source: GTP/trunk/App/Demos/Vis/FriendlyCulling/src/BvhConstructor.cpp @ 3269

#include "BvhConstructor.h"
#include "Triangle3.h"
#include "SceneEntity.h"
#include "Geometry.h"
#include "gzstream.h"

#include <queue>
#include <stack>
#include <fstream>

#define MAX_FLOAT 1e20f


#ifdef _CRT_SET
        #define _CRTDBG_MAP_ALLOC
        #include <stdlib.h>
        #include <crtdbg.h>

        // redefine new operator
        #define DEBUG_NEW new(_NORMAL_BLOCK, __FILE__, __LINE__)
        #define new DEBUG_NEW
#endif


using namespace std;


namespace CHCDemoEngine
{

BvhConstructor::BvhConstructor(SceneEntity **entities, 
                                                           int first, 
                                                           int last):
mEntities(entities),
mFirst(first),
mLast(last),
mMaxDepth(20),
mMaxObjects(1),
mMaxTriangles(1),
mNumNodes(0),
mSplitType(SAH)
{
}


float BvhConstructor::EvaluateSahCost(BvhLeaf *leaf, int axis, float position)
{
        // count triangles on the left / right
        int left = 0;
        int right = 0;
        AxisAlignedBox3 leftBox, rightBox;

        leftBox.Initialize();
        rightBox.Initialize();

        const int candidates = std::max(50, (int)(leaf->CountPrimitives() / 20));
        const float finc = leaf->CountPrimitives() / (float)candidates;

        int i = leaf->mFirst;
        float fi = leaf->mFirst + 0.5f;

        AxisAlignedBox3 box;

        for (; i <= leaf->mLast;) 
        {
                box = mEntities[i]->GetWorldBoundingBox();

                if (box.Center(axis) < position) 
                {
                        ++ left;
                        // update the box
                        leftBox.Include(box);
                } 
                else 
                {
                        ++ right;
                        rightBox.Include(box);
                }
                 
                fi += finc;
                i = (int)fi;
        }

        float bW = 1.0f;
        float leftRatio = left / (float)leaf->CountPrimitives();
        float rightRatio = right / (float)leaf->CountPrimitives();

        float saLeft = 0.0f;
        float saRight = 0.0f;

        // not a valid split
        if (!left || !right)
                return 1e25f;

        saLeft = leftBox.SurfaceArea();
        saRight = rightBox.SurfaceArea();


        return
                saLeft  * ((1.0f - bW) + bW * leftRatio) + 
                saRight * ((1.0f - bW) + bW * rightRatio);
}


float BvhConstructor::SelectPlaneSah(BvhLeaf *leaf, int &axis, float &minCost)
{
        minCost = MAX_FLOAT;
        float bestPos = minCost;
        int bestAxis = 0;

        //  cout<<"Evaluating axis..."<<endl<<flush;

        const int initialPlanes = 3;

        // initiate the costs
        for (axis = 0; axis < 3; ++ axis) 
        {
                const float size = leaf->mBox.Size(axis);

                for (int i = 0; i < initialPlanes; ++ i) 
                {
                        const float pos = leaf->mBox.Min(axis) + (i + 1) * size / (initialPlanes + 1);
                        const float cost = EvaluateSahCost(leaf, axis, pos);

                        if (cost < minCost) 
                        {
                                minCost = cost;
                                bestPos = pos;
                                bestAxis = axis;
                        }
                }
        }

        axis = bestAxis;

        //  cout<<axis<<endl<<flush;
        const float shrink = 0.5f;

