diff --git a/AABB_tree/demo/AABB_tree/Scene.cpp b/AABB_tree/demo/AABB_tree/Scene.cpp
index 96ebef00ecf..4b4bb4e69af 100644
--- a/AABB_tree/demo/AABB_tree/Scene.cpp
+++ b/AABB_tree/demo/AABB_tree/Scene.cpp
@@ -16,7 +16,6 @@
 #include <CGAL/IO/Polyhedron_iostream.h>
 #include <CGAL/Subdivision_method_3.h>
 
-#include <QOpenGLFunctions_3_3_Core>
 #include <QOpenGLShader>
 #include <QDebug>
 #include "Viewer.h"
@@ -92,9 +91,8 @@ void Scene::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-        // "#version 330 \n"
+        "#version 120 \n"
         "attribute highp vec4 vertex;\n"
-        //  "uniform highp mat4 ortho_matrix;\n"
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 f_matrix;\n"
         "void main(void)\n"
@@ -105,7 +103,7 @@ void Scene::compile_shaders()
     //Vertex source code
     const char fragment_source[] =
     {
-        //"#version 330 \n"
+        "#version 120 \n"
         "uniform highp vec4 color; \n"
         "void main(void) { \n"
         "gl_FragColor = color; \n"
@@ -141,7 +139,7 @@ void Scene::compile_shaders()
     //Vertex source code
     const char tex_vertex_source[] =
     {
-        // "#version 330 \n"
+        "#version 120 \n"
         "attribute highp vec4 vertex;\n"
         "attribute highp vec2 tex_coord; \n"
         "uniform highp mat4 mvp_matrix;\n"
@@ -156,7 +154,7 @@ void Scene::compile_shaders()
     //Vertex source code
     const char tex_fragment_source[] =
     {
-        //"#version 330 \n"
+        "#version 120 \n"
         "uniform sampler2D texture;\n"
         "varying highp vec2 texc;\n"
         "void main(void) { \n"
@@ -1318,7 +1316,7 @@ void Scene::deactivate_cutting_plane()
 }
 void Scene::initGL(Viewer * /* viewer */)
 {
-    gl = new QOpenGLFunctions_3_3_Core();
+    gl = new QOpenGLFunctions_2_1();
    if(!gl->initializeOpenGLFunctions())
     {
         qFatal("ERROR : OpenGL Functions not initialized. Check your OpenGL Verison (should be >=3.3)");
diff --git a/AABB_tree/demo/AABB_tree/Scene.h b/AABB_tree/demo/AABB_tree/Scene.h
index 450559af232..1175ad4700a 100644
--- a/AABB_tree/demo/AABB_tree/Scene.h
+++ b/AABB_tree/demo/AABB_tree/Scene.h
@@ -18,7 +18,7 @@
 #include <QtCore/qglobal.h>
 #include <QGLViewer/manipulatedFrame.h>
 #include <QGLViewer/qglviewer.h>
-#include <QOpenGLFunctions_3_3_Core>
+#include <QOpenGLFunctions_2_1>
 #include <QOpenGLVertexArrayObject>
 #include <QOpenGLBuffer>
 #include <QOpenGLShaderProgram>
@@ -86,7 +86,7 @@ public:
 
 private:
     // member data
-    QOpenGLFunctions_3_3_Core *gl;
+    QOpenGLFunctions_2_1 *gl;
     Bbox m_bbox;
     Polyhedron *m_pPolyhedron;
     std::list<Point> m_points;
diff --git a/Alpha_shapes_3/demo/Alpha_shapes_3/Viewer.cpp b/Alpha_shapes_3/demo/Alpha_shapes_3/Viewer.cpp
index e276df8661e..a5a0dd2f222 100644
--- a/Alpha_shapes_3/demo/Alpha_shapes_3/Viewer.cpp
+++ b/Alpha_shapes_3/demo/Alpha_shapes_3/Viewer.cpp
@@ -29,14 +29,14 @@ void Viewer::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-         "#version 330 \n"
-        "in highp vec4 vertex;\n"
-        "in highp vec3 normal;\n"
+         "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
+        "attribute highp vec3 normal;\n"
 
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 mv_matrix; \n"
-        "out highp vec4 fP; \n"
-        "out highp vec3 fN; \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "void main(void)\n"
         "{\n"
         "   fP = mv_matrix * vertex; \n"
@@ -44,12 +44,12 @@ void Viewer::compile_shaders()
         "   gl_Position = mvp_matrix * vertex;\n"
         "}"
     };
-    //Vertex source code
+    //Fragment source code
     const char fragment_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 fP; \n"
-        "in highp vec3 fN; \n"
+        "#version 120 \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "uniform highp vec4 color; \n"
         "uniform vec4 light_pos;  \n"
         "uniform vec4 light_diff; \n"
@@ -105,8 +105,8 @@ rendering_program.bind();
 //Vertex source code
 const char vertex_source_points[] =
 {
-     "#version 330 \n"
-    "in highp vec4 vertex;\n"
+    "#version 120 \n"
+    "attribute highp vec4 vertex;\n"
 
     "uniform highp mat4 mvp_matrix;\n"
     "void main(void)\n"
@@ -117,7 +117,7 @@ const char vertex_source_points[] =
 //Vertex source code
 const char fragment_source_points[] =
 {
-    "#version 330 \n"
+    "#version 120 \n"
     "uniform highp vec4 color; \n"
 
