source: GTP/trunk/Lib/Vis/Preprocessing/src/GvsPreprocessor.cpp @ 1996

#include "Environment.h"
#include "GvsPreprocessor.h"
#include "GlRenderer.h"
#include "VssRay.h"
#include "ViewCellsManager.h"
#include "Triangle3.h"
#include "IntersectableWrapper.h"
#include "Plane3.h"
#include "RayCaster.h"
#include "Exporter.h"
#include "SamplingStrategy.h"
#include "BvHierarchy.h"


namespace GtpVisibilityPreprocessor
{
  
#define GVS_DEBUG 0

struct VizStruct
{
        Polygon3 *enlargedTriangle;
        Triangle3 originalTriangle;
        VssRay *ray;
};

static const float MIN_DIST = 0.01f;

static vector<VizStruct> vizContainer;

GvsPreprocessor::GvsPreprocessor(): 
Preprocessor(), 
mSamplingType(SamplingStrategy::VIEWCELL_BASED_DISTRIBUTION),
//mSamplingType(SamplingStrategy::DIRECTION_BASED_DISTRIBUTION),
mProcessedViewCells(0),
mCurrentViewCell(NULL)
{
        Environment::GetSingleton()->GetIntValue("GvsPreprocessor.totalSamples", mTotalSamples);
        Environment::GetSingleton()->GetIntValue("GvsPreprocessor.initialSamples", mInitialSamples);
        Environment::GetSingleton()->GetIntValue("GvsPreprocessor.samplesPerPass", mSamplesPerPass);
        Environment::GetSingleton()->GetIntValue("GvsPreprocessor.minContribution", mMinContribution);
        Environment::GetSingleton()->GetFloatValue("GvsPreprocessor.epsilon", mEps);
        Environment::GetSingleton()->GetFloatValue("GvsPreprocessor.threshold", mThreshold);    
        Environment::GetSingleton()->GetBoolValue("GvsPreprocessor.perViewCell", mPerViewCell);
        Environment::GetSingleton()->GetIntValue("GvsPreprocessor.maxViewCells", mMaxViewCells);

        char gvsStatsLog[100];
        Environment::GetSingleton()->GetStringValue("GvsPreprocessor.stats", gvsStatsLog);
        mGvsStatsStream.open(gvsStatsLog);

        Debug << "Gvs preprocessor options" << endl;
        Debug << "number of total samples: " << mTotalSamples << endl;
        Debug << "number of initial samples: " << mInitialSamples << endl;
        Debug << "number of samples per pass: " << mSamplesPerPass << endl;
        Debug << "threshold: " << mThreshold << endl;
        Debug << "epsilon: " << mEps << endl;
        Debug << "stats: " << gvsStatsLog << endl;
        Debug << "per view cell: " << mPerViewCell << endl;
        Debug << "max view cells: " << mMaxViewCells << endl;
        Debug << "min contribution: " << mMinContribution << endl;

        if (1)
                mOnlyRandomSampling = false;            
        else
                mOnlyRandomSampling = true;

        mGvsStats.Reset();
}


GvsPreprocessor::~GvsPreprocessor()
{
        ClearRayQueue();
}


void GvsPreprocessor::ClearRayQueue()
{
        // clean ray queue
        while (!mRayQueue.empty())
        {
                // handle next ray
                VssRay *ray = mRayQueue.top();
                mRayQueue.pop();

                delete ray;
        }
}


bool GvsPreprocessor::NextViewCell()
{
        //if (mViewCellsManager->GetNumViewCells() == mProcessedViewCells)
        //      return false; // no more view cells

        if (mProcessedViewCells == (int)mViewCells.size())
                return false; // no more view cells

        mCurrentViewCell = mViewCells[mProcessedViewCells];

   if (!mCurrentViewCell->GetMesh())
                mViewCellsManager->CreateMesh(mCurrentViewCell);

        mGvsStats.mViewCellId = mCurrentViewCell->GetId();

        Debug << "vc: " << mCurrentViewCell->GetId() << endl;

