source: downloads/ogre_src_v1-9-0/OgreMain/include/OgreHardwareOcclusionQuery.h

/*
-----------------------------------------------------------------------------
This source file is part of OGRE
    (Object-oriented Graphics Rendering Engine)
For the latest info, see http://www.ogre3d.org

Copyright (c) 2000-2013 Torus Knot Software Ltd

Permission is hereby granted, free of charge, to any person obtaining a copy
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The above copyright notice and this permission notice shall be included in
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THE SOFTWARE.
-----------------------------------------------------------------------------
*/
#ifndef _HardwareOcclusionQuery__
#define _HardwareOcclusionQuery__

// Precompiler options
#include "OgrePrerequisites.h"

namespace Ogre {



        /** \addtogroup Core
        *  @{
        */
        /** \addtogroup RenderSystem
        *  @{
        */
/**
  * This is a abstract class that that provides the interface for the query class for 
  * hardware occlusion.
  *
  * @author Lee Sandberg
  * Updated on 13/8/2005 by Tuan Kuranes email: tuan.kuranes@free.fr
  */
        class _OgreExport HardwareOcclusionQuery : public RenderSysAlloc
{
//----------------------------------------------------------------------
// Public methods
//--
public:
        /**
          * Object public member functions
          */

        /**
          * Default object constructor
          * 
          */
        HardwareOcclusionQuery();

        /**
          * Object destructor
          */
        virtual ~HardwareOcclusionQuery();

        /**
          * Starts the hardware occlusion query
          * @remarks    Simple usage: Create one or more OcclusionQuery object one per outstanding query or one per tested object 
          *                             OcclusionQuery* mOcclusionQuery;
          *                             createOcclusionQuery( &mOcclusionQuery );
          *                             In the rendering loop:
          *                             Draw all occluders
          *                             mOcclusionQuery->startOcclusionQuery();
          *                             Draw the polygons to be tested
          *                             mOcclusionQuery->endOcclusionQuery();
          *
          *                             Results must be pulled using:
          *                             UINT    mNumberOfPixelsVisable;
          *                             pullOcclusionQuery( &mNumberOfPixelsVisable );
          *                     
          */
        virtual void beginOcclusionQuery() = 0;

        /**
          * Ends the hardware occlusion test
          */
        virtual void endOcclusionQuery() = 0;

        /**
      * Pulls the hardware occlusion query.
          * @note Waits until the query result is available; use isStillOutstanding
          *             if just want to test if the result is available.
      * @retval NumOfFragments will get the resulting number of fragments.
      * @return True if success or false if not.
      */
        virtual bool pullOcclusionQuery(unsigned int* NumOfFragments) = 0;

        /**
          * Let's you get the last pixel count with out doing the hardware occlusion test
          * @return The last fragment count from the last test.
          * Remarks This function won't give you new values, just the old value.
          */
        unsigned int getLastQuerysPixelcount() const { return mPixelCount; }

        /**
          * Lets you know when query is done, or still be processed by the Hardware
          * @return true if query isn't finished.
          */
         virtual bool isStillOutstanding(void) = 0; 


    //----------------------------------------------------------------------
    // protected members
    //--
    protected :
        /// Number of visible pixels determined by last query
        unsigned int mPixelCount;
        /// Has the query returned a result yet?
                bool             mIsQueryResultStillOutstanding;
};

        /** @} */
        /** @} */
}
#endif