        // now hierarchically refine the initial interval
        float size = shrink * 
                (leaf->mBox.Max(axis) - leaf->mBox.Min(axis)) / (initialPlanes + 1);

        const int steps = 4;
        float cost;

        for (int i = 0; i < steps; ++ i) 
        {
                const float left = bestPos - size;
                const float right = bestPos + size;

                cost = EvaluateSahCost(leaf, axis, left);

                if (cost < minCost) 
                {
                        minCost = cost;
                        bestPos = left;
                }

                cost = EvaluateSahCost(leaf, axis, right);

                if (cost < minCost) 
                {
                        minCost = cost;
                        bestPos = right;
                }

                size = shrink * size;
        }

        //OUT1("best axis: " << axis << " " << bestPos << " " << minCost);

        return bestPos;
}


int BvhConstructor::SortTriangles(BvhLeaf *leaf, 
                                                                  int axis, 
                                                                  float position
                                                                  )
{
        int i = leaf->mFirst;
        int j = leaf->mLast;

    while (1)
        {
                //while (mEntities[i]->GetWorldCenter()[axis] < position) ++ i;
                //while (position < mEntities[j]->GetWorldCenter()[axis]) -- j;

                while ((i < leaf->mLast) && (mEntities[i]->GetWorldCenter()[axis] < position)) ++ i;
                while ((j > leaf->mFirst) && (position < mEntities[j]->GetWorldCenter()[axis])) -- j;

                // sorting finished
                if (i >= j) break;

                // swap entities
                swap(mEntities[i], mEntities[j]);
                        
                ++ i;
                -- j;
        }

        return j;
}


void BvhConstructor::UpdateBoundingBoxes(BvhNode *node)
{
        if (node->IsLeaf())
        {
                int numEntities = node->CountPrimitives();
                SceneEntity **entities = mEntities + node->mFirst;

                node->mBox = SceneEntity::ComputeBoundingBox(entities, numEntities);
                //cout << "box: " << node->mBox << endl;
        }
        else
        {
                BvhNode *f = static_cast<BvhInterior *>(node)->GetFront();
                BvhNode *b = static_cast<BvhInterior *>(node)->GetBack();

                UpdateBoundingBoxes(f);
                UpdateBoundingBoxes(b);

                node->mBox = f->mBox;
                node->mBox.Include(b->mBox);
        }
}


int BvhConstructor::SortTrianglesSpatialMedian(BvhLeaf *leaf, 
                                                                                           int axis)
{
        // spatial median
        float m = leaf->GetBox().Center()[axis];
        return SortTriangles(leaf, axis, m);
}


int BvhConstructor::SortTrianglesObjectMedian(BvhLeaf *leaf, int axis, float &pos)
{
        // Now distribute the objects into the subnodes
        // Use QuickMedian sort
        int l = leaf->mFirst;
        int r = leaf->mLast;
        int k = (l + r) / 2;

        while (l < r) 
        {
                int i = l;
                int j = r;

                // get some estimation of the pivot
                pos = mEntities[(l + r) / 2]->GetBoundingBox().Center(axis);

                while (1) 
                {
                        while ((i <= leaf->mLast) && (mEntities[i]->GetWorldBoundingBox().Center(axis) < pos))
                                ++ i;

                        while((j >= leaf->mFirst) && (pos < mEntities[j]->GetWorldBoundingBox().Center(axis)))
                                -- j;

                        if (i <= j) 
                        {
                                std::swap(mEntities[i], mEntities[j]);
                                ++ i;
                                -- j;
                        }
                        else
                        {
                                break;
                        }
                }

                // now check the extents
                if (i >= k)
                        r = j;
                else
                        l = i;
        }

        return k;
}


BvhNode *BvhConstructor::SubdivideLeaf(BvhLeaf *leaf, 
                                                                           int parentAxis
                                                                           )
{
        if (TerminationCriteriaMet(leaf))
        {
                //if (leaf->CountPrimitives() <= 0)
                //cout << "leaf constructed:" << leaf->mBox << " " << leaf->mFirst << " " << leaf->mLast << endl;
                return leaf;
        }

        //const int axis = (parentAxis + 1) % 3;
        int axis = leaf->mBox.MajorAxis();
        const int scale = 20;

        // position of the split in the partailly sorted array of triangles
        // corresponding to this leaf
        int split = -1;
        float pos = -1.0f;