     "void main(void) { \n"
@@ -325,6 +325,7 @@ void Viewer::compute_elements()
 void
 Viewer::draw()
 {
+    glEnable(GL_DEPTH_TEST);
     if(!are_buffers_initialized)
         initialize_buffers();
     QColor color;
diff --git a/Alpha_shapes_3/demo/Alpha_shapes_3/Viewer.h b/Alpha_shapes_3/demo/Alpha_shapes_3/Viewer.h
index a5cc54aa490..5280aa622b3 100644
--- a/Alpha_shapes_3/demo/Alpha_shapes_3/Viewer.h
+++ b/Alpha_shapes_3/demo/Alpha_shapes_3/Viewer.h
@@ -3,13 +3,13 @@
 
 #include "typedefs.h"
 #include <QGLViewer/qglviewer.h>
-#include <QOpenGLFunctions_3_3_Core>
+#include <QOpenGLFunctions_2_1>
 #include <QOpenGLVertexArrayObject>
 #include <QOpenGLBuffer>
 #include <QOpenGLShaderProgram>
 
 
-class Viewer : public QGLViewer, protected QOpenGLFunctions_3_3_Core{
+class Viewer : public QGLViewer, protected QOpenGLFunctions_2_1{
   Q_OBJECT
 
   CGAL::Timer timer;
diff --git a/Circular_kernel_3/demo/Circular_kernel_3/Viewer.cpp b/Circular_kernel_3/demo/Circular_kernel_3/Viewer.cpp
index 858aa0ab7af..0036038b6de 100644
--- a/Circular_kernel_3/demo/Circular_kernel_3/Viewer.cpp
+++ b/Circular_kernel_3/demo/Circular_kernel_3/Viewer.cpp
@@ -4,9 +4,12 @@
 #include <CGAL/Exact_spherical_kernel_3.h>
 #include <vector>
 #include <CGAL/Qt/CreateOpenGLContext.h>
+
+
 Viewer::Viewer(QWidget* parent )
   : QGLViewer(CGAL::Qt::createOpenGLContext(),parent)
 {
+    extension_is_found = false;
 }
 
 void Viewer::compile_shaders()
@@ -29,16 +32,16 @@ void Viewer::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
-        "in highp vec3 normal;\n"
-        "in highp vec4 center;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
+        "attribute highp vec3 normal;\n"
+        "attribute highp vec4 center;\n"
 
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 mv_matrix; \n"
 
-        "out highp vec4 fP; \n"
-        "out highp vec3 fN; \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "void main(void)\n"
         "{\n"
         "   fP = mv_matrix * vertex; \n"
@@ -49,9 +52,9 @@ void Viewer::compile_shaders()
     //Vertex source code
     const char fragment_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 fP; \n"
-        "in highp vec3 fN; \n"
+        "#version 120 \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "uniform highp vec4 color; \n"
         "uniform vec4 light_pos;  \n"
         "uniform vec4 light_diff; \n"
@@ -101,6 +104,59 @@ void Viewer::compile_shaders()
         std::cerr<<"linking Program FAILED"<<std::endl;
     }
     rendering_program.bind();
+    if(!extension_is_found)
+    {
+
+
+             //Vertex source code
+             const char vertex_source_no_ext[] =
+             {
+                 "#version 120 \n"
+                 "attribute highp vec4 vertex;\n"
+                 "uniform highp mat4 mvp_matrix;\n"
+                 "void main(void)\n"
+                 "{\n"
+                 "   gl_Position = mvp_matrix * vertex;\n"
+                 "}"
+             };
+             //Vertex source code
+             const char fragment_source_no_ext[] =
+             {
+                 "#version 120 \n"
+                 "uniform highp vec4 color; \n"
+                 "void main(void) { \n"
+                 "gl_FragColor = color; \n"
+                 "} \n"
+                 "\n"
+             };
+             vertex_shader = new QOpenGLShader(QOpenGLShader::Vertex);
+             if(!vertex_shader->compileSourceCode(vertex_source_no_ext))
+             {
+                 std::cerr<<"Compiling vertex source FAILED"<<std::endl;
+             }
+
+             fragment_shader= new QOpenGLShader(QOpenGLShader::Fragment);
+             if(!fragment_shader->compileSourceCode(fragment_source_no_ext))
+             {
+                 std::cerr<<"Compiling fragmentsource FAILED"<<std::endl;
+             }
+
+             if(!rendering_program_no_ext.addShader(vertex_shader))
+             {
+                 std::cerr<<"adding vertex shader FAILED"<<std::endl;
+             }
+             if(!rendering_program_no_ext.addShader(fragment_shader))
+             {
+                 std::cerr<<"adding fragment shader FAILED"<<std::endl;
+             }
+             if(!rendering_program_no_ext.link())
+             {
+                 std::cerr<<"linking Program FAILED"<<std::endl;
+             }
+             rendering_program_no_ext.bind();
+    }
+
+
 
 }
 
@@ -135,8 +191,12 @@ void Viewer::initialize_buffers()
     rendering_program.enableAttributeArray(trivialCenterLocation);
     rendering_program.setAttributeBuffer(trivialCenterLocation,GL_FLOAT,0,3);
     buffers[2].release();
-    glVertexAttribDivisor(trivialCenterLocation, 1);
-    glVertexAttribDivisor(normalsLocation[0], 0);
+    if(extension_is_found)
+    {
+
+        glVertexAttribDivisor(trivialCenterLocation, 1);
+        glVertexAttribDivisor(normalsLocation[0], 0);
+    }
     vao[0].release();
 
