diff --git a/apps/nexus/extraction.cpp b/apps/nexus/extraction.cpp
new file mode 100644
index 00000000..c6d86716
--- /dev/null
+++ b/apps/nexus/extraction.cpp
@@ -0,0 +1,157 @@
+#include "extraction.h"
+#include "metric.h"
+#include "nexusmt.h"
+
+#include <algorithm>
+
+using namespace std;
+using namespace nxs;
+
+Extraction::Extraction(): target_error(4.0f), extr_max(0xffffffff),
+			  draw_max(640), disk_max(100) {
+  metric = new FrustumMetric;
+}
+
+Extraction::~Extraction() {
+  if(metric) delete metric;
+}
+
+void Extraction::Extract(NexusMt *_mt) {
+  mt = _mt;
+
+  //clear statistics
+  extr_used = draw_used = disk_used = 0;
+  
+  //first we clear the visited flags
+  visited.clear();
+  visited.resize(mt->history.n_nodes(), false);
+
+  heap.clear();
+
+  History::Node *root = mt->history.Root();
+  HeapNode hroot(root, 0);
+  Diff(hroot);
+  extr_used += hroot.extr;
+  draw_used += hroot.draw;
+  disk_used += hroot.disk;
+
+  Visit(root); 
+
+  while(heap.size()) {
+    pop_heap(heap.begin(), heap.end());
+    HeapNode hnode = heap.back();
+    heap.pop_back();
+
+    History::Node *node = hnode.node;
+    unsigned int id = node - root;
+    if(visited[id]) continue;
+
+    if(Expand(hnode)) {
+      extr_used += hnode.extr;
+      draw_used += hnode.draw;
+      disk_used += hnode.disk;
+      Visit(node);
+    }
+  }
+
+  Select();
+}
+
+void Extraction::Select() {
+  selected.clear(); 
+  History::Node *root = mt->history.Root();
+  
+  History::Node *nodes = mt->history.nodes;
+  for(unsigned int i = 0; i < visited.size(); i++) {
+    if(!visited[i]) continue;
+    History::Node &node = nodes[i];
+
+    History::Node::iterator n;
+    for(n = node.out_begin(); n != node.out_end(); n++) {
+      unsigned int n_out = (*n).node - root;
+      if(!visited[n_out]) {
+	History::Link &link = *n;
+	for(History::Link::iterator k = link.begin(); k != link.end(); k++) {
+	  unsigned int patch = (*k).patch;
+	  selected.push_back(patch);
+	}
+      }
+    }
+  }
+}
+
+void Extraction::Visit(History::Node *node) {
+  History::Node *root = mt->history.Root();
+  unsigned int n_node = node - root;
+  if(visited[n_node]) return;
+
+  visited[n_node] = true;
+
+  History::Node::iterator i;
+  for(i = node->in_begin(); i != node->in_end(); i++) {
+    unsigned int n_in = (*i).node - root;
+    if(visited[n_in]) continue;
+    HeapNode hin((*i).node, 0);
+    Diff(hin);
+    extr_used += hin.extr;
+    draw_used += hin.draw;
+    disk_used += hin.disk;
+    Visit((*i).node);
+  }
+
+  for(i = node->out_begin(); i != node->out_end(); i++) {
+    float maxerror = 0;
+    History::Link &link = *i;
+    for(History::Link::iterator k = link.begin(); k != link.end(); k++) {
+      Entry &entry = (*mt)[(*k).patch];
+      float error =  metric->GetError(entry);
+      if(error > maxerror) maxerror = error;
+    }
+    //TODO this check may be dangerous for non saturating things...
