From 5417bae113ca8c50c0eb7f62f750361477657814 Mon Sep 17 00:00:00 2001
From: "erwin.coumans" <erwin.coumans@08e121b0-ae19-0410-a57b-3be3395fd4fd>
Date: Sun, 9 Sep 2012 22:48:20 +0000
Subject: [PATCH] add zigzag heightfield for Ogre compatibility. Fixes Issue
 625. Thanks to KLLoyd!

---
 .../CollisionShapes/btHeightfieldTerrainShape.cpp            | 3 ++-
 .../CollisionShapes/btHeightfieldTerrainShape.h              | 5 ++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/BulletCollision/CollisionShapes/btHeightfieldTerrainShape.cpp b/src/BulletCollision/CollisionShapes/btHeightfieldTerrainShape.cpp
index 5cf79a974..8d4080a63 100644
--- a/src/BulletCollision/CollisionShapes/btHeightfieldTerrainShape.cpp
+++ b/src/BulletCollision/CollisionShapes/btHeightfieldTerrainShape.cpp
@@ -82,6 +82,7 @@ PHY_ScalarType hdt, bool flipQuadEdges
 	m_heightDataType = hdt;
 	m_flipQuadEdges = flipQuadEdges;
 	m_useDiamondSubdivision = false;
+	m_useZigzagSubdivision = false;
 	m_upAxis = upAxis;
 	m_localScaling.setValue(btScalar(1.), btScalar(1.), btScalar(1.));
 
@@ -360,7 +361,7 @@ void	btHeightfieldTerrainShape::processAllTriangles(btTriangleCallback* callback
 		for(int x=startX; x<endX; x++)
 		{
 			btVector3 vertices[3];
-			if (m_flipQuadEdges || (m_useDiamondSubdivision && !((j+x) & 1)))
+			if (m_flipQuadEdges || (m_useDiamondSubdivision && !((j+x) & 1))|| (m_useZigzagSubdivision  && !(j & 1)))
 			{
         //first triangle
         getVertex(x,j,vertices[0]);
diff --git a/src/BulletCollision/CollisionShapes/btHeightfieldTerrainShape.h b/src/BulletCollision/CollisionShapes/btHeightfieldTerrainShape.h
index 32c803308..4a7a4a4bd 100644
--- a/src/BulletCollision/CollisionShapes/btHeightfieldTerrainShape.h
+++ b/src/BulletCollision/CollisionShapes/btHeightfieldTerrainShape.h
@@ -93,7 +93,8 @@ protected:
 
 	PHY_ScalarType	m_heightDataType;	
 	bool	m_flipQuadEdges;
-  bool  m_useDiamondSubdivision;
+  	bool  m_useDiamondSubdivision;
+	bool m_useZigzagSubdivision;
 
 	int	m_upAxis;
 	
@@ -145,6 +146,8 @@ public:
 
 	void setUseDiamondSubdivision(bool useDiamondSubdivision=true) { m_useDiamondSubdivision = useDiamondSubdivision;}
 
+	///could help compatibility with Ogre heightfields. See https://code.google.com/p/bullet/issues/detail?id=625	
+	void setUseZigzagSubdivision(bool useZigzagSubdivision=true) { m_useZigzagSubdivision = useZigzagSubdivision;}
 
 	virtual void getAabb(const btTransform& t,btVector3& aabbMin,btVector3& aabbMax) const;