add raycast accelerator for btHeightfieldTerrainShape, thanks to Marc Zylann, see https://github.com/bulletphysics/bullet3/pull/2062

it can be disabled by setting the flag cb.m_flags |= btTriangleRaycastCallback::kF_DisableHeightfieldAccelerator;
acceleration is disabled for z axis up.
add btHeightfieldTerrainShape example to example browser

examples/Benchmarks/BenchmarkDemo.cpp

@@ -313,35 +313,6 @@ public:
 			m_guiHelper->getRenderInterface()->drawLines(&points[0].m_floats[0], lineColor, points.size(), sizeof(btVector3FloatData), &indices[0], indices.size(), 1);
 		}
 
-#if 0
-		glDisable (GL_LIGHTING);
-		glColor3f (0.0, 1.0, 0.0);
-		glBegin (GL_LINES);
-		int i;
-
-		for (i = 0; i < NUMRAYS; i++)
-		{
-			glVertex3f (source[i][0], source[i][1], source[i][2]);
-			glVertex3f (hit[i][0], hit[i][1], hit[i][2]);
-		}
-		glEnd ();
-		glColor3f (1.0, 1.0, 1.0);
-		glBegin (GL_LINES);
-		for (i = 0; i < NUMRAYS; i++)
-		{
-			glVertex3f (hit[i][0], hit[i][1], hit[i][2]);
-			glVertex3f (hit[i][0] + normal[i][0], hit[i][1] + normal[i][1], hit[i][2] + normal[i][2]);
-		}
-		glEnd ();
-		glColor3f (0.0, 1.0, 1.0);
-		glBegin (GL_POINTS);
-		for ( i = 0; i < NUMRAYS; i++)
-		{
-			glVertex3f (hit[i][0], hit[i][1], hit[i][2]);
-		}
-		glEnd ();
-		glEnable (GL_LIGHTING);
-#endif  //USE_GRAPHICAL_BENCHMARK
 	}
 };
 

examples/CommonInterfaces/CommonRigidBodyBase.h

@@ -438,6 +438,8 @@ struct CommonRigidBodyBase : public CommonExampleInterface
 	}
 
 	virtual void renderScene()
+	{
+		if (m_dynamicsWorld)
 		{
 			{
 				m_guiHelper->syncPhysicsToGraphics(m_dynamicsWorld);
@@ -447,6 +449,7 @@ struct CommonRigidBodyBase : public CommonExampleInterface
 				m_guiHelper->render(m_dynamicsWorld);
 			}
 		}
+	}
 };
 
 #endif  //COMMON_RIGID_BODY_SETUP_H

examples/ExampleBrowser/CMakeLists.txt

@@ -207,6 +207,8 @@ SET(BulletExampleBrowser_SRCS
 	../MultiThreadedDemo/MultiThreadedDemo.h
 	../MultiThreadedDemo/CommonRigidBodyMTBase.cpp
 	../MultiThreadedDemo/CommonRigidBodyMTBase.h
+	../Heightfield/HeightfieldExample.cpp
+	../Heightfield/HeightfieldExample.h
 	../BlockSolver/btBlockSolver.cpp
 	../BlockSolver/btBlockSolver.h
 	../BlockSolver/BlockSolverExample.cpp

