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*Occlusion culling* allows the GPU to skip the vertex and fragment shading overhead for objects that can be quickly proved to be invisible because they're behind other geometry. A depth prepass already eliminates most fragment shading overhead for occluded objects, but the vertex shading overhead, as well as the cost of testing and rejecting fragments against the Z-buffer, is presently unavoidable for standard meshes. We currently perform occlusion culling only for meshlets. But other meshes, such as skinned meshes, can benefit from occlusion culling too in order to avoid the transform and skinning overhead for unseen meshes. This commit adapts the same [*two-phase occlusion culling*] technique that meshlets use to Bevy's standard 3D mesh pipeline when the new `OcclusionCulling` component, as well as the `DepthPrepass` component, are present on the camera. It has these steps: 1. *Early depth prepass*: We use the hierarchical Z-buffer from the previous frame to cull meshes for the initial depth prepass, effectively rendering only the meshes that were visible in the last frame. 2. *Early depth downsample*: We downsample the depth buffer to create another hierarchical Z-buffer, this time with the current view transform. 3. *Late depth prepass*: We use the new hierarchical Z-buffer to test all meshes that weren't rendered in the early depth prepass. Any meshes that pass this check are rendered. 4. *Late depth downsample*: Again, we downsample the depth buffer to create a hierarchical Z-buffer in preparation for the early depth prepass of the next frame. This step is done after all the rendering, in order to account for custom phase items that might write to the depth buffer. Note that this patch has no effect on the per-mesh CPU overhead for occluded objects, which remains high for a GPU-driven renderer due to the lack of `cold-specialization` and retained bins. If `cold-specialization` and retained bins weren't on the horizon, then a more traditional approach like potentially visible sets (PVS) or low-res CPU rendering would probably be more efficient than the GPU-driven approach that this patch implements for most scenes. However, at this point the amount of effort required to implement a PVS baking tool or a low-res CPU renderer would probably be greater than landing `cold-specialization` and retained bins, and the GPU driven approach is the more modern one anyway. It does mean that the performance improvements from occlusion culling as implemented in this patch *today* are likely to be limited, because of the high CPU overhead for occluded meshes. Note also that this patch currently doesn't implement occlusion culling for 2D objects or shadow maps. Those can be addressed in a follow-up. Additionally, note that the techniques in this patch require compute shaders, which excludes support for WebGL 2. This PR is marked experimental because of known precision issues with the downsampling approach when applied to non-power-of-two framebuffer sizes (i.e. most of them). These precision issues can, in rare cases, cause objects to be judged occluded that in fact are not. (I've never seen this in practice, but I know it's possible; it tends to be likelier to happen with small meshes.) As a follow-up to this patch, we desire to switch to the [SPD-based hi-Z buffer shader from the Granite engine], which doesn't suffer from these problems, at which point we should be able to graduate this feature from experimental status. I opted not to include that rewrite in this patch for two reasons: (1) @JMS55 is planning on doing the rewrite to coincide with the new availability of image atomic operations in Naga; (2) to reduce the scope of this patch. A new example, `occlusion_culling`, has been added. It demonstrates objects becoming quickly occluded and disoccluded by dynamic geometry and shows the number of objects that are actually being rendered. Also, a new `--occlusion-culling` switch has been added to `scene_viewer`, in order to make it easy to test this patch with large scenes like Bistro. [*two-phase occlusion culling*]: https://medium.com/@mil_kru/two-pass-occlusion-culling-4100edcad501 [Aaltonen SIGGRAPH 2015]: https://www.advances.realtimerendering.com/s2015/aaltonenhaar_siggraph2015_combined_final_footer_220dpi.pdf [Some literature]: https://gist.github.com/reduz/c5769d0e705d8ab7ac187d63be0099b5?permalink_comment_id=5040452#gistcomment-5040452 [SPD-based hi-Z buffer shader from the Granite engine]: https://github.com/Themaister/Granite/blob/master/assets/shaders/post/hiz.comp ## Migration guide * When enqueuing a custom mesh pipeline, work item buffers are now created with `bevy::render::batching::gpu_preprocessing::get_or_create_work_item_buffer`, not `PreprocessWorkItemBuffers::new`. See the `specialized_mesh_pipeline` example. ## Showcase Occlusion culling example:  Bistro zoomed out, before occlusion culling:  Bistro zoomed out, after occlusion culling:  In this scene, occlusion culling reduces the number of meshes Bevy has to render from 1591 to 585. |
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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
- Quick Start Guide: Bevy's official Quick Start Guide. 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 Quick Start Guide for a brief introduction.
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.