     //The circles
@@ -168,43 +228,61 @@ void Viewer::initialize_buffers()
     rendering_program.enableAttributeArray(trivialCenterLocation);
     rendering_program.setAttributeBuffer(trivialCenterLocation,GL_FLOAT,0,3);
     buffers[5].release();
-    glVertexAttribDivisor(trivialCenterLocation, 1);
-    glVertexAttribDivisor(normalsLocation[0], 0);
+    if(extension_is_found)
+    {
+        glVertexAttribDivisor(trivialCenterLocation, 1);
+        glVertexAttribDivisor(normalsLocation[0], 0);
+    }
     rendering_program.release();
 
     vao[1].release();
 
     //The little green spheres
     vao[2].bind();
-    //points of the sphere
-    buffers[6].bind();
-    buffers[6].allocate(pos_sphere_inter.data(),
-                        static_cast<int>(pos_sphere_inter.size()*sizeof(float)));
-    vertexLocation[2] = rendering_program.attributeLocation("vertex");
-    rendering_program.bind();
-    rendering_program.enableAttributeArray(vertexLocation[2]);
-    rendering_program.setAttributeBuffer(vertexLocation[2],GL_FLOAT,0,3);
-    buffers[6].release();
-    //normals of the sphere
-    buffers[7].bind();
-    buffers[7].allocate(normals_inter.data(),
-                        static_cast<int>(normals_inter.size()*sizeof(float)));
-    normalsLocation[2] = rendering_program.attributeLocation("normal");
-    rendering_program.bind();
-    rendering_program.enableAttributeArray(normalsLocation[2]);
-    rendering_program.setAttributeBuffer(normalsLocation[2],GL_FLOAT,0,3);
-    buffers[7].release();
-    //center of the sphere
-    buffers[8].bind();
-    buffers[8].allocate(pos_points.data(),
-                        static_cast<int>(pos_points.size()*sizeof(float)));
-    centerLocation = rendering_program.attributeLocation("center");
-    rendering_program.bind();
-    rendering_program.enableAttributeArray(centerLocation);
-    rendering_program.setAttributeBuffer(centerLocation,GL_FLOAT,0,3);
-    buffers[8].release();
-    glVertexAttribDivisor(centerLocation, 1);
-    glVertexAttribDivisor(normalsLocation[1], 0);
+    if(extension_is_found)
+    {
+        //points of the spheres
+        buffers[6].bind();
+        buffers[6].allocate(pos_sphere_inter.data(),
+                            static_cast<int>(pos_sphere_inter.size()*sizeof(float)));
+        vertexLocation[2] = rendering_program.attributeLocation("vertex");
+        rendering_program.bind();
+        rendering_program.enableAttributeArray(vertexLocation[2]);
+        rendering_program.setAttributeBuffer(vertexLocation[2],GL_FLOAT,0,3);
+        buffers[6].release();
+        //normals of the sphere
+        buffers[7].bind();
+        buffers[7].allocate(normals_inter.data(),
+                            static_cast<int>(normals_inter.size()*sizeof(float)));
+        normalsLocation[2] = rendering_program.attributeLocation("normal");
+        rendering_program.bind();
+        rendering_program.enableAttributeArray(normalsLocation[2]);
+        rendering_program.setAttributeBuffer(normalsLocation[2],GL_FLOAT,0,3);
+        buffers[7].release();
+        //center of the sphere
+        buffers[8].bind();
+        buffers[8].allocate(pos_points.data(),
+                            static_cast<int>(pos_points.size()*sizeof(float)));
+        centerLocation = rendering_program.attributeLocation("center");
+        rendering_program.bind();
+        rendering_program.enableAttributeArray(centerLocation);
+        rendering_program.setAttributeBuffer(centerLocation,GL_FLOAT,0,3);
+        buffers[8].release();
+
+        glVertexAttribDivisor(centerLocation, 1);
+        glVertexAttribDivisor(normalsLocation[1], 0);
+    }
+    else
+    {
+        //points of the sphere
+        buffers[6].bind();
+        buffers[6].allocate(pos_points.data(),
+                            static_cast<int>(pos_points.size()*sizeof(float)));
+        rendering_program_no_ext.bind();
+        rendering_program_no_ext.enableAttributeArray("vertex");
+        rendering_program_no_ext.setAttributeBuffer("vertex",GL_FLOAT,0,3);
+        buffers[6].release();
+    }
     vao[2].release();
 
 
@@ -693,13 +771,20 @@ void Viewer::attrib_buffers(QGLViewer* viewer)
     rendering_program.setUniformValue(mvpLocation, mvpMatrix);
     rendering_program.setUniformValue(mvLocation, mvMatrix);
 
-
     rendering_program.release();
+    if(!extension_is_found)
+    {
+        rendering_program_no_ext.bind();
+        rendering_program_no_ext.setUniformValue("mvp_matrix", mvpMatrix);
+        rendering_program_no_ext.release();
+    }
+
 
 }
 
 void Viewer::draw()
 {
+    glEnable(GL_DEPTH_TEST);
     QColor color;
 
     //sphere
@@ -708,18 +793,34 @@ void Viewer::draw()
     rendering_program.bind();
     color.setRgbF(1.0f, 1.0f, 1.0f);
     rendering_program.setUniformValue(colorLocation, color);
-    glDrawArraysInstanced(GL_TRIANGLES, 0, static_cast<GLsizei>(pos_sphere.size()/3), 1);
+    if(extension_is_found)
+        glDrawArraysInstanced(GL_TRIANGLES, 0, static_cast<GLsizei>(pos_sphere.size()/3), 1);
+    else
+        glDrawArrays(GL_TRIANGLES, 0, static_cast<GLsizei>(pos_sphere.size()/3));
     rendering_program.release();
     vao[0].release();
 