examples/ExampleBrowser/ExampleEntries.cpp

@@ -5,6 +5,7 @@
 #include "../BlockSolver/RigidBodyBoxes.h"
 #include "LinearMath/btAlignedObjectArray.h"
 #include "EmptyExample.h"
+#include "../Heightfield/HeightfieldExample.h"
 #include "../RenderingExamples/RenderInstancingDemo.h"
 #include "../RenderingExamples/CoordinateSystemDemo.h"
 #include "../RenderingExamples/RaytracerSetup.h"
@@ -157,8 +158,8 @@ static ExampleEntry gDefaultExamples[] =
 		ExampleEntry(1, "Stack MultiBody MLCP PGS", "Create a stack of blocks, with heavy block at the top", BlockSolverExampleCreateFunc, BLOCK_SOLVER_SCENE_MB_STACK + BLOCK_SOLVER_MLCP_PGS),
 		ExampleEntry(1, "Stack MultiBody MLCP Dantzig", "Create a stack of blocks, with heavy block at the top", BlockSolverExampleCreateFunc, BLOCK_SOLVER_SCENE_MB_STACK + BLOCK_SOLVER_MLCP_DANTZIG),
 		ExampleEntry(1, "Stack MultiBody Block", "Create a stack of blocks, with heavy block at the top", BlockSolverExampleCreateFunc, BLOCK_SOLVER_SCENE_MB_STACK + BLOCK_SOLVER_BLOCK),
-		ExampleEntry(1, "Stack RigidBody SI", "Create a stack of blocks, with heavy block at the top", RigidBodyBoxesCreateFunc, BLOCK_SOLVER_SI),
+		//ExampleEntry(1, "Stack RigidBody SI", "Create a stack of blocks, with heavy block at the top", RigidBodyBoxesCreateFunc, BLOCK_SOLVER_SI),
-		ExampleEntry(1, "Stack RigidBody Block", "Create a stack of blocks, with heavy block at the top", RigidBodyBoxesCreateFunc, BLOCK_SOLVER_BLOCK),
+		//ExampleEntry(1, "Stack RigidBody Block", "Create a stack of blocks, with heavy block at the top", RigidBodyBoxesCreateFunc, BLOCK_SOLVER_BLOCK),
 
 		ExampleEntry(0, "Inverse Dynamics"),
 		ExampleEntry(1, "Inverse Dynamics URDF", "Create a btMultiBody from URDF. Create an inverse MultiBodyTree model from that. Use either decoupled PD control or computed torque control using the inverse model to track joint position targets", InverseDynamicsExampleCreateFunc, BT_ID_LOAD_URDF),
@@ -234,6 +235,7 @@ static ExampleEntry gDefaultExamples[] =
 		ExampleEntry(1, "Convex vs Mesh", "Benchmark the performance and stability of rigid bodies using convex hull collision shapes (btConvexHullShape), resting on a triangle mesh, btBvhTriangleMeshShape.", BenchmarkCreateFunc, 6),
 		ExampleEntry(1, "Raycast", "Benchmark the performance of the btCollisionWorld::rayTest. Note that currently the rays are not rendered.", BenchmarkCreateFunc, 7),
 		ExampleEntry(1, "Convex Pack", "Benchmark the performance of the convex hull primitive.", BenchmarkCreateFunc, 8),
+		ExampleEntry(1, "Heightfield", "Raycast against a btHeightfieldTerrainShape", HeightfieldExampleCreateFunc),
 		//#endif
 
 		ExampleEntry(0, "Importers"),

examples/ExampleBrowser/OpenGLGuiHelper.cpp

@@ -1,7 +1,7 @@
 #include "OpenGLGuiHelper.h"
 
 #include "btBulletDynamicsCommon.h"
-
+#include "BulletCollision/CollisionShapes/btHeightfieldTerrainShape.h"
 #include "../CommonInterfaces/CommonGraphicsAppInterface.h"
 #include "../CommonInterfaces/CommonRenderInterface.h"
 #include "Bullet3Common/b3Scalar.h"
@@ -255,6 +255,38 @@ void OpenGLGuiHelper::createRigidBodyGraphicsObject(btRigidBody* body, const btV
 	createCollisionObjectGraphicsObject(body, color);
 }
 
