# Objective
- Implement common traits on primitives
## Solution
- Derive PartialEq on types that were missing it.
- Derive Copy on small types that were missing it.
- Derive Serialize/Deserialize if the feature on bevy_math is enabled.
- Add a lot of cursed stuff to the bevy_reflect `impls` module.
# Objective
When creating a normalized direction from a vector, it can be useful to
get both the direction *and* the original length of the vector.
This came up when I was recreating some Parry APIs using bevy_math, and
doing it manually is quite painful. Nalgebra calls this method
[`Unit::try_new_and_get`](https://docs.rs/nalgebra/latest/nalgebra/base/struct.Unit.html#method.try_new_and_get).
## Solution
Add a `new_and_length` method to `Direction2d` and `Direction3d`.
Usage:
```rust
if let Ok((direction, length)) = Direction2d::new_and_length(Vec2::X * 10.0) {
assert_eq!(direction, Vec2::X);
assert_eq!(length, 10.0);
}
```
I'm open to different names, couldn't come up with a perfectly clear one
that isn't too long. My reasoning with the current name is that it's
like using `new` and calling `length` on the original vector.
# Objective
Implement `TryFrom<Vec2>`/`TryFrom<Vec3>` for direction primitives as
considered in #10857.
## Solution
Implement `TryFrom` for the direction primitives.
These are all equivalent:
```rust
let dir2d = Direction2d::try_from(Vec2::new(0.5, 0.5)).unwrap();
let dir2d = Vec2::new(0.5, 0.5).try_into().unwrap(); // (assumes that the type is inferred)
let dir2d = Direction2d::new(Vec2::new(0.5, 0.5)).unwrap();
```
For error cases, an `Err(InvalidDirectionError)` is returned. It
contains the type of failure:
```rust
/// An error indicating that a direction is invalid.
#[derive(Debug, PartialEq)]
pub enum InvalidDirectionError {
/// The length of the direction vector is zero or very close to zero.
Zero,
/// The length of the direction vector is `std::f32::INFINITY`.
Infinite,
/// The length of the direction vector is `NaN`.
NaN,
}
```
# Objective
This PR adds some helpers for `Triangle2d` to work with its winding
order. This could also be extended to polygons (and `Triangle3d` once
it's added).
## Solution
- Add `WindingOrder` enum with `Clockwise`, `Counterclockwise` and
`Invalid` variants
- `Invalid` is for cases where the winding order can not be reliably
computed, i.e. the points lie on a single line and the area is zero
- Add `Triangle2d::winding_order` method that uses a signed surface area
to determine the winding order
- Add `Triangle2d::reverse` method that reverses the winding order by
swapping the second and third vertices
The API looks like this:
```rust
let mut triangle = Triangle2d::new(
Vec2::new(0.0, 2.0),
Vec2::new(-0.5, -1.2),
Vec2::new(-1.0, -1.0),
);
assert_eq!(triangle.winding_order(), WindingOrder::Clockwise);
// Reverse winding order
triangle.reverse();
assert_eq!(triangle.winding_order(), WindingOrder::Counterclockwise);
```
I also added tests to make sure the methods work correctly. For now,
they live in the same file as the primitives.
## Open questions
- Should it be `Counterclockwise` or `CounterClockwise`? The first one
is more correct but perhaps a bit less readable. Counter-clockwise is
also a valid spelling, but it seems to be a lot less common than
counterclockwise.
- Is `WindingOrder::Invalid` a good name? Parry uses
`TriangleOrientation::Degenerate`, but I'm not a huge fan, at least as a
non-native English speaker. Any better suggestions?
- Is `WindingOrder` fine in `bevy_math::primitives`? It's not specific
to a dimension, so I put it there for now.
# Objective
- Implement a subset of
https://github.com/bevyengine/rfcs/blob/main/rfcs/12-primitive-shapes.md#feature-name-primitive-shapes
## Solution
- Define a very basic set of primitives in bevy_math
- Assume a 0,0,0 origin for most shapes
- Use radius and half extents to avoid unnecessary computational
overhead wherever they get used
- Provide both Boxed and const generics variants for shapes with
variable sizes
- Boxed is useful if a 3rd party crate wants to use something like
enum-dispatch for all supported primitives
- Const generics is useful when just working on a single primitive, as
it causes no allocs
#### Some discrepancies from the RFC:
- Box was changed to Cuboid, because Box is already used for an alloc
type
- Skipped Cone because it's unclear where the origin should be for
different uses
- Skipped Wedge because it's too niche for an initial PR (we also don't
implement Torus, Pyramid or a Death Star (there's an SDF for that!))
- Skipped Frustum because while it would be a useful math type, it's not
really a common primitive
- Skipped Triangle3d and Quad3d because those are just rotated 2D shapes
## Future steps
- Add more primitives
- Add helper methods to make primitives easier to construct (especially
when half extents are involved)
- Add methods to calculate AABBs for primitives (useful for physics, BVH
construction, for the mesh AABBs, etc)
- Add wrappers for common and cheap operations, like extruding 2D shapes
and translating them
- Use the primitives to generate meshes
- Provide signed distance functions and gradients for primitives (maybe)
---
## Changelog
- Added a collection of primitives to the bevy_math crate
---------
Co-authored-by: Joona Aalto <jondolf.dev@gmail.com>
