f7e112a3c9
# Objective Improve the performance of `FilteredEntity(Ref|Mut)` and `Entity(Ref|Mut)Except`. `FilteredEntityRef` needs an `Access<ComponentId>` to determine what components it can access. There is one stored in the query state, but query items cannot borrow from the state, so it has to `clone()` the access for each row. Cloning the access involves memory allocations and can be expensive. ## Solution Let query items borrow from their query state. Add an `'s` lifetime to `WorldQuery::Item` and `WorldQuery::Fetch`, similar to the one in `SystemParam`, and provide `&'s Self::State` to the fetch so that it can borrow from the state. Unfortunately, there are a few cases where we currently return query items from temporary query states: the sorted iteration methods create a temporary state to query the sort keys, and the `EntityRef::components<Q>()` methods create a temporary state for their query. To allow these to continue to work with most `QueryData` implementations, introduce a new subtrait `ReleaseStateQueryData` that converts a `QueryItem<'w, 's>` to `QueryItem<'w, 'static>`, and is implemented for everything except `FilteredEntity(Ref|Mut)` and `Entity(Ref|Mut)Except`. `#[derive(QueryData)]` will generate `ReleaseStateQueryData` implementations that apply when all of the subqueries implement `ReleaseStateQueryData`. This PR does not actually change the implementation of `FilteredEntity(Ref|Mut)` or `Entity(Ref|Mut)Except`! That will be done as a follow-up PR so that the changes are easier to review. I have pushed the changes as chescock/bevy#5. ## Testing I ran performance traces of many_foxes, both against main and against chescock/bevy#5, both including #15282. These changes do appear to make generalized animation a bit faster: (Red is main, yellow is chescock/bevy#5)  ## Migration Guide The `WorldQuery::Item` and `WorldQuery::Fetch` associated types and the `QueryItem` and `ROQueryItem` type aliases now have an additional lifetime parameter corresponding to the `'s` lifetime in `Query`. Manual implementations of `WorldQuery` will need to update the method signatures to include the new lifetimes. Other uses of the types will need to be updated to include a lifetime parameter, although it can usually be passed as `'_`. In particular, `ROQueryItem` is used when implementing `RenderCommand`. Before: ```rust fn render<'w>( item: &P, view: ROQueryItem<'w, Self::ViewQuery>, entity: Option<ROQueryItem<'w, Self::ItemQuery>>, param: SystemParamItem<'w, '_, Self::Param>, pass: &mut TrackedRenderPass<'w>, ) -> RenderCommandResult; ``` After: ```rust fn render<'w>( item: &P, view: ROQueryItem<'w, '_, Self::ViewQuery>, entity: Option<ROQueryItem<'w, '_, Self::ItemQuery>>, param: SystemParamItem<'w, '_, Self::Param>, pass: &mut TrackedRenderPass<'w>, ) -> RenderCommandResult; ``` --- Methods on `QueryState` that take `&mut self` may now result in conflicting borrows if the query items capture the lifetime of the mutable reference. This affects `get()`, `iter()`, and others. To fix the errors, first call `QueryState::update_archetypes()`, and then replace a call `state.foo(world, param)` with `state.query_manual(world).foo_inner(param)`. Alternately, you may be able to restructure the code to call `state.query(world)` once and then make multiple calls using the `Query`. Before: ```rust let mut state: QueryState<_, _> = ...; let d1 = state.get(world, e1); let d2 = state.get(world, e2); // Error: cannot borrow `state` as mutable more than once at a time println!("{d1:?}"); println!("{d2:?}"); ``` After: ```rust let mut state: QueryState<_, _> = ...; state.update_archetypes(world); let d1 = state.get_manual(world, e1); let d2 = state.get_manual(world, e2); // OR state.update_archetypes(world); let d1 = state.query(world).get_inner(e1); let d2 = state.query(world).get_inner(e2); // OR let query = state.query(world); let d1 = query.get_inner(e1); let d1 = query.get_inner(e2); println!("{d1:?}"); println!("{d2:?}"); ``` |
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Release Content
This directory contains drafts of documentation for the current development cycle, which will be published to the website during the next release. You can find more information in the release notes and migration guides files.