#include "Mesh.h"
#include "glInterface.h"
#include "OcclusionQuery.h"
#include "GlRenderer.h"
#include "ViewCellsManager.h"
#include "SceneGraph.h"
#include "Pvs.h"
#include "Viewcell.h"
#include "Beam.h"
#include "KdTree.h"
#include "Environment.h"
#include "Triangle3.h"
#include "IntersectableWrapper.h"
#include "BvHierarchy.h"
#include "KdTree.h"

#ifdef USE_CG

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

#endif

namespace GtpVisibilityPreprocessor {


static bool arbQuerySupport = false;
static bool nvQuerySupport = false;

static GLuint frontDepthMap;
static GLuint backDepthMap;

const int depthMapSize = 512;

static void InitExtensions() 
{
	GLenum err = glewInit();

	if (GLEW_OK != err) 
	{
		// problem: glewInit failed, something is seriously wrong
		cerr << "Error: " << glewGetErrorString(err) << endl;
		exit(1);
	}

	if (GLEW_ARB_occlusion_query) 
		arbQuerySupport = true;
	
	if (GLEW_NV_occlusion_query) 
		nvQuerySupport = true;
	

	if  (!arbQuerySupport && !nvQuerySupport)
	{
		cout << "I require the GL_ARB_occlusion_query or the GL_NV_occlusion_query OpenGL extension to work.\n";
		exit(1);
	}
}


GlRenderer::GlRenderer(SceneGraph *sceneGraph,
					   ViewCellsManager *viewCellsManager,
					   KdTree *tree):
  Renderer(sceneGraph, viewCellsManager),
  mKdTree(tree)
{
  mSceneGraph->CollectObjects(&mObjects);

  //  mViewCellsManager->GetViewPoint(mViewPoint);

  viewCellsManager->GetViewPoint(mViewPoint);
	//mSceneGraph->GetBox().Center();
  mViewDirection = Vector3(0,0,1);

  //  mViewPoint = Vector3(991.7, 187.8, -271);
  //  mViewDirection = Vector3(0.9, 0, -0.4);

  //  timerId = startTimer(10);
  // debug coords for atlanta
  //  mViewPoint = Vector3(3473, 6.778, -1699);
  //  mViewDirection = Vector3(-0.2432, 0, 0.97);
  
  mFrame = 0;
  mWireFrame = false;
  Environment::GetSingleton()->GetBoolValue("Preprocessor.detectEmptyViewSpace",
											mDetectEmptyViewSpace);
  mSnapErrorFrames = true;
  mSnapPrefix = "snap/";
  mUseForcedColors = false;
  mRenderBoxes = false;
  mUseGlLists = true;
  //mUseGlLists = false;

  Environment::GetSingleton()->GetIntValue("Preprocessor.pvsRenderErrorSamples", mPvsStatFrames);
  mPvsErrorBuffer.resize(mPvsStatFrames);
  ClearErrorBuffer();
  
}

GlRenderer::~GlRenderer()
{
  cerr<<"gl renderer destructor..\n";
 
  //CLEAR_CONTAINER(sQueries);
  CLEAR_CONTAINER(mOcclusionQueries);

  cerr<<"done."<<endl;
}


void
GlRenderer::RenderTriangle(TriangleIntersectable *object)
{
  Triangle3 &t = object->GetItem();
  
  glBegin(GL_TRIANGLES);
  Vector3 normal = t.GetNormal();
  glNormal3f(normal.x, normal.y, normal.z);
  glVertex3f(t.mVertices[0].x, t.mVertices[0].y, t.mVertices[0].z);
  glVertex3f(t.mVertices[1].x, t.mVertices[1].y, t.mVertices[1].z);
  glVertex3f(t.mVertices[2].x, t.mVertices[2].y, t.mVertices[2].z);
  glEnd();
}

void
GlRenderer::RenderIntersectable(Intersectable *object)
{
  if (object->Mailed())
	return;
  object->Mail();
  
