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 // Created on: 2016-06-16
 // Created by: Denis BOGOLEPOV & Danila ULYANOV
 // Copyright (c) 2016 OPEN CASCADE SAS
 //
 // This file is part of Open CASCADE Technology software library.
 //
 // This library is free software; you can redistribute it and/or modify it under
 // the terms of the GNU Lesser General Public License version 2.1 as published
 // by the Free Software Foundation, with special exception defined in the file
 // OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
 // distribution for complete text of the license and disclaimer of any warranty.
 //
 // Alternatively, this file may be used under the terms of Open CASCADE
 // commercial license or contractual agreement.
 
 #ifndef _OpenGl_TileSampler_H
 #define _OpenGl_TileSampler_H
 
 #include <OpenGl_Texture.hxx>
 #include <OpenGl_HaltonSampler.hxx>
 
 #include <Image_PixMapTypedData.hxx>
 
 #include <vector>
 
 class Graphic3d_RenderingParams;
 
 //! Tool object used for sampling screen tiles according to estimated pixel variance (used in path tracing engine).
 //! To improve GPU thread coherency, rendering window is split into pixel blocks or tiles. The important feature of
 //! this approach is that it is possible to keep the same number of tiles for any screen resolution (e.g. 256 tiles
 //! can be used for both 512 x 512 window and 1920 x 1080 window). So, a smaller number of tiles allows to increase
 //! interactivity (FPS), but at the cost of higher per-frame variance ('noise'). On the contrary a larger number of
 //! tiles decrease interactivity, but leads to lower per-frame variance. Note that the total time needed to produce
 //! final final image is the same for both cases.
 class OpenGl_TileSampler
 {
 public:
 
   //! Creates new tile sampler.
   Standard_EXPORT OpenGl_TileSampler();
 
   //! Size of individual tile in pixels.
   Graphic3d_Vec2i TileSize() const { return Graphic3d_Vec2i (myTileSize, myTileSize); }
 
   //! Scale factor for quantization of visual error (float) into signed integer.
   float VarianceScaleFactor() const { return myScaleFactor; }
 
   //! Returns number of tiles in X dimension.
   int NbTilesX() const { return (int)myTiles.SizeX; }
 
   //! Returns number of tiles in Y dimension.
   int NbTilesY() const { return (int)myTiles.SizeY; }
 
   //! Returns total number of tiles in viewport.
   int NbTiles() const { return int(myTiles.SizeX * myTiles.SizeY); }
 
   //! Returns ray-tracing viewport.
   const Graphic3d_Vec2i& ViewSize() const { return myViewSize; }
 
   //! Number of tiles within offsets texture.
   Graphic3d_Vec2i NbOffsetTiles (bool theAdaptive) const
   {
     return theAdaptive
          ? Graphic3d_Vec2i ((int )myOffsetsShrunk.SizeX, (int )myOffsetsShrunk.SizeY)
          : Graphic3d_Vec2i ((int )myOffsets.SizeX,       (int )myOffsets.SizeY);
   }
 
   //! Maximum number of tiles within offsets texture.
   Graphic3d_Vec2i NbOffsetTilesMax() const { return NbOffsetTiles (true).cwiseMax (NbOffsetTiles (false)); }
 
   //! Viewport for rendering using offsets texture.
   Graphic3d_Vec2i OffsetTilesViewport (bool theAdaptive) const { return NbOffsetTiles (theAdaptive) * myTileSize; }
 
   //! Maximum viewport for rendering using offsets texture.
   Graphic3d_Vec2i OffsetTilesViewportMax() const { return NbOffsetTilesMax() * myTileSize; }
 
   //! Return maximum number of samples per tile.
   int MaxTileSamples() const
   {
     int aNbSamples = 0;
     for (Standard_Size aRowIter = 0; aRowIter < myTiles.SizeY; ++aRowIter)
     {
       for (Standard_Size aColIter = 0; aColIter < myTiles.SizeX; ++aColIter)
       {
         aNbSamples = Max (aNbSamples, myTiles.Value (aRowIter, aColIter));
       }
     }
     return aNbSamples;
   }
 
