# Objective
Introduce isometry types for describing relative and absolute position
in mathematical contexts.
## Solution
For the time being, this is a very minimal implementation. This
implements the following faculties for two- and three-dimensional
isometry types:
- Identity transformations
- Creation from translations and/or rotations
- Inverses
- Multiplication (composition) of isometries with each other
- Application of isometries to points (as vectors)
- Conversion of isometries to affine transformations
There is obviously a lot more that could be added, so I erred on the
side of adding things that I knew would be useful, with the idea of
expanding this in the near future as needed.
(I also fixed some random doc problems in `bevy_math`.)
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## Design
One point of interest here is the matter of if/when to use aligned
types. In the implementation of 3d isometries, I used `Vec3A` rather
than `Vec3` because it has no impact on size/alignment, but I'm still
not sure about that decision (although it is easily changed).
For 2d isometries — which are encoded by four floats — the idea of
shoving them into a single 128-bit buffer (`__m128` or whatever) sounds
kind of enticing, but it's more involved and would involve writing
unsafe code, so I didn't do that for now.
## Future work
- Expand the API to include shortcuts like `inverse_mul` and
`inverse_transform` for efficiency reasons.
- Include more convenience constructors and methods (e.g. `from_xy`,
`from_xyz`).
- Refactor `bevy_math::bounding` to use the isometry types.
- Add conversions to/from isometries for `Transform`/`GlobalTransform`
in `bevy_transform`.
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