        ++ mProcessedViewCells;
    
        return true;
}


int GvsPreprocessor::CheckDiscontinuity(const VssRay &currentRay,
                                                                                const Triangle3 &hitTriangle,
                                                                                const VssRay &oldRay)
{
        // the predicted hitpoint: we expect to hit the same mesh again
        const Vector3 predictedHit = CalcPredictedHitPoint(currentRay, hitTriangle, oldRay);

        const float predictedLen = Magnitude(predictedHit - currentRay.mOrigin);
        const float len = Magnitude(currentRay.mTermination - currentRay.mOrigin);
        
        // distance large => this is likely to be a discontinuity
#if 1
        if ((predictedLen - len) > mThreshold)
#else // rather use relative distance
        if ((predictedLen / len) > mThreshold)
#endif
        {
                //cout << "r";
                // apply reverse sampling to find the gap
                VssRay *newRay = ReverseSampling(currentRay, hitTriangle, oldRay);

                if (!newRay)
                        return 1;

                // set flag for visualization
                newRay->mFlags |= VssRay::ReverseSample;
                
                // if ray is not further processed => delete ray
                if (!HandleRay(newRay))
                {
                        delete newRay;
                }
                else if (0 && GVS_DEBUG && (mVssRays.size() < 9))
                {
                        mVssRays.push_back(new VssRay(oldRay));
                        mVssRays.push_back(new VssRay(currentRay));
                        mVssRays.push_back(new VssRay(*newRay));
                }

                return 1;
        }

        return 0;
}


bool GvsPreprocessor::HandleRay(VssRay *vssRay)
{
        // store the rays + the intersected view cells
        const bool storeRaysForViz = false; //GVS_DEBUG;

        if (!mPerViewCell)
        {
                mViewCellsManager->ComputeSampleContribution(*vssRay, 
                                                                                                         true, 
                                                                                                         storeRaysForViz,
                                                                                                         true);
        }
        else
        {
                mViewCellsManager->ComputeSampleContribution(*vssRay, 
                                                                                                         true, 
                                                                                                         mCurrentViewCell,
                                                                                                         true);
        }

        // some pvs contribution for this ray?
        if (!vssRay->mPvsContribution)
                return false;

        if (GVS_DEBUG)
                mVssRays.push_back(new VssRay(*vssRay));

        // add new ray to ray queue
        mRayQueue.push(vssRay);

        if (storeRaysForViz)
        {
                VssRay *nray = new VssRay(*vssRay);
                nray->mFlags = vssRay->mFlags;

                // store ray in contributing view cell
                ViewCellContainer::const_iterator vit, vit_end = vssRay->mViewCells.end();
                for (vit = vssRay->mViewCells.begin(); vit != vit_end; ++ vit)
                {                       
                        (*vit)->GetOrCreateRays()->push_back(nray);                             
                }
        }

        ++ mGvsStats.mTotalContribution;

        return true;
}


/** Creates 3 new vertices for triangle vertex with specified index.
*/
void GvsPreprocessor::CreateDisplacedVertices(VertexContainer &vertices,
                                                                                          const Triangle3 &hitTriangle,
                                                                                          const VssRay &ray, 
                                                                                          const int index) const
{
        const int indexU = (index + 1) % 3;
        const int indexL = (index == 0) ? 2 : index - 1;

        const Vector3 a = hitTriangle.mVertices[index] - ray.GetOrigin();
        const Vector3 b = hitTriangle.mVertices[indexU] - hitTriangle.mVertices[index];
        const Vector3 c = hitTriangle.mVertices[index] - hitTriangle.mVertices[indexL];
        
        const float len = Magnitude(a);
        
        const Vector3 dir1 = Normalize(CrossProd(a, b)); //N((pi-xp)×(pi+1- pi));
        const Vector3 dir2 = Normalize(CrossProd(a, c)); // N((pi-xp)×(pi- pi-1))
        const Vector3 dir3 = DotProd(dir2, dir1) > 0 ? // N((pi-xp)×di,i-1+di,i+1×(pi-xp))
                Normalize(dir2 + dir1) : Normalize(CrossProd(a, dir1) + CrossProd(dir2, a)); 