+    if(maxerror > target_error) {
+      HeapNode hnode((*i).node, maxerror);
+      Diff(hnode);
+      heap.push_back(hnode);
+      push_heap(heap.begin(), heap.end());
+    }
+  }
+}
+
+bool Extraction::Expand(HeapNode &node) {
+  if(extr_used >= extr_max) return false; 
+  if(draw_used >= draw_max) return false;
+  //  if(disk_used >= disk_max) return false;
+  return node.error > target_error; 
+}
+
+void Extraction::Diff(HeapNode &hnode) {
+  History::Node &node = *(hnode.node);
+  History::Node::iterator i;
+  for(i = node.in_begin(); i != node.in_end(); i++) {
+    History::Link &link = *i;
+    for(History::Link::iterator k = link.begin(); k != link.end(); k++) {
+      unsigned int patch = (*k).patch;
+      Entry &entry = (*mt)[patch];
+      hnode.extr -= entry.ram_size;
+      vcg::Sphere3f &sphere = entry.sphere;
+      if(!frustum.IsOutside(sphere.Center(), sphere.Radius()))
+	hnode.draw -= entry.ram_size;
+      if(!entry.patch)
+	hnode.disk -= entry.disk_size;
+    }
+  }
+  
+  for(i = node.out_begin(); i != node.out_end(); i++) {
+    History::Link &link = *i;
+    for(History::Link::iterator k = link.begin(); k != link.end(); k++) {
+      unsigned int patch = (*k).patch;
+      Entry &entry = (*mt)[patch];
+      hnode.extr += entry.ram_size;
+      vcg::Sphere3f &sphere = entry.sphere;
+      if(!frustum.IsOutside(sphere.Center(), sphere.Radius()))
+	hnode.draw += entry.ram_size;
+      if(!entry.patch)
+	hnode.disk += entry.disk_size;
+    }
+  }
+}
diff --git a/apps/nexus/extraction.h b/apps/nexus/extraction.h
new file mode 100644
index 00000000..c53179e0
--- /dev/null
+++ b/apps/nexus/extraction.h
@@ -0,0 +1,61 @@
+#ifndef NXS_EXTRACTION_H
+#define NXS_EXTRACTION_H
+
+#include "history.h"		
+#include <vector>
+#include <wrap/gui/frustum.h>
+
+namespace nxs {
+
+class Metric;
+class NexusMt; 
+
+class Extraction {
+ public:
+  struct HeapNode {
+    History::Node *node;
+    float error;
+    unsigned int extr;
+    unsigned int draw;
+    unsigned int disk;
+    HeapNode(History::Node *_node, float _error): node(_node), error(_error),
+	 extr(0), draw(0), disk(0) {}
+    bool operator<(const HeapNode &node) const {
+      return error < node.error; }
+  };
+
+  Metric *metric;
+
+  vcg::Frustumf frustum;
+
+  float target_error;
+  unsigned int extr_used, extr_max;
+  unsigned int draw_used, draw_max;
+  unsigned int disk_used, disk_max;
+
+  std::vector<bool> visited;
+  std::vector<HeapNode> heap;
+  std::vector<unsigned int> selected;
+
+  Extraction();
+  ~Extraction();
+
+  void Extract(NexusMt *mt);
+  //  void Update(std::vector<unsigned int> &selected);
+
+
+ protected:
+  void Select();
+  void Visit(History::Node *node);
+
+  bool Expand(HeapNode &node);
+  void Diff(HeapNode &node);
+
+ private:
+  NexusMt *mt;
+};
+
+
+}//namespace
+
+#endif
diff --git a/apps/nexus/history.cpp b/apps/nexus/history.cpp
new file mode 100644
index 00000000..25668895
--- /dev/null
+++ b/apps/nexus/history.cpp
@@ -0,0 +1,297 @@
+#include <assert.h>
+#include <map>
+#include <iostream>
+
+#include "history.h"
+
+
+using namespace std;
+using namespace nxs;
+
+History::~History() {
+  if(buffer) delete []buffer;
+  nodes = NULL;
+  in_links= NULL;
+  out_links = NULL;
+  frags = NULL;
+}
+
+void History::Clear() {
+  if(buffer) delete []buffer;
+  buffer = NULL;
+  updates.clear();
+}
+
+void History::ClearQuick() {
