From e7eb912eaa30adb162938334a5313a9a94e92ecb Mon Sep 17 00:00:00 2001
From: Ian Curtis <i.curtis@gmail.com>
Date: Tue, 22 Mar 2016 13:47:28 +0000
Subject: [PATCH] add maths functions

---
 Src/Graphics/New3D/New3D.cpp | 15 +++++++++++++++
 Src/Graphics/New3D/New3D.h   |  1 +
 2 files changed, 16 insertions(+)

diff --git a/Src/Graphics/New3D/New3D.cpp b/Src/Graphics/New3D/New3D.cpp
index 78fe11f..50aa49c 100644
--- a/Src/Graphics/New3D/New3D.cpp
+++ b/Src/Graphics/New3D/New3D.cpp
@@ -1017,4 +1017,19 @@ bool CNew3D::ClockWiseWinding()
 	}
 }
 
+float CNew3D::Determinant3x3(const float m[16]) {
+
+	/*
+		| A B C |
+	M = | D E F |
+		| G H I |
+
+	then the determinant is calculated as follows:
+
+	det M = A * (EI - HF) - B * (DI - GF) + C * (DH - GE)
+	*/
+
+	return m[0] * ((m[5] * m[10]) - (m[6] * m[9])) - m[4] * ((m[1] * m[10]) - (m[2] * m[9])) + m[8] * ((m[1] * m[6]) - (m[2] * m[5]));
+}
+
 } // New3D
diff --git a/Src/Graphics/New3D/New3D.h b/Src/Graphics/New3D/New3D.h
index ae4fea4..68100f5 100644
--- a/Src/Graphics/New3D/New3D.h
+++ b/Src/Graphics/New3D/New3D.h
@@ -172,6 +172,7 @@ private:
 	enum class AlphaType{ none, poly, texture };
 	void RenderScene(int priority, bool alpha);
 	bool ClockWiseWinding();	// calculate winding with current matrix
+	float Determinant3x3(const float m[16]);
 
 	/*
 	* Data