iris/core/src/util/math.rs

pub const trait LerpUtil: Sized {
    fn lerp(self, from: Self, to: Self) -> Self;
    fn lerp_inv(self, from: Self, to: Self) -> Option<Self>;
}

const impl LerpUtil for f32 {
    /// linear interpolation
    /// from * (1.0 - self) + to * self
    fn lerp(self, from: Self, to: Self) -> Self {
        from + (to - from) * self
    }
    /// inverse of lerp, and `None` where `from` and `to` are the same point:
    /// every input lerps to it, so there is no one answer to come back to.
    fn lerp_inv(self, from: Self, to: Self) -> Option<Self> {
        match to == from {
            true => None,
            false => Some((self - from) / (to - from)),
        }
    }
}

macro_rules! impl_op {
    ($T:ident $op:ident $fn:ident $opa:ident $fna:ident; $($field:ident)*) => {
        #[allow(non_snake_case)]
        mod ${concat($T, _op_, $fn, _impl)} {
            use super::*;
            #[allow(unused_imports)]
            use std::ops::*;
            const impl $op for $T {
                type Output = Self;

                fn $fn(self, rhs: Self) -> Self::Output {
                    Self {
                        $($field: self.$field.$fn(rhs.$field),)*
                    }
                }
            }
            const impl $opa for $T {
                fn $fna(&mut self, rhs: Self) {
                    *self = self.$fn(rhs);
                }
            }
            const impl $op<f32> for $T {
                type Output = Self;

                fn $fn(self, rhs: f32) -> Self::Output {
                    Self {
                        $($field: self.$field.$fn(rhs),)*
                    }
                }
            }
            const impl $op<$T> for f32 {
                type Output = $T;

                fn $fn(self, rhs: $T) -> Self::Output {
                    $T {
                        $($field: self.$fn(rhs.$field),)*
                    }
                }
            }
            const impl $opa<f32> for $T {
                fn $fna(&mut self, rhs: f32) {
                    *self = self.$fn(rhs);
                }
            }
        }
    };
    ($T:ident $op:ident $fn:ident; $($field:ident)*) => {
        impl_op!($T $op $fn ${concat($op,Assign)} ${concat($fn,_assign)}; $($field)*);
    };
    (impl $op:ident for $T:ident: $fn:ident $($field:ident)*) => {
        impl_op!($T $op $fn ${concat($op,Assign)} ${concat($fn,_assign)}; $($field)*);
    };
}

pub(crate) use impl_op;