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# Objective - Ongoing work for #10572 - Implement the `Meshable` trait for `Triangle3d`, allowing 3d triangle primitives to produce meshes. ## Solution The `Meshable` trait for `Triangle3d` directly produces a `Mesh`, much like that of `Triangle2d`. The mesh consists only of a single triangle (the triangle itself), and its vertex data consists of: - Vertex positions, which are the triangle's vertices themselves (i.e. the triangle provides its own coordinates in mesh space directly) - Normals, which are all the normal of the triangle itself - Indices, which are directly inferred from the vertex order (note that this is slightly different than `Triangle2d` which, because of its lower dimension, has an orientation which can be corrected for so that it always faces "the right way") - UV coordinates, which are produced as follows: 1. The first coordinate is coincident with the `ab` direction of the triangle. 2. The second coordinate maps to be perpendicular to the first in mesh space, so that the UV-mapping is skew-free. 3. The UV-coordinates map to the smallest rectangle possible containing the triangle, given the preceding constraints. Here is a visual demonstration; here, the `ab` direction of the triangle is horizontal, left to right — the point `c` moves, expanding the bounding rectangle of the triangle when it pushes past `a` or `b`: <img width="1440" alt="Screenshot 2024-03-23 at 5 36 01 PM" src="https://github.com/bevyengine/bevy/assets/2975848/bef4d786-7b82-4207-abd4-ac4557d0f8b8"> <img width="1440" alt="Screenshot 2024-03-23 at 5 38 12 PM" src="https://github.com/bevyengine/bevy/assets/2975848/c0f72b8f-8e70-46fa-a750-2041ba6dfb78"> <img width="1440" alt="Screenshot 2024-03-23 at 5 37 15 PM" src="https://github.com/bevyengine/bevy/assets/2975848/db287e4f-2b0b-4fd4-8d71-88f4e7a03b7c"> The UV-mapping of `Triangle2d` has also been changed to use the same logic. --- ## Changelog - Implemented `Meshable` for `Triangle3d`. - Changed UV-mapping of `Triangle2d` to match that of `Triangle3d`. ## Migration Guide The UV-mapping of `Triangle2d` has changed with this PR; the main difference is that the UVs are no longer dependent on the triangle's absolute coordinates, but instead follow translations of the triangle itself in its definition. If you depended on the old UV-coordinates for `Triangle2d`, then you will have to update affected areas to use the new ones which, briefly, can be described as follows: - The first coordinate is parallel to the line between the first two vertices of the triangle. - The second coordinate is orthogonal to this, pointing in the direction of the third point. Generally speaking, this means that the first two points will have coordinates `[_, 0.]`, while the third coordinate will be `[_, 1.]`, with the exact values depending on the position of the third point relative to the first two. For acute triangles, the first two vertices always have UV-coordinates `[0., 0.]` and `[1., 0.]` respectively. For obtuse triangles, the third point will have coordinate `[0., 1.]` or `[1., 1.]`, with the coordinate of one of the two other points shifting to maintain proportionality. For example: - The default `Triangle2d` has UV-coordinates `[0., 0.]`, `[0., 1.]`, [`0.5, 1.]`. - The triangle with vertices `vec2(0., 0.)`, `vec2(1., 0.)`, `vec2(2., 1.)` has UV-coordinates `[0., 0.]`, `[0.5, 0.]`, `[1., 1.]`. - The triangle with vertices `vec2(0., 0.)`, `vec2(1., 0.)`, `vec2(-2., 1.)` has UV-coordinates `[2./3., 0.]`, `[1., 0.]`, `[0., 1.]`. ## Discussion ### Design considerations 1. There are a number of ways to UV-map a triangle (at least two of which are fairly natural); for instance, we could instead declare the second axis to be essentially `bc` so that the vertices are always `[0., 0.]`, `[0., 1.]`, and `[1., 0.]`. I chose this method instead because it is skew-free, so that the sampling from textures has only bilinear scaling. I think this is better for cases where a relatively "uniform" texture is mapped to the triangle, but it's possible that we might want to support the other thing in the future. Thankfully, we already have the capability of easily expanding to do that with Builders if the need arises. This could also allow us to provide things like barycentric subdivision. 2. Presently, the mesh-creation code for `Triangle3d` is set up to never fail, even in the case that the triangle is degenerate. I have mixed feelings about this, but none of our other primitive meshes fail, so I decided to take the same approach. Maybe this is something that could be worth revisiting in the future across the board. --------- Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com> Co-authored-by: Jakub Marcowski <37378746+Chubercik@users.noreply.github.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
- 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.