source: trunk/VUT/GtpVisibilityPreprocessor/src/GlRenderer.cpp @ 542

#include "Mesh.h"
#include "GlRenderer.h"
#include "ViewCellsManager.h"
#include "SceneGraph.h"
#include "Pvs.h"
#include "Viewcell.h"
#include "Beam.h"
#include "KdTree.h"

#include <GL/glext.h>
#include <Cg/cg.h>
#include <Cg/cgGL.h>

static CGcontext sCgContext = NULL;
static CGprogram sCgFragmentProgram = NULL;
static CGprofile sCgFragmentProfile;

GLuint frontDepthMap;
GLuint backDepthMap;

const int depthMapSize = 512;
static vector<int> sQueries;

GlRendererWidget *rendererWidget = NULL;
GlDebuggerWidget *debuggerWidget = NULL;


#ifdef _WIN32
PFNGLGENOCCLUSIONQUERIESNVPROC glGenOcclusionQueriesNV;
PFNGLBEGINOCCLUSIONQUERYNVPROC glBeginOcclusionQueryNV;
PFNGLENDOCCLUSIONQUERYNVPROC glEndOcclusionQueryNV;
PFNGLGETOCCLUSIONQUERYUIVNVPROC glGetOcclusionQueryuivNV;
#endif

GlRenderer::GlRenderer(SceneGraph *sceneGraph,
                                           ViewCellsManager *viewCellsManager,
                                           KdTree *tree):
  Renderer(sceneGraph, viewCellsManager),
  mKdTree(tree)
{
  mSceneGraph->CollectObjects(&mObjects);
  mViewPoint = mSceneGraph->GetBox().Center();
  mViewDirection = Vector3(0,0,1);
  //  timerId = startTimer(10);
  mFrame = 0;
  mWireFrame = false;
}

GlRenderer::~GlRenderer()
{
        cgDestroyProgram(sCgFragmentProgram);
        cgDestroyContext(sCgContext);
}


static void handleCgError() 
{
    Debug << "Cg error: " << cgGetErrorString(cgGetError()) << endl;
    exit(1);
}

void
GlRenderer::RenderIntersectable(Intersectable *object)
{

  SetupFalseColor(object->mId);

  switch (object->Type()) {
  case Intersectable::MESH_INSTANCE:
        RenderMeshInstance((MeshInstance *)object);
        break;
  case Intersectable::VIEW_CELL:
          RenderViewCell(dynamic_cast<ViewCell *>(object));
          break;
  default:
        cerr<<"Rendering this object not yet implemented\n";
        break;
  }
}


void
GlRenderer::RenderViewCell(ViewCell *vc)
{
        if (vc->GetMesh())
                RenderMesh(vc->GetMesh());
}

void
GlRenderer::RenderMeshInstance(MeshInstance *mi)
{
  RenderMesh(mi->GetMesh());
}

void
GlRenderer::SetupFalseColor(const int id)
{
  // swap bits of the color
  
  glColor3ub(id&255, (id>>8)&255, (id>>16)&255);
}


int GlRenderer::GetId(int r, int g, int b) const
{
        return r + (g << 8) + (b << 16);
}

void
GlRenderer::SetupMaterial(Material *m)
{
  if (m)
        glColor3fv(&(m->mDiffuseColor.r));
  else
        glColor3f(1.0f, 1.0f, 1.0f);
}

void
GlRenderer::RenderMesh(Mesh *mesh)
{
  int i = 0;

  if (!mUseFalseColors)
        SetupMaterial(mesh->mMaterial);
  
  for (i=0; i < mesh->mFaces.size(); i++) {
        if (mWireFrame)
          glBegin(GL_LINE_LOOP);
        else
          glBegin(GL_POLYGON);

