diff --git a/EGrUtils.h b/EGrUtils.h
index b333ca5..37b0891 100644
--- a/EGrUtils.h
+++ b/EGrUtils.h
@@ -46,3 +46,13 @@ FrameToOpenGlMatrix( const Frame3d& frFrame, double Matrix[OGLMAT_DIM])
 
    return true ;
 }
+
+//----------------------------------------------------------------------------
+inline bool
+OpenGlMatrixToFrame( const double Matrix[OGLMAT_DIM], Frame3d& frFrame)
+{
+   return frFrame.Set( Point3d( Matrix[12], Matrix[13], Matrix[14]),
+                       Vector3d( Matrix[0], Matrix[1], Matrix[2]),
+                       Vector3d( Matrix[4], Matrix[5], Matrix[6]),
+                       Vector3d( Matrix[8], Matrix[9], Matrix[10])) ;
+}
diff --git a/EgtGraphics.rc b/EgtGraphics.rc
index f42966d..0402cb5 100644
Binary files a/EgtGraphics.rc and b/EgtGraphics.rc differ
diff --git a/ObjEGrGraphics.h b/ObjEGrGraphics.h
index bec5f27..a0caa0a 100644
--- a/ObjEGrGraphics.h
+++ b/ObjEGrGraphics.h
@@ -42,7 +42,8 @@ class ObjEGrGraphics : public IObjGraphics
       virtual bool StartTriangles( int nNum, bool bAux = false) = 0 ;
       virtual bool AddTriangle( const Triangle3d& Tria, const TriFlags3d& TFlags, const TriNormals3d& TNrms) = 0 ;
       virtual bool EndTriangles( void) = 0 ;
-      virtual bool Draw( int nStat, int nMark, bool bSurfSha, bool ShowAux) = 0 ;
+      virtual bool Draw( int nStat, int nMark, bool bSurfSha, int nAlpha, bool ShowAux) = 0 ;
+      virtual bool GetLocalBBox( BBox3d& b3Loc) = 0 ;
 } ;
 
 //----------------------------------------------------------------------------
diff --git a/ObjNewGraphics.cpp b/ObjNewGraphics.cpp
index c971e9d..86bd4b5 100644
--- a/ObjNewGraphics.cpp
+++ b/ObjNewGraphics.cpp
@@ -105,6 +105,7 @@ ObjNewGraphics::AddPoint( const Point3d& ptP, bool bAux)
    glBufferData( GL_ARRAY_BUFFER, 1 * SIZEV3F, NULL, GL_STATIC_DRAW) ;
    Vert3f  v3V( ptP) ;
    glBufferSubData( GL_ARRAY_BUFFER, 0, SIZEV3F, &v3V) ;
+   m_b3Loc.Add( ptP) ;
    int nCount = 1 ;
    glVertexPointer( 3, GL_FLOAT, 0, ((void*)(0))) ;
    glEnableClientState( GL_VERTEX_ARRAY) ;
@@ -143,6 +144,7 @@ ObjNewGraphics::AddLines( const PNTVECTOR& vPnt, bool bAux)
    for ( int i = 0 ; i < nCount ; ++ i) {
       v3V.Set( vPnt[i]) ;
       glBufferSubData( GL_ARRAY_BUFFER, i * SIZEV3F, SIZEV3F, &v3V) ;
+      m_b3Loc.Add( vPnt[i]) ;
    }
    glVertexPointer( 3, GL_FLOAT, 0, ((void*)(0))) ;
    glEnableClientState( GL_VERTEX_ARRAY) ;
@@ -182,6 +184,7 @@ ObjNewGraphics::AddPolyLine( const PolyLine& PL, bool bAux)
    for ( bool bFound = PL.GetFirstPoint( ptP) ; bFound ; bFound = PL.GetNextPoint( ptP)) {
       v3V.Set( ptP) ;
       glBufferSubData( GL_ARRAY_BUFFER, nCount * SIZEV3F, SIZEV3F, &v3V) ;
+      m_b3Loc.Add( ptP) ;
       ++ nCount ;
    }
    glVertexPointer( 3, GL_FLOAT, 0, ((void*)(0))) ;
@@ -238,10 +241,11 @@ ObjNewGraphics::AddTriangle( const Triangle3d& Tria, const TriFlags3d& TFlags, c
       return false ;
   // recupero il conteggio dei vertici
    int nCount = m_ngaList.back().m_nCount ;
-  // emetto i vertici e le normali del triangolo
+  // emetto i flag, le normali e i vertici del triangolo + aggiorno bbox
    for ( int i = 0 ; i < 3 ; ++ i) {
       Vert3f v3V( Tria.GetP( i)) ;
       glBufferSubData( GL_ARRAY_BUFFER, nCount * SIZEVNF, SIZEV3F, &v3V) ;
+      m_b3Loc.Add( Tria.GetP( i)) ;
       Vert3f v3N( TNrms.vtN[i]) ;
       glBufferSubData( GL_ARRAY_BUFFER, nCount * SIZEVNF + SIZEV3F, SIZEV3F, &v3N) ;
       unsigned char cFlag = ( TFlags.bFlag[i] ? 1 : 0) ;
@@ -280,7 +284,7 @@ ObjNewGraphics::EndTriangles( void)
 