+  if(buffer) delete []buffer;
+  buffer = NULL;
+}
+
+void History::ClearUpdates() {
+  updates.clear();
+}
+
+bool History::Load(unsigned int _size, char *mem) {
+  if(buffer) delete []buffer;
+  unsigned int is_quick = *(unsigned int *)mem;
+  bool success;
+  if(is_quick == 53) {
+    //    cerr << "Load quick!\n";
+    success = LoadQuick(_size, mem);
+  } else if(is_quick == 32) {
+    //    cerr << "Load updates\n";
+    success = LoadUpdates(_size, mem);
+  } else {
+    cerr << "Invalid history: " << is_quick << "\n";
+    return false;
+  }
+  return success;
+}
+
+bool History::LoadQuick(unsigned int _size, char *mem) {
+  buffer = mem;
+  nodes = (Node *)(buffer + 5 * sizeof(int));
+  in_links = (Link *)(nodes + n_nodes());
+  out_links = in_links + n_in_links();
+  frags = (Cell *)(out_links + n_out_links());
+
+  //check size is ok;
+  assert(n_nodes() * sizeof(Node) +
+	 (n_in_links() + n_out_links()) * sizeof(Link) +
+	 n_frags() * sizeof(Cell) + 
+	 5 * sizeof(int) == size);
+  size = _size;
+  return LoadPointers();
+}
+
+bool History::LoadUpdates(unsigned int _size, char *mem) {
+  unsigned int *tmp = (unsigned int *)mem;
+  updates.resize(tmp[1]);
+
+  unsigned int pos = 2;
+  for(unsigned int i = 0; i < updates.size(); i++) {
+    unsigned int erased = tmp[pos++];
+    unsigned int created = tmp[pos++];
+    updates[i].erased.resize(erased);
+    updates[i].created.resize(created);
+    for(unsigned int e = 0; e < erased; e++) 
+      updates[i].erased[e] = tmp[pos++];
+    for(unsigned int e = 0; e < created; e++) 
+      updates[i].created[e] = tmp[pos++];
+  }
+  delete []mem;
+  buffer = 0;
+  return true;
+}
+
+bool History::LoadPointers() {
+  //now convert integer to pointers
+  for(unsigned int i = 0; i < n_nodes(); i++) {
+    Node &node = nodes[i];
+    assert(((unsigned int)node.in_link_begin) <= n_in_links());
+    assert(((unsigned int)node.out_link_begin) <= n_out_links());
+    node.in_link_begin = in_links + (unsigned int)(node.in_link_begin);
+    node.out_link_begin = out_links + (unsigned int)(node.out_link_begin);
+  }
+  
+  for(unsigned int i = 0; i < n_in_links(); i++) {
+    Link &link = in_links[i];
+    assert(((unsigned int)link.node) <= n_nodes());
+    assert(((unsigned int)link.frag_begin) <= n_frags());
+    link.node = nodes + (unsigned int)(link.node);
+    link.frag_begin = frags + (unsigned int)(link.frag_begin);
+  } 
+
+  for(unsigned int i = 0; i < n_out_links(); i++) {
+    Link &link = out_links[i];
+    assert(((unsigned int)link.node) <= n_nodes());
+    assert(((unsigned int)link.frag_begin) <= n_frags());
+    link.node = nodes + (unsigned int)(link.node);
+    link.frag_begin = frags + (unsigned int)(link.frag_begin);
+  }
+  return true;
+}
+
+char *History::Save(unsigned int &_size) {
+  if(buffer) {
+    //    cerr << "SaveQuick!\n";
+    return SaveQuick(_size);
+  } else {
+    //    cerr << "Save updates\n";
+    return SaveUpdates(_size);
+  }
+}
+
+char *History::SaveQuick(unsigned int &_size) {
+  assert(buffer);
+  for(unsigned int i = 0; i < n_nodes(); i++) {
+    Node &node = nodes[i];
+    node.in_link_begin = (Link *)(node.in_link_begin - in_links);
+    node.out_link_begin = (Link *)(node.out_link_begin - out_links);
+  }
+  
+  for(unsigned int i = 0; i < n_in_links(); i++) {
+    Link &link = in_links[i];
+    link.node = (Node *)(link.node - nodes);