  glPushAttrib(GL_CURRENT_BIT);
  if (mUseFalseColors)
	SetupFalseColor(object->mId);
  
  switch (object->Type()) {
  case Intersectable::MESH_INSTANCE:
	RenderMeshInstance((MeshInstance *)object);
	break;
  case Intersectable::VIEW_CELL:
	RenderViewCell(dynamic_cast<ViewCell *>(object));
	break;
  case Intersectable::TRANSFORMED_MESH_INSTANCE:
	RenderTransformedMeshInstance(dynamic_cast<TransformedMeshInstance *>(object));
	break;
  case Intersectable::TRIANGLE_INTERSECTABLE:
	RenderTriangle(dynamic_cast<TriangleIntersectable *>(object));
	break;
  case Intersectable::BVH_INTERSECTABLE: {

	BvhNode *node = dynamic_cast<BvhNode *>(object);
	
	if (mRenderBoxes)
	  RenderBox(node->GetBoundingBox());
	else
	  RenderBvhNode(node);
	break;
  }
  case Intersectable::KD_INTERSECTABLE: {
	KdNode *node = (dynamic_cast<KdIntersectable *>(object))->GetItem();
	
	if (mRenderBoxes)
	  RenderBox(mKdTree->GetBox(node));
	else
	  RenderKdNode(node);
	break;
  }
	
  default:
	cerr<<"Rendering this object not yet implemented\n";
	break;
  }

  glPopAttrib();
}

void
GlRenderer::RenderRays(const VssRayContainer &rays)
{
  VssRayContainer::const_iterator it = rays.begin(), it_end = rays.end();

  glBegin(GL_LINES);
  for (; it != it_end; ++it) {
	VssRay *ray = *it;
	float importance = log10(1e3*ray->mWeightedPvsContribution)/3.0f;
	//	cout<<"w="<<ray->mWeightedPvsContribution<<" r="<<ray->mWeightedPvsContribution;
	glColor3f(importance, importance, importance);
	glVertex3fv(&ray->mOrigin.x);
	glVertex3fv(&ray->mTermination.x);
  }
  glEnd();
}



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

	if (!mUseFalseColors) {
	  if (vc->GetValid()) 
		glColor3f(0,1,0);
	  else
		glColor3f(0,0,1);
	}
	
	RenderMesh(vc->GetMesh());
  } else {
	// render viewcells in the subtree
	if (!vc->IsLeaf()) {
	  ViewCellInterior *vci = (ViewCellInterior *) vc;

	  ViewCellContainer::iterator it = vci->mChildren.begin();
	  for (; it != vci->mChildren.end(); ++it) {
		RenderViewCell(*it);
	  }
	} else {
	  //	  cerr<<"Empty viewcell mesh\n";
	}
  }
}


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


void
GlRenderer::RenderTransformedMeshInstance(TransformedMeshInstance *mi)
{
	// apply world transform before rendering
	Matrix4x4 m;
	mi->GetWorldTransform(m);

	glPushMatrix();
/* cout << "\n";
	for (int i = 0; i < 4; ++ i)
		for (int j = 0; j < 4; ++ j)
			cout << m.x[i][j] << " "; cout << "\n"*/

	glMultMatrixf((float *)m.x);

	/*GLfloat dummy[16];
	glGetFloatv(GL_MODELVIEW_MATRIX, dummy);
	for (int i = 0; i < 16; ++ i)
		cout << dummy[i] << " ";
	cout << endl;*/
	RenderMesh(mi->GetMesh());
	
	glPopMatrix();
}


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


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


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


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

  if (!mUseFalseColors && !mUseForcedColors)
	  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()
{
  mSphere = (GLUquadric *)gluNewQuadric();
  
