sdfOctahedron

fn sdfOctahedron(position: vec3<f32>, size: f32) -> f32 {
  let p = abs(position);
  let m = p.x + p.y + p.z - size;
  
  // Calculate the distance
  var q: vec3<f32>;
  if (3.0 * p.x < m) {
    q = p;
  } else if (3.0 * p.y < m) {
    q = vec3<f32>(p.x, p.z, p.y);
  } else if (3.0 * p.z < m) {
    q = vec3<f32>(p.x, p.y, p.z);
  } else {
    q = p;
  }
  
  let k = clamp(0.5 * (q.z - q.y + size), 0.0, size);
  return length(vec3<f32>(q.x, q.y - size + k, q.z - k));
}