+    link.frag_begin = (Cell *)(link.frag_begin - frags);
+  }
+
+  for(unsigned int i = 0; i < n_out_links(); i++) {
+    Link &link = out_links[i];
+    link.node = (Node *)(link.node - nodes);
+    link.frag_begin = (Cell *)(link.frag_begin - frags);
+  }
+
+  _size = size;
+  char *tmp = buffer;
+  buffer = NULL;
+  return tmp;
+}
+
+char *History::SaveUpdates(unsigned int &_size) {
+  vector<unsigned int> buf;
+  buf.push_back(32);
+  buf.push_back(updates.size());
+  for(unsigned int i = 0; i < updates.size(); i++) {
+    Update &update = updates[i];
+    buf.push_back(update.erased.size());
+    buf.push_back(update.created.size());
+    for(unsigned int e = 0; e < update.erased.size(); e++)
+      buf.push_back(update.erased[e]);
+    for(unsigned int e = 0; e < update.created.size(); e++)
+      buf.push_back(update.created[e]);
+  }
+  
+  _size = buf.size() * sizeof(unsigned int);
+  char *mem = new char[_size];
+  memcpy(mem, &*buf.begin(), _size);
+  return mem;
+}
+
+bool History::UpdatesToQuick() {
+  //maps cell -> node containing it
+  map<unsigned int, unsigned int> cell_node;   
+  //maps node -> Links
+  map<unsigned int, vector<Link> > node_inlinks;
+  map<unsigned int, vector<Link> > node_outlinks;
+
+  vector<Node> tmp_nodes;
+  tmp_nodes.resize(updates.size());
+
+  vector<Link> tmp_in_links;
+  vector<Link> tmp_out_links;
+  vector<Cell> tmp_frags;
+
+  unsigned int current_node = 0;
+
+  vector<Update>::iterator u;
+  for(u = updates.begin(); u != updates.end(); u++) {      
+    
+    Node &node = tmp_nodes[current_node];
+    
+    //created cells belong to this node, we look also for max error.      
+    for(unsigned int i = 0; i < (*u).created.size(); i++) {      
+      unsigned int cell = (*u).created[i];
+      cell_node[cell] = current_node;        
+    }
+
+    //Every erased cell already belonged to a node.
+    //node -> its cells
+    map<unsigned int, vector<unsigned int> > node_erased;      
+    
+    for(unsigned int i = 0; i < (*u).erased.size(); i++) {
+      unsigned int cell = (*u).erased[i];
+      assert(cell_node.count(cell));
+      node_erased[cell_node[cell]].push_back(cell);               
+    }      
+    
+    
+    //for every node with erased cells we build a fragment and 
+    //put the corresponding cells in it.      
+    map<unsigned int, vector<unsigned int> >::iterator e;
+    for(e = node_erased.begin(); e != node_erased.end(); e++) {
+
+      //node.in.push_back(innodes.size());
+
+      unsigned int floor_node = (*e).first;
+      vector<unsigned int> &cells = (*e).second;
+
+      Node &parent = tmp_nodes[floor_node];
+
+      Link inlink;
+      inlink.node = (Node *)floor_node;
+      inlink.frag_begin = (Cell *)(tmp_frags.size());
+      inlink.frag_size = cells.size();
+
+      Link outlink;
+      outlink.node = (Node *)current_node;
+      outlink.frag_begin = (Cell *)(tmp_frags.size());
+      outlink.frag_size = cells.size();
+
+      //Fill it with erased cells.
+
+      vector<unsigned int>::iterator k;
+      for(k = cells.begin(); k != cells.end(); k++) {
+	Cell cell;
+	cell.patch = (*k);
+	tmp_frags.push_back(cell);
+      }         
+
+      //Add the new Frag to the node.
+
+      node_outlinks[floor_node].push_back(outlink);
+      node_inlinks[current_node].push_back(inlink);
+      
+      //Update in and out of the nodes.
