如何將MyGUI Render到Ogre3d' compositor的RTT

由於看到Ogre Add-ons Forum的相關討論文章，於是開啟了Render MyGUI to compositor's rtt之旅Howto render MyGUI after OGRE's compositor?

檢視一下MyGUI這一段有關RenderGUI的Code，可以發現它除了Main window viewport之外，會過濾掉所view port所要求的render queue事件，原始碼如下：
void OgreRenderManager::renderQueueStarted(Ogre::uint8 queueGroupId, const Ogre::String& invocation, bool& skipThisInvocation)
{
if(skipThisInvocation)
return;

Gui* gui = Gui::getInstancePtr();
if (gui == nullptr)
return;

if (Ogre::RENDER_QUEUE_OVERLAY != queueGroupId)
return;

if(m_pInterface)
{
if(m_pInterface->IsSkipRender(queueGroupId, invocation, skipThisInvocation))
return;
}
else
{
Ogre::Viewport* viewport = mSceneManager->getCurrentViewport();
if (nullptr == viewport
|| !viewport->getOverlaysEnabled())
return;

if (mWindow->getNumViewports() <= mActiveViewport
|| viewport != mWindow->getViewport(mActiveViewport))
return;
}

mCountBatch = 0;

static Timer timer;
static unsigned long last_time = timer.getMilliseconds();
unsigned long now_time = timer.getMilliseconds();
unsigned long time = now_time - last_time;
onFrameEvent((float)((double)(time) / (double)1000));

last_time = now_time;

//begin();
setManualRender(true);
onRenderToTarget(this, mUpdate);
//end();

// сбрасываем флаг
mUpdate = false;
}

解決方案有兩個：

1. 參考MyGUI's的RTT example，將其Render到Ogre3d compositor's RTT（但這樣可能會造成Render兩次的問題-Main window viewport and RTT）。
2. 自行設計Filter viewport 介面，Filter viewport實作導到外面。
   範例程式如下：
   ...
   if(m_pInterface)
   {
   if(m_pInterface->IsSkipRender(queueGroupId, invocation, kipThisInvocation))
          {
   return;
          }
   else
         {
                  Ogre::Viewport* viewport = mSceneManager->getCurrentViewport();
                  if (nullptr == viewport || !viewport->getOverlaysEnabled())
   return;
                  if (mWindow->getNumViewports() <= mActiveViewport
                        || viewport != mWindow->getViewport(mActiveViewport))
                          return;
         }
   }
   ...
   //IsSkipRender的實作：
   bool CPostEffectManager::IsSkipRender(Ogre::uint8 queueGroupId, const Ogre::String& invocation, bool& skipThisInvocation)
   {
   Ogre::SceneManager* pSceneManager =
           Ogre::Root::getSingleton()._getCurrentSceneManager();
   if(!pSceneManager)
   return true;
   Ogre::Viewport* viewport = pSceneManager->getCurrentViewport();
   if(!viewport)
   return true;
   Ogre::RenderTarget* pRenderTarget = viewport->getTarget();
   if(!pRenderTarget)
   return true;
   const std::string& strTargetName = pRenderTarget->getName();
   
   //check is other custom rtt
   if(strTargetName.find("MainWindow") == std::string::npos)
   return true;
   
   //is main window viewport
   if(strTargetName == "MainWindow")
   return m_bEnableAnyState;
   
   //post effet rtt block
   return false;
   }

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