     //intersection
     vao[2].bind();
     attrib_buffers(this);
-    rendering_program.bind();
     color.setRgbF(0.0f, 1.0f, 0.0f);
-    rendering_program.setUniformValue(colorLocation, color);
-    glDrawArraysInstanced(GL_TRIANGLES, 0, static_cast<GLsizei>(pos_sphere_inter.size()/3), static_cast<GLsizei>(pos_points.size()/3));
-    rendering_program.release();
+    if(extension_is_found)
+    {
+        rendering_program.bind();
+        rendering_program.setUniformValue(colorLocation, color);
+        glDrawArraysInstanced(GL_TRIANGLES, 0, static_cast<GLsizei>(pos_sphere_inter.size()/3), static_cast<GLsizei>(pos_points.size()/3));
+        rendering_program.release();
+    }
+    else
+    {
+        glPointSize(4.0f);
+        rendering_program_no_ext.bind();
+        rendering_program_no_ext.setUniformValue(colorLocation, color);
+        glDrawArrays(GL_POINTS, 0, static_cast<GLsizei>(pos_points.size()/3));
+        rendering_program_no_ext.release();
+        glPointSize(1.0f);
+    }
+
     vao[2].release();
 
     //circles
@@ -738,6 +839,24 @@ void Viewer::draw()
 
 void Viewer::init()
 {
+
+    glDrawArraysInstanced = (PFNGLDRAWARRAYSINSTANCEDARBPROC)this->context()->getProcAddress("glDrawArraysInstancedARB");
+    if(!glDrawArraysInstanced)
+    {
+        qDebug()<<"glDrawArraysInstancedARB : extension not found. Spheres will be displayed as points.";
+        extension_is_found = false;
+    }
+    else
+        extension_is_found = true;
+
+    glVertexAttribDivisor = (PFNGLVERTEXATTRIBDIVISORARBPROC)this->context()->getProcAddress("glVertexAttribDivisorARB");
+    if(!glDrawArraysInstanced)
+    {
+        qDebug()<<"glVertexAttribDivisorARB : extension not found. Spheres will be displayed as points.";
+        extension_is_found = false;
+    }
+    else
+        extension_is_found = true;
     compile_shaders();
     compute_elements();
     initialize_buffers();
@@ -748,6 +867,7 @@ void Viewer::init()
     glEnable(GL_POINT_SMOOTH);
     glEnable(GL_LINE_SMOOTH);
 
+
 }
 
 template<class Output_iterator>
diff --git a/Circular_kernel_3/demo/Circular_kernel_3/Viewer.h b/Circular_kernel_3/demo/Circular_kernel_3/Viewer.h
index 81b20ba1746..378fc42114d 100644
--- a/Circular_kernel_3/demo/Circular_kernel_3/Viewer.h
+++ b/Circular_kernel_3/demo/Circular_kernel_3/Viewer.h
@@ -1,14 +1,14 @@
 #include <QGLViewer/qglviewer.h>
 #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
 
-#include <QOpenGLFunctions_3_3_Core>
+#include <QOpenGLFunctions_2_1>
 #include <QOpenGLVertexArrayObject>
 #include <QOpenGLBuffer>
 #include <QOpenGLShaderProgram>
 
 typedef CGAL::Exact_predicates_inexact_constructions_kernel EPIC;
 
-class Viewer : public QGLViewer, QOpenGLFunctions_3_3_Core
+class Viewer : public QGLViewer, QOpenGLFunctions_2_1
 {
 public:
     Viewer(QWidget* parent = 0);
@@ -29,7 +29,7 @@ private:
   int mvLocation;
   int colorLocation;
   int lightLocation[5];
-
+  bool extension_is_found;
 
   std::vector<float> pos_points;
   std::vector<float> pos_lines;
@@ -43,6 +43,11 @@ private:
   QOpenGLBuffer buffers[9];
   QOpenGLVertexArrayObject vao[3];
   QOpenGLShaderProgram rendering_program;
+  QOpenGLShaderProgram rendering_program_no_ext;
+  typedef void (APIENTRYP PFNGLDRAWARRAYSINSTANCEDARBPROC) (GLenum mode, GLint first, GLsizei count, GLsizei primcount);
+  typedef void (APIENTRYP PFNGLVERTEXATTRIBDIVISORARBPROC) (GLuint index, GLuint divisor);
+  PFNGLDRAWARRAYSINSTANCEDARBPROC glDrawArraysInstanced;
+  PFNGLVERTEXATTRIBDIVISORARBPROC glVertexAttribDivisor;
 
   void initialize_buffers();
   void compute_elements();
diff --git a/Documentation/doc/Documentation/Installation.txt b/Documentation/doc/Documentation/Installation.txt
index 9864272873d..f97e1a58731 100644
--- a/Documentation/doc/Documentation/Installation.txt
+++ b/Documentation/doc/Documentation/Installation.txt
@@ -423,7 +423,8 @@ it from <A HREF="http://qt-project.org/">`http://qt-project.org/`</A>.
 Older demos of \cgal use libCGAL_Qt3 and \sc{Qt}3, while newer and newly
 developed demos require libCGAL_Qt5 and \sc{Qt}5.
 The exhaustive list of \sc{Qt}5 components used in demos is:
-`Core`, `Gui`, `Help`, `OpenGL`, `Script`, `ScriptTools`, `Svg`, `Widgets` and `Xml`.
+`Core`, `Gui`, `Help`, `OpenGL`, `Script`, `ScriptTools`, `Svg`, `Widgets`,
+`qcollectiongenerator` (with `sqlite` driver plugin) and `Xml`.
 
