */}
fn len(&self) -> usize {/* ... */}
fn is_empty(&self) -> bool {/* ... */}
fn iter(&self) -> ArrayIter {/* ... */}
fn drain(self: Box<Self>) -> Vec<Box<dyn Reflect>> {/* ... */}
fn clone_dynamic(&self) -> DynamicArray {/* ... */}
}
impl List for Foo {
fn insert(&mut self, index: usize, element: Box<dyn Reflect>) {/* ... */}
fn remove(&mut self, index: usize) -> Box<dyn Reflect> {/* ... */}
fn push(&mut self, value: Box<dyn Reflect>) {/* ... */}
fn pop(&mut self) -> Option<Box<dyn Reflect>> {/* ... */}
fn clone_dynamic(&self) -> DynamicList {/* ... */}
}
// AFTER
impl List for Foo {
fn get(&self, index: usize) -> Option<&dyn Reflect> {/* ... */}
fn get_mut(&mut self, index: usize) -> Option<&mut dyn Reflect> {/* ... */}
fn insert(&mut self, index: usize, element: Box<dyn Reflect>) {/* ... */}
fn remove(&mut self, index: usize) -> Box<dyn Reflect> {/* ... */}
fn push(&mut self, value: Box<dyn Reflect>) {/* ... */}
fn pop(&mut self) -> Option<Box<dyn Reflect>> {/* ... */}
fn len(&self) -> usize {/* ... */}
fn is_empty(&self) -> bool {/* ... */}
fn iter(&self) -> ListIter {/* ... */}
fn drain(self: Box<Self>) -> Vec<Box<dyn Reflect>> {/* ... */}
fn clone_dynamic(&self) -> DynamicList {/* ... */}
}
```
Some other small tweaks that will need to be made include:
- Use `ListIter` for `List::iter` instead of `ArrayIter` (the return type from `Array::iter`)
- Replace `array_hash` with `list_hash` in `Reflect::reflect_hash` for implementors of `List`
# Objective
- rebased version of #6155
The `MaterialPipeline` cannot be integrated into other pipelines like the `MeshPipeline`.
## Solution
Implement `Clone` for `MaterialPipeline`. Expose systems and resources part of the `MaterialPlugin` to allow custom assembly - especially combining existing systems and resources with a custom `queue_material_meshes` system.
# Changelog
## Added
- Clone impl for MaterialPipeline
## Changed
- ExtractedMaterials, extract_materials and prepare_materials are now public
# Objective
- Fixes: #7187
Since avoiding the `SRes::into_inner` call does not seem to be possible, this PR tries to at least document its usage.
I am not sure if I explained the lifetime issue correctly, please let me know if something is incorrect.
## Solution
- Add information about the `SRes::into_inner` usage on both `RenderCommand` and `Res`
# Objective
Add doc tests for the `Size` constructor functions.
Also changed the function descriptions so they explicitly state the values that elided values are given.
## Changelog
* Added doc tests for the `Size` constructor functions.
# Objective
The `size` field of `CalculatedSize` shouldn't be a `Size` as it only ever stores (unscaled) pixel values. By default its fields are `Val::Auto` but these are converted to `0`s before being sent to Taffy.
## Solution
Change the `size` field of `CalculatedSize` to a Vec2.
## Changelog
* Changed the `size` field of `CalculatedSize` to a Vec2.
* Removed the `Val` <-> `f32` conversion code for `CalculatedSize`.
## Migration Guide
* The size field of `CalculatedSize` has been changed to a `Vec2`.
Profiles show that in extremely hot loops, like the draw loops in the renderer, invoking the trace! macro has noticeable overhead, even if the trace log level is not enabled.
Solve this by introduce a 'wrapper' detailed_trace macro around trace, that wraps the trace! log statement in a trivially false if statement unless a cargo feature is enabled
# Objective
- Eliminate significant overhead observed with trace-level logging in render hot loops, even when trace log level is not enabled.
- This is an alternative solution to the one proposed in #7223
## Solution
- Introduce a wrapper around the `trace!` macro called `detailed_trace!`. This macro wraps the `trace!` macro with an if statement that is conditional on a new cargo feature, `detailed_trace`. When the feature is not enabled (the default), then the if statement is trivially false and should be optimized away at compile time.
- Convert the observed hot occurrences of trace logging in `TrackedRenderPass` with this new macro.
Testing the results of
```
cargo run --profile stress-test --features bevy/trace_tracy --example many_cubes -- spheres
```
shows significant improvement of the `main_opaque_pass_3d` of the renderer, a median time decrease from 6.0ms to 3.5ms.
---
## Changelog
- For performance reasons, some detailed renderer trace logs now require the use of cargo feature `detailed_trace` in addition to setting the log level to `TRACE` in order to be shown.
## Migration Guide
- Some detailed bevy trace events now require the use of the cargo feature `detailed_trace` in addition to enabling `TRACE` level logging to view. Should you wish to see these logs, please compile your code with the bevy feature `detailed_trace`. Currently, the only logs that are affected are the renderer logs pertaining to `TrackedRenderPass` functions
# Objective
- Required features were added to some examples in #7051 even though those features aren't the main focus of the examples
- Don't require features on examples that are useful without them
## Solution
- Remove required features on examples `load_gltf` and `scene_viewer`, but log a warning when they are not enabled
# Objective
Related to #7530.
`EventReader` iterators currently use the default impl for `.count()`, which unnecessarily loops over all unread events.
# Solution
Add specialized impls that mark the `EventReader` as consumed and return the number of unread events.