        Face *face = mesh->mFaces[i];
        for (int j = 0; j < face->mVertexIndices.size(); j++) {
          glVertex3fv(&mesh->mVertices[face->mVertexIndices[j]].x);
        }
        glEnd();
  }
}
        
void
GlRenderer::InitGL()
{
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();

  glEnable(GL_CULL_FACE);
  glShadeModel(GL_FLAT);
  glEnable(GL_DEPTH_TEST);
  glEnable(GL_CULL_FACE);
  
  glGenOcclusionQueriesNV = (PFNGLGENOCCLUSIONQUERIESNVPROC)
        wglGetProcAddress("glGenOcclusionQueriesNV");
  glBeginOcclusionQueryNV = (PFNGLBEGINOCCLUSIONQUERYNVPROC)
        wglGetProcAddress("glBeginOcclusionQueryNV");
  glEndOcclusionQueryNV = (PFNGLENDOCCLUSIONQUERYNVPROC)
        wglGetProcAddress("glEndOcclusionQueryNV");
  glGetOcclusionQueryuivNV = (PFNGLGETOCCLUSIONQUERYUIVNVPROC)
        wglGetProcAddress("glGetOcclusionQueryuivNV");
}



void
GlRenderer::SetupProjection(const int w, const int h)
{
  glViewport(0, 0, w, h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluPerspective(70.0, 1.0, 0.1, 2.0*Magnitude(mSceneGraph->GetBox().Diagonal()));
  glMatrixMode(GL_MODELVIEW);
}

void
GlRenderer::SetupCamera()
{
  Vector3 target = mViewPoint + mViewDirection;
  Vector3 up(0,1,0);
  
  glLoadIdentity();
  gluLookAt(mViewPoint.x, mViewPoint.y, mViewPoint.z,
                        target.x, target.y, target.z,
                        up.x, up.y, up.z);
}

void
GlRenderer::RandomViewPoint()
{
  Vector3 pVector = Vector3(halton.GetNumber(1),
                                                        halton.GetNumber(2),
                                                        halton.GetNumber(3));
  
  Vector3 dVector = Vector3(2*M_PI*halton.GetNumber(4),
                                                        M_PI*halton.GetNumber(5),
                                                        0.0f);
  
  mViewPoint = mSceneGraph->GetBox().GetPoint(pVector);
  
  mViewDirection = Normalize(Vector3(sin(dVector.x),
                                                                         //                                                                      cos(dVector.y),
                                                                         0.0f,
                                                                         cos(dVector.x)));

  halton.GenerateNext();
}


float
GlRenderer::GetPixelError()
{
  float pErrorPixels = -1.0f;

  glReadBuffer(GL_BACK);
  
  mUseFalseColors = true;

  SetupCamera();
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  glEnable( GL_CULL_FACE );
  
  RenderScene();

  // now check whether any backfacing polygon would pass the depth test
  static int query = -1;
  if (query == -1)
        glGenOcclusionQueriesNV(1, (unsigned int *)&query);
  
  glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
  glDepthMask(GL_FALSE);
  glDisable( GL_CULL_FACE );
  
  glBeginOcclusionQueryNV(query);
  
  RenderScene();
  
  glEndOcclusionQueryNV();

  // at this point, if possible, go and do some other computation
  glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
  glDepthMask(GL_TRUE);
  glEnable( GL_CULL_FACE );
  
  unsigned int pixelCount;
  // reenable other state
  glGetOcclusionQueryuivNV(query,
                                                   GL_PIXEL_COUNT_NV,
                                                   &pixelCount);

  if (pixelCount > 0)
        return -1.0f; // backfacing polygon found -> not a valid viewspace sample

  ViewCell *viewcell = mViewCellsManager->GetViewCell(mViewPoint);
  
  if (viewcell) {
        SetupCamera();
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // Render PVS
        std::map<Intersectable *,
          PvsData<Intersectable *>,
          LtSample<Intersectable *> >::const_iterator it = viewcell->GetPvs().mEntries.begin();
        
        for (; it != viewcell->GetPvs().mEntries.end(); ++ it) {
          Intersectable *object = (*it).first;
          RenderIntersectable(object);
        }

        glBeginOcclusionQueryNV(query);

        SetupCamera();

        RenderScene();
        
        glEndOcclusionQueryNV();
        

        unsigned int pixelCount;
        // reenable other state
        glGetOcclusionQueryuivNV(query,
                                                         GL_PIXEL_COUNT_NV,
                                                         &pixelCount);
        
        pErrorPixels = (100.f*pixelCount)/(GetWidth()*GetHeight());
  }
  
  return pErrorPixels;
}


float
GlRendererWidget::RenderErrors()
{
  float pErrorPixels = -1.0f;

  glReadBuffer(GL_BACK);
  
  mUseFalseColors = true;

