From e523852cd48be561a3ecf812b98c95a1ae7682d3 Mon Sep 17 00:00:00 2001
From: Jon Janzen <jonjanzen@me.com>
Date: Fri, 3 Sep 2021 19:42:49 -0600
Subject: [PATCH] added scaling

---
 features/src/transformations.rs | 45 ++++++++++++++++++++++++++++++---
 1 file changed, 42 insertions(+), 3 deletions(-)

diff --git a/features/src/transformations.rs b/features/src/transformations.rs
index 4c069e2..01f9e57 100644
--- a/features/src/transformations.rs
+++ b/features/src/transformations.rs
@@ -5,9 +5,18 @@ use crate::structs::Tuple;
 impl Matrix {
     pub fn translation(x: f32, y: f32, z: f32) -> Self {
         Matrix::from_array([
-            [1.0, 0.0, 0.0, x],
-            [0.0, 1.0, 0.0, y],
-            [0.0, 0.0, 1.0, z],
+            [1.0, 0.0, 0.0, x  ],
+            [0.0, 1.0, 0.0, y  ],
+            [0.0, 0.0, 1.0, z  ],
+            [0.0, 0.0, 0.0, 1.0],
+        ])
+    }
+
+    pub fn scaling(x: f32, y: f32, z: f32) -> Self {
+        Matrix::from_array([
+            [  x, 0.0, 0.0, 0.0],
+            [0.0,   y, 0.0, 0.0],
+            [0.0, 0.0,   z, 0.0],
             [0.0, 0.0, 0.0, 1.0],
         ])
     }
@@ -47,4 +56,34 @@ mod tests {
 
         assert_eq!(&transform * &v, v);
     }
+
+    #[test]
+    fn scaling_matrix_applied_to_point() {
+        let transform = Matrix::scaling(2.0, 3.0, 4.0);
+        let p = Tuple::point(-4.0, 6.0, 8.0);
+        let expected = Tuple::point(-8.0, 18.0, 32.0);
+        assert_eq!(&transform * &p, expected);
+    }
+
+    #[test]
+    fn scaling_matrix_apled_to_vector() {
+        let transform = Matrix::scaling(2.0, 3.0, 4.0);
+        let v = Tuple::vector(-4.0, 6.0, 8.0);
+        assert_eq!(&transform * &v, Tuple::vector(-8.0, 18.0, 32.0));
+    }
+
+    #[test]
+    fn multiplying_inverse_of_scaling_matrix() {
+        let transform = Matrix::scaling(2.0, 3.0, 4.0);
+        let inv = transform.inverse();
+        let v = Tuple::vector(-4.0, 6.0, 8.0);
+        assert_eq!(&inv * &v, Tuple::vector(-2.0, 2.0, 2.0));
+    }
+
+    #[test]
+    fn reflection_is_scaling_by_a_negative_value() {
+        let transform = Matrix::scaling(-1.0, 1.0, 1.0);
+        let p = Tuple::point(2.0, 3.0, 4.0);
+        assert_eq!(&transform * &p, Tuple::point(-2.0, 3.0, 4.0));
+    }
 }