Fix torus when a point is exactly at the center of the torus

src/geom/region.rs

@@ -91,7 +91,15 @@ impl Region for Torus {
         // 3. Consider the distance from `p` to `q`.
         let rel_p = *p - *self.center;
         let p_on_plane = rel_p - self.normal.with_mag(self.normal.dot(rel_p));
-        let q = p_on_plane.with_mag(self.major_rad.into_inner());
+        let q = if p_on_plane == Vec3::zero() {
+            // avoid division by zero.
+            // The point is precisely on the axis of the torus.
+            // We can choose any point on the major radius to compare it to
+            // and they all give the same answer
+            Vec3::new(self.major_rad.into(), 0.0, 0.0)
+        } else {
+            p_on_plane.with_mag(self.major_rad.into_inner())
+        };
         let distance_to_circle = (rel_p - q).mag();
         distance_to_circle < self.minor_rad.into_inner()
     }