b6ead2be95
# Objective - Improve rendering performance, particularly by avoiding the large system commands costs of using the ECS in the way that the render world does. ## Solution - Define `EntityHasher` that calculates a hash from the `Entity.to_bits()` by `i | (i.wrapping_mul(0x517cc1b727220a95) << 32)`. `0x517cc1b727220a95` is something like `u64::MAX / N` for N that gives a value close to π and that works well for hashing. Thanks for @SkiFire13 for the suggestion and to @nicopap for alternative suggestions and discussion. This approach comes from `rustc-hash` (a.k.a. `FxHasher`) with some tweaks for the case of hashing an `Entity`. `FxHasher` and `SeaHasher` were also tested but were significantly slower. - Define `EntityHashMap` type that uses the `EntityHashser` - Use `EntityHashMap<Entity, T>` for render world entity storage, including: - `RenderMaterialInstances` - contains the `AssetId<M>` of the material associated with the entity. Also for 2D. - `RenderMeshInstances` - contains mesh transforms, flags and properties about mesh entities. Also for 2D. - `SkinIndices` and `MorphIndices` - contains the skin and morph index for an entity, respectively - `ExtractedSprites` - `ExtractedUiNodes` ## Benchmarks All benchmarks have been conducted on an M1 Max connected to AC power. The tests are run for 1500 frames. The 1000th frame is captured for comparison to check for visual regressions. There were none. ### 2D Meshes `bevymark --benchmark --waves 160 --per-wave 1000 --mode mesh2d` #### `--ordered-z` This test spawns the 2D meshes with z incrementing back to front, which is the ideal arrangement allocation order as it matches the sorted render order which means lookups have a high cache hit rate. <img width="1112" alt="Screenshot 2023-09-27 at 07 50 45" src="https://github.com/bevyengine/bevy/assets/302146/e140bc98-7091-4a3b-8ae1-ab75d16d2ccb"> -39.1% median frame time. #### Random This test spawns the 2D meshes with random z. This not only makes the batching and transparent 2D pass lookups get a lot of cache misses, it also currently means that the meshes are almost certain to not be batchable. <img width="1108" alt="Screenshot 2023-09-27 at 07 51 28" src="https://github.com/bevyengine/bevy/assets/302146/29c2e813-645a-43ce-982a-55df4bf7d8c4"> -7.2% median frame time. ### 3D Meshes `many_cubes --benchmark` <img width="1112" alt="Screenshot 2023-09-27 at 07 51 57" src="https://github.com/bevyengine/bevy/assets/302146/1a729673-3254-4e2a-9072-55e27c69f0fc"> -7.7% median frame time. ### Sprites **NOTE: On `main` sprites are using `SparseSet<Entity, T>`!** `bevymark --benchmark --waves 160 --per-wave 1000 --mode sprite` #### `--ordered-z` This test spawns the sprites with z incrementing back to front, which is the ideal arrangement allocation order as it matches the sorted render order which means lookups have a high cache hit rate. <img width="1116" alt="Screenshot 2023-09-27 at 07 52 31" src="https://github.com/bevyengine/bevy/assets/302146/bc8eab90-e375-4d31-b5cd-f55f6f59ab67"> +13.0% median frame time. #### Random This test spawns the sprites with random z. This makes the batching and transparent 2D pass lookups get a lot of cache misses. <img width="1109" alt="Screenshot 2023-09-27 at 07 53 01" src="https://github.com/bevyengine/bevy/assets/302146/22073f5d-99a7-49b0-9584-d3ac3eac3033"> +0.6% median frame time. ### UI **NOTE: On `main` UI is using `SparseSet<Entity, T>`!** `many_buttons` <img width="1111" alt="Screenshot 2023-09-27 at 07 53 26" src="https://github.com/bevyengine/bevy/assets/302146/66afd56d-cbe4-49e7-8b64-2f28f6043d85"> +15.1% median frame time. ## Alternatives - Cart originally suggested trying out `SparseSet<Entity, T>` and indeed that is slightly faster under ideal conditions. However, `PassHashMap<Entity, T>` has better worst case performance when data is randomly distributed, rather than in sorted render order, and does not have the worst case memory usage that `SparseSet`'s dense `Vec<usize>` that maps from the `Entity` index to sparse index into `Vec<T>`. This dense `Vec` has to be as large as the largest Entity index used with the `SparseSet`. - I also tested `PassHashMap<u32, T>`, intending to use `Entity.index()` as the key, but this proved to sometimes be slower and mostly no different. - The only outstanding approach that has not been implemented and tested is to _not_ clear the render world of its entities each frame. That has its own problems, though they could perhaps be solved. - Performance-wise, if the entities and their component data were not cleared, then they would incur table moves on spawn, and should not thereafter, rather just their component data would be overwritten. Ideally we would have a neat way of either updating data in-place via `&mut T` queries, or inserting components if not present. This would likely be quite cumbersome to have to remember to do everywhere, but perhaps it only needs to be done in the more performance-sensitive systems. - The main problem to solve however is that we want to both maintain a mapping between main world entities and render world entities, be able to run the render app and world in parallel with the main app and world for pipelined rendering, and at the same time be able to spawn entities in the render world in such a way that those Entity ids do not collide with those spawned in the main world. This is potentially quite solvable, but could well be a lot of ECS work to do it in a way that makes sense. --- ## Changelog - Changed: Component data for entities to be drawn are no longer stored on entities in the render world. Instead, data is stored in a `EntityHashMap<Entity, T>` in various resources. This brings significant performance benefits due to the way the render app clears entities every frame. Resources of most interest are `RenderMeshInstances` and `RenderMaterialInstances`, and their 2D counterparts. ## Migration Guide Previously the render app extracted mesh entities and their component data from the main world and stored them as entities and components in the render world. Now they are extracted into essentially `EntityHashMap<Entity, T>` where `T` are structs containing an appropriate group of data. This means that while extract set systems will continue to run extract queries against the main world they will store their data in hash maps. Also, systems in later sets will either need to look up entities in the available resources such as `RenderMeshInstances`, or maintain their own `EntityHashMap<Entity, T>` for their own data. Before: ```rust fn queue_custom( material_meshes: Query<(Entity, &MeshTransforms, &Handle<Mesh>), With<InstanceMaterialData>>, ) { ... for (entity, mesh_transforms, mesh_handle) in &material_meshes { ... } } ``` After: ```rust fn queue_custom( render_mesh_instances: Res<RenderMeshInstances>, instance_entities: Query<Entity, With<InstanceMaterialData>>, ) { ... for entity in &instance_entities { let Some(mesh_instance) = render_mesh_instances.get(&entity) else { continue; }; // The mesh handle in `AssetId<Mesh>` form, and the `MeshTransforms` can now // be found in `mesh_instance` which is a `RenderMeshInstance` ... } } ``` --------- Co-authored-by: robtfm <50659922+robtfm@users.noreply.github.com> |
||
|---|---|---|
| .cargo | ||
| .github | ||
| assets | ||
| benches | ||
| crates | ||
| docs | ||
| docs-template | ||
| errors | ||
| examples | ||
| src | ||
| tests | ||
| tools | ||
| .gitattributes | ||
| .gitignore | ||
| Cargo.toml | ||
| CHANGELOG.md | ||
| clippy.toml | ||
| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
| CREDITS.md | ||
| deny.toml | ||
| LICENSE-APACHE | ||
| LICENSE-MIT | ||
| README.md | ||
| rustfmt.toml | ||
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.
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.
Libraries Used
Bevy is only possible because of the hard work put into these foundational technologies:
- wgpu: modern / low-level / cross-platform graphics library based on the WebGPU API.
- glam-rs: a simple and fast 3D math library for games and graphics
- winit: cross-platform window creation and management in Rust
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.
Third Party Plugins
Plugins are very welcome to extend Bevy's features. Guidelines are available to help integration and usage.
Thanks and Alternatives
Additionally, we would like to thank the Amethyst, macroquad, coffee, ggez, Fyrox, and Piston projects for providing solid examples of game engine development in Rust. If you are looking for a Rust game engine, it is worth considering all of your options. Each engine has different design goals, and some will likely resonate with you more than others.
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.