 //----------------------------------------------------------------------------
 bool
-ObjNewGraphics::Draw( int nStat, int nMark, bool bSurfSha, bool bShowAux)
+ObjNewGraphics::Draw( int nStat, int nMark, bool bSurfSha, int nAlpha, bool bShowAux)
 {
    if ( ! m_bValid  ||  m_pScene == nullptr  ||  ! m_pScene->MakeCurrent())
       return false ;
@@ -305,15 +309,19 @@ ObjNewGraphics::Draw( int nStat, int nMark, bool bSurfSha, bool bShowAux)
       if ( nMark == GDB_MK_ON) {
          bStdCol = false ;
          Color colMark = ( ( GetScene() != nullptr) ? GetScene()->GetMark() : Color( 192, 192, 0)) ;
+         colMark.SetAlpha( nAlpha) ;
          colMark.GetFloat( fSelMarkCol) ;
          Color colMarkBack = GetSurfBackColor( colMark) ;
+         colMarkBack.SetAlpha( nAlpha) ;
          colMarkBack.GetFloat( fSelMarkBackCol) ;
       }
       else if ( nStat == GDB_ST_SEL) {
          bStdCol = false ;
          Color colSelSurf = ( ( GetScene() != nullptr) ? GetScene()->GetSelSurf() : Color( 255, 255, 192)) ;
+         colSelSurf.SetAlpha( nAlpha) ;
          colSelSurf.GetFloat( fSelMarkCol) ;
          Color colSelSurfBack = GetSurfBackColor( colSelSurf) ;
+         colSelSurfBack.SetAlpha( nAlpha) ;
          colSelSurfBack.GetFloat( fSelMarkBackCol) ;
       }
    }
diff --git a/ObjNewGraphics.h b/ObjNewGraphics.h
index 3bfa4f2..b589451 100644
--- a/ObjNewGraphics.h
+++ b/ObjNewGraphics.h
@@ -76,7 +76,9 @@ class ObjNewGraphics : public ObjEGrGraphics
       virtual bool StartTriangles( int nNum, bool bAux = false) ;
       virtual bool AddTriangle( const Triangle3d& Tria, const TriFlags3d& TFlags, const TriNormals3d& TNrms) ;
       virtual bool EndTriangles( void) ;
-      virtual bool Draw( int nStat, int nMark, bool bSurfSha, bool bShowAux) ;
+      virtual bool Draw( int nStat, int nMark, bool bSurfSha, int nAlpha, bool bShowAux) ;
+      virtual bool GetLocalBBox( BBox3d& b3Loc)
+                      { b3Loc = m_b3Loc ; return ! m_b3Loc.IsEmpty() ; }
 
    public :
       ObjNewGraphics( void) : m_pScene( nullptr), m_bValid( false) {}
@@ -109,6 +111,7 @@ class ObjNewGraphics : public ObjEGrGraphics
       bool    m_bValid ;           // flag
       int     m_nCurrMode ;        // modo corrente
       NGALIST m_ngaList ;          // liste di atomi per nuova grafica
+      BBox3d  m_b3Loc ;            // BoundingBox locale
 } ;
 