  SetupCamera();
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  glEnable( GL_CULL_FACE );
  
  ObjectContainer::const_iterator oi = mObjects.begin();
  for (; oi != mObjects.end(); oi++)
        RenderIntersectable(*oi);

  ViewCell *viewcell = mViewCellsManager->GetViewCell(mViewPoint);
  
  QImage im1, im2;
  QImage diff;
  
  if (viewcell) {
        // read back the texture
        im1 = grabFrameBuffer(true);
        
        SetupCamera();
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        
        std::map<Intersectable *,
          PvsData<Intersectable *>,
          LtSample<Intersectable *> >::const_iterator it = viewcell->GetPvs().mEntries.begin();
        
        for (; it != viewcell->GetPvs().mEntries.end(); ++ it) {
          Intersectable *object = (*it).first;
          RenderIntersectable(object);
        }

        // read back the texture
        im2 = grabFrameBuffer(true);
        
        diff = im1;
        int x, y;
        int errorPixels = 0;
        
        for (y = 0; y < im1.height(); y++)
          for (x = 0; x < im1.width(); x++)
                if (im1.pixel(x, y) == im2.pixel(x, y))
                  diff.setPixel(x, y, qRgba(0,0,0,0));
                else {
                  diff.setPixel(x, y, qRgba(255,128,128,255));
                  errorPixels++;
                }
        pErrorPixels = (100.f*errorPixels)/(im1.height()*im1.width());
  }

  // now render the pvs again
  SetupCamera();
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  mUseFalseColors = false;
        
  oi = mObjects.begin();
  for (; oi != mObjects.end(); oi++)
        RenderIntersectable(*oi);

  // now render im1
  if (viewcell) {
        if (mTopView) {
          mWireFrame = true;
          RenderMeshInstance(viewcell);
          mWireFrame = false;
        }
        
        // init ortographic projection
        glMatrixMode(GL_PROJECTION);
        glPushMatrix();
        
        glLoadIdentity();
        gluOrtho2D(0, 1.0f, 0, 1.0f);
        
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        
        bindTexture(diff);
        
        glPushAttrib(GL_ENABLE_BIT);
        glEnable( GL_ALPHA_TEST );
        glDisable( GL_CULL_FACE );
        glAlphaFunc( GL_GREATER, 0.5 );
        
        glEnable( GL_TEXTURE_2D );
        glBegin(GL_QUADS);
        
        glTexCoord2f(0,0);
        glVertex3f(0,0,0);
        
        glTexCoord2f(1,0);
        glVertex3f( 1, 0, 0);
        
        glTexCoord2f(1,1);
        glVertex3f( 1, 1, 0);
        
        glTexCoord2f(0,1);
        glVertex3f(0, 1, 0);
        glEnd();
        
        glPopAttrib();
        
        // restore the projection matrix
        glMatrixMode(GL_PROJECTION);
        glPopMatrix();
        glMatrixMode(GL_MODELVIEW);
  }

  return pErrorPixels;
}


bool
GlRenderer::RenderScene()
{
  static int glList = -1;
  if (glList == -1)
  {
        glList = glGenLists(1);
        glNewList(glList, GL_COMPILE);
        ObjectContainer::const_iterator oi = mObjects.begin();
        for (; oi != mObjects.end(); oi++)
          RenderIntersectable(*oi);
        glEndList();
  }
  
  glCallList(glList);
  
  return true;
}


void
GlRendererBuffer::ClearErrorBuffer()
{
  for (int i=0; i < mPvsStatFrames; i++) {
        mPvsErrorBuffer[i] = 1.0f;
  }
}


void
GlRendererBuffer::EvalPvsStat()
{
  mPvsStat.Reset();
  halton.Reset();

  makeCurrent();
  SetupProjection(GetWidth(), GetHeight());
  
  for (int i=0; i < mPvsStatFrames; i++) {
        float err;
        RandomViewPoint();
        if (mPvsErrorBuffer[i] > 0.0f) {
          mPvsErrorBuffer[i] = GetPixelError();
          cout<<"("<<i<<","<<mPvsErrorBuffer[i]<<")";
          //      swapBuffers();
        }
        
        err = mPvsErrorBuffer[i];
        
        if (err >= 0.0f) {
          if (err > mPvsStat.maxError)
                mPvsStat.maxError = err;
          mPvsStat.sumError += err;
          if (err == 0.0f)
                mPvsStat.errorFreeFrames++;
          mPvsStat.frames++;
        }
  }
  
  doneCurrent();

  cout<<endl<<flush;
  mRenderingFinished.wakeAll();
}





void
GlRendererWidget::mousePressEvent(QMouseEvent *e)
{
  int x = e->pos().x();
  int y = e->pos().y();

  mousePoint.x = x;
  mousePoint.y = y;
  
