From 3c482467eaf1d11eb7980538b22051eccf974b2d Mon Sep 17 00:00:00 2001
From: Hartwig <git@skywind.eu>
Date: Thu, 29 Dec 2016 21:43:20 +0100
Subject: [PATCH] BUG FIX - Wrong calculation of terrain normals

The partial derivative for the x-coordinate has been wrongly calculated: only a single sided derivative was calculated.
---
 src/osgTerrain/GeometryTechnique.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/osgTerrain/GeometryTechnique.cpp b/src/osgTerrain/GeometryTechnique.cpp
index b363f4a52..b2a15e4c1 100644
--- a/src/osgTerrain/GeometryTechnique.cpp
+++ b/src/osgTerrain/GeometryTechnique.cpp
@@ -329,11 +329,11 @@ class VertexNormalGenerator
             osg::Vec3 zero(0.0f,0.0f,0.0f);
             if (left_valid)
             {
-                dx = center-left;
+                dx += center-left;
             }
             if (right_valid)
             {
-                dx = right-center;
+                dx += right-center;
             }
             if (bottom_valid)
             {