+    }
+    current_node++; 
+  }
+  
+  map<unsigned int, vector<Link> >::iterator k;
+  for(k = node_outlinks.begin(); k != node_outlinks.end(); k++) {
+    unsigned int inode = (*k).first;
+    vector<Link> &links = (*k).second;
+    tmp_nodes[inode].out_link_begin = (Link *)(tmp_out_links.size());
+    tmp_nodes[inode].out_link_size = links.size();
+    
+    for(unsigned int i = 0; i < links.size(); i++) 
+      tmp_out_links.push_back(links[i]);
+  }
+  
+  for(k = node_inlinks.begin(); k != node_inlinks.end(); k++) {
+    unsigned int inode = (*k).first;
+    vector<Link> &links = (*k).second;
+    tmp_nodes[inode].in_link_begin = (Link *)(tmp_in_links.size());
+    tmp_nodes[inode].in_link_size = links.size();
+    
+    for(unsigned int i = 0; i < links.size(); i++) 
+      tmp_in_links.push_back(links[i]);
+  }
+  size = tmp_nodes.size() * sizeof(Node) +
+    tmp_in_links.size() * sizeof(Link) + 
+    tmp_out_links.size() * sizeof(Link) + 
+    tmp_frags.size() * sizeof(Cell) +
+    5 * sizeof(int);
+  
+  if(buffer) delete []buffer;
+  buffer = new char[size];
+
+  quick() = 53;
+  n_nodes() = tmp_nodes.size();
+  n_in_links() = tmp_in_links.size();
+  n_out_links() = tmp_out_links.size();
+  n_frags() = tmp_frags.size();
+
+  nodes = (Node *)(buffer + 5 * sizeof(int));
+  in_links = (Link *)(nodes + n_nodes());
+  out_links = in_links + n_in_links();
+  frags = (Cell *)(out_links + n_out_links());
+  
+  memcpy(nodes, &*tmp_nodes.begin(), tmp_nodes.size()*sizeof(Node));
+  memcpy(in_links, &*tmp_in_links.begin(), tmp_in_links.size()*sizeof(Node));
+  memcpy(out_links, &*tmp_out_links.begin(), 
+	 tmp_out_links.size()*sizeof(Node));
+  memcpy(frags, &*tmp_frags.begin(), tmp_frags.size() * sizeof(Cell));
+
+  return LoadPointers();
+}
diff --git a/apps/nexus/history.h b/apps/nexus/history.h
new file mode 100644
index 00000000..e0da7913
--- /dev/null
+++ b/apps/nexus/history.h
@@ -0,0 +1,103 @@
+#ifndef NXS_HISTORY_H
+#define NXS_HISTORY_H
+
+#include <vector>
+
+//TODO fix a bit better the quick <-> updates duality
+
+namespace nxs {
+  
+  class History {
+  public:
+
+    enum Mode { QUICK = 1, UPDATES = 2 };
+    
+    struct Update {
+      std::vector<unsigned int> erased;
+      std::vector<unsigned int> created;
+    };
+
+    struct Cell {
+      unsigned int patch;
+      //      float error;
+    };
+
+    struct Node;
+
+    struct Link {
+      Node *node;
+
+      typedef Cell *iterator;
+      iterator begin() { return frag_begin; }
+      iterator end() { return frag_begin + frag_size; }
+      unsigned int size() { return frag_size; }
+
+      Cell *frag_begin;
+      unsigned int frag_size;
+    };
+
+    struct Node {
+      typedef Link *iterator;
+    
+      iterator in_begin() { return in_link_begin; }
+      iterator in_end() { return in_link_begin + in_link_size; }
+      unsigned int size() { return in_link_size; }
+
+      iterator out_begin() { return out_link_begin; }
+      iterator out_end() { return out_link_begin + out_link_size; }
+      unsigned int out_size() { return out_link_size; }
+
+      Link *in_link_begin;
+      unsigned int in_link_size;
+      Link *out_link_begin;
+      unsigned int out_link_size;
+    };
+
+    Node *nodes;
+    Link *in_links;
+    Link *out_links;
+    Cell *frags;
+
+    std::vector<Update> updates;
+
+    History(): nodes(NULL), in_links(NULL), out_links(NULL), frags(NULL), 
+      buffer(NULL) {}
+    ~History();
+   
+    Node *Root() { return &nodes[0]; }
+
+    void Clear();
+    void ClearQuick();
+    void ClearUpdates();
+    //Owns memory afterwards.. do not free mem.