        // Spatial median subdivision
        switch (mSplitType) 
        {
        case SPATIAL_MEDIAN:
                split = SortTrianglesSpatialMedian(leaf, axis);
                pos = leaf->mBox.Center()[axis];
                break;
        case OBJECT_MEDIAN:
                // Object median subdivision: approximately the same number
                // of objects on the left of the the splitting point.
                split = SortTrianglesObjectMedian(leaf, axis, pos);
                break;
        case SAH:
                {
                        float cost;
                        pos = SelectPlaneSah(leaf, axis, cost);

                        if (pos != MAX_FLOAT)
                        {
                                split = SortTriangles(leaf, axis, pos);
                        }

                        if ((pos == MAX_FLOAT) || (split == leaf->mLast))
                        {
                                split = -1;
                                split = SortTrianglesObjectMedian(leaf, axis, pos);
                        }
                }
                break;
        default:
                cerr << "should not come here" << endl;
                break;
        }
        
        if (split == leaf->mLast)
        {
                // no split could be achieved => just halve number of objects
                split = (leaf->mLast + leaf->mFirst) / 2;
                //cerr << "no reduction " << leaf->CountPrimitives() << " " << leaf->mFirst << " " << leaf->mLast << endl;
        }

        // create two more nodes
        mNumNodes += 2;
        BvhInterior *parent = new BvhInterior(leaf->GetParent());
        parent->mFirst = leaf->mFirst;
        parent->mLast = leaf->mLast;
        
        parent->mAxis = axis;
        parent->mBox = leaf->mBox;
        parent->mDepth = leaf->mDepth;

        BvhLeaf *front = new BvhLeaf(parent);

        parent->mBack = leaf;
        parent->mFront = front;
                
        // now assign the triangles to the subnodes
        front->mFirst = split + 1;
        front->mLast = leaf->mLast;
        front->mDepth = leaf->mDepth + 1;

        leaf->mLast = split;
        leaf->mDepth = front->mDepth;
        leaf->mParent = parent;
        
        front->mBox = SceneEntity::ComputeBoundingBox(mEntities + front->mFirst, front->CountPrimitives());
        leaf->mBox = SceneEntity::ComputeBoundingBox(mEntities + leaf->mFirst, leaf->CountPrimitives());

        // recursively continue subdivision
        parent->mBack = SubdivideLeaf(static_cast<BvhLeaf *>(parent->mBack), axis);
        parent->mFront = SubdivideLeaf(static_cast<BvhLeaf *>(parent->mFront), axis);
        
        return parent;
}


int BvhConstructor::CountTriangles(BvhNode *node) const
{
        int numTriangles = 0;

        for (int i = node->mFirst; i <= node->mLast; ++ i)
        {
                numTriangles += mEntities[i]->CountNumTriangles(0);
        }

        return numTriangles;
}


bool BvhConstructor::TerminationCriteriaMet(BvhLeaf *leaf) const
{
        const bool criteriaMet = 
                (leaf->mDepth > mMaxDepth) ||
                (leaf->CountPrimitives() <= mMaxObjects) ||
                (CountTriangles(leaf) <= mMaxTriangles);

        return criteriaMet;
}


BvhNode *BvhConstructor::Construct(int &numNodes)
{
        BvhNode *root;
        mNumNodes = 1;

        BvhLeaf *l = new BvhLeaf(NULL);
        
        l->mFirst = mFirst;
        l->mLast = mLast;

        cout << "\n================================" << endl;
        cout << "constructing bvh for " << l->mLast - l->mFirst + 1 << " entities" << endl;

        l->mBox = SceneEntity::ComputeBoundingBox(mEntities + mFirst, mLast - mFirst + 1);
        l->mArea = l->mBox.SurfaceArea();
        
        root = SubdivideLeaf(l, 0);

        UpdateBoundingBoxes(root);

        numNodes = mNumNodes;

        return root;
}


}