use glam::{Vec2, Vec3};

/// Encode a 3d direction vector to a 2d vector using octahedron mapping.
/// The output vector is in the range [-1..1]. The input vector doesn't have to be normalized.
pub fn encode_oct(dir: Vec3) -> Vec2 {
    let norm = dir.x.abs() + dir.y.abs() + dir.z.abs();
    let nx = dir.x / norm;
    let ny = dir.y / norm;
    if dir.z.is_sign_positive() {
        Vec2::new(nx, ny)
    } else {
        // fold over negative z
        Vec2::new(
            (1.0 - ny.abs()) * nx.signum(),
            (1.0 - nx.abs()) * ny.signum(),
        )
    }
}

/// Decode an octahedron mapped direction vector back to the original one.
/// The output is normalized.
pub fn decode_oct(mut oct: Vec2) -> Vec3 {
    let z = 1.0 - oct.x.abs() - oct.y.abs();
    oct += oct.signum() * z.min(0.0);
    Vec3::new(oct.x, oct.y, z).normalize()
}