+    bool Load(unsigned int size, char *mem);
+    bool LoadQuick(unsigned int size, char *mem);
+    bool LoadUpdates(unsigned int size, char *mem);
+
+    //after these call history is invalid! and memory returned must be freed...
+    char *Save(unsigned int &size); //autodetect
+    char *SaveQuick(unsigned int &size);
+    char *SaveUpdates(unsigned int &size);
+
+    bool QuickToUpdates();
+    bool UpdatesToQuick();
+    bool IsQuick() { return buffer != NULL; }
+
+    int &quick() { return ((int *)buffer)[0]; }
+    int &n_nodes() { return ((int *)buffer)[1]; }
+    int &n_in_links() { return ((int *)buffer)[2]; }
+    int &n_out_links() { return ((int *)buffer)[3]; }
+    int &n_frags() { return ((int *)buffer)[4]; }
+
+    typedef Node *iterator;
+    iterator begin() { return nodes; }
+    iterator end() { return nodes + n_nodes(); }
+  protected:
+    unsigned int size;
+    char *buffer;
+
+    bool LoadPointers();
+  };
+  
+}
+#endif
diff --git a/apps/nexus/index_file.h b/apps/nexus/index_file.h
new file mode 100644
index 00000000..da6b05f1
--- /dev/null
+++ b/apps/nexus/index_file.h
@@ -0,0 +1,79 @@
+#ifndef NXS_INDEX_FILE_H
+#define NXS_INDEX_FILE_H
+
+#include <assert.h>
+
+#include <vector>
+
+#include "mfile.h"
+
+namespace nxs {
+
+  /* WARINING when subclassing this class you must add a Close() 
+     in the destructor! */
+
+template <class T> 
+class IndexFile: public MFile, public std::vector<T> {
+
+ public:
+  virtual ~IndexFile() {}
+
+  bool Create(const std::string &filename, unsigned int header_size, 
+	      unsigned int max_file_size = MFILE_MAX_SIZE) {
+    clear();
+    if(!MFile::Create(filename, max_file_size)) return false;
+    MFile::Redim(header_size);
+    offset = header_size;
+    return true;
+  }
+
+  bool Load(const std::string &filename, bool readonly = false) {
+    clear();
+    if(!MFile::Load(filename, readonly)) return false;
+    SetPosition(0);
+    LoadHeader();
+
+    SetPosition(offset);
+    unsigned int tot;
+    ReadBuffer(&tot, sizeof(unsigned int));
+    resize(tot);
+    ReadBuffer(&*begin(), size() * sizeof(T));
+    return true;
+  }
+
+  void Close() {
+    if(IsReadOnly()) return;
+    if(files.size() == 0) return; //not loaded, not created or closed
+
+    MFile::Redim(offset + size() * sizeof(T));
+    SetPosition(offset);
+    unsigned int tot = size();
+    WriteBuffer(&tot, sizeof(unsigned int));
+    WriteBuffer(&*begin(), size() * sizeof(T));
+    SetPosition(0);
+    SaveHeader();
+    MFile::Close();
+  }
+
+  int64 Length() { //count the header but not the index...
