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 // Created by: Kirill GAVRILOV
 // Copyright (c) 2013-2014 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_VertexBufferEditor_HeaderFile
 #define OpenGl_VertexBufferEditor_HeaderFile
 
 #include <OpenGl_Buffer.hxx>
 #include <OpenGl_Context.hxx>
 
 #include <NCollection_Array1.hxx>
 
 //! Auxiliary class to iteratively modify data of existing VBO.
 //! It provides iteration interface with delayed CPU->GPU memory transfer to avoid slow per-element
 //! data transfer. User should explicitly call Flush() method to ensure that all data is transferred
 //! to VBO. Temporary buffer on CPU side can be initialized with lesser capacity than  VBO to allow
 //! re-usage of shared buffer with fixed size between VBOs.
 //!
 //! You should use NCollection_Vec2/NCollection_Vec3/NCollection_Vec4 with appropriate length
 //! to instantiate this template and access elements in VBO.
 //!
 //! Notice that this technique designed for VBO streaming scenarios (when VBO is modified from time
 //! to time). Also this class doesn't retrieve existing data from VBO - data transferred only in one
 //! direction! In case of static data this is preferred to upload it within one call during VBO
 //! initialization.
 template <typename theVec_t>
 class OpenGl_VertexBufferEditor
 {
 
 public:
   //! Creates empty editor
   //! theTmpBufferLength[in]  temporary buffer length
   explicit OpenGl_VertexBufferEditor(const Standard_Integer theTmpBufferLength = 0)
       : myElemFrom(0),
         myElemsNb(0),
         myTmpBuffer(0, theTmpBufferLength > 0 ? (theTmpBufferLength - 1) : 2047)
   {
   }
 
   //! Creates empty editor
   //! theTmpBuffer[in]        pointer to temporary buffer
   //! theTmpBufferLength[in]  temporary buffer length
   OpenGl_VertexBufferEditor(theVec_t* theTmpBuffer, const Standard_Integer theTmpBufferLength)
       : myElemFrom(0),
         myElemsNb(0),
         myTmpBuffer(theTmpBuffer[0], 0, theTmpBufferLength - 1)
   {
   }
 
   //! Initialize editor for specified buffer object.
   //! theGlCtx[in]  bound OpenGL context to edit buffer object
   //! theVbo[in]    buffer to edit
   Standard_Boolean Init(const Handle(OpenGl_Context)& theGlCtx, const Handle(OpenGl_Buffer)& theVbo)
   {
     myGlCtx = theGlCtx;
     myVbo   = theVbo;
     if (myGlCtx.IsNull() || myVbo.IsNull() || !myVbo->IsValid()
         || myVbo->GetComponentsNb() != GLuint(theVec_t::Length()))
     {
       return Standard_False;
     }
 
     myElemFrom = myElemsNb = 0;
     return Standard_True;
   }
 
   //! Modify current element in VBO.
   theVec_t& Value() { return myTmpBuffer.ChangeValue(myElemsNb); }
 
   //! Move to the next position in VBO.
   Standard_Boolean Next()
   {
     if (++myElemsNb > myTmpBuffer.Upper())
     {
       return Flush();
     }
     return Standard_True;
   }
 
   //! Push current data from local buffer to VBO.
   Standard_Boolean Flush()
   {
     if (myElemsNb <= 0)
     {
       return Standard_True;
     }
 
     if (myVbo.IsNull() || !myVbo->SubData(myGlCtx, myElemFrom, myElemsNb, &myTmpBuffer.Value(0)[0]))
     {
       // should never happens
       return Standard_False;
     }
     myElemFrom += myElemsNb;
     myElemsNb = 0;
 
     return Standard_True;
   }
 
   //! @return assigned VBO
   const Handle(OpenGl_Buffer)& GetVBO() const { return myVbo; }
 
 private:
   Handle(OpenGl_Context)       myGlCtx;     //!< handle to current OpenGL context
   Handle(OpenGl_Buffer)        myVbo;       //!< edited VBO
   Standard_Integer             myElemFrom;  //!< element in VBO to upload from
   Standard_Integer             myElemsNb;   //!< current element in temporary buffer
   NCollection_Array1<theVec_t> myTmpBuffer; //!< temporary array
 };
 
 #endif // _OpenGl_VertexBufferEditor_H__

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