}

void
GlRendererWidget::mouseMoveEvent(QMouseEvent *e)
{
  float MOVE_SENSITIVITY = Magnitude(mSceneGraph->GetBox().Diagonal())*1e-3;
  float TURN_SENSITIVITY=0.1f;
  float TILT_SENSITIVITY=32.0 ;
  float TURN_ANGLE= M_PI/36.0 ;

  int x = e->pos().x();
  int y = e->pos().y();
  
  if (e->modifiers() & Qt::ControlModifier) {
        mViewPoint.y += (y-mousePoint.y)*MOVE_SENSITIVITY/2.0;
        mViewPoint.x += (x-mousePoint.x)*MOVE_SENSITIVITY/2.0;
  } else {
        mViewPoint += mViewDirection*((mousePoint.y - y)*MOVE_SENSITIVITY);
        float adiff = TURN_ANGLE*(x - mousePoint.x)*-TURN_SENSITIVITY;
        float angle = atan2(mViewDirection.x, mViewDirection.z);
        mViewDirection.x = sin(angle+adiff);
        mViewDirection.z = cos(angle+adiff);
  }
  
  mousePoint.x = x;
  mousePoint.y = y;
  
  updateGL();
}

void
GlRendererWidget::mouseReleaseEvent(QMouseEvent *)
{


}

void
GlRendererWidget::resizeGL(int w, int h)
{
  SetupProjection(w, h);
  updateGL();
}

void
GlRendererWidget::paintGL()
{
        RenderErrors();
        
        mFrame++;
}


void
GlRendererWidget::SetupCamera()
{
  if (!mTopView)
        GlRenderer::SetupCamera();
  else {
        float dist = Magnitude(mSceneGraph->GetBox().Diagonal())*0.05;
        Vector3 pos = mViewPoint - dist*Vector3(mViewDirection.x,
                                                                                        -1,
                                                                                        mViewDirection.y);
        
        Vector3 target = mViewPoint + dist*mViewDirection;
        Vector3 up(0,1,0);
        
        glLoadIdentity();
        gluLookAt(pos.x, pos.y, pos.z,
                          target.x, target.y, target.z,
                          up.x, up.y, up.z);
  }

}

void
GlRendererWidget::keyPressEvent ( QKeyEvent * e )
{
  switch (e->key()) {
  case Qt::Key_T:
        mTopView = !mTopView;
        updateGL();
        break;
  default:
        e->ignore();
        break;
  }
  
}


void GlRendererBuffer::SampleBeamContributions(Intersectable *sourceObject,
                                                                                           Beam &beam,
                                                                                           const int desiredSamples,
                                                                                           BeamSampleStatistics &stat)
{
        // create beam mesh if not already doen
        //TODO: should this be done here?
        
        beam.CreateMesh(2.0f * Magnitude(mSceneGraph->GetBox().Diagonal()));

        // TODO: should not be done every time here
        // only back faces are interesting for the depth pass
        glShadeModel(GL_FLAT);
        glDisable(GL_LIGHTING);
        // needed to kill the fragments for the front buffer
        glEnable(GL_ALPHA_TEST);
        glAlphaFunc(GL_GREATER, 0);

        // assumes that the beam is constructed and contains kd-tree nodes
        // and viewcells which it intersects
  
  
        // Get the number of viewpoints to be sampled
        // Now it is a sqrt but in general a wiser decision could be made.
        // The less viewpoints the better for rendering performance, since less passes
        // over the beam is needed.
        // The viewpoints could actually be generated outside of the bounding box which
        // would distribute the 'efective viewpoints' of the object surface and thus
        // with a few viewpoints better sample the vipoint space....
  //TODO: remove
        //int viewPointSamples = sqrt((float)desiredSamples);
        int viewPointSamples = max(desiredSamples / (GetWidth() * GetHeight()), 1);
        