 //----------------------------------------------------------------------------
diff --git a/ObjOldGraphics.cpp b/ObjOldGraphics.cpp
index e5b4e42..5ba08b6 100644
--- a/ObjOldGraphics.cpp
+++ b/ObjOldGraphics.cpp
@@ -83,6 +83,8 @@ ObjOldGraphics::AddPoint( const Point3d& ptP, bool bAux)
    AddStart( GL_POINTS, bAux) ;
   // inserisco il nuovo vertice
    AddVert3f( ptP) ;
+  // aggiorno bbox
+   m_b3Loc.Add( ptP) ;
   // fine
    AddEnd() ;
   // dichiaro valida la grafica
@@ -100,9 +102,11 @@ ObjOldGraphics::AddLines( const PNTVECTOR& vPnt, bool bAux)
       return false ;
   // start
    AddStart( GL_LINES, bAux) ;
-  // inserisco i vertici
-   for ( int i = 0 ; i < int( vPnt.size()) ; ++ i)
+  // inserisco i vertici + aggiorno bbox
+   for ( int i = 0 ; i < int( vPnt.size()) ; ++ i) {
       AddVert3f( vPnt[i]) ;
+      m_b3Loc.Add( vPnt[i]) ;
+   }
   // fine
    AddEnd() ;
   // dichiaro valida la grafica
@@ -120,10 +124,12 @@ ObjOldGraphics::AddPolyLine( const PolyLine& PL, bool bAux)
       return false ;
   // start
    AddStart( GL_LINE_STRIP, bAux) ;
-  // inserisco i nuovi vertici
+  // inserisco i nuovi vertici + aggiorno bbox
    Point3d  ptP ;
-   for ( bool bFound = PL.GetFirstPoint( ptP) ; bFound ; bFound = PL.GetNextPoint( ptP))
+   for ( bool bFound = PL.GetFirstPoint( ptP) ; bFound ; bFound = PL.GetNextPoint( ptP)) {
       AddVert3f( ptP) ;
+      m_b3Loc.Add( ptP) ;
+   }
   // fine
    AddEnd() ;
   // dichiaro valida la grafica
@@ -152,11 +158,12 @@ ObjOldGraphics::AddTriangle( const Triangle3d& Tria, const TriFlags3d& TFlags, c
   // modo corrente deve essere triangoli
    if ( m_nCurrMode != GL_TRIANGLES)
       return false ;
-  // emetto le normali e i vertici del triangolo
+  // emetto i flag, le normali e i vertici del triangolo + aggiorno bbox
    for ( int i = 0 ; i < 3 ; ++ i) {
       AddBndFlag( TFlags.bFlag[i]) ;
       AddNormal3f( TNrms.vtN[i]) ;
       AddVert3f( Tria.GetP( i)) ;
+      m_b3Loc.Add( Tria.GetP( i)) ;
    }
    return true ;
 }
@@ -179,7 +186,7 @@ ObjOldGraphics::EndTriangles( void)
 
 //----------------------------------------------------------------------------
 bool
-ObjOldGraphics::Draw( int nStat, int nMark, bool bSurfSha, bool bShowAux)
+ObjOldGraphics::Draw( int nStat, int nMark, bool bSurfSha, int nAlpha, bool bShowAux)
 {
   // se vuoto non faccio alcunché
    if ( m_ogaList.size() == 0)
@@ -201,15 +208,19 @@ ObjOldGraphics::Draw( int nStat, int nMark, bool bSurfSha, bool bShowAux)
       if ( nMark == GDB_MK_ON) {
          bStdCol = false ;
          Color colMark = ( ( GetScene() != nullptr) ? GetScene()->GetMark() : Color( 255, 255, 0)) ;
+         colMark.SetAlpha( nAlpha) ;
          colMark.GetFloat( fSelMarkCol) ;
          Color colMarkBack = GetSurfBackColor( colMark) ;
+         colMarkBack.SetAlpha( nAlpha) ;
          colMarkBack.GetFloat( fSelMarkBackCol) ;
       }
       else if ( nStat == GDB_ST_SEL) {
          bStdCol = false ;
          Color colSelSurf = ( ( GetScene() != nullptr) ? GetScene()->GetSelSurf() : Color( 255, 255, 192)) ;
+         colSelSurf.SetAlpha( nAlpha) ;
          colSelSurf.GetFloat( fSelMarkCol) ;
          Color colSelSurfBack = GetSurfBackColor( colSelSurf) ;
+         colSelSurfBack.SetAlpha( nAlpha) ;
          colSelSurfBack.GetFloat( fSelMarkBackCol) ;
       }
    }
diff --git a/ObjOldGraphics.h b/ObjOldGraphics.h
index f90b24d..b54721d 100644
--- a/ObjOldGraphics.h
+++ b/ObjOldGraphics.h
@@ -80,7 +80,9 @@ class ObjOldGraphics : public ObjEGrGraphics
       virtual bool StartTriangles( int nNum, bool bAux = false) ;
       virtual bool AddTriangle( const Triangle3d& Tria, const TriFlags3d& TFlags, const TriNormals3d& TNrms) ;
       virtual bool EndTriangles( void) ;
-      virtual bool Draw( int nStat, int nMark, bool bSurfSha, bool bShowAux) ;
+      virtual bool Draw( int nStat, int nMark, bool bSurfSha, int nAlpha, bool bShowAux) ;
+      virtual bool GetLocalBBox( BBox3d& b3Loc)
+                      { b3Loc = m_b3Loc ; return ! m_b3Loc.IsEmpty() ; }
 
