Function lerp 

pub(in worldgen::feature) fn lerp<F>(
    alpha: F,
    a: F,
    b: F,
) -> F
where
    F: Copy + Mul<Output = F> + Add<Output = F> + Sub<Output = F>,

Linear interpolation.

Formula: a + alpha * (b - a)

Java reference: Mth.lerp(double, double, double)