matrices: implement Matrix4x4::scaling

rtchallenge/src/matrices.rs

@@ -249,6 +249,40 @@ impl Matrix4x4 {
         )
     }
 
+    /// Creates a 4x4 matrix representing a scaling of x,y,z.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use rtchallenge::{matrices::Matrix4x4, tuples::Tuple};
+    ///
+    /// // A scaling matrix applied to a point.
+    /// let transform = Matrix4x4::scaling(2., 3., 4.);
+    /// let p = Tuple::point(-4., 6., 8.);
+    /// assert_eq!(transform * p, Tuple::point(-8., 18., 32.));
+    ///
+    /// // A scaling matrix applied to a vector.
+    /// let v = Tuple::vector(-4., 6., 8.);
+    /// assert_eq!(transform * v, Tuple::vector(-8., 18., 32.));
+    ///
+    /// // Multiplying by the inverse of a scaling matrix.
+    /// let inv = transform.inverse();
+    /// assert_eq!(inv * v, Tuple::vector(-2., 2., 2.));
+    ///
+    /// // Reflection is scaling by a negative value.
+    /// let transform = Matrix4x4::scaling(-1., 1., 1.);
+    /// let p = Tuple::point(2., 3., 4.);
+    /// assert_eq!(transform * p, Tuple::point(-2., 3., 4.));
+    /// ```
+    pub fn scaling(x: f32, y: f32, z: f32) -> Matrix4x4 {
+        Matrix4x4::new(
+            [x, 0., 0., 0.],
+            [0., y, 0., 0.],
+            [0., 0., z, 0.],
+            [0., 0., 0., 1.],
+        )
+    }
+
     /// Transpose self, returning a new matrix that has been reflected across the diagonal.
     /// # Examples
     ///