+
+class MyTriangleCollector2 : public btTriangleCallback
+{
+public:
+	btAlignedObjectArray<GLInstanceVertex>* m_pVerticesOut;
+	btAlignedObjectArray<int>* m_pIndicesOut;
+
+	MyTriangleCollector2()
+	{
+		m_pVerticesOut = 0;
+		m_pIndicesOut = 0;
+	}
+
+	virtual void processTriangle(btVector3* tris, int partId, int triangleIndex)
+	{
+		for (int k = 0; k < 3; k++)
+		{
+			GLInstanceVertex v;
+			v.xyzw[3] = 0;
+			v.uv[0] = v.uv[1] = 0.5f;
+			btVector3 normal = (tris[0] - tris[1]).cross(tris[0] - tris[2]);
+			normal.safeNormalize();
+			for (int l = 0; l < 3; l++)
+			{
+				v.xyzw[l] = tris[k][l];
+				v.normal[l] = normal[l];
+			}
+			m_pIndicesOut->push_back(m_pVerticesOut->size());
+			m_pVerticesOut->push_back(v);
+		}
+	}
+};
 void OpenGLGuiHelper::createCollisionObjectGraphicsObject(btCollisionObject* body, const btVector3& color)
 {
 	if (body->getUserIndex() < 0)
@@ -409,6 +441,30 @@ void OpenGLGuiHelper::createCollisionShapeGraphicsObject(btCollisionShape* colli
 	//if (collisionShape->getShapeType()==BOX_SHAPE_PROXYTYPE)
 	{
 	}
+
+
+	if (collisionShape->getShapeType() == TERRAIN_SHAPE_PROXYTYPE)
+	{
+		const btHeightfieldTerrainShape* heightField = static_cast<const btHeightfieldTerrainShape*>(collisionShape);
+		MyTriangleCollector2  col;
+		col.m_pVerticesOut = &gfxVertices;
+		col.m_pIndicesOut = &indices;
+		btVector3 aabbMin, aabbMax;
+		for (int k = 0; k < 3; k++)
+		{
+			aabbMin[k] = -BT_LARGE_FLOAT;
+			aabbMax[k] = BT_LARGE_FLOAT;
+		}
+		heightField->processAllTriangles(&col, aabbMin, aabbMax);
+		if (gfxVertices.size() && indices.size())
+		{
+			int shapeId = m_data->m_glApp->m_renderer->registerShape(&gfxVertices[0].xyzw[0], gfxVertices.size(), &indices[0], indices.size());
+			collisionShape->setUserIndex(shapeId);
+		}
+		return;
+	}
+
+
 	if (collisionShape->getShapeType() == SOFTBODY_SHAPE_PROXYTYPE)
 	{
 		computeSoftBodyVertices(collisionShape, gfxVertices, indices);

examples/ExampleBrowser/premake4.lua

@@ -169,6 +169,7 @@ project "App_BulletExampleBrowser"
 		"../Collision/Internal/*",
 		"../Benchmarks/*",
 		"../MultiThreadedDemo/*",
+		"../Heightfield/HeightfieldExample.*",
 		"../CommonInterfaces/*.h",
 		"../ForkLift/ForkLiftDemo.*",
 		"../Importers/**",

examples/Heightfield/HeightfieldExample.h

@@ -0,0 +1,21 @@
+/*
+Bullet Continuous Collision Detection and Physics Library
+Copyright (c) 2015 Google Inc. http://bulletphysics.org
+
+This software is provided 'as-is', without any express or implied warranty.
+In no event will the authors be held liable for any damages arising from the use of this software.
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it freely,
+subject to the following restrictions:
+
+1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.
+*/
+
+#ifndef HEIGHTFIELD_EXAMPLE_H
+#define HEIGHTFIELD_EXAMPLE_H
+
+class CommonExampleInterface* HeightfieldExampleCreateFunc(struct CommonExampleOptions& options);
+
+#endif  //HEIGHTFIELD_EXAMPLE_H

