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Huge thanks to @maniwani, @devil-ira, @hymm, @cart, @superdump and @jakobhellermann for the help with this PR. # Objective - Followup #6587. - Minimal integration for the Stageless Scheduling RFC: https://github.com/bevyengine/rfcs/pull/45 ## Solution - [x] Remove old scheduling module - [x] Migrate new methods to no longer use extension methods - [x] Fix compiler errors - [x] Fix benchmarks - [x] Fix examples - [x] Fix docs - [x] Fix tests ## Changelog ### Added - a large number of methods on `App` to work with schedules ergonomically - the `CoreSchedule` enum - `App::add_extract_system` via the `RenderingAppExtension` trait extension method - the private `prepare_view_uniforms` system now has a public system set for scheduling purposes, called `ViewSet::PrepareUniforms` ### Removed - stages, and all code that mentions stages - states have been dramatically simplified, and no longer use a stack - `RunCriteriaLabel` - `AsSystemLabel` trait - `on_hierarchy_reports_enabled` run criteria (now just uses an ad hoc resource checking run condition) - systems in `RenderSet/Stage::Extract` no longer warn when they do not read data from the main world - `RunCriteriaLabel` - `transform_propagate_system_set`: this was a nonstandard pattern that didn't actually provide enough control. The systems are already `pub`: the docs have been updated to ensure that the third-party usage is clear. ### Changed - `System::default_labels` is now `System::default_system_sets`. - `App::add_default_labels` is now `App::add_default_sets` - `CoreStage` and `StartupStage` enums are now `CoreSet` and `StartupSet` - `App::add_system_set` was renamed to `App::add_systems` - The `StartupSchedule` label is now defined as part of the `CoreSchedules` enum - `.label(SystemLabel)` is now referred to as `.in_set(SystemSet)` - `SystemLabel` trait was replaced by `SystemSet` - `SystemTypeIdLabel<T>` was replaced by `SystemSetType<T>` - The `ReportHierarchyIssue` resource now has a public constructor (`new`), and implements `PartialEq` - Fixed time steps now use a schedule (`CoreSchedule::FixedTimeStep`) rather than a run criteria. - Adding rendering extraction systems now panics rather than silently failing if no subapp with the `RenderApp` label is found. - the `calculate_bounds` system, with the `CalculateBounds` label, is now in `CoreSet::Update`, rather than in `CoreSet::PostUpdate` before commands are applied. - `SceneSpawnerSystem` now runs under `CoreSet::Update`, rather than `CoreStage::PreUpdate.at_end()`. - `bevy_pbr::add_clusters` is no longer an exclusive system - the top level `bevy_ecs::schedule` module was replaced with `bevy_ecs::scheduling` - `tick_global_task_pools_on_main_thread` is no longer run as an exclusive system. Instead, it has been replaced by `tick_global_task_pools`, which uses a `NonSend` resource to force running on the main thread. ## Migration Guide - Calls to `.label(MyLabel)` should be replaced with `.in_set(MySet)` - Stages have been removed. Replace these with system sets, and then add command flushes using the `apply_system_buffers` exclusive system where needed. - The `CoreStage`, `StartupStage, `RenderStage` and `AssetStage` enums have been replaced with `CoreSet`, `StartupSet, `RenderSet` and `AssetSet`. The same scheduling guarantees have been preserved. - Systems are no longer added to `CoreSet::Update` by default. Add systems manually if this behavior is needed, although you should consider adding your game logic systems to `CoreSchedule::FixedTimestep` instead for more reliable framerate-independent behavior. - Similarly, startup systems are no longer part of `StartupSet::Startup` by default. In most cases, this won't matter to you. - For example, `add_system_to_stage(CoreStage::PostUpdate, my_system)` should be replaced with - `add_system(my_system.in_set(CoreSet::PostUpdate)` - When testing systems or otherwise running them in a headless fashion, simply construct and run a schedule using `Schedule::new()` and `World::run_schedule` rather than constructing stages - Run criteria have been renamed to run conditions. These can now be combined with each other and with states. - Looping run criteria and state stacks have been removed. Use an exclusive system that runs a schedule if you need this level of control over system control flow. - For app-level control flow over which schedules get run when (such as for rollback networking), create your own schedule and insert it under the `CoreSchedule::Outer` label. - Fixed timesteps are now evaluated in a schedule, rather than controlled via run criteria. The `run_fixed_timestep` system runs this schedule between `CoreSet::First` and `CoreSet::PreUpdate` by default. - Command flush points introduced by `AssetStage` have been removed. If you were relying on these, add them back manually. - Adding extract systems is now typically done directly on the main app. Make sure the `RenderingAppExtension` trait is in scope, then call `app.add_extract_system(my_system)`. - the `calculate_bounds` system, with the `CalculateBounds` label, is now in `CoreSet::Update`, rather than in `CoreSet::PostUpdate` before commands are applied. You may need to order your movement systems to occur before this system in order to avoid system order ambiguities in culling behavior. - the `RenderLabel` `AppLabel` was renamed to `RenderApp` for clarity - `App::add_state` now takes 0 arguments: the starting state is set based on the `Default` impl. - Instead of creating `SystemSet` containers for systems that run in stages, simply use `.on_enter::<State::Variant>()` or its `on_exit` or `on_update` siblings. - `SystemLabel` derives should be replaced with `SystemSet`. You will also need to add the `Debug`, `PartialEq`, `Eq`, and `Hash` traits to satisfy the new trait bounds. - `with_run_criteria` has been renamed to `run_if`. Run criteria have been renamed to run conditions for clarity, and should now simply return a bool. - States have been dramatically simplified: there is no longer a "state stack". To queue a transition to the next state, call `NextState::set` ## TODO - [x] remove dead methods on App and World - [x] add `App::add_system_to_schedule` and `App::add_systems_to_schedule` - [x] avoid adding the default system set at inappropriate times - [x] remove any accidental cycles in the default plugins schedule - [x] migrate benchmarks - [x] expose explicit labels for the built-in command flush points - [x] migrate engine code - [x] remove all mentions of stages from the docs - [x] verify docs for States - [x] fix uses of exclusive systems that use .end / .at_start / .before_commands - [x] migrate RenderStage and AssetStage - [x] migrate examples - [x] ensure that transform propagation is exported in a sufficiently public way (the systems are already pub) - [x] ensure that on_enter schedules are run at least once before the main app - [x] re-enable opt-in to execution order ambiguities - [x] revert change to `update_bounds` to ensure it runs in `PostUpdate` - [x] test all examples - [x] unbreak directional lights - [x] unbreak shadows (see 3d_scene, 3d_shape, lighting, transparaency_3d examples) - [x] game menu example shows loading screen and menu simultaneously - [x] display settings menu is a blank screen - [x] `without_winit` example panics - [x] ensure all tests pass - [x] SubApp doc test fails - [x] runs_spawn_local tasks fails - [x] [Fix panic_when_hierachy_cycle test hanging](https://github.com/alice-i-cecile/bevy/pull/120) ## Points of Difficulty and Controversy **Reviewers, please give feedback on these and look closely** 1. Default sets, from the RFC, have been removed. These added a tremendous amount of implicit complexity and result in hard to debug scheduling errors. They're going to be tackled in the form of "base sets" by @cart in a followup. 2. The outer schedule controls which schedule is run when `App::update` is called. 3. I implemented `Label for `Box<dyn Label>` for our label types. This enables us to store schedule labels in concrete form, and then later run them. I ran into the same set of problems when working with one-shot systems. We've previously investigated this pattern in depth, and it does not appear to lead to extra indirection with nested boxes. 4. `SubApp::update` simply runs the default schedule once. This sucks, but this whole API is incomplete and this was the minimal changeset. 5. `time_system` and `tick_global_task_pools_on_main_thread` no longer use exclusive systems to attempt to force scheduling order 6. Implemetnation strategy for fixed timesteps 7. `AssetStage` was migrated to `AssetSet` without reintroducing command flush points. These did not appear to be used, and it's nice to remove these bottlenecks. 8. Migration of `bevy_render/lib.rs` and pipelined rendering. The logic here is unusually tricky, as we have complex scheduling requirements. ## Future Work (ideally before 0.10) - Rename schedule_v3 module to schedule or scheduling - Add a derive macro to states, and likely a `EnumIter` trait of some form - Figure out what exactly to do with the "systems added should basically work by default" problem - Improve ergonomics for working with fixed timesteps and states - Polish FixedTime API to match Time - Rebase and merge #7415 - Resolve all internal ambiguities (blocked on better tools, especially #7442) - Add "base sets" to replace the removed default sets.