+    return offset;
+  }
+
+  void Redim(int64 size) {
+    MFile::Redim(size);
+    offset = size;
+    assert(MFile::Length() == offset);
+  }
+
+ protected:
+  int64 offset;
+  
+  //MUST set offset to its correct value
+  virtual bool LoadHeader() = 0;
+  //MUST save offset somewhere
+  virtual void SaveHeader() = 0;
+};
+
+} //namespace
+
+#endif
diff --git a/apps/nexus/metric.h b/apps/nexus/metric.h
new file mode 100644
index 00000000..9de3949f
--- /dev/null
+++ b/apps/nexus/metric.h
@@ -0,0 +1,40 @@
+#ifndef NXS_METRIC_H
+#define NXS_METRIC_H
+
+#include <wrap/gui/frustum.h>
+#include <vcg/space/sphere3.h>
+#include "nexus.h"
+
+namespace nxs {
+  
+  enum MetricKind { FRUSTUM, FLAT, DELTA };
+
+  class Metric {
+  public:
+    virtual void GetView() {}
+    virtual float GetError(Entry &entry) = 0;
+  };
+  
+  class FlatMetric: public Metric {
+  public:
+    float GetError(Entry &entry) { return entry.error; }
+  };
+
+  class FrustumMetric: public Metric {
+  public:
+    vcg::Frustumf frustum;
+
+    virtual void GetView() { frustum.GetView(); }
+    float GetError(Entry &entry) {
+      vcg::Sphere3f &sphere = entry.sphere;
+      float dist = Distance(sphere, frustum.ViewPoint());
+      if(dist < 0) 
+	return 1e20f;
+      if(frustum.IsOutside(sphere.Center(), sphere.Radius()))
+	return -1;
+      return entry.error/frustum.Resolution(dist);
+    }
+  };
+}
+
+#endif
diff --git a/apps/nexus/preload.cpp b/apps/nexus/preload.cpp
new file mode 100644
index 00000000..88df625c
--- /dev/null
+++ b/apps/nexus/preload.cpp
@@ -0,0 +1,159 @@
+#include "preload.h"
+#include "nexusmt.h"
+
+using namespace std;
+using namespace nxs;
+
+ void Preload::execute() {
+    assert(mt);
+    while(!get_signaled()) {
+      lock.enter();
+      while(!queue.size()) {
+	lock.leave();
+	pt::psleep(10);
+	lock.enter();
+      }
+      //TODO check we are not loading too much memory!
+      assert(queue.size());
+      unsigned int patch = queue.back();
+      mt->GetPatch(patch, false);
+      queue.pop_back();
+      lock.leave();
+    }
+  }
+  
+/*void Preload::init(NexusMt *m, std::vector<unsigned int> &selected,
+		    std::vector<PServer::Item> &visited) {
+
+  //  cerr << "Init\n";
+
+  safety.lock();
+  mt = m;
+  missing.clear();
+  mt->todraw.clear();
+  float loaded = 0;  
+  unsigned int notloaded = 0;
+  set<unsigned int> tmp;
+  //std::map<unsigned int, float> tmp;
+  vector<QueuePServer::Data> flush;
+  for(unsigned int i = 0; i < selected.size(); i++) {
+    unsigned int patch = selected[i];
+    tmp.insert(patch);   
+    
+    if(!mt->patches.entries[patch].patch) {         
+      PServer::Entry &entry = mt->patches.entries[patch];
+      load.post(patch);
+      loaded += entry.disk_size;
+    } else {
+       PatchInfo &info = mt->index[patch];             
+       //WORKING QueuePServer::Data &data = mt->patches.Lookup(patch, info.nvert, info.nface, 0.0f, flush);
+       QueuePServer::Data &data = mt->patches.Lookup(patch, info.nvert, info.nface, flush);
+       for(unsigned int i = 0; i < flush.size(); i++) {
+          QueuePServer::Data  *data = new QueuePServer::Data;
+          *data = flush[i];
+          draw.post(FLUSH, (unsigned int)data);
+       }
+       // WORKING if(flush.size() != 0) {
+       //  cerr << "Flushing!\n";
+       //   exit(0);
+       //} 
+       mt->todraw.push_back(&data);      
+    }    
+    //missing.push_back(PServer::Item(patch, 0.0f));
+  }
+  loading = 0.2 * loaded + 0.8 * loading;
+
+  for(unsigned int i = 0; i < visited.size(); i++) {
+    PServer::Item &item = visited[i];
+    if(tmp.count(item.patch)) continue;
+//    if(mt->patches.entries[item.patch].patch)    
+//      tmp[item.patch] = item.priority;    
+    if(item.priority != 0.0f)
+      missing.push_back(item);
+      }*/
+
+/*  WORKING QueuePServer &ps = mt->patches;
+  for(unsigned int i = 0; i < ps.heap.size(); i++) {
+    PServer::Item &item = ps.heap[i];
+    if(tmp.count(item.patch)) 
+      item.priority = 0;
+    else {
+      if(item.priority == 0)
+        item.priority = 1;
+      item.priority *= 1.1;
+    }    
+  }
+  make_heap(ps.heap.begin(), ps.heap.end());*/
+
+/*  sort(missing.begin(), missing.end()); //CRITICAL reverse pero'!