src/BulletCollision/CollisionDispatch/btCollisionWorld.cpp

@@ -22,6 +22,7 @@ subject to the following restrictions:
 #include "BulletCollision/CollisionShapes/btSphereShape.h"                 //for raycasting
 #include "BulletCollision/CollisionShapes/btBvhTriangleMeshShape.h"        //for raycasting
 #include "BulletCollision/CollisionShapes/btScaledBvhTriangleMeshShape.h"  //for raycasting
+#include "BulletCollision/CollisionShapes/btHeightfieldTerrainShape.h"     //for raycasting
 #include "BulletCollision/NarrowPhaseCollision/btRaycastCallback.h"
 #include "BulletCollision/CollisionShapes/btCompoundShape.h"
 #include "BulletCollision/NarrowPhaseCollision/btSubSimplexConvexCast.h"
@@ -413,6 +414,21 @@ void btCollisionWorld::rayTestSingleInternal(const btTransform& rayFromTrans, co
 				rcb.m_hitFraction = resultCallback.m_closestHitFraction;
 				triangleMesh->performRaycast(&rcb, rayFromLocalScaled, rayToLocalScaled);
 			}
+			else if (((resultCallback.m_flags&btTriangleRaycastCallback::kF_DisableHeightfieldAccelerator)==0) 
+				&& collisionShape->getShapeType() == TERRAIN_SHAPE_PROXYTYPE && 
+				(((btHeightfieldTerrainShape*)collisionShape)->getUpAxis()==1)//accelerator only supports Y axis at the moment
+				)
+			{
+				///optimized version for btHeightfieldTerrainShape
+				btHeightfieldTerrainShape* heightField = (btHeightfieldTerrainShape*)collisionShape;
+				btTransform worldTocollisionObject = colObjWorldTransform.inverse();
+				btVector3 rayFromLocal = worldTocollisionObject * rayFromTrans.getOrigin();
+				btVector3 rayToLocal = worldTocollisionObject * rayToTrans.getOrigin();
+
+				BridgeTriangleRaycastCallback rcb(rayFromLocal, rayToLocal, &resultCallback, collisionObjectWrap->getCollisionObject(), heightField, colObjWorldTransform);
+				rcb.m_hitFraction = resultCallback.m_closestHitFraction;
+				heightField->performRaycast(&rcb, rayFromLocal, rayToLocal);
+			}
 			else
 			{
 				//generic (slower) case

src/BulletCollision/CollisionShapes/btHeightfieldTerrainShape.cpp

@@ -74,6 +74,10 @@ void btHeightfieldTerrainShape::initialize(
 	m_upAxis = upAxis;
 	m_localScaling.setValue(btScalar(1.), btScalar(1.), btScalar(1.));
 	
+	m_vboundsChunkSize = 0;
+	m_vboundsGridWidth = 0;
+	m_vboundsGridLength = 0;
+
 	// determine min/max axis-aligned bounding box (aabb) values
 	switch (m_upAxis)
 	{
@@ -108,6 +112,7 @@ void btHeightfieldTerrainShape::initialize(
 
 btHeightfieldTerrainShape::~btHeightfieldTerrainShape()
 {
+	clearAccelerator();
 }
 
 void btHeightfieldTerrainShape::getAabb(const btTransform& t, btVector3& aabbMin, btVector3& aabbMax) const
@@ -323,6 +328,8 @@ void btHeightfieldTerrainShape::processAllTriangles(btTriangleCallback* callback
 		}
 	}
 
