void FakeShadow::nodeUpdated(const Ogre::Node* node)
{
  //如果位置没有被改变则不需要重新得到地面的法线
  if(m_LastPos != node->getPosition())
  {
    m_LastPos = node->getPosition();
    m_pSceneNode->setPosition(node->getPosition()+Ogre::Vector3(0, 0.05, 0));

Ogre::Vector3 newNormal = getTerrainNormal(node);

//将影子片面旋转到朝向法线
    Ogre::Vector3 s(0, 1, 0);
    Ogre::Quaternion quat = s.getRotationTo(newNormal);
    m_pSceneNode->setOrientation(quat);
  }
}

Ogre::Vector3 FakeShadow::getTerrainNormal(const Ogre::Node* node)
{
  //得到法线策略如下
  //从当前位置周围放出三条射线（近似构成正三角形）
  //得到三个点交点，其构成三角形
  //求其三角形的法线，即位当前位置地形的法线

Ogre::Vector3 originPos1 = node->getPosition() + Ogre::Vector3(0, 1000, 0.5);
  Ogre::Vector3 originPos2 = node->getPosition() + Ogre::Vector3(0.3, 1000, -0.15);
  Ogre::Vector3 originPos3 = node->getPosition() + Ogre::Vector3(-0.3, 1000, -0.15);

Ogre::Vector3 intersectP1 = originPos1;
  Ogre::Vector3 intersectP2 = originPos2;
  Ogre::Vector3 intersectP3 = originPos3;
  intersectP1.y = node->getPosition().y;
  intersectP2.y = node->getPosition().y;
  intersectP3.y = node->getPosition().y;

m_pDScene->intersectWithRay(Ogre::Ray(originPos1, Ogre::Vector3::NEGATIVE_UNIT_Y), intersectP1);
  m_pDScene->intersectWithRay(Ogre::Ray(originPos2, Ogre::Vector3::NEGATIVE_UNIT_Y), intersectP2);
  m_pDScene->intersectWithRay(Ogre::Ray(originPos3, Ogre::Vector3::NEGATIVE_UNIT_Y), intersectP3);

return Ogre::Math::calculateBasicFaceNormal(intersectP1, intersectP2, intersectP3);
}