Function transform_angle 

pub fn transform_angle<'out, T>(
    out: &'out mut [T; 2],
    v: &[T; 2],
    a: &T,
) -> &'out mut [T; 2]
where
    T: Real,
    for<'a, 'b> &'a T: Mul<&'b T, Output = T>,

Example

use std::f32::consts::FRAC_PI_2;
let mut v = vec2::new_zero();
vec2::transform_angle(&mut v, &[0_f32, 1_f32], &FRAC_PI_2);
let c = FRAC_PI_2.cos();
let s = FRAC_PI_2.sin();
assert_eq!(v, [0_f32 * c - 1_f32 * s, 0_f32 * s + 1_f32 * c]);