 Having \sc{Qt}5 version 5.3.0 is recommended.
 
diff --git a/GraphicsView/include/CGAL/Qt/CreateOpenGLContext.h b/GraphicsView/include/CGAL/Qt/CreateOpenGLContext.h
index 514b6e8007e..7e321582f36 100644
--- a/GraphicsView/include/CGAL/Qt/CreateOpenGLContext.h
+++ b/GraphicsView/include/CGAL/Qt/CreateOpenGLContext.h
@@ -27,7 +27,7 @@ inline QGLContext* createOpenGLContext()
 {
     QOpenGLContext *context = new QOpenGLContext();
     QSurfaceFormat format;
-    format.setVersion(3,3);
+    format.setVersion(2,1);
     format.setProfile(QSurfaceFormat::CompatibilityProfile);
     context->setFormat(format);
     return QGLContext::fromOpenGLContext(context);
diff --git a/Linear_cell_complex/demo/Linear_cell_complex/Viewer.cpp b/Linear_cell_complex/demo/Linear_cell_complex/Viewer.cpp
index cf92a3804e3..48569ec0990 100644
--- a/Linear_cell_complex/demo/Linear_cell_complex/Viewer.cpp
+++ b/Linear_cell_complex/demo/Linear_cell_complex/Viewer.cpp
@@ -232,32 +232,32 @@ void Viewer::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-        "#version 140 \n"
-        "in highp vec4 vertex;\n"
-        "in highp vec3 normal;\n"
-        "in highp vec4 color;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
+        "attribute highp vec3 normal;\n"
+        "attribute highp vec3 color;\n"
 
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 mv_matrix; \n"
 
-        "out highp vec4 fP; \n"
-        "out highp vec3 fN; \n"
-        "out highp vec4 fColor; \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
+        "varying highp vec4 fColor; \n"
         "void main(void)\n"
         "{\n"
         "   fP = mv_matrix * vertex; \n"
         "   fN = mat3(mv_matrix)* normal; \n"
-        "   fColor = color; \n"
+        "   fColor = vec4(color, 1.0); \n"
         "   gl_Position = mvp_matrix * vertex;\n"
         "}"
     };
     //Vertex source code
     const char fragment_source[] =
     {
-        "#version 140 \n"
-        "in highp vec4 fP; \n"
-        "in highp vec3 fN; \n"
-        "in highp vec4 fColor; \n"
+        "#version 120 \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
+        "varying highp vec4 fColor; \n"
         "uniform vec4 light_pos;  \n"
         "uniform vec4 light_diff; \n"
         "uniform vec4 light_spec; \n"
@@ -310,8 +310,8 @@ void Viewer::compile_shaders()
     //Vertex source code
     const char vertex_source_p_l[] =
     {
-        "#version 140 \n"
-        "in highp vec4 vertex;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
         "uniform highp mat4 mvp_matrix;\n"
         "void main(void)\n"
         "{\n"
@@ -321,7 +321,7 @@ void Viewer::compile_shaders()
     //Vertex source code
     const char fragment_source_p_l[] =
     {
-        "#version 140 \n"
+        "#version 120 \n"
         "uniform highp vec4 color; \n"
         "void main(void) { \n"
         "gl_FragColor = color; \n"
@@ -657,20 +657,20 @@ void Viewer::attrib_buffers(QGLViewer* viewer)
 void
 Viewer::sceneChanged()
 {
-
+  compute_elements();
   this->camera()->setSceneBoundingBox(qglviewer::Vec(bb.xmin(),
 						     bb.ymin(),
 						     bb.zmin()),
 				      qglviewer::Vec(bb.xmax(),
 						     bb.ymax(),
 						     bb.zmax()));
-    compute_elements();
-    are_buffers_initialized = false;
+  are_buffers_initialized = false;
   this->showEntireScene();
 }
 
 void Viewer::draw()
 {
+    glEnable(GL_DEPTH_TEST);
 if(!are_buffers_initialized)
     initialize_buffers();
 
diff --git a/Linear_cell_complex/demo/Linear_cell_complex/Viewer.h b/Linear_cell_complex/demo/Linear_cell_complex/Viewer.h
index e5dc086f76f..c03977f900a 100644
--- a/Linear_cell_complex/demo/Linear_cell_complex/Viewer.h
+++ b/Linear_cell_complex/demo/Linear_cell_complex/Viewer.h
@@ -25,11 +25,11 @@
 #include <QGLViewer/qglviewer.h>
 #include <QKeyEvent>
 
-#include <QOpenGLFunctions_3_3_Core>
+#include <QOpenGLFunctions_2_1>
 #include <QOpenGLVertexArrayObject>
 #include <QGLBuffer>
 #include <QOpenGLShaderProgram>
-class Viewer : public QGLViewer, QOpenGLFunctions_3_3_Core
+class Viewer : public QGLViewer, QOpenGLFunctions_2_1
 {
   Q_OBJECT
 
diff --git a/Mesh_3/demo/Mesh_3/Scene_c3t3_item.cpp b/Mesh_3/demo/Mesh_3/Scene_c3t3_item.cpp
index cc894397138..1b82b6b3d63 100644
--- a/Mesh_3/demo/Mesh_3/Scene_c3t3_item.cpp
+++ b/Mesh_3/demo/Mesh_3/Scene_c3t3_item.cpp
@@ -51,16 +51,16 @@ void Scene_c3t3_item::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
-        "in highp vec3 normal;\n"
-        "in highp vec3 inColor; \n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
+        "attribute highp vec3 normal;\n"
+        "attribute highp vec3 inColor; \n"
 