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();

  glFrontFace(GL_CCW);
  glCullFace(GL_BACK);
  glEnable(GL_CULL_FACE);
  glShadeModel(GL_FLAT);
  glDepthFunc( GL_LESS );
  glEnable(GL_DEPTH_TEST);
  glEnable(GL_CULL_FACE);
  
  InitExtensions();

  glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE );

  glEnable( GL_NORMALIZE );
  
  glClearColor(0.0f, 0.0f, 1.0f, 1.0f);
  
  OcclusionQuery::GenQueries(mOcclusionQueries, 10);
}


void
GlRenderer::SetupProjection(const int w, const int h, const float angle)
{
  glViewport(0, 0, w, h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluPerspective(angle, 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);
  
  if (abs(DotProd(mViewDirection, up)) > 0.99f)
	up = Vector3(1, 0, 0);
  
  glLoadIdentity();
  gluLookAt(mViewPoint.x, mViewPoint.y, mViewPoint.z,
			target.x, target.y, target.z,
			up.x, up.y, up.z);
}

void
GlRenderer::_RenderScene()
{
  ObjectContainer::const_iterator oi = mObjects.begin();
  for (; oi != mObjects.end(); oi++)
	RenderIntersectable(*oi);
}

void
GlRenderer::_RenderSceneTriangles()
{
  glBegin(GL_TRIANGLES);

  ObjectContainer::const_iterator oi = mObjects.begin();
  for (; oi != mObjects.end(); oi++) {
	
	if ((*oi)->Type() == Intersectable::TRIANGLE_INTERSECTABLE) {
	  TriangleIntersectable *object = (TriangleIntersectable *)*oi;
	  Triangle3 &t = object->GetItem();
	  
	  Vector3 normal = t.GetNormal();
	  glNormal3f(normal.x, normal.y, normal.z);
	  glVertex3f(t.mVertices[0].x, t.mVertices[0].y, t.mVertices[0].z);
	  glVertex3f(t.mVertices[1].x, t.mVertices[1].y, t.mVertices[1].z);
	  glVertex3f(t.mVertices[2].x, t.mVertices[2].y, t.mVertices[2].z);
	  
	}
  }

  glEnd();
  
}

bool
GlRenderer::RenderScene()
{
  Intersectable::NewMail();
  static int glList = -1;
  if (mUseGlLists) {
	if (glList == -1) {
	  glList = glGenLists(1);
	  glNewList(glList, GL_COMPILE);
	  _RenderSceneTriangles();
	  glEndList();
	}
	
	glCallList(glList);
  } else
	_RenderSceneTriangles();
	
  
  return true;
}


void
GlRendererBuffer::EvalQueryWithItemBuffer(
										  //RenderCostSample &sample
									   )
{
	// read back the texture
	glReadPixels(0, 0,
				GetWidth(), GetHeight(),
				GL_RGBA,
				GL_UNSIGNED_BYTE,
				mPixelBuffer);
		
			
	unsigned int *p = mPixelBuffer;
			
	for (int y = 0; y < GetHeight(); y++)
	{
		for (int x = 0; x < GetWidth(); x++, p++) 
		{
			unsigned int id = (*p) & 0xFFFFFF;

			if (id != 0xFFFFFF)
				++ mObjects[id]->mCounter;
		}
	}
}



/****************************************************************/
/*               GlRendererBuffer implementation                */
/****************************************************************/



GlRendererBuffer::GlRendererBuffer(SceneGraph *sceneGraph,
								   ViewCellsManager *viewcells,
								   KdTree *tree):
GlRenderer(sceneGraph, viewcells, tree)  
{
  
  mPixelBuffer = NULL;
  
  // implement width and height in subclasses
}


void
GlRendererBuffer::EvalQueryWithOcclusionQueries(
									   //RenderCostSample &sample
									   )
{
	glDepthFunc(GL_LEQUAL);
		
	glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
	glDepthMask(GL_FALSE);


