From 5866f779154a4f982961b641b8905031e95373ab Mon Sep 17 00:00:00 2001
From: NADAL Jean-Baptiste <jbnadal@cabassegroup.com>
Date: Fri, 2 Feb 2024 14:50:07 +0100
Subject: [PATCH] [FEAT] Add identity matrix

---
 raytracing/src/matrix.cpp | 20 ++++++++++++++++++++
 raytracing/src/matrix.h   |  3 +++
 tests/03_matrix.cpp       | 23 +++++++++++++++++++++++
 3 files changed, 46 insertions(+)

diff --git a/raytracing/src/matrix.cpp b/raytracing/src/matrix.cpp
index 8e9f0b5..755d3e3 100644
--- a/raytracing/src/matrix.cpp
+++ b/raytracing/src/matrix.cpp
@@ -58,6 +58,12 @@ Matrix::Matrix(uint8_t a_rows, uint8_t a_cols) : m_rows(a_rows), m_cols(a_cols)
 
 /* ------------------------------------------------------------------------- */
 
+Matrix::Matrix(const Matrix &an_other) : m_rows(an_other.m_rows), m_cols(an_other.m_cols), m_data(an_other.m_data)
+{
+}
+
+/* ------------------------------------------------------------------------- */
+
 Matrix::Matrix(const std::initializer_list<std::initializer_list<double>> &a_values) :
     m_rows(a_values.size()), m_cols(a_values.size())
 {
@@ -167,6 +173,20 @@ const Tuple Matrix::operator*(const Tuple &a_tuple) const
 
 /* ------------------------------------------------------------------------- */
 
+Matrix Matrix::identity(void)
+{
+    Matrix the_identity = {
+        {1, 0, 0, 0},
+        {0, 1, 0, 0},
+        {0, 0, 1, 0},
+        {0, 0, 0, 1}
+    };
+
+    return the_identity;
+}
+
+/* ------------------------------------------------------------------------- */
+
 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 17cdd4f..c6fc741 100644
--- a/raytracing/src/matrix.h
+++ b/raytracing/src/matrix.h
@@ -43,6 +43,7 @@ namespace Raytracer
     public:
         Matrix(void);
         Matrix(uint8_t a_rows, uint8_t a_cols);
+        Matrix(const Matrix &an_other);
         Matrix(const std::initializer_list<std::initializer_list<double>> &a_values);
 
         uint8_t rows(void);
@@ -56,6 +57,8 @@ namespace Raytracer
         const Matrix operator*(const Matrix &a_matrix) const;
         const Tuple operator*(const Tuple &a_tuple) const;
 
+        static Matrix identity(void);
+
     private:
         bool validate_dimensions(const std::initializer_list<std::initializer_list<double>> &a_values) const;
 
diff --git a/tests/03_matrix.cpp b/tests/03_matrix.cpp
index 5d383fa..0ca4959 100644
--- a/tests/03_matrix.cpp
+++ b/tests/03_matrix.cpp
@@ -171,3 +171,26 @@ TEST_CASE("[Matrix] a matrix multiplied by a tuple", "[Matrix]")
 
     REQUIRE((a * b) == Tuple(18, 24, 33, 1));
 }
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("[Matrix] Multiplying a matrix by the identity matrix", "[Matrix]")
+{
+    Matrix a = {
+        {0, 1,  2,  4},
+        {1, 2,  4,  8},
+        {2, 4,  8, 16},
+        {4, 8, 16, 32}
+    };
+
+    REQUIRE((a * Matrix::identity()) == a);
+}
+
+/* ------------------------------------------------------------------------- */
+
+TEST_CASE("[Matrix] Multiplying the identity matrix by a tuple", "[Matrix]")
+{
+    Tuple a(1, 2, 3, 4);
+
+    REQUIRE((Matrix::identity() * a) == a);
+}