+	// TODO If m_vboundsGrid is available, use it to determine if we really need to process this area
+
 	for (int j = startJ; j < endJ; j++)
 	{
 		for (int x = startX; x < endX; x++)
@@ -373,3 +380,447 @@ const btVector3& btHeightfieldTerrainShape::getLocalScaling() const
 {
 	return m_localScaling;
 }
+
+namespace
+{
+	struct GridRaycastState
+	{
+		int x;  // Next quad coords
+		int z;
+		int prev_x;  // Previous quad coords
+		int prev_z;
+		btScalar param;      // Exit param for previous quad
+		btScalar prevParam;  // Enter param for previous quad
+		btScalar maxDistanceFlat;
+		btScalar maxDistance3d;
+	};
+}
+
+// TODO Does it really need to take 3D vectors?
+/// Iterates through a virtual 2D grid of unit-sized square cells,
+/// and executes an action on each cell intersecting the given segment, ordered from begin to end.
+/// Initially inspired by http://www.cse.yorku.ca/~amana/research/grid.pdf
+template <typename Action_T>
+void gridRaycast(Action_T& quadAction, const btVector3& beginPos, const btVector3& endPos)
+{
+	GridRaycastState rs;
+	rs.maxDistance3d = beginPos.distance(endPos);
+	if (rs.maxDistance3d < 0.0001)
+	{
+		// Consider the ray is too small to hit anything
+		return;
+	}
+
+	btScalar rayDirectionFlatX = endPos[0] - beginPos[0];
+	btScalar rayDirectionFlatZ = endPos[2] - beginPos[2];
+	rs.maxDistanceFlat = btSqrt(rayDirectionFlatX * rayDirectionFlatX + rayDirectionFlatZ * rayDirectionFlatZ);
+
+	if (rs.maxDistanceFlat < 0.0001)
+	{
+		// Consider the ray vertical
+		rayDirectionFlatX = 0;
+		rayDirectionFlatZ = 0;
+	}
+	else
+	{
+		rayDirectionFlatX /= rs.maxDistanceFlat;
+		rayDirectionFlatZ /= rs.maxDistanceFlat;
+	}
+
+	const int xiStep = rayDirectionFlatX > 0 ? 1 : rayDirectionFlatX < 0 ? -1 : 0;
+	const int ziStep = rayDirectionFlatZ > 0 ? 1 : rayDirectionFlatZ < 0 ? -1 : 0;
+
+	const float infinite = 9999999;
+	const btScalar paramDeltaX = xiStep != 0 ? 1.f / btFabs(rayDirectionFlatX) : infinite;
+	const btScalar paramDeltaZ = ziStep != 0 ? 1.f / btFabs(rayDirectionFlatZ) : infinite;
+
+	// pos = param * dir
+	btScalar paramCrossX;  // At which value of `param` we will cross a x-axis lane?
+	btScalar paramCrossZ;  // At which value of `param` we will cross a z-axis lane?
+
+	// paramCrossX and paramCrossZ are initialized as being the first cross
+	// X initialization
+	if (xiStep != 0)
+	{
+		if (xiStep == 1)
+		{
+			paramCrossX = (ceil(beginPos[0]) - beginPos[0]) * paramDeltaX;
+		}
+		else
+		{
+			paramCrossX = (beginPos[0] - floor(beginPos[0])) * paramDeltaX;
+		}
+	}
+	else
+	{
+		paramCrossX = infinite;  // Will never cross on X
+	}
+
+	// Z initialization
+	if (ziStep != 0)
+	{
+		if (ziStep == 1)
+		{
+			paramCrossZ = (ceil(beginPos[2]) - beginPos[2]) * paramDeltaZ;
+		}
+		else
+		{
+			paramCrossZ = (beginPos[2] - floor(beginPos[2])) * paramDeltaZ;
+		}
+	}
+	else
+	{
+		paramCrossZ = infinite;  // Will never cross on Z
+	}
+
+	rs.x = static_cast<int>(floor(beginPos[0]));
+	rs.z = static_cast<int>(floor(beginPos[2]));
+
+	// Workaround cases where the ray starts at an integer position
+	if (paramCrossX == 0.0)
+	{
+		paramCrossX += paramDeltaX;
+		// If going backwards, we should ignore the position we would get by the above flooring,
+		// because the ray is not heading in that direction
+		if (xiStep == -1)
+		{
+			rs.x -= 1;
+		}
+	}
+
+	if (paramCrossZ == 0.0)
+	{
+		paramCrossZ += paramDeltaZ;
+		if (ziStep == -1)
+			rs.z -= 1;
+	}
+
+	rs.prev_x = rs.x;
+	rs.prev_z = rs.z;
+	rs.param = 0;
+
+	while (true)
+	{
+		rs.prev_x = rs.x;
+		rs.prev_z = rs.z;
+		rs.prevParam = rs.param;
+
+		if (paramCrossX < paramCrossZ)
+		{
+			// X lane
+			rs.x += xiStep;
+			// Assign before advancing the param,
+			// to be in sync with the initialization step
+			rs.param = paramCrossX;
+			paramCrossX += paramDeltaX;
+		}
+		else
+		{
+			// Z lane
+			rs.z += ziStep;
+			rs.param = paramCrossZ;
+			paramCrossZ += paramDeltaZ;
+		}
+
+		if (rs.param > rs.maxDistanceFlat)
+		{
+			rs.param = rs.maxDistanceFlat;
+			quadAction(rs);
+			break;
+		}
