From 8f39f12549779e776faa68ae8bf933990fbd25e5 Mon Sep 17 00:00:00 2001
From: Harald Christian Joachim Wolff <info@lupus-nobilis.de>
Date: Sat, 6 May 2017 12:34:21 +0200
Subject: [PATCH] static class Geometry: static Geometric helper methods (e.g.
 intersection)

---
 org.niclasundharald.engine/Geometry.cs | 56 ++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 org.niclasundharald.engine/Geometry.cs

diff --git a/org.niclasundharald.engine/Geometry.cs b/org.niclasundharald.engine/Geometry.cs
new file mode 100644
index 0000000..2578ae0
--- /dev/null
+++ b/org.niclasundharald.engine/Geometry.cs
@@ -0,0 +1,56 @@
+using System;
+
+using OpenTK;
+
+namespace org.niclasundharald.engine
+{
+	public static class Geometry
+	{
+
+		/**
+		 * Intersect Triangle and Ray: 
+		 * 
+		 * A 	+ i * (B-A) + j * (C-A) 			= P +	n * V
+		 * A-P 	+ i * (B-A) + j * (C-A) 			= 		n * V
+		 * 		  i * (B-A) + j * (C-A) - n * V		= P-A
+		 * 
+		 * =>
+		 * 
+		 * -n * V	+ i * (B-A)	+ j * (C-A)			= P-A
+		 * 
+		 * 
+		 **/
+		public static bool intersectTriangle(Vector3 P,Vector3 V,Vector3 A,Vector3 B,Vector3 C,out Vector3 p){
+			Vector3 BA,CA,PA;
+
+			BA = B-A;
+			CA = C-A;
+			PA = P-A;
+
+			Console.WriteLine("Interesction:");
+			Console.WriteLine("Ray:           {0} + i * {1}",P,V);
+			Console.WriteLine("Triangle:      {0}",A);
+			Console.WriteLine("               {0}",B);
+			Console.WriteLine("               {0}",C);
+
+
+			if (!Linear.Solve4x3(V,BA,CA,PA,out p)){
+				return false;
+			}
+
+			p.X = -p.X;
+			if (p.X < 0){
+				return false;
+			}
+
+			if ((p.Y < 0) || (p.Y > 1.0f) ||  (p.Z < 0) || (p.Z > 1.0f)){
+				return false;
+			}
+
+			p = P + (p.X * V);
+
+			return true;
+		}
+
+	}
+}