    public :
       ObjOldGraphics( void) : m_pScene( nullptr), m_nCurrMode( GL_NONE), m_bValid( false) {}
@@ -130,6 +132,7 @@ class ObjOldGraphics : public ObjEGrGraphics
       bool    m_bValid ;           // flag
       int     m_nCurrMode ;        // modo corrente
       OGALIST m_ogaList ;          // lista di atomi per vecchia grafica
+      BBox3d  m_b3Loc ;            // BoundingBox locale
 } ;
 
 //----------------------------------------------------------------------------
diff --git a/Scene.h b/Scene.h
index 5e65121..583ede9 100644
--- a/Scene.h
+++ b/Scene.h
@@ -20,17 +20,17 @@
 
 class IGdbIterator ;
 class ICurve ;
+class ObjEGrGraphics ;
 
 //----------------------------------------------------------------------------
-class MdStMk
+struct MdStMkCol
 {
-   public :
-      MdStMk( int nMd, int nSt, int nMk) : nMode( nMd), nStat( nSt), nMark( nMk) {}
-
-   public :
-      int nMode ;
-      int nStat ;
-      int nMark ;
+   int nMode ;
+   int nStat ;
+   int nMark ;
+   Color colObj ;
+   MdStMkCol( int nMd, int nSt, int nMk, Color colC)
+      : nMode( nMd), nStat( nSt), nMark( nMk), colObj( colC) {}
 } ;
 
 //----------------------------------------------------------------------------
@@ -41,6 +41,19 @@ struct SelRec {            // record di selezione per OpenGL (buffer di GLuint)
    GLuint nId ;            // nome dell'oggetto
 } ;
 
+//----------------------------------------------------------------------------
+struct AlphaSurf {
+   ObjEGrGraphics* pGraph ;
+   int nStat ;
+   int nMark ;
+   int nAlpha ;
+   bool bShowAux ;
+   double dZmin ;
+   double dZmax ;
+   AlphaSurf( ObjEGrGraphics* pG, int nS, int nM, int nA, bool bSA, double dZm, double dZM)
+      : pGraph( pG), nStat( nS), nMark( nM), nAlpha( nA), bShowAux( bSA), dZmin( dZm), dZmax( dZM) {}
+} ;
+typedef std::vector<AlphaSurf> ASURFVECTOR ;
 
