# Objective
The first part of #10569, split up from #11007.
The goal is to implement meshing support for Bevy's new geometric
primitives, starting with 2D primitives. 3D meshing will be added in a
follow-up, and we can consider removing the old mesh shapes completely.
## Solution
Add a `Meshable` trait that primitives need to implement to support
meshing, as suggested by the
[RFC](https://github.com/bevyengine/rfcs/blob/main/rfcs/12-primitive-shapes.md#meshing).
```rust
/// A trait for shapes that can be turned into a [`Mesh`].
pub trait Meshable {
/// The output of [`Self::mesh`]. This can either be a [`Mesh`]
/// or a builder used for creating a [`Mesh`].
type Output;
/// Creates a [`Mesh`] for a shape.
fn mesh(&self) -> Self::Output;
}
```
This PR implements it for the following primitives:
- `Circle`
- `Ellipse`
- `Rectangle`
- `RegularPolygon`
- `Triangle2d`
The `mesh` method typically returns a builder-like struct such as
`CircleMeshBuilder`. This is needed to support shape-specific
configuration for things like mesh resolution or UV configuration:
```rust
meshes.add(Circle { radius: 0.5 }.mesh().resolution(64));
```
Note that if no configuration is needed, you can even skip calling
`mesh` because `From<MyPrimitive>` is implemented for `Mesh`:
```rust
meshes.add(Circle { radius: 0.5 });
```
I also updated the `2d_shapes` example to use primitives, and tweaked
the colors to have better contrast against the dark background.
Before:
After:
Here you can see the UVs and different facing directions: (taken from
#11007, so excuse the 3D primitives at the bottom left)
---
## Changelog
- Added `bevy_render::mesh::primitives` module
- Added `Meshable` trait and implemented it for:
- `Circle`
- `Ellipse`
- `Rectangle`
- `RegularPolygon`
- `Triangle2d`
- Implemented `Default` and `Copy` for several 2D primitives
- Updated `2d_shapes` example to use primitives
- Tweaked colors in `2d_shapes` example to have better contrast against
the (new-ish) dark background
---------
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2bf481c03b