        // compute the new three hit points
        // pi, i + 1:  pi+ e·|pi-xp|·di, j
        const Vector3 pt1 = hitTriangle.mVertices[index] + mEps * len * dir1;
        // pi, i - 1:  pi+ e·|pi-xp|·di, j
    const Vector3 pt2 = hitTriangle.mVertices[index] + mEps * len * dir2;
        // pi, i:  pi+ e·|pi-xp|·di, j
        const Vector3 pt3 = hitTriangle.mVertices[index] + mEps * len * dir3;
        
        vertices.push_back(pt2);
        vertices.push_back(pt3);
        vertices.push_back(pt1);
}


void GvsPreprocessor::EnlargeTriangle(VertexContainer &vertices,
                                                                          const Triangle3 &hitTriangle,
                                                                          const VssRay &ray) const
{
        CreateDisplacedVertices(vertices, hitTriangle, ray, 0);
        CreateDisplacedVertices(vertices, hitTriangle, ray, 1);
        CreateDisplacedVertices(vertices, hitTriangle, ray, 2);
}


Vector3 GvsPreprocessor::CalcPredictedHitPoint(const VssRay &newRay, 
                                                                                           const Triangle3 &hitTriangle,
                                                                                           const VssRay &oldRay) const
{
        // find the intersection of the plane induced by the 
        // hit triangle with the new ray
        Plane3 plane(hitTriangle.GetNormal(), hitTriangle.mVertices[0]);

        const Vector3 hitPt = 
                plane.FindIntersection(newRay.mTermination, newRay.mOrigin);
        
        return hitPt;
}


static bool EqualVisibility(const VssRay &a, const VssRay &b)
{
        return a.mTerminationObject == b.mTerminationObject;
}


int GvsPreprocessor::SubdivideEdge(const Triangle3 &hitTriangle,
                                                                   const Vector3 &p1, 
                                                                   const Vector3 &p2, 
                                                                   const VssRay &ray1, 
                                                                   const VssRay &ray2,
                                                                   const VssRay &oldRay)
{
        int castRays = 0;

        // cast reverse rays if necessary
        castRays += CheckDiscontinuity(ray1, hitTriangle, oldRay);
        castRays += CheckDiscontinuity(ray2, hitTriangle, oldRay);

        if (EqualVisibility(ray1, ray2) || (Magnitude(p1 - p2) <= MIN_DIST))
        {
                return castRays;
        }
        
        // the new subdivision point
        const Vector3 p = (p1 + p2) * 0.5f;

        // cast ray into the new point
        SimpleRay sray(oldRay.mOrigin, p - oldRay.mOrigin, SamplingStrategy::GVS, 1.0f);

        VssRay *newRay = mRayCaster->CastRay(sray, mViewCellsManager->GetViewSpaceBox(), !mPerViewCell);
        
        ++ castRays;

        if (!newRay) return castRays;

        newRay->mFlags |= VssRay::BorderSample;

        // add new ray to queue
        const bool enqueued = HandleRay(newRay);

        // subdivide further
        castRays += SubdivideEdge(hitTriangle, p1, p, ray1, *newRay, oldRay);
        castRays += SubdivideEdge(hitTriangle, p, p2, *newRay, ray2, oldRay);

        // this ray will not be further processed
        if (!enqueued)
                delete newRay;

        return castRays;
}


int GvsPreprocessor::AdaptiveBorderSampling(const VssRay &currentRay)
{
        Intersectable *tObj = currentRay.mTerminationObject;
        Triangle3 hitTriangle;

        // other types not implemented yet
        if (tObj->Type() == Intersectable::TRIANGLE_INTERSECTABLE)
        {
                hitTriangle = dynamic_cast<TriangleIntersectable *>(tObj)->GetItem();
        }
        else
        {
                cout << "not yet implemented" << endl;
        }

        VertexContainer enlargedTriangle;
        
        /// create 3 new hit points for each vertex
        EnlargeTriangle(enlargedTriangle, hitTriangle, currentRay);
        
        /// create rays from sample points and handle them
        SimpleRayContainer simpleRays;
        simpleRays.reserve(9);