 //----------------------------------------------------------------------------
 class Scene : public IEGrScene
@@ -167,9 +180,10 @@ class Scene : public IEGrScene
       bool CalcDirUp( void) ;
       bool CalcCameraFrame( Frame3d& frView) ;
      // Geometry
-      bool DrawGroup( int nId, int nPass, MdStMk siParent) ;
-      bool DrawGroup( const IGdbIterator& iIter, int nPass, MdStMk siParent) ;
-      bool DrawGeoObj( const IGdbIterator& iIter, int nPass, MdStMk siObj) ;
+      bool DrawGroup( int nId, int nPass, const MdStMkCol& siParent) ;
+      bool DrawGroup( const IGdbIterator& iIter, int nPass, const MdStMkCol& siParent) ;
+      bool DrawGeoObj( const IGdbIterator& iIter, int nPass, const MdStMkCol& siObj) ;
+      bool DrawAlphaSurfVector( void) ;
       bool DeleteObjGraphicsGroup( int nId) ;
      // Grid
       const Frame3d& GetGridFrame( void)
@@ -233,7 +247,9 @@ class Scene : public IEGrScene
       IGeomDB* m_pGeomDB ;                // puntatore al DB geometrico
       Color    m_colDef ;                 // colore di default
       Color    m_colMark ;                // colore per marcatura
-      Color    m_colSelSurf ;             // colore di superficie selezionata 
+      Color    m_colSelSurf ;             // colore di superficie selezionata
+     // Superfici semitrasparenti
+      ASURFVECTOR m_vAlphaSurf ;          // vettore temporaneo di superfici semitrasparenti
      // Extension
       BBox3d   m_b3ExtWorld ;             // estensione della geometria nel riferimento globale (mondo)
       BBox3d   m_b3ExtView ;              // estensione nel riferimento di vista
diff --git a/SceneBasic.cpp b/SceneBasic.cpp
index 8abcc3f..b8e4406 100644
--- a/SceneBasic.cpp
+++ b/SceneBasic.cpp
@@ -70,6 +70,8 @@ Scene::Scene( void)
    m_colDef.Set( 0, 0, 0) ;
    m_colMark.Set( 255, 255, 0) ;
    m_colSelSurf.Set( 255, 255, 192) ;
+  // Superfici semitrasparenti
+   m_vAlphaSurf.reserve( 100) ;
   // Extension
    SetExtension( BBox3d( -MIN_EXTENSION, -MIN_EXTENSION, -MIN_EXTENSION,
                          MIN_EXTENSION, MIN_EXTENSION, MIN_EXTENSION)) ;
@@ -685,7 +687,7 @@ Scene::Draw( void)
      // imposto disegno wireframe anche per poligoni
       glPolygonMode( GL_FRONT_AND_BACK, GL_LINE) ;
      // disegno le geometrie del DB in una sola passata
-      DrawGroup( GDB_ID_ROOT, 1, MdStMk( GDB_MD_STD, GDB_ST_ON, GDB_MK_OFF)) ;
+      DrawGroup( GDB_ID_ROOT, 1, MdStMkCol( GDB_MD_STD, GDB_ST_ON, GDB_MK_OFF, m_colDef)) ;
       break ;
    case SM_HIDDENLINE :
      // disabilito illuminazione
@@ -696,14 +698,14 @@ Scene::Draw( void)
       glEnable( GL_POLYGON_OFFSET_FILL) ;
       glPolygonOffset( 1.0, 1.0) ;
       glColorMask( GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE) ;
-      DrawGroup( GDB_ID_ROOT, 1, MdStMk( GDB_MD_STD, GDB_ST_ON, GDB_MK_OFF)) ;
+      DrawGroup( GDB_ID_ROOT, 1, MdStMkCol( GDB_MD_STD, GDB_ST_ON, GDB_MK_OFF, m_colDef)) ;
       glColorMask( GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE) ;
       glDisable( GL_POLYGON_OFFSET_FILL) ;
      // disegno griglia senza illuminazione (già impostato)
       DrawGrid() ;
       // seconda passata per tutto in forma 0dim e curve
       glPolygonMode( GL_FRONT_AND_BACK, GL_LINE) ;
-      DrawGroup( GDB_ID_ROOT, 2, MdStMk( GDB_MD_STD, GDB_ST_ON, GDB_MK_OFF)) ;
+      DrawGroup( GDB_ID_ROOT, 2, MdStMkCol( GDB_MD_STD, GDB_ST_ON, GDB_MK_OFF, m_colDef)) ;
       break ;
    case SM_SHADING :
      // disegno griglia senza illuminazione
@@ -730,16 +732,34 @@ Scene::Draw( void)
       glLightfv( GL_LIGHT1, GL_POSITION, Light1Pos) ;
       glEnable( GL_LIGHT1) ;
      // disegno le geometrie del DB
-      // prima passata per superfici con illuminazione abilitata
+      // annullo vettore superfici traslucide
+      m_vAlphaSurf.clear() ;
+      // prima passata per superfici completamente opache con illuminazione abilitata
       glEnable( GL_POLYGON_OFFSET_FILL) ;
       glPolygonOffset( 0.75, 0.75) ;
       glEnable( GL_LIGHTING) ;
-      DrawGroup( GDB_ID_ROOT, 1, MdStMk( GDB_MD_STD, GDB_ST_ON, GDB_MK_OFF)) ;
+      DrawGroup( GDB_ID_ROOT, 1, MdStMkCol( GDB_MD_STD, GDB_ST_ON, GDB_MK_OFF, m_colDef)) ;
       glDisable( GL_POLYGON_OFFSET_FILL) ;
       // seconda passata per 0dim e curve con illuminazione disabilitata
       glDisable( GL_LIGHTING) ;
       glPolygonMode( GL_FRONT_AND_BACK, GL_LINE) ;
-      DrawGroup( GDB_ID_ROOT, 2, MdStMk( GDB_MD_STD, GDB_ST_ON, GDB_MK_OFF)) ;
+      DrawGroup( GDB_ID_ROOT, 2, MdStMkCol( GDB_MD_STD, GDB_ST_ON, GDB_MK_OFF, m_colDef)) ;
+      // terza passata su vettore di superfici trasparenti con :
+      // illuminazione abilitata, blend abilitato e Zdepth solo in lettura
+      if ( m_vAlphaSurf.size() > 0) {
+         glPolygonMode( GL_FRONT_AND_BACK, GL_FILL) ;
+         glEnable( GL_POLYGON_OFFSET_FILL) ;
+         glPolygonOffset( 0.75, 0.75) ;
+         glEnable( GL_LIGHTING) ;
+         glEnable( GL_BLEND) ;
+         glDepthMask( GL_FALSE) ;
+         glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) ;
+         DrawAlphaSurfVector() ;
+         m_vAlphaSurf.clear() ;
+         glDepthMask( GL_TRUE) ;
+         glDisable( GL_BLEND) ;
+         glDisable( GL_POLYGON_OFFSET_FILL) ;
+      }
       break ;
    }
 