        // the number of direction samples per pass is given by the number of viewpoints
        int directionalSamples = desiredSamples / viewPointSamples;
        
        Debug << "directional samples: " << directionalSamples << endl;
        for (int i = 0; i < viewPointSamples; ++ i) 
        {
                Vector3 viewPoint = beam.mBox.GetRandomPoint();
                
                // perhaps the viewpoint should be shifted back a little bit so that it always lies
                // inside the source object
                // 'ideally' the viewpoints would be distributed on the soureObject surface, but this
        // would require more complicated sampling (perhaps hierarchical rejection sampling of
                // the object surface is an option here - only the mesh faces which are inside the box
                // are considered as candidates) 
                
                SampleViewpointContributions(sourceObject,
                                                                         viewPoint,
                                                                         beam,
                                                                         directionalSamples,
                                                                         stat);
        }


        // note:
        // this routine would be called only if the number of desired samples is sufficiently
        // large - for other rss tree cells the cpu based sampling is perhaps more efficient
        // distributing the work between cpu and gpu would also allow us to place more sophisticated
        // sample distributions (silhouette ones) using the cpu and the jittered once on the GPU
        // in order that thios scheme is working well the gpu render buffer should run in a separate
        // thread than the cpu sampler, which would not be such a big problem....
}


void GlRendererBuffer::SampleViewpointContributions(Intersectable *sourceObject,
                                                                                                        const Vector3 viewPoint,
                                                                                                        Beam &beam,
                                                                                                        const int samples,
                                                    BeamSampleStatistics &stat)
{
    // 1. setup the view port to match the desired samples
        glViewport(0, 0, GetWidth(), GetHeight());

        // 2. setup the projection matrix and view matrix to match the viewpoint + beam.mDirBox
        SetupProjectionForViewPoint(viewPoint, beam, sourceObject);

        // 3. reset z-buffer to 0 and render the source object for the beam
        //    with glCullFace(Enabled) and glFrontFace(GL_CW)
        //    save result to depth map

        // front depth buffer must bé initialised to 0
        float clearDepth;
        glGetFloatv(GL_DEPTH_CLEAR_VALUE, &clearDepth);
        glClearDepth(0.0f);
        

        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
        //glFrontFace(GL_CW);
        glEnable(GL_CULL_FACE);
        glCullFace(GL_FRONT);
        glColorMask(0, 0, 0, 0);
        

        // stencil is increased where the source object is located
        glEnable(GL_STENCIL_TEST);      
        glStencilFunc(GL_ALWAYS, 0x1, 0x1);
        glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);

#if 0
        static int glSourceObjList = -1;         
        if (glSourceObjList != -1) 
        {
                glSourceObjList = glGenLists(1);
                glNewList(glSourceObjList, GL_COMPILE);

                RenderIntersectable(sourceObject);
        
                glEndList();
        }
        glCallList(glSourceObjList);

#else
        RenderIntersectable(sourceObject);

#endif  
        // reset clear function
        glClearDepth(clearDepth);

        // copy contents of depth buffer into depth texture
        // depth buffer holds ray origins
        glBindTexture(GL_TEXTURE_2D, frontDepthMap);    
        glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, depthMapSize, depthMapSize);


#if 0
        // only the samples which are inside the beam AND on the source object
        // should be considered => only where stencil == 2
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        glStencilFunc(GL_ALWAYS, 0x2, 0x2);
        glStencilOp(GL_INCR, GL_INCR, GL_INCR);

        // render back face of frustum beam
        RenderMesh(beam.mMesh);
#endif


        // 4. set back to normal rendering and clear the ray termination depth buffer
        //    only rays which have non-zero entry in the origin buffer are valid since
        //    they realy start on the object surface (this can also be tagged by setting a
        //    stencil buffer bit at step 3)

        //glDisable(GL_STENCIL_TEST);
        glEnable(GL_STENCIL_TEST);
        glStencilFunc(GL_EQUAL, 0x1, 0x1);
        //glStencilFunc(GL_EQUAL, 0x2, 0x2);
        glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);

