[转]使用RenderQueueListener针对不同的渲染组改变摄像机的裁剪面

http://ogre3d.org/forums/viewtopic.php?f=2&t=30450

I am currently working on a small project where I have to render objects back-to-front, and clear the depth buffer between each rendered object. After some digging on the wiki and the forum, I was led to believe that a combination of a frame listener and render queue listeners (one for each object rendered) would be able to solve this problem.

Basically, what I have done is this:
I have one registered frame listener, that is responsible for sorting a list of the objects to be rendered in back-to-front order. Each object also has its own render queue listener, that is added to the scene manager on start-up, and the frame listener sets the render queue group ID of each listener in ascending order (one unique id per object) after sorting the list.
The code of the frame listener is tested, and appears to be working as intended (far away objects in the beginning of the list, with low render queue group ID's).

The render queue listener, in turn, tests if queueGroupID = id, and if so calculates the near and far clipping distances needed to be able to render the object without clipping it, set the camera's clipping distances to these values and then clear the depth buffer:

class CCustomRenderQueueListener : public Ogre::RenderQueueListener
{
  void CObject::RenderQueueListener::renderQueueStarted(uint8 queueGroupID, const String &, bool &)
  {
    if (queueGroupId == id)
    {
      oldNear = cam->getNearClipDistance();
      oldFar = cam->getFarClipDistance();
 
      // Calculate near and far clipping distances here
 
      cam->setFarClipDistance(farClip);
      cam->setNearClipDistance(nearClip);
      Root::getSingleton().getRenderSystem()->clearFrameBuffer(FBT_DEPTH);
    }
  }
 
  void CCustomRenderQueueListener::renderQueueEnded(uint8 queueGroupId, const String &, bool &)
  {
    if (queueGroupId == id)
    {
      cam->setNearClipDistance(oldNear);
      cam->setFarClipDistance(oldFar);
    }
  }
 
  // Some other stuff here
};

在ogre初始后将RenderQueueListener添加到场景管理器中。

…

// 设置RenderQueueListener
CCustomRenderQueueListener* pCustomRenderQueueListener = new CCustomRenderQueueListener;
m_pSceneManager->addRenderQueueListener(pCustomRenderQueueListener);

…