+		else
+		{
+			quadAction(rs);
+		}
+	}
+}
+
+struct ProcessTrianglesAction
+{
+	const btHeightfieldTerrainShape* shape;
+	bool flipQuadEdges;
+	bool useDiamondSubdivision;
+	int width;
+	int length;
+	btTriangleCallback* callback;
+
+	void exec(int x, int z) const
+	{
+		if (x < 0 || z < 0 || x >= width || z >= length)
+		{
+			return;
+		}
+
+		btVector3 vertices[3];
+
+		// TODO Since this is for raycasts, we could greatly benefit from an early exit on the first hit
+
+		// Check quad
+		if (flipQuadEdges || (useDiamondSubdivision && (((z + x) & 1) > 0)))
+		{
+			// First triangle
+			shape->getVertex(x, z, vertices[0]);
+			shape->getVertex(x + 1, z, vertices[1]);
+			shape->getVertex(x + 1, z + 1, vertices[2]);
+			callback->processTriangle(vertices, x, z);
+
+			// Second triangle
+			shape->getVertex(x, z, vertices[0]);
+			shape->getVertex(x + 1, z + 1, vertices[1]);
+			shape->getVertex(x, z + 1, vertices[2]);
+			callback->processTriangle(vertices, x, z);
+		}
+		else
+		{
+			// First triangle
+			shape->getVertex(x, z, vertices[0]);
+			shape->getVertex(x, z + 1, vertices[1]);
+			shape->getVertex(x + 1, z, vertices[2]);
+			callback->processTriangle(vertices, x, z);
+
+			// Second triangle
+			shape->getVertex(x + 1, z, vertices[0]);
+			shape->getVertex(x, z + 1, vertices[1]);
+			shape->getVertex(x + 1, z + 1, vertices[2]);
+			callback->processTriangle(vertices, x, z);
+		}
+	}
+
+	void operator()(const GridRaycastState& bs) const
+	{
+		exec(bs.prev_x, bs.prev_z);
+	}
+};
+
+struct ProcessVBoundsAction
+{
+	const btAlignedObjectArray<btHeightfieldTerrainShape::Range>& vbounds;
+	int width;
+	int length;
+	int chunkSize;
+
+	btVector3 rayBegin;
+	btVector3 rayEnd;
+	btVector3 rayDir;
+
+	ProcessTrianglesAction processTriangles;
+
+	ProcessVBoundsAction(const btAlignedObjectArray<btHeightfieldTerrainShape::Range>& bnd)
+		: vbounds(bnd)
+	{
+	}
+	void operator()(const GridRaycastState& rs) const
+	{
+		int x = rs.prev_x;
+		int z = rs.prev_z;
+
+		if (x < 0 || z < 0 || x >= width || z >= length)
+		{
+			return;
+		}
+
+		const btHeightfieldTerrainShape::Range chunk = vbounds[x + z * width];
+
+		btVector3 enterPos;
+		btVector3 exitPos;
+
+		if (rs.maxDistanceFlat > 0.0001)
+		{
+			btScalar flatTo3d = chunkSize * rs.maxDistance3d / rs.maxDistanceFlat;
+			btScalar enterParam3d = rs.prevParam * flatTo3d;
+			btScalar exitParam3d = rs.param * flatTo3d;
+			enterPos = rayBegin + rayDir * enterParam3d;
+			exitPos = rayBegin + rayDir * exitParam3d;
+
+			// We did enter the flat projection of the AABB,
+			// but we have to check if we intersect it on the vertical axis
+			if (enterPos[1] > chunk.max && exitPos[1] > chunk.max)
+			{
+				return;
+			}
+			if (enterPos[1] < chunk.min && exitPos[1] < chunk.min)
+			{
+				return;
+			}
+		}
+		else
+		{
+			// Consider the ray vertical
+			// (though we shouldn't reach this often because there is an early check up-front)
+			enterPos = rayBegin;
+			exitPos = rayEnd;
+		}
+
+		gridRaycast(processTriangles, enterPos, exitPos);
+		// Note: it could be possible to have more than one grid at different levels,
+		// to do this there would be a branch using a pointer to another ProcessVBoundsAction
+	}
+};
+
+// TODO How do I interrupt the ray when there is a hit? `callback` does not return any result
+/// Performs a raycast using a hierarchical Bresenham algorithm.
+/// Does not allocate any memory by itself.
+void btHeightfieldTerrainShape::performRaycast(btTriangleCallback* callback, const btVector3& raySource, const btVector3& rayTarget) const
+{
+	// Transform to cell-local
+	btVector3 beginPos = raySource / m_localScaling;
+	btVector3 endPos = rayTarget / m_localScaling;
+	beginPos += m_localOrigin;
+	endPos += m_localOrigin;
+
+	ProcessTrianglesAction processTriangles;
+	processTriangles.shape = this;
+	processTriangles.flipQuadEdges = m_flipQuadEdges;
+	processTriangles.useDiamondSubdivision = m_useDiamondSubdivision;
+	processTriangles.callback = callback;
+	processTriangles.width = m_heightStickWidth - 1;