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65 lines
4.0 KiB
Markdown
# Style guide: Examples
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For more advice on writing examples, see the [relevant section](../../CONTRIBUTING.md#writing-examples) of CONTRIBUTING.md.
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## Organization
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1. Examples should live in an appropriate subfolder of `/examples`.
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2. Examples should be a single file if possible.
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3. Assets live in `./assets`. Try to avoid adding new assets unless strictly necessary to keep the repo small. Don't add "large" asset files.
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4. Each example should try to follow this order:
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1. Imports
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2. A `fn main()` block
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3. Example logic
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5. Try to structure app / plugin construction in the same fashion as the actual code.
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6. Examples should typically not have tests, as they are not directly reusable by the Bevy user.
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## Stylistic preferences
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1. Use simple, descriptive variable names.
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1. Avoid names like `MyComponent` in favor of more descriptive terms like `Events`.
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2. Prefer single letter differentiators like `EventsA` and `EventsB` to nonsense words like `EventsFoo` and `EventsBar`.
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3. Avoid repeating the type of variables in their name where possible. For example, `Color` should be preferred to `ColorComponent`.
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2. Prefer glob imports of `bevy::prelude::*` and `bevy::sub_crate::*` over granular imports (for terseness).
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3. Use a consistent comment style:
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1. `///` doc comments belong above `#[derive(Trait)]` invocations.
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2. `//` comments should generally go above the line in question, rather than in-line.
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3. Avoid `/* */` block comments, even when writing long comments.
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4. Use \`variable_name\` code blocks in comments to signify that you're referring to specific types and variables.
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5. Start comments with capital letters; end them with a period if they are sentence-like.
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4. Use comments to organize long and complex stretches of code that can't sensibly be refactored into separate functions.
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5. Avoid making variables `pub` unless it is needed for your example.
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## Code conventions
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1. Refactor configurable values ("magic numbers") out into constants with clear names.
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2. Prefer `for` loops over `.for_each`. The latter is faster (for now), but it is less clear for beginners, less idiomatic, and less flexible.
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3. Use `.single` and `.single_mut` where appropriate.
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4. In Queries, prefer `With<T>` filters over actually fetching unused data with `&T`.
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5. Prefer disjoint queries using `With` and `Without` over param sets when you need more than one query in a single system.
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6. Prefer structs with named fields over tuple structs except in the case of single-field wrapper types.
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7. Use enum-labels over string-labels for system / schedule / etc. labels.
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## "Feature" examples
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These examples demonstrate the usage of specific engine features in clear, minimal ways.
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1. Focus on demonstrating exactly one feature in an example
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2. Try to keep your names divorced from the context of a specific game, and focused on the feature you are demonstrating.
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3. Where they exist, show good alternative approaches to accomplish the same task and explain why you may prefer one over the other.
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4. Examples should have a visible effect when run, either in the command line or a graphical window.
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## "Game" examples
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These examples show how to build simple games in Bevy in a cohesive way.
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1. Each of these examples lives in the [/examples/games] folder.
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2. Aim for minimum but viable status: the game should be playable and not obviously buggy but does not need to be polished, featureful, or terribly fun.
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3. Focus on code quality and demonstrating good, extensible patterns for users.
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1. Make good use of enums and states to organize your game logic.
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2. Keep components as small as possible but no smaller: all of the data on a component should generally be accessed at once.
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3. Keep systems small: they should have a clear single purpose.
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4. Avoid duplicating logic across similar entities whenever possible by sharing systems and components.
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4. Use `///` doc comments to explain what each function / struct does as if the example were part of a polished production codebase.
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5. Arrange your code into modules within the same file to allow for simple code folding / organization.
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