        VertexContainer::const_iterator vit, vit_end = enlargedTriangle.end();

        for (vit = enlargedTriangle.begin(); vit != vit_end; ++ vit)
        {
                const Vector3 rayDir = (*vit) - currentRay.GetOrigin();

                SimpleRay sr(currentRay.GetOrigin(), rayDir, SamplingStrategy::GVS, 1.0f);
                simpleRays.AddRay(sr);  
        }

        if (0)
        {
                // visualize enlarged triangles
                VizStruct dummy;
                dummy.enlargedTriangle = new Polygon3(enlargedTriangle);
                dummy.originalTriangle = hitTriangle;
                vizContainer.push_back(dummy);
        }

        // cast rays to triangle vertices and determine visibility
        VssRayContainer vssRays;

        // don't cast double rays as we need only the forward rays
        const bool castDoubleRays = !mPerViewCell;
        // cannot prune invalid rays because we have to compare adjacent  rays.
        const bool pruneInvalidRays = false;


        //////////
        //-- fill up simple rays with random rays so we can cast 16

        //const int numRandomRays = 0;
        const int numRandomRays = 16 - (int)simpleRays.size();
        ViewCellBasedDistribution vcStrat(*this, mCurrentViewCell);

        GenerateRays(numRandomRays, vcStrat, simpleRays);

        /////////////////////


        // keep origin for per view cell sampling
        CastRays(simpleRays, vssRays, castDoubleRays, pruneInvalidRays);

        const int numBorderSamples = (int)vssRays.size() - numRandomRays;

        // set flags
        VssRayContainer::const_iterator rit, rit_end = vssRays.end();
        int i = 0;
  
        for (rit = vssRays.begin(); rit != rit_end; ++ rit, ++ i)
        {
                if (i < numBorderSamples)
                        (*rit)->mFlags |= VssRay::BorderSample;
        }

        // handle rays
        EnqueueRays(vssRays);
        
        int castRays = simpleRays.size();
        
    // recursivly subdivide each edge
        for (int i = 0; i < numBorderSamples; ++ i)
        {
                castRays += SubdivideEdge(hitTriangle,
                                                                  enlargedTriangle[i], 
                                                                  enlargedTriangle[(i + 1) % numBorderSamples], 
                                                                  *vssRays[i], 
                                                                  *vssRays[(i + 1) % numBorderSamples],
                                                                  currentRay);
        }

        mGvsStats.mBorderSamples += castRays;

        return castRays;
}


bool GvsPreprocessor::GetPassingPoint(const VssRay &currentRay,
                                                                          const Triangle3 &occluder,
                                                                          const VssRay &oldRay,
                                                                          Vector3 &newPoint) const
{
        //-- The plane p = (xp, hit(x), hit(xold)) is intersected
        //-- with the newly found occluder (xold is the previous ray from
        //-- which x was generated). On the intersecting line, we select a point
        //-- pnew which lies just outside of the new triangle so the ray
        //-- just passes through the gap

        const Plane3 plane(currentRay.GetOrigin(), 
                                           currentRay.GetTermination(), 
                                           oldRay.GetTermination());
        
        Vector3 pt1, pt2;

        const bool intersects = occluder.GetPlaneIntersection(plane, pt1, pt2);

        if (!intersects)
        {
                cerr << "big error!! no intersection " << pt1 << " " << pt2 << endl;
                return false;
        }

        // get the intersection point on the old ray
        const Plane3 triPlane(occluder.GetNormal(), occluder.mVertices[0]);

        const float t = triPlane.FindT(oldRay.mOrigin, oldRay.mTermination);
        const Vector3 pt3 = oldRay.mOrigin + t * (oldRay.mTermination - oldRay.mOrigin);

        // Evaluate new hitpoint just outside the triangle
        const float eps = mEps;

        // the point is chosen to be on the side closer to the original ray
        if (Distance(pt1, pt3) < Distance(pt2, pt3))
        {
                newPoint = pt1 + eps * (pt1 - pt2);
        }       
        else
        {
                newPoint = pt2 + eps * (pt2 - pt1);
        }

