# Objective
Currently, the `Ellipse` primitive is represented by a `half_width` and
`half_height`. To improve consistency (similarly to #11434), it might
make more sense to use a `Vec2` `half_size` instead.
Alternatively, to make the elliptical nature clearer, the properties
could also be called `radius_x` and `radius_y`.
Secondly, `Ellipse::new` currently takes a *full* width and height
instead of two radii. I would expect it to take the half-width and
half-height because ellipses and circles are almost always defined using
radii. I wouldn't expect `Circle::new` to take a diameter (if we had
that method).
## Solution
Change `Ellipse` to store a `half_size` and `new` to take the half-width
and half-height.
I also added a `from_size` method similar to `Rectangle::from_size`, and
added the `semi_minor` and `semi_major` helpers to get the
semi-minor/major radius.
# Objective
The `Rectangle` and `Cuboid` primitives currently use different
representations:
```rust
pub struct Rectangle {
/// The half width of the rectangle
pub half_width: f32,
/// The half height of the rectangle
pub half_height: f32,
}
pub struct Cuboid {
/// Half of the width, height and depth of the cuboid
pub half_extents: Vec3,
}
```
The property names and helpers are also inconsistent. `Cuboid` has
`half_extents`, but it also has a method called `from_size`. Most
existing code also uses "size" instead of "extents".
## Solution
Represent both `Rectangle` and `Cuboid` with `half_size` properties.
# Objective
Closes#10570.
#10946 added bounding volume types and traits, but didn't use them for
anything yet. This PR implements `Bounded2d` and `Bounded3d` for Bevy's
primitive shapes.
## Solution
Implement `Bounded2d` and `Bounded3d` for primitive shapes. This allows
computing AABBs and bounding circles/spheres for them.
For most shapes, there are several ways of implementing bounding
volumes. I took inspiration from [Parry's bounding
volumes](https://github.com/dimforge/parry/tree/master/src/bounding_volume),
[Inigo Quilez](http://iquilezles.org/articles/diskbbox/), and figured
out the rest myself using geometry. I tried to comment all slightly
non-trivial or unclear math to make it understandable.
Parry uses support mapping (finding the farthest point in some direction
for convex shapes) for some AABBs like cones, cylinders, and line
segments. This involves several quat operations and normalizations, so I
opted for the simpler and more efficient geometric approaches shown in
[Quilez's article](http://iquilezles.org/articles/diskbbox/).
Below you can see some of the bounding volumes working in 2D and 3D.
Note that I can't conveniently add these examples yet because they use
primitive shape meshing, which is still WIP.
https://github.com/bevyengine/bevy/assets/57632562/4465cbc6-285b-4c71-b62d-a2b3ee16f8b4https://github.com/bevyengine/bevy/assets/57632562/94b4ac84-a092-46d7-b438-ce2e971496a4
---
## Changelog
- Implemented `Bounded2d`/`Bounded3d` for primitive shapes
- Added `from_point_cloud` method for bounding volumes (used by many
bounding implementations)
- Added `point_cloud_2d/3d_center` and `rotate_vec2` utility functions
- Added `RegularPolygon::vertices` method (used in regular polygon AABB
construction)
- Added `Triangle::circumcenter` method (used in triangle bounding
circle construction)
- Added bounding circle/sphere creation from AABBs and vice versa
## Extra
Do we want to implement `Bounded2d` for some "3D-ish" shapes too? For
example, capsules are sort of dimension-agnostic and useful for 2D, so I
think that would be good to implement. But a cylinder in 2D is just a
rectangle, and a cone is a triangle, so they wouldn't make as much sense
to me. A conical frustum would be an isosceles trapezoid, which could be
useful, but I'm not sure if computing the 2D AABB of a 3D frustum makes
semantic sense.
