/// Ajout du terrain à la scene.
ITexture *texture=driver->getTexture("media/terrain.png");
ITerrainSceneNode *terrain=smgr->addTerrainSceneNode(texture->getName(), 0 , -1, vector3df(0.0f, 0.0f, 0.0f), vector3df(0.0f, 0.0f, 0.0f), vector3df(1.0f, 1.0f, 1.0f));

terrain->setMaterialFlag(EMF_LIGHTING, false);
terrain->setMaterialTexture(0, driver->getTexture("media/terrain.png"));
terrain->setPosition(vector3df(0.0f, 0.0f, 0.0f));
terrain->setScale(vector3df(4.0f, 1.0f, 4.0f));

 /// btHeightfieldTerrainShape.
vector3df scale=terrain->getScale();
aabbox3d<f32> box=terrain->getBoundingBox();
const vector3df size=box.getExtent()/scale;
f32 minHeight=((ITerrainSceneNode*)terrain)->getHeight(0, 0);
f32 maxHeight=minHeight;

int arraySize=texture->getSize().Height;
///f32 heightData[512*arraySize];
f32 heightData[512*arraySize];
const f32 stepWidthX=size.X/arraySize;
const f32 stepWidthZ=size.Z/arraySize;

u32 runVal=0;

vector3df minEdge=box.MinEdge/scale;
vector3df maxEdge=box.MaxEdge/scale;

 //Récupération du min et du max de la hauteur du terrain
for(f32 z=minEdge.Z; z<maxEdge.Z; z+=stepWidthZ)
{
    for(f32 x=minEdge.X; x<maxEdge.X; x+=stepWidthX)
    {
        const f32 curVal=((ITerrainSceneNode*)terrain)->getHeight(x, z);

        heightData[runVal++]=curVal;

        if(curVal>maxHeight){maxHeight=curVal;}
        if(curVal<minHeight){minHeight=curVal;}
    }
}

f32 *heightDataPtr=heightData;

  // Collision Objects.   
btCollisionShape *groundShape=new btHeightfieldTerrainShape(arraySize, arraySize, heightDataPtr, 1.f, minHeight, maxHeight, 1, PHY_FLOAT, false);
//btCollisionShape * groundShape = new btHeightfieldTerrainShape(512, 512, heightDataPtr, 1.f, minHeight, maxHeight, 1, PHY_FLOAT, true);

groundShape->setLocalScaling(btVector3(4.0f, 1.0f, 4.0f));
//btCollisionShape *sphereShape= new btSphereShape(10);

 // Ground Motion State.
btTransform transform;
transform.setIdentity();
transform.setOrigin(btVector3(0.0f, 0.0f, 0.0f));
btDefaultMotionState *groundMotionState=new btDefaultMotionState(transform);

  // Ground Rigid Body.
btRigidBody::btRigidBodyConstructionInfo groundRigidBodyCI(0, groundMotionState, groundShape, btVector3(0, 0, 0));
btRigidBody *groundRigidBody=new btRigidBody(groundRigidBodyCI);
groundRigidBody->setUserPointer((void *)terrain);

  // Adding ground rigid body to the world.
World->addRigidBody(groundRigidBody);

static bool myCustomMaterialCombinerCallback(
    btManifoldPoint& cp,
    const btCollisionObjectWrapper* colObj0Wrap,
    int partId0,
    int index0,
    const btCollisionObjectWrapper* colObj1Wrap,
    int partId1,
    int index1
    )
{
    // one-sided triangles
   if (colObj1Wrap->getCollisionShape()->getShapeType() == TRIANGLE_SHAPE_PROXYTYPE)
    {
        auto triShape = static_cast<const btTriangleShape*>( colObj1Wrap->getCollisionShape() );
        const btVector3* v = triShape->m_vertices1;
        btVector3 faceNormalLs = btCross(v[1] - v[0], v[2] - v[0]);
        faceNormalLs.normalize();
        btVector3 faceNormalWs = colObj1Wrap->getWorldTransform().getBasis() * faceNormalLs;
        float nDotF = btDot( faceNormalWs, cp.m_normalWorldOnB );
        if ( nDotF <= 0.0f )
        {
            // flip the contact normal to be aligned with the face normal
            cp.m_normalWorldOnB += -2.0f * nDotF * faceNormalWs;
        }
    }

    //this return value is currently ignored, but to be on the safe side: return false if you don't calculate friction
    return false;
}

void BulletPhysics::init()
{
    // somewhere in your init code you need to setup the callback
    gContactAddedCallback = myCustomMaterialCombinerCallback;
}