# Objective
The `new` constructors for our ray types currently take a `Vec2`/`Vec3`
instead of a `Dir2`/`Dir3`. This is confusing and footgunny for several
reasons.
- Which one of these is the direction? You can't see it from the type.
```rust
let ray = Ray2d::new(Vec2::X, Vec2::X);
```
- Many engines allow unnormalized rays, and this can affect ray cast
results by scaling the time of impact. However, in Bevy, rays are
*always* normalized despite what the input argument in this case
implies, and ray cast results are *not* scaled.
```rust
// The true ray direction is still normalized, unlike what you'd expect.
let ray = Ray2d::new(Vec2::X, Vec2::new(5.0, 0.0, 0.0)));
```
These cases are what the direction types are intended for, and we should
use them as such.
## Solution
Use `Dir2`/`Dir3` in the constructors.
```rust
let ray = Ray2d::new(Vec2::X, Dir2::X);
```
We *could* also use `impl TryInto<DirN>`, which would allow both vectors
and direction types, and then panic if the input is not normalized. This
could be fine for ergonomics in some cases, but especially for rays, I
think it's better to take an explicit direction type here.
---
## Migration Guide
`Ray2d::new` and `Ray3d::new` now take a `Dir2` and `Dir3` instead of
`Vec2` and `Vec3` respectively for the ray direction.
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