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# Objective Add interactive system debugging capabilities to bevy, providing step/break/continue style capabilities to running system schedules. * Original implementation: #8063 - `ignore_stepping()` everywhere was too much complexity * Schedule-config & Resource discussion: #8168 - Decided on selective adding of Schedules & Resource-based control ## Solution Created `Stepping` Resource. This resource can be used to enable stepping on a per-schedule basis. Systems within schedules can be individually configured to: * AlwaysRun: Ignore any stepping state and run every frame * NeverRun: Never run while stepping is enabled - this allows for disabling of systems while debugging * Break: If we're running the full frame, stop before this system is run Stepping provides two modes of execution that reflect traditional debuggers: * Step-based: Only execute one system at a time * Continue/Break: Run all systems, but stop before running a system marked as Break ### Demo https://user-images.githubusercontent.com/857742/233630981-99f3bbda-9ca6-4cc4-a00f-171c4946dc47.mov Breakout has been modified to use Stepping. The game runs normally for a couple of seconds, then stepping is enabled and the game appears to pause. A list of Schedules & Systems appears with a cursor at the first System in the list. The demo then steps forward full frames using the spacebar until the ball is about to hit a brick. Then we step system by system as the ball impacts a brick, showing the cursor moving through the individual systems. Finally the demo switches back to frame stepping as the ball changes course. ### Limitations Due to architectural constraints in bevy, there are some cases systems stepping will not function as a user would expect. #### Event-driven systems Stepping does not support systems that are driven by `Event`s as events are flushed after 1-2 frames. Although game systems are not running while stepping, ignored systems are still running every frame, so events will be flushed. This presents to the user as stepping the event-driven system never executes the system. It does execute, but the events have already been flushed. This can be resolved by changing event handling to use a buffer for events, and only dropping an event once all readers have read it. The work-around to allow these systems to properly execute during stepping is to have them ignore stepping: `app.add_systems(event_driven_system.ignore_stepping())`. This was done in the breakout example to ensure sound played even while stepping. #### Conditional Systems When a system is stepped, it is given an opportunity to run. If the conditions of the system say it should not run, it will not. Similar to Event-driven systems, if a system is conditional, and that condition is only true for a very small time window, then stepping the system may not execute the system. This includes depending on any sort of external clock. This exhibits to the user as the system not always running when it is stepped. A solution to this limitation is to ensure any conditions are consistent while stepping is enabled. For example, all systems that modify any state the condition uses should also enable stepping. #### State-transition Systems Stepping is configured on the per-`Schedule` level, requiring the user to have a `ScheduleLabel`. To support state-transition systems, bevy generates needed schedules dynamically. Currently it’s very difficult (if not impossible, I haven’t verified) for the user to get the labels for these schedules. Without ready access to the dynamically generated schedules, and a resolution for the `Event` lifetime, **stepping of the state-transition systems is not supported** --- ## Changelog - `Schedule::run()` updated to consult `Stepping` Resource to determine which Systems to run each frame - Added `Schedule.label` as a `BoxedSystemLabel`, along with supporting `Schedule::set_label()` and `Schedule::label()` methods - `Stepping` needed to know which `Schedule` was running, and prior to this PR, `Schedule` didn't track its own label - Would have preferred to add `Schedule::with_label()` and remove `Schedule::new()`, but this PR touches enough already - Added calls to `Schedule.set_label()` to `App` and `World` as needed - Added `Stepping` resource - Added `Stepping::begin_frame()` system to `MainSchedulePlugin` - Run before `Main::run_main()` - Notifies any `Stepping` Resource a new render frame is starting ## Migration Guide - Add a call to `Schedule::set_label()` for any custom `Schedule` - This is only required if the `Schedule` will be stepped --------- Co-authored-by: Carter Anderson <mcanders1@gmail.com> |
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What is Bevy?
Bevy is a refreshingly simple data-driven game engine built in Rust. It is free and open-source forever!