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 mv_matrix; \n"
-        "out highp vec4 fP; \n"
-        "out highp vec3 fN; \n"
-        "out highp vec4 color; \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
+        "varying highp vec4 color; \n"
         "void main(void)\n"
         "{\n"
         "   color = vec4(inColor, 1.0); \n"
@@ -73,9 +73,9 @@ void Scene_c3t3_item::compile_shaders()
     const char fragment_source[] =
     {
         "#version 330 \n"
-        "in highp vec4 fP; \n"
-        "in highp vec3 fN; \n"
-        "in vec4 color; \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
+        "varying vec4 color; \n"
         "uniform highp vec4 light_pos;  \n"
         "uniform highp vec4 light_diff; \n"
         "uniform highp vec4 light_spec; \n"
@@ -130,8 +130,8 @@ void Scene_c3t3_item::compile_shaders()
     //Vertex source code
     const char vertex_source_grid[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
 
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 f_matrix; \n"
@@ -143,7 +143,7 @@ void Scene_c3t3_item::compile_shaders()
     //Fragment source code
     const char fragment_source_grid[] =
     {
-        "#version 330 \n"
+        "#version 120 \n"
         "uniform vec4 color; \n"
         "void main(void) { \n"
         "gl_FragColor = color; \n"
diff --git a/Mesh_3/demo/Mesh_3/Scene_implicit_function_item.cpp b/Mesh_3/demo/Mesh_3/Scene_implicit_function_item.cpp
index e8690bcf679..2b89086350e 100644
--- a/Mesh_3/demo/Mesh_3/Scene_implicit_function_item.cpp
+++ b/Mesh_3/demo/Mesh_3/Scene_implicit_function_item.cpp
@@ -68,8 +68,8 @@ void Scene_implicit_function_item::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
 
         "uniform highp mat4 mvp_matrix;\n"
         "void main(void)\n"
@@ -80,7 +80,7 @@ void Scene_implicit_function_item::compile_shaders()
     //Fragment source code
     const char fragment_source[] =
     {
-        "#version 330 \n"
+        "#version 120 \n"
         "uniform vec4 color; \n"
         "void main(void) { \n"
          "gl_FragColor = color; \n"
@@ -115,24 +115,24 @@ void Scene_implicit_function_item::compile_shaders()
     //Vertex source code
     const char tex_vertex_source[] =
     {
-         "#version 330 \n"
-        "in highp vec4 vertex;\n"
-        "in highp vec2 tex_coord; \n"
+         "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
+        "attribute highp vec2 tex_coord; \n"
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 f_matrix;\n"
-        "out highp vec2 texc;\n"
+        "varying highp vec2 texc;\n"
         "void main(void)\n"
         "{\n"
         "   gl_Position = mvp_matrix * f_matrix * vertex;\n"
         "    texc = tex_coord;\n"
         "}"
     };
-    //Vertex source code
+    //Fragment source code
     const char tex_fragment_source[] =
     {
-        "#version 330 \n"
+        "#version 120 \n"
         "uniform sampler2D texture;\n"
-        "in highp vec2 texc;\n"
+        "varying highp vec2 texc;\n"
         "void main(void) { \n"
         "gl_FragColor = texture2D(texture, texc.st);\n"
         "} \n"
diff --git a/Mesh_3/demo/Mesh_3/Scene_polygon_soup.cpp b/Mesh_3/demo/Mesh_3/Scene_polygon_soup.cpp
index dcaaa23c337..9a2a9a14fdf 100644
--- a/Mesh_3/demo/Mesh_3/Scene_polygon_soup.cpp
+++ b/Mesh_3/demo/Mesh_3/Scene_polygon_soup.cpp
@@ -125,14 +125,14 @@ void Scene_polygon_soup::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
-        "in highp vec3 normal;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
+        "attribute highp vec3 normal;\n"
 
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 mv_matrix; \n"
-        "out highp vec4 fP; \n"
-        "out highp vec3 fN; \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "void main(void)\n"
         "{\n"
         "   fP = mv_matrix * vertex; \n"
@@ -143,9 +143,9 @@ void Scene_polygon_soup::compile_shaders()
     //Fragment source code
     const char fragment_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 fP; \n"
-        "in highp vec3 fN; \n"
+        "#version 120 \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "uniform vec4 color; \n"
         "uniform bool is_two_side; \n"
         "uniform highp vec4 light_pos;  \n"
diff --git a/Mesh_3/demo/Mesh_3/Scene_polyhedron_item.cpp b/Mesh_3/demo/Mesh_3/Scene_polyhedron_item.cpp
index 6d410ba491e..c1e552e2311 100644
--- a/Mesh_3/demo/Mesh_3/Scene_polyhedron_item.cpp
+++ b/Mesh_3/demo/Mesh_3/Scene_polyhedron_item.cpp
@@ -54,14 +54,14 @@ void Scene_polyhedron_item::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
-        "in highp vec3 normal;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
+        "attribute highp vec3 normal;\n"
 
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 mv_matrix; \n"
-        "out highp vec4 fP; \n"
-        "out highp vec3 fN; \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "void main(void)\n"
         "{\n"
         "   fP = mv_matrix * vertex; \n"
@@ -72,9 +72,9 @@ void Scene_polyhedron_item::compile_shaders()
     //Fragment source code
     const char fragment_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 fP; \n"
-        "in highp vec3 fN; \n"
+        "#version 120 \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "uniform vec4 color; \n"
         "uniform bool is_two_side; \n"
         "uniform highp vec4 light_pos;  \n"
diff --git a/Mesh_3/demo/Mesh_3/Scene_segmented_image_item.cpp b/Mesh_3/demo/Mesh_3/Scene_segmented_image_item.cpp
index 408c2e93ac1..a8d3c81a9d5 100644
--- a/Mesh_3/demo/Mesh_3/Scene_segmented_image_item.cpp
+++ b/Mesh_3/demo/Mesh_3/Scene_segmented_image_item.cpp
@@ -497,16 +497,16 @@ void Scene_segmented_image_item::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
-        "in highp vec3 normal;\n"
-        "in highp vec4 inColor;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
+        "attribute highp vec3 normal;\n"
+        "attribute highp vec4 inColor;\n"
 