+  reverse(missing.begin(), missing.end());    
+  load.post(0xffffffff);
+ 
+  safety.unlock();
+}
+
+void Preload::execute() {      
+
+  float preload;
+  prefetching = 0;
+  loading = 0;
+    while(1) {
+      if(get_signaled()) return;               
+      vector<QueuePServer::Data> flush;      
+      
+      if(load.get_count() || missing.size() == 0) {  
+        preload = 0;
+        pt::message *msg = load.getmessage();
+        if(msg->id != 0xffffffff) {          
+          safety.lock();
+          PatchInfo &info = mt->index[msg->id];                   
+          PServer::Entry &entry = mt->patches.entries[msg->id];
+          loading += entry.disk_size;
+          //posting draw message
+          //WORKING QueuePServer::Data &data = mt->patches.Lookup(msg->id, info.nvert, info.nface, 0.0f, flush);
+          QueuePServer::Data &data = mt->patches.Lookup(msg->id, info.nvert, info.nface, flush);
+          pt::message *msg = new pt::message(DRAW, (unsigned int)&data);
+          msg->result = msg->id;
+          draw.post(msg);
+
+          //p;osting flush messages
+          for(unsigned int i = 0; i < flush.size(); i++) {
+            QueuePServer::Data *data = new QueuePServer::Data;
+            *data = flush[i];
+            draw.post(FLUSH, (unsigned int)data);
+          }
+          safety.unlock();
+        } else {
+          prefetching = 0.2 * preload + 0.8 * prefetching;
+        }
+        delete msg;        
+      } else {             
+        safety.lock();
+        if(missing.size() != 0) {          
+          PServer::Item item = missing.back();
+          missing.pop_back();
+
+/*Working          if(item.priority > mt->patches.MaxPriority()) {	        
+            missing.clear();
+            
+          } else {        */
+/*PatchInfo &info = mt->index[item.patch];      
+            //cerr << "prefetching: " << item.patch << endl;
+            //WORKING mt->patches.Lookup(item.patch, info.nvert, info.nface, item.priority, flush);
+            if(!mt->patches.entries[item.patch].patch) {
+              PServer::Entry &entry = mt->patches.entries[item.patch];
+              preload += entry.disk_size;
+          
+              mt->patches.Lookup(item.patch, info.nvert, info.nface, flush);              
+              for(unsigned int i = 0; i < flush.size(); i++) {
+                QueuePServer::Data  *data = new QueuePServer::Data;
+                *data = flush[i];
+                draw.post(FLUSH, (unsigned int)data);
+              }
+            }
+        //  }
+        }
+        safety.unlock();
+      }      
+    }    
+}*/
diff --git a/apps/nexus/preload.h b/apps/nexus/preload.h
new file mode 100644
index 00000000..6a532ac8
--- /dev/null
+++ b/apps/nexus/preload.h
@@ -0,0 +1,40 @@
+#ifndef NXS_PRELOAD_H
+#define NXS_PRELOAD_H
+
+#include <assert.h>
+
+#include <vector>
+
+#include <ptypes/pasync.h>
+
+namespace nxs {
+
+class NexusMt;
+
+class Preload: public pt::thread{
+ public:
+
+  NexusMt *mt;
+  
+  pt::mutex lock;
+  
+  std::vector<unsigned int> queue;
+
+  Preload(): thread(false) {}
+  ~Preload() {
+    waitfor();
+  }
+  
+  void execute();
+  
+  void post(std::vector<unsigned int> &patches) {
+    lock.enter();
+    queue = patches;
+    lock.leave();
+  }
+
+  void cleanup() {}
+};
+
+}
+#endif