From f4f7a71964f3fd4a689db4fd5a1a1f9350bad71c Mon Sep 17 00:00:00 2001
From: Christophe Riccio <mail@g-truc.net>
Date: Tue, 28 May 2013 03:47:26 +0200
Subject: [PATCH] Back ported resolution for issue #71 for znear == 0 bug into
 branch 0.9.4

---
 glm/gtc/matrix_transform.inl | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/glm/gtc/matrix_transform.inl b/glm/gtc/matrix_transform.inl
index 2b0bb2a1..6f20b4cd 100644
--- a/glm/gtc/matrix_transform.inl
+++ b/glm/gtc/matrix_transform.inl
@@ -236,21 +236,19 @@ namespace glm
 		valType const & zFar
 	)
 	{
+		assert(aspect != valType(0));
+		assert(zFar != zNear);
+
 #ifdef GLM_FORCE_RADIANS
 		valType const rad = fovy;
 #else
 		valType const rad = glm::radians(fovy);
 #endif
-        
-		valType range = tan(rad / valType(2)) * zNear;	
-		valType left = -range * aspect;
-		valType right = range * aspect;
-		valType bottom = -range;
-		valType top = range;
 
+		valType tanHalfFovy = tan(rad / valType(2));
 		detail::tmat4x4<valType> Result(valType(0));
-		Result[0][0] = (valType(2) * zNear) / (right - left);
-		Result[1][1] = (valType(2) * zNear) / (top - bottom);
+		Result[0][0] = valType(1) / (aspect * tanHalfFovy);
+		Result[1][1] = valType(1) / (tanHalfFovy);
 		Result[2][2] = - (zFar + zNear) / (zFar - zNear);
 		Result[2][3] = - valType(1);
 		Result[3][2] = - (valType(2) * zFar * zNear) / (zFar - zNear);