        //cout << "passing point: " << newPoint << endl << endl;
        return true;
}


VssRay *GvsPreprocessor::ReverseSampling(const VssRay &currentRay,
                                                                                 const Triangle3 &hitTriangle,
                                                                                 const VssRay &oldRay)
{
        // get triangle occluding the path to the hit mesh
        Triangle3 occluder;
        Intersectable *tObj = currentRay.mTerminationObject;

        // q: why can this happen?
        if (!tObj)
                return NULL;

        // other types not implemented yet
        if (tObj->Type() == Intersectable::TRIANGLE_INTERSECTABLE)
                occluder = dynamic_cast<TriangleIntersectable *>(tObj)->GetItem();
        else
                cout << "not yet implemented" << endl;
        
        // get a point which is passing just outside of the occluder
    Vector3 newPoint;

        // why is there sometimes no intersecton found?
        if (!GetPassingPoint(currentRay, occluder, oldRay, newPoint))
                return NULL;

        const Vector3 predicted = CalcPredictedHitPoint(currentRay, hitTriangle, oldRay);

        Vector3 newDir, newOrigin;

        //-- Construct the mutated ray with xnew,
        //-- dir = predicted(x)- pnew as direction vector
        newDir = predicted - newPoint;

        // take xnew, p = intersect(viewcell, line(pnew, predicted(x)) as origin ?
        // difficult to say!!
        const float offset = 0.5f;
        newOrigin = newPoint - newDir * offset;
        
        //////////////
        //-- for per view cell sampling, we must check for intersection
        //-- with the current view cell

    if (mPerViewCell)
        {
                // send ray to view cell
                static Ray ray;
                ray.Clear();
                ray.Init(newOrigin, -newDir, Ray::LOCAL_RAY);
                
                //cout << "z";
                // check if ray intersects view cell
                if (!mCurrentViewCell->CastRay(ray))
                        return NULL;

                Ray::Intersection &hit = ray.intersections[0];
        
                //cout << "q";
                // the ray starts from the view cell
                newOrigin = ray.Extrap(hit.mT);
        }

        const SimpleRay simpleRay(newOrigin, newDir, SamplingStrategy::GVS, 1.0f);

        VssRay *reverseRay = 
                mRayCaster->CastRay(simpleRay, mViewCellsManager->GetViewSpaceBox(), !mPerViewCell);

    ++ mGvsStats.mReverseSamples;

        return reverseRay;
}


int GvsPreprocessor::CastInitialSamples(const int numSamples, 
                                                                                const int sampleType)
{       
        const long startTime = GetTime();

        // generate simple rays
        SimpleRayContainer simpleRays;
        
        ViewCellBasedDistribution vcStrat(*this, mCurrentViewCell);
    GenerateRays(numSamples, vcStrat, simpleRays);

        //cout << "sr: " << simpleRays.size() << endl;
        // generate vss rays
        VssRayContainer samples;
        
        const bool castDoubleRays = !mPerViewCell;
        const bool pruneInvalidRays = true;
        
        CastRays(simpleRays, samples, castDoubleRays, pruneInvalidRays);
        
        // add to ray queue
        EnqueueRays(samples);

        //Debug << "generated " <<  numSamples << " samples in " << TimeDiff(startTime, GetTime()) * 1e-3 << " secs" << endl;
        return (int)simpleRays.size();
}


void GvsPreprocessor::EnqueueRays(VssRayContainer &samples)
{
        // add samples to ray queue
        VssRayContainer::const_iterator vit, vit_end = samples.end();
        for (vit = samples.begin(); vit != vit_end; ++ vit)
        {
                HandleRay(*vit);
        }
}


int GvsPreprocessor::ProcessQueue()
{
        int castSamples = 0;
        ++ mGvsStats.mGvsPass;

        while (!mRayQueue.empty() 
                )//&& (mGvsStats.mTotalSamples + castSamples < mTotalSamples) )
        {
                // handle next ray
                VssRay *ray = mRayQueue.top();
                mRayQueue.pop();
                
                const int newSamples = AdaptiveBorderSampling(*ray);

                castSamples += newSamples;

