From dbac8a37c4253031c3c12c73894f2129da9c90eb Mon Sep 17 00:00:00 2001
From: NADAL Jean-Baptiste <jbnadal@cabassegroup.com>
Date: Mon, 5 Feb 2024 17:32:22 +0100
Subject: [PATCH] [FEAT] Add scaling

---
 raytracing/src/matrix.cpp    | 14 ++++++++++++
 raytracing/src/matrix.h      |  1 +
 tests/04_transformations.cpp | 41 ++++++++++++++++++++++++++++++++++++
 3 files changed, 56 insertions(+)

diff --git a/raytracing/src/matrix.cpp b/raytracing/src/matrix.cpp
index 3e8b968..d7c56aa 100644
--- a/raytracing/src/matrix.cpp
+++ b/raytracing/src/matrix.cpp
@@ -326,6 +326,20 @@ Matrix Matrix::translation(double an_x, double an_y, double an_z)
 
 /* ------------------------------------------------------------------------- */
 
+Matrix Matrix::scaling(double an_x, double an_y, double an_z)
+{
+    Matrix the_scaling = {
+        {an_x,    0,    0, 0},
+        {   0, an_y,    0, 0},
+        {   0,    0, an_z, 0},
+        {   0,    0,    0, 1}
+    };
+
+    return the_scaling;
+}
+
+/* ------------------------------------------------------------------------- */
+
 bool Matrix::validate_dimensions(const std::initializer_list<std::initializer_list<double>> &a_values) const
 {
     for (const auto &the_row : a_values)
diff --git a/raytracing/src/matrix.h b/raytracing/src/matrix.h
index bfaf2a3..da797e4 100644
--- a/raytracing/src/matrix.h
+++ b/raytracing/src/matrix.h
@@ -72,6 +72,7 @@ namespace Raytracer
 
         static Matrix identity(void);
         static Matrix translation(double an_x, double an_y, double an_z);
+        static Matrix scaling(double an_x, double an_y, double an_z);
 
     private:
         bool validate_dimensions(const std::initializer_list<std::initializer_list<double>> &a_values) const;
diff --git a/tests/04_transformations.cpp b/tests/04_transformations.cpp
index 418e6ac..77d0de1 100644
--- a/tests/04_transformations.cpp
+++ b/tests/04_transformations.cpp
@@ -61,3 +61,44 @@ TEST_CASE("[04][TRANSFORMATION] Translation does not affect vectors", "[Matrix]"
 
     REQUIRE(transform * v == v);
 }
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("[04][TRANSFORMATION] A scaling matrix applied to a point", "[Matrix]")
+{
+    Matrix transform = Matrix::scaling(2, 3, 4);
+    Tuple p = Tuple::Point(-4, 6, 8);
+
+    REQUIRE(transform * p == Tuple::Point(-8, 18, 32));
+}
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("[04][TRANSFORMATION] A scaling matrix applied to a vector", "[Matrix]")
+{
+    Matrix transform = Matrix::scaling(2, 3, 4);
+    Tuple v = Tuple::Vector(-4, 6, 8);
+
+    REQUIRE(transform * v == Tuple::Vector(-8, 18, 32));
+}
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("[04][TRANSFORMATION] Multiplying by the inverse of a scaling matrix", "[Matrix]")
+{
+    Matrix transform = Matrix::scaling(2, 3, 4);
+    Matrix inv = transform.inverse();
+    Tuple v = Tuple::Vector(-4, 6, 8);
+
+    REQUIRE(inv * v == Tuple::Vector(-2, 2, 2));
+}
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("[04][TRANSFORMATION] Reflection is scaling by a negative value", "[Matrix]")
+{
+    Matrix transform = Matrix::scaling(-1, 1, 1);
+    Tuple p = Tuple::Point(2, 3, 4);
+
+    REQUIRE(transform * p == Tuple::Point(-2, 3, 4));
+}