rays: implement Ray::transform

rtchallenge/src/rays.rs

@@ -1,5 +1,6 @@
-use crate::tuples::Tuple;
+use crate::{matrices::Matrix4x4, tuples::Tuple};
 
+/// Rays have an origin and a direction. This datatype is the 'ray' in 'raytracer'.
 pub struct Ray {
     pub origin: Tuple,
     pub direction: Tuple,
@@ -40,4 +41,31 @@ impl Ray {
     pub fn position(&self, t: f32) -> Tuple {
         self.origin + self.direction * t
     }
+
+    /// Apply Matrix4x4 transforms to Ray.
+    ///
+    /// # Examples
+    /// ```
+    /// use rtchallenge::{matrices::Matrix4x4, rays::Ray, tuples::Tuple};
+    ///
+    /// // Translating a ray
+    /// let r = Ray::new(Tuple::point(1., 2., 3.), Tuple::vector(0., 1., 0.));
+    /// let m = Matrix4x4::translate(3., 4., 5.);
+    /// let r2 = r.transform(m);
+    /// assert_eq!(r2.origin, Tuple::point(4., 6., 8.));
+    /// assert_eq!(r2.direction, Tuple::vector(0., 1., 0.));
+    ///
+    /// // Scaling a ray
+    /// let r = Ray::new(Tuple::point(1., 2., 3.), Tuple::vector(0., 1., 0.));
+    /// let m = Matrix4x4::scaling(2., 3., 4.);
+    /// let r2 = r.transform(m);
+    /// assert_eq!(r2.origin, Tuple::point(2., 6., 12.));
+    /// assert_eq!(r2.direction, Tuple::vector(0., 3., 0.));
+    /// ```
+    pub fn transform(&self, m: Matrix4x4) -> Ray {
+        Ray {
+            origin: m * self.origin,
+            direction: m * self.direction,
+        }
+    }
 }