                //cout << newSamples << " ";    
                delete ray;
        }

        return castSamples;
}


void ExportVssRays(Exporter *exporter, const VssRayContainer &vssRays)
{
        VssRayContainer vcRays, vcRays2, vcRays3;

        VssRayContainer::const_iterator rit, rit_end = vssRays.end();

        // prepare some rays for output
        for (rit = vssRays.begin(); rit != rit_end; ++ rit)
        {
                //const float p = RandomValue(0.0f, (float)vssRays.size());

                if (1)//(p < raysOut)
                {
                        if ((*rit)->mFlags & VssRay::BorderSample)
                        {
                                vcRays.push_back(*rit);
                        }
                        else if ((*rit)->mFlags & VssRay::ReverseSample)
                        {
                                vcRays2.push_back(*rit);
                        }
                        else
                        {
                                vcRays3.push_back(*rit);
                        }       
                }
        }

        //exporter->ExportRays(vcRays, RgbColor(1, 0, 0));
        //exporter->ExportRays(vcRays2, RgbColor(0, 1, 0));
        //exporter->ExportRays(vcRays3, RgbColor(1, 1, 1));
}


void GvsPreprocessor::VisualizeViewCell(ViewCell *vc)
{
    Intersectable::NewMail();

        Material m;
        
        char str[64]; sprintf(str, "pass%06d.wrl", mProcessedViewCells);

        Exporter *exporter = Exporter::GetExporter(str);
        if (!exporter)
                return;

        ObjectPvsIterator pit = vc->GetPvs().GetIterator();

        // output PVS of view cell
        while (pit.HasMoreEntries())
        {               
                ObjectPvsEntry entry = pit.Next();

                Intersectable *intersect = entry.mObject;
                
                if (intersect->Mailed())
                        continue;
                
                intersect->Mail();
                //m.mDiffuseColor = RgbColor(1, 0, 0);
                m = RandomMaterial();
                exporter->SetForcedMaterial(m);

                exporter->ExportIntersectable(intersect);
        }

        cout << "vssrays: " << (int)mVssRays.size() << endl;
        ExportVssRays(exporter, mVssRays);

        /////////////////
        //-- export view cell geometry

        exporter->SetWireframe();

        m.mDiffuseColor = RgbColor(0, 1, 0);
        exporter->SetForcedMaterial(m);

        mViewCellsManager->ExportViewCellGeometry(exporter, vc, NULL, NULL);
        //exporter->SetFilled();

        DEL_PTR(exporter);
}


void GvsPreprocessor::VisualizeViewCells()
{
        char str[64]; sprintf(str, "tmp/pass%06d_%04d-", mProcessedViewCells, mPass);
                        
        // visualization
        if (mGvsStats.mPassContribution > 0)
        {
                const bool exportRays = true;
                const bool exportPvs = true;

                mViewCellsManager->ExportSingleViewCells(mObjects, 
                                                                                                 10, 
                                                                                                 false, 
                                                                                                 exportPvs, 
                                                                                                 exportRays, 
                                                                                                 1000, 
                                                                                                 str);
        }

        // remove pass samples
        ViewCellContainer::const_iterator vit, vit_end = mViewCellsManager->GetViewCells().end();

        for (vit = mViewCellsManager->GetViewCells().begin(); vit != vit_end; ++ vit)
        {
                (*vit)->DelRayRefs();
        }
}


void GvsPreprocessor::ProcessViewCell()
{
        mGvsStats.mPerViewCellSamples = 0;
        int oldContribution = mGvsStats.mTotalContribution;
        int passSamples = 0;

        //while (mGvsStats.mPerViewCellSamples < mTotalSamples) 
        while (1) 
        {
                // Ray queue empty => 
                // cast a number of uniform samples to fill ray queue
                int newSamples = CastInitialSamples(mInitialSamples, mSamplingType);

                if (!mOnlyRandomSampling)
                        newSamples += ProcessQueue();

                passSamples += newSamples;
                mGvsStats.mPerViewCellSamples += newSamples;
                //cout << "here4 " << passSamples % (mSamplesPerPass + 1) << endl;

                if (passSamples >= mSamplesPerPass)
                {
                        ++ mPass;

                        mGvsStats.mPassContribution = mGvsStats.mTotalContribution - oldContribution;