	// simulate detectemptyviewspace using backface culling
	if (mDetectEmptyViewSpace) 
	{
		glEnable(GL_CULL_FACE);
		//cout << "culling" << endl;
	}
	else
	{
		//cout << "not culling" << endl;
		glDisable(GL_CULL_FACE);
	}

	
	//const int numQ = 1;
	const int numQ = (int)mOcclusionQueries.size();
	
	//glFinish();
#if 0
	//-- now issue queries for all objects
	for (int j = 0; j < (int)mObjects.size(); ++ j) 
	{
		mOcclusionQueries[j]->BeginQuery();
		RenderIntersectable(mObjects[j]);
		mOcclusionQueries[j]->EndQuery();

		unsigned int pixelCount;

		pixelCount = mOcclusionQueries[j]->GetQueryResult();
		mObjects[j]->mCounter += pixelCount;
	}
#else

	int q = 0;

	//-- now issue queries for all objects
	for (int j = 0; j < (int)mObjects.size(); j += q) 
	{	
		for (q = 0; ((j + q) < (int)mObjects.size()) && (q < numQ); ++ q) 
		{
			//glFinish();
			mOcclusionQueries[q]->BeginQuery();
			
			RenderIntersectable(mObjects[j + q]);
		
			mOcclusionQueries[q]->EndQuery();
			//glFinish();
		}
		//cout << "q: " << q << endl;
		// collect results of the queries
		for (int t = 0; t < q; ++ t) 
		{
			unsigned int pixelCount;
		
			//-- reenable other state
#if 0
			bool available;

			do 
			{
				available = mOcclusionQueries[t]->ResultAvailable();
				
				if (!available) cout << "W";
			} 
			while (!available);
#endif

			pixelCount = mOcclusionQueries[t]->GetQueryResult();

			//if (pixelCount > 0)
			//	cout <<"o="<<j+q<<" q="<<mOcclusionQueries[q]->GetQueryId()<<" pc="<<pixelCount<<" ";
			mObjects[j + t]->mCounter += pixelCount;
		}

		//j += q;
	}
#endif
	//glFinish();
	glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
	glDepthMask(GL_TRUE);
	
	glEnable(GL_CULL_FACE);
}


void
GlRenderer::RandomViewPoint()
{ 
  // do not use this function since it could return different viewpoints for
  // different executions of the algorithm

  //  mViewCellsManager->GetViewPoint(mViewPoint);

  while (1) {
	Vector3 pVector = Vector3(halton.GetNumber(1),
							  halton.GetNumber(2),
							  halton.GetNumber(3));
	
	mViewPoint =  mViewCellsManager->GetViewSpaceBox().GetPoint(pVector);
	ViewCell *v = mViewCellsManager->GetViewCell(mViewPoint);
	if (v && v->GetValid())
	  break;
	// generate a new vector
	halton.GenerateNext();
  }
  
  Vector3 dVector = Vector3(2*M_PI*halton.GetNumber(4),
							M_PI*halton.GetNumber(5),
							0.0f);
  
  mViewDirection = Normalize(Vector3(sin(dVector.x),
									 //									 cos(dVector.y),
									 0.0f,
									 cos(dVector.x)));
  halton.GenerateNext();
}


void
GlRenderer::RenderBox(const AxisAlignedBox3 &box)
{

  glBegin(GL_LINE_LOOP);
  glVertex3d(box.Min().x, box.Max().y, box.Min().z );
  glVertex3d(box.Max().x, box.Max().y, box.Min().z );
  glVertex3d(box.Max().x, box.Min().y, box.Min().z );
  glVertex3d(box.Min().x, box.Min().y, box.Min().z );
  glEnd();

  glBegin(GL_LINE_LOOP);
  glVertex3d(box.Min().x, box.Min().y, box.Max().z );
  glVertex3d(box.Max().x, box.Min().y, box.Max().z );
  glVertex3d(box.Max().x, box.Max().y, box.Max().z );
  glVertex3d(box.Min().x, box.Max().y, box.Max().z );
  glEnd();

