tweening doesn't work

#[derive(Debug, Copy, Clone, PartialEq)]
struct CameraFovLens {
    pub start: f32,
    pub end: f32,
}

impl Lens<Projection> for CameraFovLens {
    fn lerp(&mut self, target: &mut Projection, ratio: f32) {
        if let Projection::Perspective(ref mut proj) = &mut *target {
            let value = self.start + (self.end - self.start) * ratio;
            proj.fov = value;
        }
    }
}

// todo this stuff doesn't actually work
pub fn camera_fov_animator(start: f32, end: f32) -> Animator<Projection> {
    let tween = Tween::new(
        EaseFunction::QuadraticOut,
        Duration::from_millis(100),
        CameraFovLens { start, end },
    );

    Animator::new(tween)
}