diff --git a/SceneGeom.cpp b/SceneGeom.cpp
index cdc84ea..8266747 100644
--- a/SceneGeom.cpp
+++ b/SceneGeom.cpp
@@ -68,7 +68,7 @@ Scene::SetSelSurf( Color colSelSurf)
 
 //----------------------------------------------------------------------------
 bool
-Scene::DrawGroup( int nId, int nPass, MdStMk cParent)
+Scene::DrawGroup( int nId, int nPass, const MdStMkCol& cParent)
 {
   // creo un iteratore
    PtrOwner<IGdbIterator> pIter( CreateGdbIterator( m_pGeomDB)) ;
@@ -85,7 +85,7 @@ Scene::DrawGroup( int nId, int nPass, MdStMk cParent)
 
 //----------------------------------------------------------------------------
 bool
-Scene::DrawGroup( const IGdbIterator& iIter, int nPass, MdStMk cParent)
+Scene::DrawGroup( const IGdbIterator& iIter, int nPass, const MdStMkCol& cParent)
 {
   // creo un iteratore
    PtrOwner<IGdbIterator> pIter( CreateGdbIterator( m_pGeomDB)) ;
@@ -123,6 +123,9 @@ Scene::DrawGroup( const IGdbIterator& iIter, int nPass, MdStMk cParent)
       int nMark = GDB_MK_OFF ;
       pIter->GetMark( nMark) ;
       nMark = ::CalcMark( nMark, cParent.nMark) ;
+     // recupero e aggiorno il colore dell'oggetto
+      Color colObj = cParent.colObj ;
+      pIter->GetMaterial( colObj) ;
      // se in modalità selezione, verifico sia selezionabile
       bool bSel = true ;
       if ( m_bSelect  &&  UnselectableFind( pIter->GetId()))
@@ -131,7 +134,7 @@ Scene::DrawGroup( const IGdbIterator& iIter, int nPass, MdStMk cParent)
       if ( nGdbType == GDB_TY_GEO) {
         // se non nascosto e selezionabile, lo disegno
          if ( nStat != GDB_ST_OFF  &&  bSel) {
-            if ( ! DrawGeoObj( *pIter, nPass, MdStMk( nMode, nStat, nMark)))
+            if ( ! DrawGeoObj( *pIter, nPass, MdStMkCol( nMode, nStat, nMark, colObj)))
                bOk = false ;
          }
       }
@@ -139,7 +142,7 @@ Scene::DrawGroup( const IGdbIterator& iIter, int nPass, MdStMk cParent)
       else if ( nGdbType == GDB_TY_GROUP) {
         // se non nascosto e selezionabile, lo disegno
          if ( nStat != GDB_ST_OFF  &&  bSel) {
-            if ( ! DrawGroup( *pIter, nPass, MdStMk( nMode, nStat, nMark)))
+            if ( ! DrawGroup( *pIter, nPass, MdStMkCol( nMode, nStat, nMark, colObj)))
                bOk = false ;
          }
       }
@@ -153,8 +156,11 @@ Scene::DrawGroup( const IGdbIterator& iIter, int nPass, MdStMk cParent)
 