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 mv_matrix; \n"
-        "out highp vec4 fP; \n"
-        "out highp vec3 fN; \n"
-        "out highp vec4 color; \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
+        "varying highp vec4 color; \n"
         "void main(void)\n"
         "{\n"
         "   color=inColor; \n"
@@ -518,10 +518,10 @@ void Scene_segmented_image_item::compile_shaders()
     //Fragment source code
     const char fragment_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 fP; \n"
-        "in highp vec3 fN; \n"
-        "in highp vec4 color; \n"
+        "#version 120 \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
+        "varying highp vec4 color; \n"
         "uniform bool is_two_side; \n"
         "uniform highp vec4 light_pos;  \n"
         "uniform highp vec4 light_diff; \n"
diff --git a/Mesh_3/demo/Mesh_3/Volume_plane.h b/Mesh_3/demo/Mesh_3/Volume_plane.h
index 4cc1e3e04f8..0efdaab4fb1 100644
--- a/Mesh_3/demo/Mesh_3/Volume_plane.h
+++ b/Mesh_3/demo/Mesh_3/Volume_plane.h
@@ -423,9 +423,6 @@ void Volume_plane<T>::init() {
 
 template<typename T>
 void Volume_plane<T>::initShaders() {
-    program.create();
-
-
   QOpenGLShader *vertex = new QOpenGLShader(QOpenGLShader::Vertex);
 
   vertex->compileSourceCode(vertexShader_source);
@@ -436,7 +433,6 @@ void Volume_plane<T>::initShaders() {
   program.link();
 
 
-  program_bordures.create();
   QOpenGLShader *vertex_bordures = new QOpenGLShader(QOpenGLShader::Vertex);
 
   vertex_bordures->compileSourceCode(vertexShader_bordures_source);
diff --git a/Mesh_3/demo/Mesh_3/Volume_plane_intersection.cpp b/Mesh_3/demo/Mesh_3/Volume_plane_intersection.cpp
index 379f5585c39..c2b3891aad2 100644
--- a/Mesh_3/demo/Mesh_3/Volume_plane_intersection.cpp
+++ b/Mesh_3/demo/Mesh_3/Volume_plane_intersection.cpp
@@ -16,8 +16,8 @@ void Volume_plane_intersection::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 f_matrix; \n"
         "void main(void)\n"
@@ -28,7 +28,7 @@ void Volume_plane_intersection::compile_shaders()
     //Fragment source code
     const char fragment_source[] =
     {
-        "#version 330 \n"
+        "#version 120 \n"
         "void main(void) { \n"
         "gl_FragColor = vec4(1.0,0.0,0.0,1.0); \n"
         "} \n"
diff --git a/Mesh_3/demo/Mesh_3/include/CGAL_demo/Viewer.h b/Mesh_3/demo/Mesh_3/include/CGAL_demo/Viewer.h
index 3e590acd239..9712cc45787 100644
--- a/Mesh_3/demo/Mesh_3/include/CGAL_demo/Viewer.h
+++ b/Mesh_3/demo/Mesh_3/include/CGAL_demo/Viewer.h
@@ -4,13 +4,13 @@
 #include <CGAL_demo/Viewer_config.h>
 #include <QGLViewer/qglviewer.h>
 #include <QPoint>
-#include <QOpenGLFunctions_3_3_Core>
+#include <QOpenGLFunctions_2_1>
 
 // forward declarations
 class QWidget;
 class Scene_draw_interface;
 
-class VIEWER_EXPORT Viewer : public QGLViewer, public QOpenGLFunctions_3_3_Core {
+class VIEWER_EXPORT Viewer : public QGLViewer, public QOpenGLFunctions_2_1 {
 
   Q_OBJECT
 
diff --git a/Mesh_3/demo/Mesh_3/src/CGAL_demo/Viewer.cpp b/Mesh_3/demo/Mesh_3/src/CGAL_demo/Viewer.cpp
index 564ec702e70..e9ef91d85d2 100644
--- a/Mesh_3/demo/Mesh_3/src/CGAL_demo/Viewer.cpp
+++ b/Mesh_3/demo/Mesh_3/src/CGAL_demo/Viewer.cpp
@@ -53,6 +53,7 @@ void Viewer::initializeGL()
 void Viewer::draw_aux(bool with_names)
 {
   QGLViewer::draw();
+  glEnable(GL_DEPTH_TEST);
   if(scene == 0)
     return;
 
diff --git a/Periodic_3_triangulation_3/demo/Periodic_3_triangulation_3/Scene.cpp b/Periodic_3_triangulation_3/demo/Periodic_3_triangulation_3/Scene.cpp
index e922b37f0f3..b530307cb5a 100644
--- a/Periodic_3_triangulation_3/demo/Periodic_3_triangulation_3/Scene.cpp
+++ b/Periodic_3_triangulation_3/demo/Periodic_3_triangulation_3/Scene.cpp
@@ -34,8 +34,8 @@ void Scene::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
         "uniform highp mat4 mvp_matrix;\n"
         "void main(void)\n"
         "{\n"
@@ -45,7 +45,7 @@ void Scene::compile_shaders()
     //Fragment source code
     const char fragment_source[] =
     {
-        "#version 330 \n"
+        "#version 120 \n"
         "uniform highp vec4 color; \n"
         "void main(void) { \n"
         "gl_FragColor = color; \n"
@@ -82,15 +82,15 @@ void Scene::compile_shaders()
     //Vertex source code
     const char vertex_source_spheres[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
-        "in highp vec3 normal;\n"
-        "in highp vec4 center;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
+        "attribute highp vec3 normal;\n"
+        "attribute highp vec4 center;\n"
 