+	processTriangles.length = m_heightStickLength - 1;
+
+	// TODO Transform vectors to account for m_upAxis
+	int iBeginX = static_cast<int>(floor(beginPos[0]));
+	int iBeginZ = static_cast<int>(floor(beginPos[2]));
+	int iEndX = static_cast<int>(floor(endPos[0]));
+	int iEndZ = static_cast<int>(floor(endPos[2]));
+
+	if (iBeginX == iEndX && iBeginZ == iEndZ)
+	{
+		// The ray will never cross quads within the plane,
+		// so directly process triangles within one quad
+		// (typically, vertical rays should end up here)
+		processTriangles.exec(iBeginX, iEndZ);
+		return;
+	}
+
+	if (m_vboundsGrid.size()==0)
+	{
+		// Process all quads intersecting the flat projection of the ray
+		gridRaycast(processTriangles, beginPos, endPos);
+	}
+	else
+	{
+		btVector3 rayDiff = endPos - beginPos;
+		btScalar flatDistance2 = rayDiff[0] * rayDiff[0] + rayDiff[2] * rayDiff[2];
+		if (flatDistance2 < m_vboundsChunkSize * m_vboundsChunkSize)
+		{
+			// Don't use chunks, the ray is too short in the plane
+			gridRaycast(processTriangles, beginPos, endPos);
+		}
+
+		ProcessVBoundsAction processVBounds(m_vboundsGrid);
+		processVBounds.width = m_vboundsGridWidth;
+		processVBounds.length = m_vboundsGridLength;
+		processVBounds.rayBegin = beginPos;
+		processVBounds.rayEnd = endPos;
+		processVBounds.rayDir = rayDiff.normalized();
+		processVBounds.processTriangles = processTriangles;
+		processVBounds.chunkSize = m_vboundsChunkSize;
+		// The ray is long, run raycast on a higher-level grid
+		gridRaycast(processVBounds, beginPos / m_vboundsChunkSize, endPos / m_vboundsChunkSize);
+	}
+}
+
+/// Builds a grid data structure storing the min and max heights of the terrain in chunks.
+/// if chunkSize is zero, that accelerator is removed.
+/// If you modify the heights, you need to rebuild this accelerator.
+void btHeightfieldTerrainShape::buildAccelerator(int chunkSize)
+{
+	if (chunkSize <= 0)
+	{
+		clearAccelerator();
+		return;
+	}
+
+	m_vboundsChunkSize = chunkSize;
+	int nChunksX = m_heightStickWidth / chunkSize;
+	int nChunksZ = m_heightStickLength / chunkSize;
+
+	if (m_heightStickWidth % chunkSize > 0)
+	{
+		++nChunksX;  // In case terrain size isn't dividable by chunk size
+	}
+	if (m_heightStickLength % chunkSize > 0)
+	{
+		++nChunksZ;
+	}
+
+	if (m_vboundsGridWidth != nChunksX || m_vboundsGridLength != nChunksZ)
+	{
+		clearAccelerator();
+		m_vboundsGridWidth = nChunksX;
+		m_vboundsGridLength = nChunksZ;
+	}
+
+	if (nChunksX == 0 || nChunksZ == 0)
+	{
+		return;
+	}
+
+	// This data structure is only reallocated if the required size changed
+	m_vboundsGrid.resize(nChunksX * nChunksZ);
+	
+	// Compute min and max height for all chunks
+	for (int cz = 0; cz < nChunksZ; ++cz)
+	{
+		int z0 = cz * chunkSize;
+
+		for (int cx = 0; cx < nChunksX; ++cx)
+		{
+			int x0 = cx * chunkSize;
+
+			Range r;
+
+			r.min = getRawHeightFieldValue(x0, z0);
+			r.max = r.min;
+
+			// Compute min and max height for this chunk.
+			// We have to include one extra cell to account for neighbors.
+			// Here is why:
+			// Say we have a flat terrain, and a plateau that fits a chunk perfectly.
+			//
+			//   Left        Right
+			// 0---0---0---1---1---1
+			// |   |   |   |   |   |
+			// 0---0---0---1---1---1
+			// |   |   |   |   |   |
+			// 0---0---0---1---1---1
+			//           x
+			//
+			// If the AABB for the Left chunk did not share vertices with the Right,
+			// then we would fail collision tests at x due to a gap.
+			//
+			for (int z = z0; z < z0 + chunkSize + 1; ++z)
+			{
+				if (z >= m_heightStickLength)
+				{
+					continue;
+				}
+
+				for (int x = x0; x < x0 + chunkSize + 1; ++x)
+				{
+					if (x >= m_heightStickWidth)
+					{
+						continue;
+					}
+
+					btScalar height = getRawHeightFieldValue(x, z);
+
+					if (height < r.min)
+					{
+						r.min = height;
+					}
+					else if (height > r.max)
+					{
+						r.max = height;
+					}
+				}
+			}
+
+			m_vboundsGrid[cx + cz * nChunksX] = r;
+		}
+	}
+}
+
+void btHeightfieldTerrainShape::clearAccelerator()
+{
+	m_vboundsGrid.clear();
+}