 //----------------------------------------------------------------------------
 bool
-Scene::DrawGeoObj( const IGdbIterator& iIter, int nPass, MdStMk siObj)
+Scene::DrawGeoObj( const IGdbIterator& iIter, int nPass, const MdStMkCol& siObj)
 {
+  // valore limite di opacità oltre il quale è considerata completa
+   const int ALPHA_LIM = 90 ;
+
   // recupero l'oggetto geometrico e il suo tipo
    IGeoObj* pGeoObj = (const_cast<IGdbIterator*>(&iIter))->GetGeoObj() ;
    if ( pGeoObj == nullptr)
@@ -181,10 +187,6 @@ Scene::DrawGeoObj( const IGdbIterator& iIter, int nPass, MdStMk siObj)
   // se la grafica associata non è valida la ricalcolo
    ObjEGrGraphics* pGraphics = GetObjEGrGraphics( pGeoObj) ;
    if ( ! pGraphics->IsValid()) {
-      // recupero il colore
-      Color cCol ;
-      if ( ! iIter.GetCalcMaterial( cCol))
-         cCol = m_colDef ;
      // se vettore
       if ( nGeoType == GEO_VECT3D) {
         // recupero il vettore
@@ -195,7 +197,7 @@ Scene::DrawGeoObj( const IGdbIterator& iIter, int nPass, MdStMk siObj)
          PolyLine PL ;
          pVector->GetDrawWithArrowHead( 0.1, 10, PL) ;
          pGraphics->Clear() ;
-         pGraphics->AddColor( cCol) ;
+         pGraphics->AddColor( siObj.colObj) ;
          pGraphics->AddPolyLine( PL) ;
       }
      // se punto
@@ -206,7 +208,7 @@ Scene::DrawGeoObj( const IGdbIterator& iIter, int nPass, MdStMk siObj)
             return false ;
         // calcolo la grafica
          pGraphics->Clear() ;
-         pGraphics->AddColor( cCol) ;
+         pGraphics->AddColor( siObj.colObj) ;
          pGraphics->AddPoint( pPoint->GetPoint()) ;
       }
      // se riferimento
@@ -236,7 +238,7 @@ Scene::DrawGeoObj( const IGdbIterator& iIter, int nPass, MdStMk siObj)
          PolyLine PL ;
          pCurve->ApproxWithLines( 0.005, 5, PL) ;
          pGraphics->Clear() ;
-         pGraphics->AddColor( cCol) ;
+         pGraphics->AddColor( siObj.colObj) ;
          pGraphics->AddPolyLine( PL) ; 
          // eventuali segni ausiliari (mark, frecce, ...)
          Vector3d vtRef ;
@@ -275,7 +277,7 @@ Scene::DrawGeoObj( const IGdbIterator& iIter, int nPass, MdStMk siObj)
             mMat.Set( m_colDef) ;
         // impostazioni iniziali
          pGraphics->Clear() ;
-         pGraphics->AddColor( cCol) ;  // per wireframe
+         pGraphics->AddColor( siObj.colObj) ;  // per wireframe
          pGraphics->AddMaterial( mMat.GetAmbient(), mMat.GetDiffuse(),
                                  mMat.GetSpecular(), mMat.GetShininess()) ;
          pGraphics->AddBackMaterial( GetSurfBackColor( mMat.GetDiffuse())) ;
@@ -313,29 +315,55 @@ Scene::DrawGeoObj( const IGdbIterator& iIter, int nPass, MdStMk siObj)
          POLYLINELIST lstPL ;
          pTXT->ApproxWithLines( 0.01, 5, lstPL) ;
          pGraphics->Clear() ;
-         pGraphics->AddColor( cCol) ;
+         pGraphics->AddColor( siObj.colObj) ;
          POLYLINELIST::iterator Iter ;
          for ( Iter = lstPL.begin() ; Iter != lstPL.end() ; ++ Iter)
             pGraphics->AddPolyLine( *Iter) ; 
       }
    }
 
+  // se richiesto, visualizzo la grafica associata
+   bool bShowAux = false ;
+   if ( ( nGeoType & GEO_CURVE) != 0  &&  m_bShowCurveDirection)
+      bShowAux = true ;
+
+  // recupero il valore di opacità (solo per le superfici può esserci trasparenza)
+   int nAlpha = siObj.colObj.GetIntAlpha() ;
+
   // se hiddenline e non selezione
    if ( m_nShowMode == SM_HIDDENLINE  &&  ! m_bSelect) {
-     // in prima passata disegno solo le superfici
-      if ( nPass == 1  &&  ( nGeoType & GEO_SURF) == 0)
+     // in prima passata disegno solo le superfici opache
+      if ( nPass == 1  &&  ( ( nGeoType & GEO_SURF) == 0  ||  nAlpha <= ALPHA_LIM))
          return true ;
    }
 
