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 // Created on: 2014-09-15
 // Created by: Denis BOGOLEPOV
 // 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 _BVH_QueueBuilder_Header
 #define _BVH_QueueBuilder_Header
 
 #include <BVH_Builder.hxx>
 #include <BVH_BuildThread.hxx>
 #include <NCollection_DynamicArray.hxx>
 
 #include <mutex>
 
 //! Abstract BVH builder based on the concept of work queue.
 //! Queue based BVH builders support parallelization with a
 //! fixed number of threads (maximum efficiency is achieved
 //! by setting the number of threads equal to the number of
 //! CPU cores plus one). Note that to support parallel mode,
 //! a corresponding BVH primitive set should provide thread
 //! safe implementations of interface functions (e.g., Swap,
 //! Box, Center). Otherwise, the results will be undefined.
 //! \tparam T Numeric data type
 //! \tparam N Vector dimension
 template <class T, int N>
 class BVH_QueueBuilder : public BVH_Builder<T, N>
 {
 public:
   //! Creates new BVH queue based builder.
   BVH_QueueBuilder(const int theLeafNodeSize,
                    const int theMaxTreeDepth,
                    const int theNumOfThreads = 1)
       : BVH_Builder<T, N>(theLeafNodeSize, theMaxTreeDepth),
         myNumOfThreads(theNumOfThreads)
   {
   }
 
   //! Releases resources of BVH queue based builder.
   ~BVH_QueueBuilder() override = default;
 
 public:
   //! Builds BVH using specific algorithm.
   void Build(BVH_Set<T, N>*       theSet,
              BVH_Tree<T, N>*      theBVH,
              const BVH_Box<T, N>& theBox) const override;
 
 protected:
   //! Stores range of primitives belonging to a BVH node.
   struct BVH_PrimitiveRange
   {
     int Start;
     int Final;
 
     //! Creates new primitive range.
     BVH_PrimitiveRange(int theStart = -1, int theFinal = -1)
         : Start(theStart),
           Final(theFinal)
     {
       //
     }
 
     //! Returns total number of primitives.
     int Size() const { return Final - Start + 1; }
 
     //! Checks if the range is initialized.
     bool IsValid() const { return Start != -1; }
   };
 
   //! Stores parameters of constructed child nodes.
   struct BVH_ChildNodes
   {
     //! Bounding boxes of child nodes.
     BVH_Box<T, N> Boxes[2];
 
     //! Primitive ranges of child nodes.
     BVH_PrimitiveRange Ranges[2];
 
     //! Creates new parameters of BVH child nodes.
     BVH_ChildNodes() = default;
 
     //! Creates new parameters of BVH child nodes.
     BVH_ChildNodes(const BVH_Box<T, N>&      theLftBox,
                    const BVH_Box<T, N>&      theRghBox,
                    const BVH_PrimitiveRange& theLftRange,
                    const BVH_PrimitiveRange& theRghRange)
     {
       Boxes[0]  = theLftBox;
       Boxes[1]  = theRghBox;
       Ranges[0] = theLftRange;
       Ranges[1] = theRghRange;
     }
 
     //! Returns number of primitives in the given child.
     int NbPrims(const int theChild) const { return Ranges[theChild].Size(); }
 
     //! Checks if the parameters is initialized.
     bool IsValid() const { return Ranges[0].IsValid() && Ranges[1].IsValid(); }
   };
 
   //! Wrapper for BVH build data.
   class BVH_TypedBuildTool : public BVH_BuildTool
   {
   public:
     //! Creates new BVH build thread.
     BVH_TypedBuildTool(BVH_Set<T, N>*                theSet,
                        BVH_Tree<T, N>*               theBVH,
                        BVH_BuildQueue&               theBuildQueue,
                        const BVH_QueueBuilder<T, N>* theAlgo)
         : mySet(theSet),
           myBVH(theBVH),
           myBuildQueue(&theBuildQueue),
           myAlgo(theAlgo)
     {
       Standard_ASSERT_RAISE(myAlgo != nullptr, "Error! BVH builder should be queue based");
     }
 
     //! Performs splitting of the given BVH node.
     void Perform(const int theNode) override
     {
       const typename BVH_QueueBuilder<T, N>::BVH_ChildNodes aChildren =
         myAlgo->buildNode(mySet, myBVH, theNode);
       myAlgo->addChildren(myBVH, *myBuildQueue, theNode, aChildren);
     }
 
   protected:
     BVH_Set<T, N>*                mySet; //!< Primitive set to build BVH
     BVH_Tree<T, N>*               myBVH; //!< Output BVH tree for the set
     BVH_BuildQueue*               myBuildQueue;
     const BVH_QueueBuilder<T, N>* myAlgo; //!< Queue based BVH builder to use
   };
 
 protected:
   //! Performs splitting of the given BVH node.
   virtual typename BVH_QueueBuilder<T, N>::BVH_ChildNodes buildNode(BVH_Set<T, N>*  theSet,
                                                                     BVH_Tree<T, N>* theBVH,
                                                                     const int theNode) const = 0;
 