  glBegin(GL_LINE_LOOP);
  glVertex3d(box.Max().x, box.Min().y, box.Min().z );
  glVertex3d(box.Max().x, box.Min().y, box.Max().z );
  glVertex3d(box.Max().x, box.Max().y, box.Max().z );
  glVertex3d(box.Max().x, box.Max().y, box.Min().z );
  glEnd();

  glBegin(GL_LINE_LOOP);
  glVertex3d(box.Min().x, box.Min().y, box.Min().z );
  glVertex3d(box.Min().x, box.Min().y, box.Max().z );
  glVertex3d(box.Min().x, box.Max().y, box.Max().z );
  glVertex3d(box.Min().x, box.Max().y, box.Min().z );
  glEnd();

  glBegin(GL_LINE_LOOP);
  glVertex3d(box.Min().x, box.Min().y, box.Min().z );
  glVertex3d(box.Max().x, box.Min().y, box.Min().z );
  glVertex3d(box.Max().x, box.Min().y, box.Max().z );
  glVertex3d(box.Min().x, box.Min().y, box.Max().z );
  glEnd();

  glBegin(GL_LINE_LOOP);
  glVertex3d(box.Min().x, box.Max().y, box.Min().z );
  glVertex3d(box.Max().x, box.Max().y, box.Min().z );
  glVertex3d(box.Max().x, box.Max().y, box.Max().z );
  glVertex3d(box.Min().x, box.Max().y, box.Max().z );

  glEnd();

}

void
GlRenderer::RenderBvhNode(BvhNode *node)
{
  if (node->IsLeaf()) {
	BvhLeaf *leaf = (BvhLeaf *) node;

#if 0
	if (leaf->mGlList == 0) {
	  leaf->mGlList = glGenLists(1);
	  if (leaf->mGlList != 0)
		glNewList(leaf->mGlList, GL_COMPILE);
	  
	  for (int i=0; i < leaf->mObjects.size(); i++)
		RenderIntersectable(leaf->mObjects[i]);
	  
	  if (leaf->mGlList != 0)
		glEndList();
	}
	
	if (leaf->mGlList != 0)
	  glCallList(leaf->mGlList);
#else
	for (int i=0; i < leaf->mObjects.size(); i++)
	  RenderIntersectable(leaf->mObjects[i]);
#endif
  } else {
	BvhInterior *in = (BvhInterior *)node;
	RenderBvhNode(in->GetBack());
	RenderBvhNode(in->GetFront());
  }

  //cout << "leaf obj " << i << endl;

}

void
GlRenderer::RenderKdNode(KdNode *node)
{
  if (node->IsLeaf()) {
	KdLeaf *leaf = (KdLeaf *) node;
	for (int i=0; i < leaf->mObjects.size(); i++) {
	  RenderIntersectable(leaf->mObjects[i]);
	}
  } else {
	KdInterior *in = (KdInterior *)node;
	RenderKdNode(in->mBack);
	RenderKdNode(in->mFront);
  }
  
}







void
GlRendererBuffer::EvalRenderCostSample(RenderCostSample &sample,
									   const bool useOcclusionQueries,
									   const int threshold
									   )
{
  // choose a random view point
  mViewCellsManager->GetViewPoint(mViewPoint);
  sample.mPosition = mViewPoint;
  //cout << "viewpoint: " << mViewPoint << endl;
  
  // take a render cost sample by rendering a cube
  Vector3 directions[6];
  
  directions[0] = Vector3(1,0,0);
  directions[1] = Vector3(0,1,0);
  directions[2] = Vector3(0,0,1);
  directions[3] = Vector3(-1,0,0);
  directions[4] = Vector3(0,-1,0);
  directions[5] = Vector3(0,0,-1);
  
  sample.mVisibleObjects = 0;
  