WARNING
Bevy is still in the early stages of development. Important features are missing. Documentation is sparse. A new version of Bevy containing breaking changes to the API is released approximately once every 3 months. We provide migration guides, but we can't guarantee migrations will always be easy. Use only if you are willing to work in this environment.
MSRV: Bevy relies heavily on improvements in the Rust language and compiler. As a result, the Minimum Supported Rust Version (MSRV) is generally close to "the latest stable release" of Rust.
Design Goals
- Capable: Offer a complete 2D and 3D feature set
- Simple: Easy for newbies to pick up, but infinitely flexible for power users
- Data Focused: Data-oriented architecture using the Entity Component System paradigm
- Modular: Use only what you need. Replace what you don't like
- Fast: App logic should run quickly, and when possible, in parallel
- Productive: Changes should compile quickly ... waiting isn't fun
About
- Features: A quick overview of Bevy's features.
- News: A development blog that covers our progress, plans and shiny new features.
Docs
- The Bevy Book: Bevy's official documentation. The best place to start learning Bevy.
- Bevy Rust API Docs: Bevy's Rust API docs, which are automatically generated from the doc comments in this repo.
- Official Examples: Bevy's dedicated, runnable examples, which are great for digging into specific concepts.
- Community-Made Learning Resources: More tutorials, documentation, and examples made by the Bevy community.
Community
Before contributing or participating in discussions with the community, you should familiarize yourself with our Code of Conduct.
- Discord: Bevy's official discord server.
- Reddit: Bevy's official subreddit.
- GitHub Discussions: The best place for questions about Bevy, answered right here!
- Bevy Assets: A collection of awesome Bevy projects, tools, plugins and learning materials.
Contributing
If you'd like to help build Bevy, check out the Contributor's Guide. For simple problems, feel free to open an issue or PR and tackle it yourself!
For more complex architecture decisions and experimental mad science, please open an RFC (Request For Comments) so we can brainstorm together effectively!
Getting Started
We recommend checking out The Bevy Book for a full tutorial.
Follow the Setup guide to ensure your development environment is set up correctly. Once set up, you can quickly try out the examples by cloning this repo and running the following commands:
# Switch to the correct version (latest release, default is main development branch)
git checkout latest
# Runs the "breakout" example
cargo run --example breakout
To draw a window with standard functionality enabled, use:
use bevy::prelude::*;
fn main(){
App::new()
.add_plugins(DefaultPlugins)
.run();
}
Fast Compiles
Bevy can be built just fine using default configuration on stable Rust. However for really fast iterative compiles, you should enable the "fast compiles" setup by following the instructions here.
Bevy Cargo Features
This list outlines the different cargo features supported by Bevy. These allow you to customize the Bevy feature set for your use-case.
Thanks
Bevy is the result of the hard work of many people. A huge thanks to all Bevy contributors, the many open source projects that have come before us, the Rust gamedev ecosystem, and the many libraries we build on.
A huge thanks to Bevy's generous sponsors. Bevy will always be free and open source, but it isn't free to make. Please consider sponsoring our work if you like what we're building.
This project is tested with BrowserStack.
License
Bevy is free, open source and permissively licensed! Except where noted (below and/or in individual files), all code in this repository is dual-licensed under either:
- MIT License (LICENSE-MIT or http://opensource.org/licenses/MIT)
- Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
at your option. This means you can select the license you prefer! This dual-licensing approach is the de-facto standard in the Rust ecosystem and there are very good reasons to include both.
Some of the engine's code carries additional copyright notices and license terms due to their external origins.
These are generally BSD-like, but exact details vary by crate:
If the README of a crate contains a 'License' header (or similar), the additional copyright notices and license terms applicable to that crate will be listed.
The above licensing requirement still applies to contributions to those crates, and sections of those crates will carry those license terms.
The license field of each crate will also reflect this.
For example, bevy_mikktspace has code under the Zlib license (as well as a copyright notice when choosing the MIT license).
The assets included in this repository (for our examples) typically fall under different open licenses. These will not be included in your game (unless copied in by you), and they are not distributed in the published bevy crates. See CREDITS.md for the details of the licenses of those files.
Your contributions
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.