   //! Processes child nodes of the split BVH node.
   virtual void addChildren(BVH_Tree<T, N>*       theBVH,
                            BVH_BuildQueue&       theBuildQueue,
                            const int             theNode,
                            const BVH_ChildNodes& theSubNodes) const;
 
 protected:
   int myNumOfThreads; //!< Number of threads used to build BVH
 };
 
 //=================================================================================================
 
 template <class T, int N>
 void BVH_QueueBuilder<T, N>::addChildren(
   BVH_Tree<T, N>*                                        theBVH,
   BVH_BuildQueue&                                        theBuildQueue,
   const int                                              theNode,
   const typename BVH_QueueBuilder<T, N>::BVH_ChildNodes& theSubNodes) const
 {
   int aChildren[] = {-1, -1};
   if (!theSubNodes.IsValid())
   {
     return;
   }
 
   // Add child nodes
   {
     std::lock_guard<std::mutex> aLock(theBuildQueue.myMutex);
 
     for (int anIdx = 0; anIdx < 2; ++anIdx)
     {
       aChildren[anIdx] = theBVH->AddLeafNode(theSubNodes.Boxes[anIdx],
                                              theSubNodes.Ranges[anIdx].Start,
                                              theSubNodes.Ranges[anIdx].Final);
     }
 
     BVH_Builder<T, N>::updateDepth(theBVH, theBVH->Level(theNode) + 1);
   }
 
   // Set parameters of child nodes and generate new tasks
   for (int anIdx = 0; anIdx < 2; ++anIdx)
   {
     const int aChildIndex = aChildren[anIdx];
 
     theBVH->Level(aChildIndex) = theBVH->Level(theNode) + 1;
 
     (anIdx == 0 ? theBVH->template Child<0>(theNode) : theBVH->template Child<1>(theNode)) =
       aChildIndex;
 
     // Check to see if the child node must be split
     const bool isLeaf = theSubNodes.NbPrims(anIdx) <= BVH_Builder<T, N>::myLeafNodeSize
                         || theBVH->Level(aChildIndex) >= BVH_Builder<T, N>::myMaxTreeDepth;
 
     if (!isLeaf)
     {
       theBuildQueue.Enqueue(aChildIndex);
     }
   }
 }
 
 // =======================================================================
 // function : Build
 // purpose  : Builds BVH using specific algorithm
 // =======================================================================
 template <class T, int N>
 void BVH_QueueBuilder<T, N>::Build(BVH_Set<T, N>*       theSet,
                                    BVH_Tree<T, N>*      theBVH,
                                    const BVH_Box<T, N>& theBox) const
 {
   Standard_ASSERT_RETURN(theBVH != nullptr,
                          "Error! BVH tree to construct is NULL",
                          Standard_VOID_RETURN);
 
   theBVH->Clear();
   const int aSetSize = theSet->Size();
   if (aSetSize == 0)
   {
     return;
   }
 
   const int aRoot = theBVH->AddLeafNode(theBox, 0, aSetSize - 1);
   if (theSet->Size() == 1)
   {
     return;
   }
 
   BVH_BuildQueue aBuildQueue;
   aBuildQueue.Enqueue(aRoot);
 
   BVH_TypedBuildTool aBuildTool(theSet, theBVH, aBuildQueue, this);
   if (myNumOfThreads > 1)
   {
     // Reserve the maximum possible number of nodes in the BVH
     theBVH->Reserve(2 * aSetSize - 1);
 
     NCollection_DynamicArray<occ::handle<BVH_BuildThread>> aThreads;
 
     // Run BVH build threads
     for (int aThreadIndex = 0; aThreadIndex < myNumOfThreads; ++aThreadIndex)
     {
       aThreads.Append(new BVH_BuildThread(aBuildTool, aBuildQueue));
       aThreads.Last()->Run();
     }
 
     // Wait until all threads finish their work
     for (int aThreadIndex = 0; aThreadIndex < myNumOfThreads; ++aThreadIndex)
     {
       aThreads.ChangeValue(aThreadIndex)->Wait();
     }
 
     // Free unused memory
     theBVH->Reserve(theBVH->Length());
   }
   else
   {
     BVH_BuildThread aThread(aBuildTool, aBuildQueue);
 
     // Execute thread function inside current thread
     aThread.execute();
   }
 }
 
 #endif // _BVH_QueueBuilder_Header

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