   // se shading e non modalità selezione
    bool bSurfSha = false ;
    if ( m_nShowMode == SM_SHADING  &&  ! m_bSelect) {
-     // in prima passata disegno solo le superfici
-      if ( nPass == 1)
-         if ( ( nGeoType & GEO_SURF) != 0)
-            bSurfSha = true ;
-         else
+     // in prima passata disegno solo le superfici opache e metto in un vettore quelle semitrasparenti
+      if ( nPass == 1) {
+         if ( ( nGeoType & GEO_SURF) == 0)
             return true ;
+         else {
+            if ( nAlpha > ALPHA_LIM)
+               bSurfSha = true ;
+            else {
+              // recupero matrice MODELVIEW corrente
+               GLdouble ModelView[ OGLMAT_DIM] ;
+               glGetDoublev( GL_MODELVIEW_MATRIX, ModelView) ;
+               Frame3d frModView ;
+               OpenGlMatrixToFrame( ModelView, frModView) ;
+              // recupero il box dell'oggetto e lo porto nel riferimento MODELVIEW
+               BBox3d b3Box ;
+               pGraphics->GetLocalBBox( b3Box) ;
+               b3Box.ToGlob( frModView) ;
+              // inserisco i dati nel vettore
+               m_vAlphaSurf.emplace_back( pGraphics, siObj.nStat, siObj.nMark, nAlpha, bShowAux,
+                                          b3Box.GetMin().z, b3Box.GetMax().z) ;
+               return true ;
+            }
+         }
+      }
      // in seconda passata disegno solo dimensioni 0 e curve
       if ( nPass == 2  &&  ( nGeoType & GEO_SURF) != 0)
          return true ;
@@ -345,11 +373,25 @@ Scene::DrawGeoObj( const IGdbIterator& iIter, int nPass, MdStMk siObj)
    if ( m_bSelect)
       glLoadName( iIter.GetId()) ;
 
-  // se richiesto, visualizzo la grafica associata
-   bool bShowAux = false ;
-   if ( ( nGeoType & GEO_CURVE) != 0  &&  m_bShowCurveDirection)
-      bShowAux = true ;
-   return pGraphics->Draw( siObj.nStat, siObj.nMark, bSurfSha, bShowAux) ;
+  // eseguo visualizzazione
+   return pGraphics->Draw( siObj.nStat, siObj.nMark, bSurfSha, nAlpha, bShowAux) ;
+}
+
+//----------------------------------------------------------------------------
+bool
+Scene::DrawAlphaSurfVector( void)
+{
+  // ordino vettore in senso crescente secondo Zmin
+   sort( m_vAlphaSurf.begin(), m_vAlphaSurf.end(), 
+         []( const AlphaSurf& a, const AlphaSurf&b) { return a.dZmin < b.dZmin ; }) ;
+
+  // eseguo visualizzazione
+   for ( int i = 0 ; i < int( m_vAlphaSurf.size()) ; ++i) {
+      if ( ! m_vAlphaSurf[i].pGraph->Draw( m_vAlphaSurf[i].nStat, m_vAlphaSurf[i].nMark, true,
+                                           m_vAlphaSurf[i].nAlpha, m_vAlphaSurf[i].bShowAux))
+         return false ;
+   }
+   return true ;
 }
 
 //----------------------------------------------------------------------------
diff --git a/SceneSelect.cpp b/SceneSelect.cpp
index f5a6e78..91a3205 100644
--- a/SceneSelect.cpp
+++ b/SceneSelect.cpp
@@ -87,7 +87,7 @@ Scene::Select( const Point3d& ptSelCenter, int nW, int nH, int& nSel)
    glDisable( GL_LIGHTING) ;
    // non imposto glPolygonMode secondo il tipo di rendering perchè ignorato in selezione
    // disegno le geometrie del DB in una sola passata
-   DrawGroup( GDB_ID_ROOT, 1, MdStMk( GDB_MD_STD, GDB_ST_ON, GDB_MK_OFF)) ;
+   DrawGroup( GDB_ID_ROOT, 1, MdStMkCol( GDB_MD_STD, GDB_ST_ON, GDB_MK_OFF, m_colDef)) ;
 
   // pulisco stack nomi
    glPopName() ;