  // reset object counters
  ObjectContainer::const_iterator it, it_end = mObjects.end();
  
  for (it = mObjects.begin(); it != it_end; ++ it) 
	{
	  (*it)->mCounter = 0;
	}

  ++ mFrame;
  
  //glCullFace(GL_FRONT);
  glCullFace(GL_BACK);
  glDisable(GL_CULL_FACE);
  
  
	// query all 6 directions for a full point sample
  for (int i = 0; i < 6; ++ i) 
	{
	  mViewDirection = directions[i];
	  SetupCamera();
	  
	  glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
	  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	  //glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);	glDepthMask(GL_TRUE);
	  glDepthFunc(GL_LESS);
	  
	  mUseFalseColors = true;
	  
	  // the actual scene rendering fills the depth (for occlusion queries)
	  // and the frame buffer (for item buffer)
	  RenderScene();
	  
	  
	  if (0) 
		{
		  char filename[256];
		  sprintf(filename, "snap/frame-%04d-%d.png", mFrame, i);
		  //		  QImage im = toImage();
		  //		  im.save(filename, "PNG");
		}
	  
	  // evaluate the sample
	  if (useOcclusionQueries) 
		{
		  EvalQueryWithOcclusionQueries();
		}
	  else 
		{
		  EvalQueryWithItemBuffer();
		}
	}  
  
  // now evaluate the statistics over that sample
  // currently only the number of visible objects is taken into account
  sample.Reset();
  
  for (it = mObjects.begin(); it != it_end; ++ it) 
	{
	  Intersectable *obj = *it;
	  if (obj->mCounter >= threshold) 
		{
		  ++ sample.mVisibleObjects;
		  sample.mVisiblePixels += obj->mCounter;
		}
	}
  
  //cout << "RS=" << sample.mVisibleObjects << " ";
}


GlRendererBuffer::~GlRendererBuffer()
{
#if 0
#ifdef USE_CG
	if (sCgFragmentProgram)
		cgDestroyProgram(sCgFragmentProgram);
	if (sCgContext)
		cgDestroyContext(sCgContext);
#endif
#endif
}


void
GlRendererBuffer::SampleRenderCost(const int numSamples,
								   vector<RenderCostSample> &samples,
								   const bool useOcclusionQueries,
								   const int threshold
								   )
{
  MakeCurrent();

  if (mPixelBuffer == NULL)
	  mPixelBuffer = new unsigned int[GetWidth()*GetHeight()];
  
  // using 90 degree projection to capture 360 view with 6 samples
  SetupProjection(GetHeight(), GetHeight(), 90.0f);

  //samples.resize(numSamples);
  halton.Reset();
  
  // the number of queries queried in batch mode
  const int numQ = 500;

  //const int numQ = (int)mObjects.size();
  if (useOcclusionQueries)
  {
	  cout << "\ngenerating " << numQ << " queries ... ";
	  OcclusionQuery::GenQueries(mOcclusionQueries, numQ);
	  cout << "finished" << endl;
  }

  // sampling queries 
  for (int i = 0; i < numSamples; ++ i)
  {
	  cout << ".";
	  EvalRenderCostSample(samples[i], useOcclusionQueries, threshold);
  }

  DoneCurrent();
}
  




void
GlRenderer::ClearErrorBuffer()
{
  for (int i=0; i < mPvsStatFrames; i++) {
	mPvsErrorBuffer[i].mError = 1.0f;
  }
  mPvsStat.maxError = 0.0f;
}


void
GlRendererBuffer::EvalPvsStat()
{

  MakeCurrent();

  GlRenderer::EvalPvsStat();
  
  DoneCurrent();
  
  //  mRenderingFinished.wakeAll();
}


void GlRendererBuffer::SampleBeamContributions(Intersectable *sourceObject,
											   Beam &beam,
											   const int desiredSamples,
											   BeamSampleStatistics &stat)
{
	// TODO: should be moved out of here (not to be done every time)
	// 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 viewpoint space....

	//TODO: comment in
	//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....

