====== Irrlicht Particle System （irrlicht粒子系统）======
===== 使用流程 =====
  auto particles = scene->addParticleSystemSceneNode(false,n);//创建粒子节点
  auto emitter = particles->createXXXEmitter(...);//创建发射器
  
  particles->setEmitter(emitter);//设置发射器
  
  particles->setParticlesAreGlobal(false);//粒子不受场景节点运动影响，可选
  
  emitter->drop(); 
  
  auto delAct=scene->createDeleteAnimator(1000);//添加删除动作，使发射器在指定毫秒后消失，可选
  particles->addAnimator(delAct);//应用删除动作
  delAct->drop();
===== setParticlesAreGlobal =====
文档原文:  \\
Sets if the particles should be global.  \\
If they are, the particles are affected by the movement of the particle system scene node too, otherwise they completely ignore it. Default is true.   \\
意思就是，设置为true，粒子将受场景节点移动影响
==== 底层原理（来自于irrlicht源码）: ====
  if (ParticlesAreGlobal)
  AbsoluteTransformation.transformVect(Particles[i].pos);//设置为true，节点的绝对矩阵将会乘以粒子的位置
	if ( !(behavior & EPB_EMITTER_VECTOR_IGNORE_ROTATION) )
	{
		if (!ParticlesAreGlobal)
			AbsoluteTransformation.rotateVect(Particles[i].pos);
		AbsoluteTransformation.rotateVect(Particles[i].startVector);
		AbsoluteTransformation.rotateVect(Particles[i].vector);
	}