        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        glColorMask(1, 1, 1, 1);
        glDepthMask(1);
        glEnable(GL_DEPTH_TEST);
        //glDisable(GL_STENCIL_TEST);   
        glEnable(GL_CULL_FACE);
        glCullFace(GL_BACK);


        // 5. render all objects inside the beam using id based false color
        //    (objects can be compiled to a gl list now so that subsequent rendering for
        //     this beam is fast - the same hold for step 3)

        if (beam.mFlags & !Beam::STORE_OBJECTS)
        {
                vector<KdNode *>::const_iterator it, it_end = beam.mKdNodes.end();

                Intersectable::NewMail();
                for (it = beam.mKdNodes.begin(); it != it_end; ++ it)
                {
                        mKdTree->CollectObjects(*it, beam.mObjects);
                }
        }

        // list of objects intersected by the frustum
#if 0
        static int glObjList = -1; 
        if (glObjList != -1) 
        {
                glObjList = glGenLists(1);
                glNewList(glObjList, GL_COMPILE);
        
                ObjectContainer::const_iterator it, it_end = beam.mObjects.end();
                for (it = beam.mObjects.begin(); it != it_end; ++ it)
                {
                        if (*it != sourceObject)
                                RenderIntersectable(*it);
                }
                
                glEndList();
        }
        glCallList(glObjList);
#else
        ObjectContainer::const_iterator it, it_end = beam.mObjects.end();
        for (it = beam.mObjects.begin(); it != it_end; ++ it)
        {       
                if (*it != sourceObject)
                        RenderIntersectable(*it);
        }
#endif

        
    // 6. Now we have a two depth buffers defining the ray origin and termination

        
        // bind depth texture
        glEnable(GL_TEXTURE_2D);
        
        // bind depth cull pixel shader
        cgGLBindProgram(sCgFragmentProgram);
        cgGLEnableProfile(sCgFragmentProfile);

        // 7. Use occlusion queries for all viewcell meshes associated with the beam ->
        // a fragment passes if the corresponding stencil fragment is set and its depth is
        // between origin and termination buffer

        // create new queries if necessary
        GenQueries((int)beam.mViewCells.size());

        // now check whether any backfacing polygon would pass the depth test?
        //matt: should check both back /front facing because of dual depth buffer
        //and danger of cutting the near plane with front facing polys.
        glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
        glDepthMask(GL_FALSE);
        glDisable(GL_CULL_FACE);
  
        ViewCellContainer::const_iterator vit, vit_end = beam.mViewCells.end();

        int queryIdx = 0;

        for (vit = beam.mViewCells.begin(); vit != vit_end; ++ vit)
        {
                glBeginOcclusionQueryNV(sQueries[queryIdx ++]);

                RenderIntersectable(*vit);
                
                glEndOcclusionQueryNV();
        }

        // at this point, if possible, go and do some other computation

        queryIdx = 0;
        unsigned int pixelCount;

        // 8. The number of visible pixels is the number of sample rays which see the source
        //    object from the corresponding viewcell -> remember these values for later update
        //   of the viewcell pvs - or update immediately?

        for (vit = beam.mViewCells.begin(); vit != vit_end; ++ vit)
        {
                // fetch queries
                glGetOcclusionQueryuivNV(sQueries[queryIdx ++],
                                                                 GL_PIXEL_COUNT_NV,
                                                                 &pixelCount);
                if (pixelCount)
                        Debug << "view cell " << (*vit)->GetId() << " visible pixels: " << pixelCount << endl;
        }
        

        //  In general it is not neccessary to remember to extract all the rays cast. I hope it
        // would be sufficient to gain only the intergral statistics about the new contributions
        // and so the rss tree would actually store no new rays (only the initial ones)
        // the subdivision of the tree would only be driven by the statistics (the glrender could
        // evaluate the contribution entropy for example)
        // However might be an option to extract/store only those the rays which made a contribution
        // (new viewcell has been discovered) or relative contribution greater than a threshold ... 