	// disable alpha test again
	glDisable(GL_ALPHA_TEST);
}



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, samples, samples);

	// 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 the front depth map
	//    the front depth map holds ray origins


	// front depth buffer must be 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_CCW);
	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	

	 // copy contents of the front depth buffer into depth texture
	glBindTexture(GL_TEXTURE_2D, frontDepthMap);	
	glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, depthMapSize, depthMapSize);

	// reset clear function
	glClearDepth(clearDepth);
	
	
	// 4. set up the termination depth buffer (= standard depth buffer)
	//    only rays which have non-zero entry in the origin buffer are valid since
	//    they realy start on the object surface (this is tagged by setting a
	//    stencil buffer bit at step 3).
	
	glStencilFunc(GL_EQUAL, 0x1, 0x1);
	glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glDepthMask(1);

	glEnable(GL_DEPTH_TEST);
		
	glEnable(GL_CULL_FACE);
	glCullFace(GL_BACK);

	// setup front depth buffer
	glEnable(GL_TEXTURE_2D);
	
#if 0
#ifdef USE_CG
	// bind pixel shader implementing the front depth buffer functionality
	cgGLBindProgram(sCgFragmentProgram);
	cgGLEnableProfile(sCgFragmentProfile);
#endif
#endif
	// 5. render all objects inside the beam 
	//    we can use id based false color to read them back for gaining the pvs

	glColorMask(1, 1, 1, 1);

	
	// if objects not stored in beam => extract objects
	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);
		}
	}


	//    (objects can be compiled to a gl list now so that subsequent rendering for
	//    this beam is fast - the same hold for step 3)
	//    Afterwards we have two depth buffers defining the ray origin and termination
	

#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)
		{
			// render all objects except the source object
			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)
	{	
		// render all objects except the source object
		if (*it != sourceObject)
			RenderIntersectable(*it);
	}
#endif
	
   	// 6. 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
	OcclusionQuery::GenQueries(mOcclusionQueries, (int)beam.mViewCells.size());

	// 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)
	{
		mOcclusionQueries[queryIdx ++]->BeginQuery();

		RenderIntersectable(*vit);
		
		mOcclusionQueries[queryIdx]->EndQuery();

		++ queryIdx;
	}

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

	// 7. 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?

	queryIdx = 0;

	for (vit = beam.mViewCells.begin(); vit != vit_end; ++ vit)
	{
		// fetch queries
		unsigned int pixelCount = mOcclusionQueries[queryIdx ++]->GetQueryResult();

		if (pixelCount)
			Debug << "view cell " << (*vit)->GetId() << " visible pixels: " << pixelCount << endl;
	}
	

	// 8. Copmpute rendering statistics
	// 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);
	
	// to gain ray source and termination
	// copy contents of ray termination buffer into depth texture
	// and compare with ray source buffer
#if 0
	VssRayContainer rays;

	glBindTexture(GL_TEXTURE_2D, backDepthMap);	
	glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, depthMapSize, depthMapSize);

	ComputeRays(Intersectable *sourceObj, rays);

#endif

	////////
	//-- cleanup

	// reset gl state
	glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
	glDepthMask(GL_TRUE);
	glEnable(GL_CULL_FACE);
	glDisable(GL_STENCIL_TEST);

#if 0
#ifdef USE_CG
	cgGLDisableProfile(sCgFragmentProfile);
#endif
#endif

	glDisable(GL_TEXTURE_2D);

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


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) * 0.3f;
	const Vector3 up = 
		Normalize(CrossProd(beam.mPlanes[0].mNormal, beam.mPlanes[4].mNormal));

#ifdef GTP_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()
{
	MakeCurrent(); 
	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);

#if 0
#ifdef USE_CG

	// 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";

#endif

#endif
  DoneCurrent();
}


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


void
GlRenderer::EvalPvsStat()
{

  mPvsStat.Reset();
  halton.Reset();

