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 // Created by: Kirill GAVRILOV
 // Copyright (c) 2014 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_BufferCompatT_HeaderFile
 #define _OpenGl_BufferCompatT_HeaderFile
 
 #include <NCollection_Buffer.hxx>
 #include <OpenGl_Buffer.hxx>
 
 //! Compatibility layer for old OpenGL without VBO.
 //! Make sure to pass pointer from GetDataOffset() instead of NULL.
 //! Method GetDataOffset() returns pointer to real data in this class
 //! (while base class OpenGl_VertexBuffer always return NULL).
 //!
 //! Methods Bind()/Unbind() do nothing (do not affect OpenGL state)
 //! and ::GetTarget() is never used.
 //! For this reason there is no analog for OpenGl_IndexBuffer.
 //! Just pass GetDataOffset() to glDrawElements() directly as last argument.
 //!
 //! Class overrides methods init() and subData() to copy data into own memory buffer.
 //! Extra method initLink() might be used to pass existing buffer through handle without copying the
 //! data.
 //!
 //! Method Create() creates dummy identifier for this object which should NOT be passed to OpenGL
 //! functions.
 template <class BaseBufferT>
 class OpenGl_BufferCompatT : public BaseBufferT
 {
 
 public:
   //! Create uninitialized VBO.
   OpenGl_BufferCompatT()
   {
     //
   }
 
   //! Destroy object.
   ~OpenGl_BufferCompatT() override { Release(nullptr); }
 
   //! Return TRUE.
   bool IsVirtual() const override { return true; }
 
   //! Creates VBO name (id) if not yet generated.
   //! Data should be initialized by another method.
   inline bool Create(const occ::handle<OpenGl_Context>& theGlCtx) override;
 
   //! Destroy object - will release memory if any.
   inline void Release(OpenGl_Context* theGlCtx) override;
 
   //! Bind this VBO.
   void Bind(const occ::handle<OpenGl_Context>&) const override
   {
     //
   }
 
   //! Unbind this VBO.
   void Unbind(const occ::handle<OpenGl_Context>&) const override
   {
     //
   }
 
 public: //! @name advanced methods
   //! Initialize buffer with existing data.
   //! Data will NOT be copied by this method!
   inline bool initLink(const occ::handle<NCollection_Buffer>& theData,
                        const unsigned int                     theComponentsNb,
                        const int                              theElemsNb,
                        const unsigned int                     theDataType);
 
   //! Initialize buffer with new data (data will be copied).
   inline bool init(const occ::handle<OpenGl_Context>& theGlCtx,
                    const unsigned int                 theComponentsNb,
                    const int                          theElemsNb,
                    const void*                        theData,
                    const unsigned int                 theDataType,
                    const int                          theStride) override;
 
   //! Update part of the buffer with new data.
   inline bool subData(const occ::handle<OpenGl_Context>& theGlCtx,
                       const int                          theElemFrom,
                       const int                          theElemsNb,
                       const void*                        theData,
                       const unsigned int                 theDataType) override;
 
   //! Read back buffer sub-range.
   inline bool getSubData(const occ::handle<OpenGl_Context>& theGlCtx,
                          const int                          theElemFrom,
                          const int                          theElemsNb,
                          void*                              theData,
                          const unsigned int                 theDataType) override;
 
 protected:
   occ::handle<NCollection_Buffer> myData; //!< buffer data
 };
 
 //=================================================================================================
 
 template <class BaseBufferT>
 bool OpenGl_BufferCompatT<BaseBufferT>::Create(const occ::handle<OpenGl_Context>&)
 {
   if (BaseBufferT::myBufferId == OpenGl_Buffer::NO_BUFFER)
   {
     BaseBufferT::myBufferId = (unsigned int)-1; // dummy identifier...
     myData                  = new NCollection_Buffer(Graphic3d_Buffer::DefaultAllocator());
   }
   return BaseBufferT::myBufferId != OpenGl_Buffer::NO_BUFFER;
 }
 
 //=================================================================================================
 
 template <class BaseBufferT>
 void OpenGl_BufferCompatT<BaseBufferT>::Release(OpenGl_Context*)
 {
   if (BaseBufferT::myBufferId == OpenGl_Buffer::NO_BUFFER)
   {
     return;
   }
 
