From 9da11ffdb1283931ee83cd04f7413229a4b587ec Mon Sep 17 00:00:00 2001
From: Russell Greene <russellgreene8@gmail.com>
Date: Sat, 22 Aug 2015 14:30:36 -0600
Subject: [PATCH] add glm::ortho_2d

---
 glm/gtc/matrix_transform.hpp | 15 +++++++++++++++
 glm/gtc/matrix_transform.inl | 17 +++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/glm/gtc/matrix_transform.hpp b/glm/gtc/matrix_transform.hpp
index d4ff3cfe..504bb5c8 100644
--- a/glm/gtc/matrix_transform.hpp
+++ b/glm/gtc/matrix_transform.hpp
@@ -151,6 +151,21 @@ namespace glm
 		T right,
 		T bottom,
 		T top);
+		
+	/// Creates a matrix for projecting two-dimensional coordinates onto the screen.
+	/// 
+	/// @param left 
+	/// @param right 
+	/// @param bottom 
+	/// @param top 
+	/// @tparam T Value type used to build the matrix. Currently supported: half (not recommanded), float or double.
+	/// @see gtc_matrix_transform
+	template <typename T>
+	GLM_FUNC_DECL tmat3x3<T, defaultp> ortho_2d(
+		T left,
+		T right,
+		T bottom,
+		T top);
 
 	/// Creates a frustum matrix.
 	/// 
diff --git a/glm/gtc/matrix_transform.inl b/glm/gtc/matrix_transform.inl
index d60494e3..a35482f1 100644
--- a/glm/gtc/matrix_transform.inl
+++ b/glm/gtc/matrix_transform.inl
@@ -185,6 +185,23 @@ namespace glm
 		Result[3][1] = - (top + bottom) / (top - bottom);
 		return Result;
 	}
+	
+	template <typename T> 
+	GLM_FUNC_QUALIFIER tmat3x3<T, defaultp> ortho_2d
+	(
+		T left, 
+		T right, 
+		T bottom, 
+		T top
+	)
+	{
+		tmat3x3<T, defaultp> Result(1);
+		Result[0][0] = static_cast<T>(2) / (right - left);
+		Result[1][1] = static_cast<T>(2) / (top - bottom);
+		Result[2][0] = -(right + left) / (right - left);
+		Result[2][1] = -(top + bottom) / (top - bottom);
+		return Result;
+	}
 
 	template <typename T>
 	GLM_FUNC_QUALIFIER tmat4x4<T, defaultp> frustum