src/BulletCollision/CollisionShapes/btHeightfieldTerrainShape.h

@@ -17,6 +17,7 @@ subject to the following restrictions:
 #define BT_HEIGHTFIELD_TERRAIN_SHAPE_H
 
 #include "btConcaveShape.h"
+#include "LinearMath/btAlignedObjectArray.h"
 
 ///btHeightfieldTerrainShape simulates a 2D heightfield terrain
 /**
@@ -71,6 +72,13 @@ subject to the following restrictions:
 ATTRIBUTE_ALIGNED16(class)
 btHeightfieldTerrainShape : public btConcaveShape
 {
+public:
+	struct Range
+	{
+		btScalar min;
+		btScalar max;
+	};
+
 protected:
 	btVector3 m_localAabbMin;
 	btVector3 m_localAabbMax;
@@ -100,9 +108,14 @@ protected:
 
 	btVector3 m_localScaling;
 
+	// Accelerator
+	btAlignedObjectArray<Range> m_vboundsGrid;
+	int m_vboundsGridWidth;
+	int m_vboundsGridLength;
+	int m_vboundsChunkSize;
+
 	virtual btScalar getRawHeightFieldValue(int x, int y) const;
 	void quantizeWithClamp(int* out, const btVector3& point, int isMax) const;
-	void getVertex(int x, int y, btVector3& vertex) const;
 
 	/// protected initialization
 	/**
@@ -155,6 +168,17 @@ public:
 
 	virtual const btVector3& getLocalScaling() const;
 
+	void getVertex(int x, int y, btVector3& vertex) const;
+
+	void performRaycast(btTriangleCallback * callback, const btVector3& raySource, const btVector3& rayTarget) const;
+
+	void buildAccelerator(int chunkSize = 16);
+	void clearAccelerator();
+
+	int getUpAxis() const
+	{
+		return m_upAxis;
+	}
 	//debugging
 	virtual const char* getName() const { return "HEIGHTFIELD"; }
 };

src/BulletCollision/NarrowPhaseCollision/btRaycastCallback.h

@@ -37,6 +37,7 @@ public:
 													 ///SubSimplexConvexCastRaytest is the default, even if kF_None is set.
 		kF_UseSubSimplexConvexCastRaytest = 1 << 2,  // Uses an approximate but faster ray versus convex intersection algorithm
 		kF_UseGjkConvexCastRaytest = 1 << 3,
+		kF_DisableHeightfieldAccelerator  = 1 << 4, //don't use the heightfield raycast accelerator. See https://github.com/bulletphysics/bullet3/pull/2062
 		kF_Terminator = 0xFFFFFFFF
 	};
 	unsigned int m_flags;