   BaseBufferT::myOffset   = nullptr;
   BaseBufferT::myBufferId = OpenGl_Buffer::NO_BUFFER;
   myData.Nullify();
 }
 
 //=================================================================================================
 
 template <class BaseBufferT>
 bool OpenGl_BufferCompatT<BaseBufferT>::initLink(const occ::handle<NCollection_Buffer>& theData,
                                                  const unsigned int theComponentsNb,
                                                  const int          theElemsNb,
                                                  const unsigned int theDataType)
 {
   if (theData.IsNull())
   {
     BaseBufferT::myOffset = nullptr;
     return false;
   }
 
   if (BaseBufferT::myBufferId == OpenGl_Buffer::NO_BUFFER)
   {
     BaseBufferT::myBufferId = (unsigned int)-1; // dummy identifier...
   }
   myData                      = theData;
   BaseBufferT::myDataType     = theDataType;
   BaseBufferT::myComponentsNb = theComponentsNb;
   BaseBufferT::myElemsNb      = theElemsNb;
   BaseBufferT::myOffset       = myData->ChangeData();
   return true;
 }
 
 //=================================================================================================
 
 template <class BaseBufferT>
 bool OpenGl_BufferCompatT<BaseBufferT>::init(const occ::handle<OpenGl_Context>& theCtx,
                                              const unsigned int                 theComponentsNb,
                                              const int                          theElemsNb,
                                              const void*                        theData,
                                              const unsigned int                 theDataType,
                                              const int                          theStride)
 {
   if (!Create(theCtx))
   {
     BaseBufferT::myOffset = nullptr;
     return false;
   }
 
   BaseBufferT::myDataType     = theDataType;
   BaseBufferT::myComponentsNb = theComponentsNb;
   BaseBufferT::myElemsNb      = theElemsNb;
 
   const size_t aNbBytes = size_t(BaseBufferT::myElemsNb) * theStride;
   if (!myData->Allocate(aNbBytes))
   {
     BaseBufferT::myOffset = nullptr;
     return false;
   }
 
   BaseBufferT::myOffset = myData->ChangeData();
   if (theData != nullptr)
   {
     memcpy(myData->ChangeData(), theData, aNbBytes);
   }
   return true;
 }
 
 //=================================================================================================
 
 template <class BaseBufferT>
 bool OpenGl_BufferCompatT<BaseBufferT>::subData(const occ::handle<OpenGl_Context>&,
                                                 const int          theElemFrom,
                                                 const int          theElemsNb,
                                                 const void*        theData,
                                                 const unsigned int theDataType)
 {
   if (!BaseBufferT::IsValid() || BaseBufferT::myDataType != theDataType || theElemFrom < 0
       || ((theElemFrom + theElemsNb) > BaseBufferT::myElemsNb))
   {
     return false;
   }
   else if (theData == nullptr)
   {
     return true;
   }
 
   const size_t aDataSize = BaseBufferT::sizeOfGlType(theDataType);
   const size_t anOffset  = size_t(theElemFrom) * size_t(BaseBufferT::myComponentsNb) * aDataSize;
   const size_t aNbBytes  = size_t(theElemsNb) * size_t(BaseBufferT::myComponentsNb) * aDataSize;
   memcpy(myData->ChangeData() + anOffset, theData, aNbBytes);
   return true;
 }
 
 //=================================================================================================
 
 template <class BaseBufferT>
 bool OpenGl_BufferCompatT<BaseBufferT>::getSubData(const occ::handle<OpenGl_Context>&,
                                                    const int          theElemFrom,
                                                    const int          theElemsNb,
                                                    void*              theData,
                                                    const unsigned int theDataType)
 {
   if (!BaseBufferT::IsValid() || BaseBufferT::myDataType != theDataType || theElemFrom < 0
       || ((theElemFrom + theElemsNb) > BaseBufferT::myElemsNb) || theData == nullptr)
   {
     return false;
   }
 
   const size_t aDataSize = BaseBufferT::sizeOfGlType(theDataType);
   const size_t anOffset  = size_t(theElemFrom) * size_t(BaseBufferT::myComponentsNb) * aDataSize;
   const size_t aNbBytes  = size_t(theElemsNb) * size_t(BaseBufferT::myComponentsNb) * aDataSize;
   memcpy(theData, myData->Data() + anOffset, aNbBytes);
   return true;
 }
 
 #endif // _OpenGl_VertexBufferCompat_HeaderFile

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