   //! Specifies size of ray-tracing viewport and recomputes tile size.
   Standard_EXPORT void SetSize (const Graphic3d_RenderingParams& theParams,
                                 const Graphic3d_Vec2i& theSize);
 
   //! Fetches current error estimation from the GPU and
   //! builds 2D discrete distribution for tile sampling.
   Standard_EXPORT void GrabVarianceMap (const Handle(OpenGl_Context)& theContext,
                                         const Handle(OpenGl_Texture)& theTexture);
 
   //! Resets (restart) tile sampler to initial state.
   void Reset() { myLastSample = 0; }
 
   //! Uploads tile samples to the given OpenGL texture.
   bool UploadSamples (const Handle(OpenGl_Context)& theContext,
                       const Handle(OpenGl_Texture)& theSamplesTexture,
                       const bool theAdaptive)
   {
     return upload (theContext, theSamplesTexture, Handle(OpenGl_Texture)(), theAdaptive);
   }
 
   //! Uploads offsets of sampled tiles to the given OpenGL texture.
   bool UploadOffsets (const Handle(OpenGl_Context)& theContext,
                       const Handle(OpenGl_Texture)& theOffsetsTexture,
                       const bool theAdaptive)
   {
     return upload (theContext, Handle(OpenGl_Texture)(), theOffsetsTexture, theAdaptive);
   }
 
 protected:
 
   //! Returns number of pixels in the given tile.
   int tileArea (int theX, int theY) const
   {
     const int aSizeX = Min (myTileSize, myViewSize.x() - theX * myTileSize);
     const int aSizeY = Min (myTileSize, myViewSize.y() - theY * myTileSize);
     return aSizeX * aSizeY;
   }
 
   //! Samples tile location according to estimated error.
   Standard_EXPORT Graphic3d_Vec2i nextTileToSample();
 
   //! Uploads offsets of sampled tiles to the given OpenGL texture.
   Standard_EXPORT bool upload (const Handle(OpenGl_Context)& theContext,
                                const Handle(OpenGl_Texture)& theSamplesTexture,
                                const Handle(OpenGl_Texture)& theOffsetsTexture,
                                const bool theAdaptive);
 
   //! Auxiliary method for dumping 2D image map into stream (e.g. for debugging).
   Standard_EXPORT void dumpMap (std::ostream& theStream,
                                 const Image_PixMapTypedData<int>& theMap,
                                 const char* theTitle) const;
 
 protected:
 
   Image_PixMapTypedData<unsigned int>    myTiles;         //!< number of samples per tile (initially all 1)
   Image_PixMapTypedData<unsigned int>    myTileSamples;   //!< number of samples for all pixels within the tile (initially equals to Tile area)
   Image_PixMapTypedData<float>           myVarianceMap;   //!< Estimation of visual error per tile
   Image_PixMapTypedData<int>             myVarianceRaw;   //!< Estimation of visual error per tile (raw data)
   Image_PixMapTypedData<Graphic3d_Vec2i> myOffsets;       //!< 2D array of tiles redirecting to another tile
   Image_PixMapTypedData<Graphic3d_Vec2i> myOffsetsShrunk; //!< 2D array of tiles redirecting to another tile (shrunk)
   std::vector<float>                     myMarginalMap;   //!< Marginal distribution of 2D error map
   OpenGl_HaltonSampler                   mySampler;       //!< Halton sequence generator
   unsigned int                           myLastSample;    //!< Index of generated sample
   float                                  myScaleFactor;   //!< scale factor for quantization of visual error (float) into signed integer
   int                                    myTileSize;      //!< tile size
   Graphic3d_Vec2i                        myViewSize;      //!< ray-tracing viewport
 
 };
 
 #endif // _OpenGl_TileSampler_H

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