auburn 0.1.4

Fast and simple physics library.
Documentation 
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//! Imagine you have transformations `A` and `B`.
//! You can calculate the difference between them by `A.inverse().compose(&B)`.

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
pub struct IdentityTransform;

pub trait Invertible {
    /// Inversion of the transformation.
    ///
    /// The operation holds this property:
    /// ```
    /// use auburn::col2d::*;
    /// let p = Vec2::new(1.0, 1.0);
    /// let a = Translate2d::from(Vec2::new(1.0, 0.0));
    /// assert_eq!(p, a.inverse().apply(a.apply(p)))
    /// ```
    fn inverse(&self) -> Self;
}

pub trait Composable {
    /// Compose two transformations.
    ///
    /// The operation holds this property:
    /// ```rust
    /// use auburn::col2d::*;
    /// let p = Vec2::new(1.0, 1.0);
    /// let a = Translate2d::from(Vec2::new(1.0, 0.0));
    /// let b = Translate2d::from(Vec2::new(0.0, 1.0));
    /// assert_eq!(
    ///     a.apply(b.apply(p)),
    ///     a.compose(&b).apply(p),
    /// )
    /// ```
    fn compose(&self, other: &Self) -> Self;
}

pub trait DeltaTransform {
    /// Computes the difference between two transformations.
    ///
    /// Useful for functions expecting a relative transform:
    ///
    /// ```
    /// use auburn::col2d::*;
    /// let a = Translate2d::from(Vec2::new(1.0, 0.0));
    /// let b = Translate2d::from(Vec2::new(0.0, 1.0));
    /// assert_eq!(
    ///     a.delta_transform(&b),
    ///     // Translate2d::from(Vec2::new(1.0, -1.0)),
    ///     Translate2d::from(Vec2::new(-1.0, 1.0)),
    /// )
    /// ```
    fn delta_transform(&self, other: &Self) -> Self;
}

impl<T: Invertible + Composable> DeltaTransform for T {
    fn delta_transform(&self, other: &Self) -> Self {
        self.inverse().compose(other)
    }
}