  SetupProjection(GetWidth(), GetHeight());

  cout<<"mPvsStatFrames="<<mPvsStatFrames<<endl;
  
  for (int i=0; i < mPvsStatFrames; i++) {
	float err;
	// set frame id for saving the error buffer
	mFrame = i;
	RandomViewPoint();

 	if (mPvsErrorBuffer[i].mError == 1.0f) {
	  // check if the view point is valid
	  if (!ValidViewPoint())
		mPvsErrorBuffer[i].mError = -1.0f;

	  // manualy corrected view point
	  if (mFrame == 5105)
		mPvsErrorBuffer[i].mError = -1.0f;
	}
	
	
	// atlanta problematic frames: 325 525 691 1543
#if 0
	if (mFrame != 325 &&
		mFrame != 525 &&
		mFrame != 691 &&
		mFrame != 1543)
	  mPvsErrorBuffer[i] = -1;
	else {
	  Debug<<"frame ="<<mFrame<<" vp="<<mViewPoint<<" vd="<<mViewDirection<<endl;
	}
#endif
	
 	if (mPvsErrorBuffer[i].mError > 0.0f) {
	  int pvsSize;
	  
	  float error = GetPixelError(pvsSize);
	  mPvsErrorBuffer[i].mError = error;
	  mPvsErrorBuffer[i].mPvsSize = pvsSize;

	  //	  emit UpdatePvsErrorItem(i,
	  //							  mPvsErrorBuffer[i]);
	  cout<<"("<<i<<","<<mPvsErrorBuffer[i].mError<<")";
	  //	  swapBuffers();
	}
	
	err = mPvsErrorBuffer[i].mError;
	
	if (err >= 0.0f) {
	  if (err > mPvsStat.maxError)
		mPvsStat.maxError = err;
	  mPvsStat.sumError += err;
	  mPvsStat.sumPvsSize += mPvsErrorBuffer[i].mPvsSize;
	  
	  if (err == 0.0f)
		mPvsStat.errorFreeFrames++;
	  mPvsStat.frames++;
	}
  }
  
  glFinish();
  cout<<endl<<flush;
}

bool
GlRenderer::ValidViewPoint()
{
  if (!mDetectEmptyViewSpace)
	return true;

  OcclusionQuery *query = mOcclusionQueries[0];

  // now check whether any backfacing polygon would pass the depth test
  SetupCamera();
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  glEnable( GL_CULL_FACE );
  glCullFace(GL_BACK);
  
  //  cout<<"VV1 ";
  RenderScene();
  
  glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
  glDepthMask(GL_FALSE);
  glDisable( GL_CULL_FACE );
  
  query->BeginQuery();
  
  //  cout<<"VV2 ";
  RenderScene();
  //  cout<<"VV3 ";
  
  query->EndQuery();
  
  // 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 );

  //  int wait = 0;
  //  while (!query.ResultAvailable()) {
  //	wait++;
  //  }
  
  // reenable other state
  unsigned int pixelCount = query->GetQueryResult();
  //  cout<<"VV4 ";
  
  if (pixelCount > 0)
	return false; // backfacing polygon found -> not a valid viewspace sample

  return true;
}

float
GlRenderer::GetPixelError(int &pvsSize)
{
  return -1.0f;
}

void
GlRenderer::RenderViewPoint()
{
  mWireFrame = true;
  glPushMatrix();
  glTranslatef(mViewPoint.x, mViewPoint.y, mViewPoint.z);
  glScalef(5.0f,5.0f,5.0f);
  glPushAttrib(GL_CURRENT_BIT);
  glColor3f(1.0f, 0.0f, 0.0f);
  gluSphere((::GLUquadric *)mSphere,
			1e-3*Magnitude(mViewCellsManager->GetViewSpaceBox().Size()), 6, 6);
  glPopAttrib();
  glPopMatrix();
  mWireFrame = false;
}





}