# Objective

- Expand the documentation for `EasingCurve`.
- I suspect this might have avoided the confusion in
#17711.
- Also add a shortcut for simple cases.

## Solution

- Added various examples and extra context.
- Implemented `Curve<T>` for `EaseFunction`.
- This means `EasingCurve::new(0.0, 1.0, EaseFunction::X)` can be
shortened to `EaseFunction::X`.
    - In some cases this will be a minor performance improvement.
    - Added test to confirm they're the same.
- ~~Added some benchmarks for bonus points.~~


## Side Notes

- I would have liked to rename `EaseFunction` to `EaseFn` for brevity,
but that would be a breaking change and maybe controversial.
    - Also suspect `EasingCurve` should be `EaseCurve`, but say la vee.
- Benchmarks show that calling `EaseFunction::Smoothstep` is still
slower than calling `smoothstep` directly.
- I think this is because the compiler refuses to inline
`EaseFunction::eval`.
- I don't see any good solution - might need a whole different
interface.

## Testing

```sh
cargo test --package bevy_math

cargo doc --package bevy_math
./target/doc/bevy_math/curve/easing/struct.EasingCurve.html

cargo bench --package benches --bench math -- easing
```