# Objective
Citing @mweatherley
> There is a lot of shortfall for simple cases— e.g., we should have
library functions for making a curve connecting two points, eased
versions of that, and so on.
## Solution
This PR implements
- a simple `Easing` trait which is implemented for all `impl Curve<f32>`
types. We can't really guarantee that these curves have unit interval
domain, which some people would probably expect, but it is documented
that this isn't the case for these types and we redirect to
`EasingCurve` which is used for that purpose
- an `EasingCurve` struct, which is used to interpolate between two
values `start` and `end` using a `impl Easing` curve where the curve
will be guaranteed to be reparametrized
- a `LinearCurve` which linearly interpolates between two values `start`
and `end`
- a `CubicBezierCurve` which interpolates between `start` and `end`
values using a `CubicSegment`
- a `StepCurve` which interpolates between `start` and `end` with an
step-function with `n` steps
- an `ElasticCurve` which interpolates between `start` and `end` with
spring like behavior where the elasticity of the spring is configurable
- some `FunctionCurve` easing curves for different popular functions
including: `quadratic_ease_in`, `quadratic_ease_out`, `smoothstep`,
`identity`
## Testing
- there are a few new tests for all of these in the main module
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Co-authored-by: eckz <567737+eckz@users.noreply.github.com>
Co-authored-by: Miles Silberling-Cook <NthTensor@users.noreply.github.com>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: Matty <weatherleymatthew@gmail.com>
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