From d8db86e40c571bf140dc0ff6844eaaa70e2c78e0 Mon Sep 17 00:00:00 2001
From: Henrik Hautakoski <henrik.hautakoski@gmail.com>
Date: Fri, 18 Aug 2023 17:54:19 +0200
Subject: [PATCH] include/Spectre/Math/Matrix3.h: Add inverse()

---
 include/Spectre/Math/Matrix3.h   |  3 +++
 include/Spectre/Math/Matrix3.inl | 24 ++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/Spectre/Math/Matrix3.h b/include/Spectre/Math/Matrix3.h
index 04c47d0..1576348 100644
--- a/include/Spectre/Math/Matrix3.h
+++ b/include/Spectre/Math/Matrix3.h
@@ -78,6 +78,9 @@ struct Matrix3
 
 	// Transpose matrix.
 	Matrix3<T> transpose() const;
+
+	// Inverse
+	Matrix3<T> inverse() const;
 };
 
 template <typename T>
diff --git a/include/Spectre/Math/Matrix3.inl b/include/Spectre/Math/Matrix3.inl
index 465f770..9425c89 100644
--- a/include/Spectre/Math/Matrix3.inl
+++ b/include/Spectre/Math/Matrix3.inl
@@ -136,6 +136,30 @@ float Matrix3<T>::det() const
 	return det;
 }
 
+template<typename T>
+Matrix3<T> Matrix3<T>::inverse() const
+{
+	float d = det();
+
+	if (d != 0.0f) {
+		float a00 =   (v[4] * v[8]) - (v[7] * v[5]);
+		float a01 = -((v[1] * v[8]) - (v[7] * v[2]));
+		float a02 =   (v[1] * v[5]) - (v[4] * v[2]);
+
+		float a10 = -((v[3] * v[8]) - (v[6] * v[5]));
+		float a11 =   (v[0] * v[8]) - (v[6] * v[2]);
+		float a12 = -((v[0] * v[5]) - (v[3] * v[2]));
+
+		float a20 =   (v[3] * v[7]) - (v[6] * v[4]);
+		float a21 = -((v[0] * v[7]) - (v[6] * v[1]));
+		float a22 =   (v[0] * v[4]) - (v[3] * v[1]);
+
+		return Matrix3<T>(a00, a01, a02, a10, a11, a12, a20, a21, a22) / d;
+	}
+
+	return Matrix3<T>::Identity;
+}
+
 template<typename T>
 Matrix3<T> Matrix3<T>::transpose() const
 {