                        ////////
                        //-- stats

                        mGvsStats.mPass = mPass;

                        cout << "\nPass " << mPass << " #samples: " << mGvsStats.mPerViewCellSamples << endl;
                        cout << "contribution=" << mGvsStats.mPassContribution << " (of " << mMinContribution << ")" << endl;

                        // termination criterium
                        if (mGvsStats.mPassContribution < mMinContribution)
                        {
                                break;
                        }

                        // reset
                        oldContribution = mGvsStats.mTotalContribution;
                        mGvsStats.mPassContribution = 0;
                        passSamples = 0;
                }
        }
}


void GvsPreprocessor::CompileViewCellsList()
{
        while ((int)mViewCells.size() < mMaxViewCells)
    {
                if (0)
                {
                        mViewCells.push_back(mViewCellsManager->GetViewCell((int)mViewCells.size()));
                }
                else
                {
                        // HACK
                        const int tries = 10000;
                        int i = 0;

                        for (i = 0; i < tries; ++ i)
                        {
                                const int idx = (int)RandomValue(0.0f, (float)mViewCellsManager->GetNumViewCells() - 0.5f);
        
                                ViewCell *viewCell = mViewCellsManager->GetViewCell(idx);

                                if (!viewCell->Mailed())
                                {
                                        viewCell->Mail();
                                        break;
                                }

                                mViewCells.push_back(viewCell);
                        }

                        if (i == tries)
                        {
                                cerr << "big error! no view cell found" << endl;
                                return;
                        }
                }
        }
}


void GvsPreprocessor::PerViewCellComputation()
{
        while (NextViewCell())
        {
                cout << "\n***********************\nprocessing view cell " << mProcessedViewCells << endl;

                // compute the pvs of the current view cell
                ProcessViewCell();

                mGvsStats.mTrianglePvs = mCurrentViewCell->GetPvs().GetSize();

                // exchange triangle pvs with objects
                UpdatePvs(mCurrentViewCell);

                if (GVS_DEBUG)
                {
                        VisualizeViewCell(mCurrentViewCell);
                        CLEAR_CONTAINER(mVssRays);
                }

                ////////
                //-- stats
                
                mGvsStats.mViewCells = mProcessedViewCells;//mPass;
                mGvsStats.mPerViewCellPvs = mCurrentViewCell->GetPvs().GetSize();
                mGvsStats.mTotalPvs += mCurrentViewCell->GetPvs().GetSize();
                mGvsStats.mTotalSamples += mGvsStats.mPerViewCellSamples;

                mGvsStats.Stop();
                mGvsStats.Print(mGvsStatsStream);

                // is this really necessary?
                ClearRayQueue();
        }
}


void GvsPreprocessor::UpdatePvs(ViewCell *currentViewCell)
{
        ObjectPvs newPvs;
        BvhLeaf::NewMail();

        ObjectPvsIterator pit = currentViewCell->GetPvs().GetIterator();

        // output PVS of view cell
        while (pit.HasMoreEntries())
        {               
                ObjectPvsEntry entry = pit.Next();

                Intersectable *intersect = entry.mObject;
        
                BvhLeaf *bv = intersect->mBvhLeaf;

                if (!bv || bv->Mailed())
                        continue;
                
                bv->Mail();

                //m.mDiffuseColor = RgbColor(1, 0, 0);
                newPvs.AddSampleDirty(bv, 1.0f);
        }

        newPvs.SimpleSort();

        currentViewCell->SetPvs(newPvs);
}


void GvsPreprocessor::GlobalComputation()
{
        int passSamples = 0;
        int oldContribution = 0;

        while (mGvsStats.mTotalSamples < mTotalSamples) 
        {
                // Ray queue empty => 
                // cast a number of uniform samples to fill ray queue
                int newSamples = CastInitialSamples(mInitialSamples, mSamplingType);

                if (!mOnlyRandomSampling)
                        newSamples += ProcessQueue();

                passSamples += newSamples;
                mGvsStats.mTotalSamples += newSamples;

                if (passSamples % (mSamplesPerPass + 1) == mSamplesPerPass)
                {
                        ++ mPass;

