# Objective
Filling a hole in the API: Previously, there was no particularly
ergonomic way to go from, e.g., a pair of directions to the rotation
that links them.
## Solution
We introduce a small suite of API methods to `Dir2` to address this:
```rust
/// Get the rotation that rotates this direction to `other`.
pub fn rotation_to(self, other: Self) -> Rotation2d { //... }
/// Get the rotation that rotates `other` to this direction.
pub fn rotation_from(self, other: Self) -> Rotation2d { //... }
/// Get the rotation that rotates the X-axis to this direction.
pub fn rotation_from_x(self) -> Rotation2d { //... }
/// Get the rotation that rotates this direction to the X-axis.
pub fn rotation_to_x(self) -> Rotation2d { //... }
/// Get the rotation that rotates this direction to the Y-axis.
pub fn rotation_from_y(self) -> Rotation2d { //... }
/// Get the rotation that rotates the Y-axis to this direction.
pub fn rotation_to_y(self) -> Rotation2d { //... }
```
I also removed some language from the `Rotation2d` docs that is
misleading: the radian and angle conversion functions are already clear
about which angles they spit out, and `Rotation2d` itself doesn't have
any bounds on angles or anything.
39609f1708