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# Objective Add support for drawing outlines outside the borders of UI nodes. ## Solution Add a new `Outline` component with `width`, `offset` and `color` fields. Added `outline_width` and `outline_offset` fields to `Node`. This is set after layout recomputation by the `resolve_outlines_system`. Properties of outlines: * Unlike borders, outlines have to be the same width on each edge. * Outlines do not occupy any space in the layout. * The `Outline` component won't be added to any of the UI node bundles, it needs to be inserted separately. * Outlines are drawn outside the node's border, so they are clipped using the clipping rect of their entity's parent UI node (if it exists). * `Val::Percent` outline widths are resolved based on the width of the outlined UI node. * The offset of the `Outline` adds space between an outline and the edge of its node. I was leaning towards adding an `outline` field to `Style` but a separate component seems more efficient for queries and change detection. The `Outline` component isn't added to bundles for the same reason. --- ## Examples * This image is from the `borders` example from the Bevy UI examples but modified to include outlines. The UI nodes are the dark red rectangles, the bright red rectangles are borders and the white lines offset from each node are the outlines. The yellow rectangles are separate nodes contained with the dark red nodes: <img width="406" alt="outlines" src="https://github.com/bevyengine/bevy/assets/27962798/4e6f315a-019f-42a4-94ee-cca8e684d64a"> * This is from the same example but using a branch that implements border-radius. Here the the outlines are in orange and there is no offset applied. I broke the borders implementation somehow during the merge, which is why some of the borders from the first screenshot are missing 😅. The outlines work nicely though (as long as you can forgive the lack of anti-aliasing):  --- ## Notes As I explained above, I don't think the `Outline` component should be added to UI node bundles. We can have helper functions though, perhaps something as simple as: ```rust impl NodeBundle { pub fn with_outline(self, outline: Outline) -> (Self, Outline) { (self, outline) } } ``` I didn't include anything like this as I wanted to keep the PR's scope as narrow as possible. Maybe `with_outline` should be in a trait that we implement for each UI node bundle. --- ## Changelog Added support for outlines to Bevy UI. * The `Outline` component adds an outline to a UI node. * The `outline_width` field added to `Node` holds the resolved width of the outline, which is set by the `resolve_outlines_system` after layout recomputation. * Outlines are drawn by the system `extract_uinode_outlines`. |
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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.
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.