                        mGvsStats.mPassContribution = mGvsStats.mTotalContribution - oldContribution;

                        ////////
                        //-- stats

                        //cout << "\nPass " << mPass << " #samples: " << mGvsStats.mTotalSamples << " of " << mTotalSamples << endl;
                        mGvsStats.mPass = mPass;
                        mGvsStats.Stop();
                        mGvsStats.Print(mGvsStatsStream);

                        // reset
                        oldContribution = mGvsStats.mTotalContribution;
                        mGvsStats.mPassContribution = 0;
                        passSamples = 0;

                        if (GVS_DEBUG)
                                VisualizeViewCells();
                }
        }
}


bool GvsPreprocessor::ComputeVisibility()
{
        cout << "Gvs Preprocessor started\n" << flush;
        const long startTime = GetTime();

        //Randomize(0);
        
        mGvsStats.Reset();
        mGvsStats.Start();

        if (!mLoadViewCells)
        {       
                /// construct the view cells from the scratch
                ConstructViewCells();
                // reset pvs already gathered during view cells construction
                mViewCellsManager->ResetPvs();
                cout << "finished view cell construction" << endl;
        }
        else if (0)
        {       
                //-- test successful view cells loading by exporting them again
                VssRayContainer dummies;
                mViewCellsManager->Visualize(mObjects, dummies);
                mViewCellsManager->ExportViewCells("test.xml.gz", mViewCellsManager->GetExportPvs(), mObjects);
        }

        mGvsStats.Stop();
        mGvsStats.Print(mGvsStatsStream);

        if (mPerViewCell)
        {
                // list of view cells to compute
                CompileViewCellsList();

                PerViewCellComputation();
        }
        else
        {
                GlobalComputation();
        }

        cout << "cast " << 2 * mGvsStats.mTotalSamples / (1e3f * TimeDiff(startTime, GetTime())) << "M rays/s" << endl;

        if (GVS_DEBUG)
        {
                Visualize();
                CLEAR_CONTAINER(mVssRays);
        }

        return true;
}


void GvsPreprocessor::Visualize()
{
        Exporter *exporter = Exporter::GetExporter("gvs.wrl");

        if (!exporter)
                return;
        
        vector<VizStruct>::const_iterator vit, vit_end = vizContainer.end();
        for (vit = vizContainer.begin(); vit != vit_end; ++ vit)
        {
                exporter->SetWireframe();
                exporter->ExportPolygon((*vit).enlargedTriangle);
                //Material m;
                exporter->SetFilled();
                Polygon3 poly = Polygon3((*vit).originalTriangle);
                exporter->ExportPolygon(&poly);
        }

        VssRayContainer::const_iterator rit, rit_end = mVssRays.end();
        for (rit = mVssRays.begin(); rit != rit_end; ++ rit)
        {
                Intersectable *obj = (*rit)->mTerminationObject;
                exporter->ExportIntersectable(obj);
        }

        ExportVssRays(exporter, mVssRays);
        
        delete exporter;
}


void GvsStatistics::Print(ostream &app) const
{
        app << "#Pass\n" << mPass << endl;
        app << "#ViewCellId\n" << mViewCellId << endl;
        app << "#Time\n" << Time() << endl;
        app << "#TotalSamples\n" << mTotalSamples << endl;
        app << "#ScDiff\n" << mPassContribution << endl;
        app     << "#SamplesContri\n" << mTotalContribution << endl;
        app << "#ReverseSamples\n" << mReverseSamples << endl;
        app << "#BorderSamples\n" << mBorderSamples << endl;            
        app << "#GvsRuns\n" << mGvsPass << endl;
        app << "#ViewCells\n" << mViewCells << endl;
        app << "#TotalPvs\n" << mTotalPvs << endl;
        app << "#PerViewCellPvs\n" << mPerViewCellPvs << endl;
        app << "#TrianglePvs\n" << mTrianglePvs << endl;
        app << "#RaysPerSec\n" << RaysPerSec() << endl;
        app << "#PerViewCellSamples\n" << mPerViewCellSamples << endl << endl;
}


}