        ObjectContainer pvsObj;
        stat.pvsSize = ComputePvs(beam.mObjects, pvsObj);
        
        
#if 0
        // copy contents of back depth buffer into depth texture
        // depth buffer holds ray origins
        glBindTexture(GL_TEXTURE_2D, backDepthMap);     
        glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, depthMapSize, depthMapSize);
#endif
        // reset state
        glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
        glDepthMask(GL_TRUE);
        glEnable(GL_CULL_FACE);
        glDisable(GL_STENCIL_TEST);
        cgGLDisableProfile(sCgFragmentProfile);
        glDisable(GL_TEXTURE_2D);

        // remove objects again
        if (beam.mFlags & !Beam::STORE_OBJECTS)
                beam.mObjects.clear();
}


void GlRendererBuffer::GenQueries(const int numQueries)
{
        if ((int)sQueries.size() < numQueries)
        {
                const int n = numQueries - (int)sQueries.size();
                unsigned int *newQueries = new unsigned int[n];

                glGenOcclusionQueriesNV(n, (unsigned int *)newQueries);

                for (int i = 0; i < n; ++ i)
                {
                        sQueries.push_back(newQueries[i]);
                }

                delete [] newQueries;
        }
}


void GlRendererBuffer::SetupProjectionForViewPoint(const Vector3 &viewPoint, 
                                                                                                   const Beam &beam, 
                                                                                                   Intersectable *sourceObject)
{
        float left, right, bottom, top, znear, zfar;

        beam.ComputePerspectiveFrustum(left, right, bottom, top, znear, zfar,
                                                                   mSceneGraph->GetBox());

        //Debug << left << " " << right << " " << bottom << " " << top << " " << znear << " " << zfar << endl;
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glFrustum(left, right, bottom, top, znear, zfar);
        //glFrustum(-1, 1, -1, 1, 1, 20000);

    const Vector3 center = viewPoint + beam.GetMainDirection() * (zfar - znear) * 0.3;
        const Vector3 up = 
                Normalize(CrossProd(beam.mPlanes[0].mNormal, beam.mPlanes[4].mNormal));

#ifdef _DEBUG
        Debug << "view point: " << viewPoint << endl;
        Debug << "eye: " << center << endl;
        Debug << "up: " << up << endl;
#endif

        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        gluLookAt(viewPoint.x, viewPoint.y, viewPoint.z, 
                          center.x, center.y, center.z,                   
                          up.x, up.y, up.z);
}               

  
void GlRendererBuffer::InitGL()
{
        GlRenderer::InitGL();
        // initialise dual depth buffer textures
        glGenTextures(1, &frontDepthMap);
        glBindTexture(GL_TEXTURE_2D, frontDepthMap);
        
        glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, depthMapSize, 
                depthMapSize, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, NULL);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

        glGenTextures(1, &backDepthMap);
        glBindTexture(GL_TEXTURE_2D, backDepthMap);
        
        glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, depthMapSize, 
                depthMapSize, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, NULL);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

        // cg initialization
        cgSetErrorCallback(handleCgError);
        sCgContext = cgCreateContext();
        
        if (cgGLIsProfileSupported(CG_PROFILE_ARBFP1))
                sCgFragmentProfile = CG_PROFILE_ARBFP1;
        else 
        {
          // try FP30
          if (cgGLIsProfileSupported(CG_PROFILE_FP30))
            sCgFragmentProfile = CG_PROFILE_FP30;
          else 
          {
                  Debug << "Neither arbfp1 or fp30 fragment profiles supported on this system" << endl;
                  exit(1);
          }
  }

  sCgFragmentProgram = cgCreateProgramFromFile(sCgContext,              
                                                                                           CG_SOURCE, "../src/dual_depth.cg",
                                                                                           sCgFragmentProfile,
                                                                                           NULL, 
                                                                                           NULL);

  if (!cgIsProgramCompiled(sCgFragmentProgram))
          cgCompileProgram(sCgFragmentProgram);

  cgGLLoadProgram(sCgFragmentProgram);
  cgGLBindProgram(sCgFragmentProgram);
 
  Debug << "---- PROGRAM BEGIN ----\n" << 
          cgGetProgramString(sCgFragmentProgram, CG_COMPILED_PROGRAM) << "---- PROGRAM END ----\n";
}


void GlRendererBuffer::ComputeRays(Intersectable *sourceObj, VssRayContainer &rays)
{
        for (int i = 0; i < depthMapSize * depthMapSize; ++ i)
        {
                //todo glGetTexImage()
        }
}



inline bool ilt(Intersectable *obj1, Intersectable *obj2)
{
        return obj1->mId < obj2->mId;
}


int GlRendererBuffer::ComputePvs(ObjectContainer &objects, 
                                                                 ObjectContainer &pvs) const
{
        int pvsSize = 0;
        QImage image = toImage();
        Intersectable::NewMail();

        std::stable_sort(objects.begin(), objects.end(), ilt);

