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spheres: fix normal_at for transformed spheres.

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This commit is contained in:
Bill Thiede 2021-07-17 08:44:26 -07:00
parent ac4f5eb9a6
commit e529710d5d
1 changed files with 19 additions and 13 deletions
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32
rtchallenge/src/spheres.rs
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@ -76,21 +76,27 @@ impl Sphere {
/// 3_f32.sqrt() / 3.,
/// ));
/// assert_eq!(n, n.normalize());
/// ```
/// ```should_panic
/// use rtchallenge::{spheres::Sphere, tuples::Tuple};
///
/// // In debug builds points not on the sphere should fail.
/// let s = Sphere::default();
/// let n = s.normal_at(Tuple::point(0., 0., 0.5));
/// // Compute the normal on a translated sphere.
/// let mut s = Sphere::default();
/// s.transform = Matrix4x4::translation(0., 1., 0.);
/// let n = s.normal_at(Tuple::point(0., 1.70711, -0.70711));
/// assert_eq!(n, Tuple::vector(0., 0.70711, -0.70711));
/// // Compute the normal on a transformed sphere.
/// use std::f32::consts::PI;
///
/// let mut s = Sphere::default();
/// s.transform = Matrix4x4::scaling(1.,0.5,1.) * Matrix4x4::rotation_z(PI/5.);
/// let n = s.normal_at(Tuple::point(0., 2_f32.sqrt()/2., -2_f32.sqrt()/2.));
/// assert_eq!(n, Tuple::vector(0., 0.97014, -0.24254));
/// ```
pub fn normal_at(&self, point: Tuple) -> Tuple {
debug_assert!(
((point - Tuple::point(0., 0., 0.)).magnitude() - 1.).abs() < EPSILON,
"{} != 1.",
(point - Tuple::point(0., 0., 0.)).magnitude()
);
(point - Tuple::point(0., 0., 0.)).normalize()
pub fn normal_at(&self, world_point: Tuple) -> Tuple {
let object_point = self.transform.inverse() * world_point;
let object_normal = object_point - Tuple::point(0., 0., 0.);
let mut world_normal = self.transform.inverse().transpose() * object_normal;
world_normal.w = 0.;
world_normal.normalize()
}
}