        MeshInstance dummy(NULL);

        Intersectable *obj = NULL;
                        
        for (int x = 0; x < image.width(); ++ x)
        {
                for (int y = 0; y < image.height(); ++ y)
                {
                        QRgb pix = image.pixel(x, y);
                        const int id = GetId(qRed(pix), qGreen(pix), qBlue(pix));

                        dummy.SetId(id);

                        ObjectContainer::iterator oit =
                                lower_bound(objects.begin(), objects.end(), &dummy, ilt);
                        
                        
                        if (//(oit != oit.end()) && 
                                ((*oit)->GetId() == id) && 
                                !obj->Mailed())
                        {
                                obj = *oit;
                                obj->Mail();
                                ++ pvsSize;
                                pvs.push_back(obj);
                        }
                }
        }

        return pvsSize;
}

/***********************************************************************/
/*                     GlDebuggerWidget implementation                             */
/***********************************************************************/


GlDebuggerWidget::GlDebuggerWidget(GlRendererBuffer *buf, QWidget *parent)
      : QGLWidget(QGLFormat(QGL::SampleBuffers), parent), mRenderBuffer(buf)
{
        // create the pbuffer
    //pbuffer = new QGLPixelBuffer(QSize(512, 512), format(), this);
    timerId = startTimer(20);
    setWindowTitle(("OpenGL pbuffers"));
}


GlDebuggerWidget::~GlDebuggerWidget()
{
        mRenderBuffer->releaseFromDynamicTexture();
        glDeleteTextures(1, &dynamicTexture);
        
        DEL_PTR(mRenderBuffer);
}


void GlDebuggerWidget::initializeGL()
{
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();

        glFrustum(-1, 1, -1, 1, 10, 100);
        glTranslatef(-0.5f, -0.5f, -0.5f);
        glTranslatef(0.0f, 0.0f, -15.0f);
        glMatrixMode(GL_MODELVIEW);

        glEnable(GL_CULL_FACE);
        initCommon();
        initPbuffer();

}


void GlDebuggerWidget::resizeGL(int w, int h)
{
        glViewport(0, 0, w, h);
}


void GlDebuggerWidget::paintGL()
{
        // draw a spinning cube into the pbuffer..
        mRenderBuffer->makeCurrent();
        
        BeamSampleStatistics stats;
        mRenderBuffer->SampleBeamContributions(mSourceObject, mBeam, mSamples, stats);

        glFlush();

        // rendering directly to a texture is not supported on X11, unfortunately
    mRenderBuffer->updateDynamicTexture(dynamicTexture);
   
    // and use the pbuffer contents as a texture when rendering the
    // background and the bouncing cubes
    makeCurrent();
    glBindTexture(GL_TEXTURE_2D, dynamicTexture);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // draw the background
    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();
    glLoadIdentity();
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();
    glLoadIdentity();

        glPopMatrix();
        glMatrixMode(GL_MODELVIEW);
        glPopMatrix();
}


void GlDebuggerWidget::initPbuffer()
{
        // set up the pbuffer context
    mRenderBuffer->makeCurrent();
        /*mRenderBuffer->InitGL();

        glViewport(0, 0, mRenderBuffer->size().width(), mRenderBuffer->size().height());
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(-1, 1, -1, 1, -99, 99);
        glTranslatef(-0.5f, -0.5f, 0.0f);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();

        glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);*/
        
        // generate a texture that has the same size/format as the pbuffer
    dynamicTexture = mRenderBuffer->generateDynamicTexture();

        // bind the dynamic texture to the pbuffer - this is a no-op under X11
        mRenderBuffer->bindToDynamicTexture(dynamicTexture);
        makeCurrent();
}

void GlDebuggerWidget::initCommon()
{
        glEnable(GL_TEXTURE_2D);
        glEnable(GL_DEPTH_TEST);

        glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
}