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 mv_matrix; \n"
-        "out highp vec4 fP; \n"
-        "out highp vec3 fN; \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "void main(void)\n"
         "{\n"
         "   fP = mv_matrix * vertex; \n"
@@ -101,9 +101,9 @@ void Scene::compile_shaders()
     //Fragment source code
     const char fragment_source_spheres[] =
     {
-        "#version 330 \n"
-        "in highp vec4 fP; \n"
-        "in highp vec3 fN; \n"
+        "#version 120 \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "uniform highp vec4 light_pos;  \n"
         "uniform highp vec4 light_diff; \n"
         "uniform highp vec4 light_spec; \n"
@@ -159,18 +159,18 @@ void Scene::compile_shaders()
     //Vertex source code
     const char vertex_source_cylinders[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
-        "in highp vec3 normal;\n"
-        "in highp vec4 transfo1;\n"
-        "in highp vec4 transfo2;\n"
-        "in highp vec4 transfo3;\n"
-        "in highp vec4 transfo4;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
+        "attribute highp vec3 normal;\n"
+        "attribute highp vec4 transfo1;\n"
+        "attribute highp vec4 transfo2;\n"
+        "attribute highp vec4 transfo3;\n"
+        "attribute highp vec4 transfo4;\n"
         "mat4 transfo = mat4(transfo1, transfo2, transfo3, transfo4); \n"
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 mv_matrix; \n"
-        "out highp vec4 fP; \n"
-        "out highp vec3 fN; \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "void main(void)\n"
         "{\n"
         "   fP = mv_matrix * vertex; \n"
@@ -488,8 +488,11 @@ void Scene::initialize_buffers()
     rendering_program_spheres.enableAttributeArray(centerLocation[0]);
     rendering_program_spheres.setAttributeBuffer(centerLocation[0],GL_FLOAT,0,3);
     buffers[0].release();
-    glVertexAttribDivisor(centerLocation[0],1);
-    glVertexAttribDivisor(normalsLocation[0],0);
+    if(extension_is_found)
+    {
+        glVertexAttribDivisor(centerLocation[0],1);
+        glVertexAttribDivisor(normalsLocation[0],0);
+    }
     vao[3].release();
     rendering_program_spheres.release();
 
@@ -538,13 +541,15 @@ void Scene::initialize_buffers()
     rendering_program_cylinders.setAttributeBuffer(centerLocation[4],GL_FLOAT,0,4);
     buffers[13].release();
 
+    if(extension_is_found)
+    {
+        glVertexAttribDivisor(centerLocation[1],1);
+        glVertexAttribDivisor(centerLocation[2],1);
+        glVertexAttribDivisor(centerLocation[3],1);
+        glVertexAttribDivisor(centerLocation[4],1);
 
-    glVertexAttribDivisor(centerLocation[1],1);
-    glVertexAttribDivisor(centerLocation[2],1);
-    glVertexAttribDivisor(centerLocation[3],1);
-    glVertexAttribDivisor(centerLocation[4],1);
-
-    glVertexAttribDivisor(normalsLocation[1],0);
+        glVertexAttribDivisor(normalsLocation[1],0);
+    }
 
     vao[8].release();
     vao[9].bind();
@@ -590,13 +595,15 @@ void Scene::initialize_buffers()
     rendering_program_cylinders.setAttributeBuffer(centerLocation[4],GL_FLOAT,0,4);
     buffers[18].release();
 
+    if(extension_is_found)
+    {
+        glVertexAttribDivisor(centerLocation[1],1);
+        glVertexAttribDivisor(centerLocation[2],1);
+        glVertexAttribDivisor(centerLocation[3],1);
+        glVertexAttribDivisor(centerLocation[4],1);
 
-    glVertexAttribDivisor(centerLocation[1],1);
-    glVertexAttribDivisor(centerLocation[2],1);
-    glVertexAttribDivisor(centerLocation[3],1);
-    glVertexAttribDivisor(centerLocation[4],1);
-
-    glVertexAttribDivisor(normalsLocation[1],0);
+        glVertexAttribDivisor(normalsLocation[1],0);
+    }
 
     vao[9].release();
 
@@ -642,14 +649,15 @@ void Scene::initialize_buffers()
     rendering_program_cylinders.setAttributeBuffer(centerLocation[4],GL_FLOAT,0,4);
     buffers[22].release();
 
+    if(extension_is_found)
+    {
+        glVertexAttribDivisor(centerLocation[1],1);
+        glVertexAttribDivisor(centerLocation[2],1);
+        glVertexAttribDivisor(centerLocation[3],1);
+        glVertexAttribDivisor(centerLocation[4],1);
 
-    glVertexAttribDivisor(centerLocation[1],1);
-    glVertexAttribDivisor(centerLocation[2],1);
-    glVertexAttribDivisor(centerLocation[3],1);
-    glVertexAttribDivisor(centerLocation[4],1);
-
-    glVertexAttribDivisor(normalsLocation[1],0);
-
+        glVertexAttribDivisor(normalsLocation[1],0);
+    }
     vao[10].release();
 
     rendering_program_cylinders.release();
@@ -727,6 +735,25 @@ void Scene::init() {
     // undo from QGLViewer internal initializeGL function
     // glDisable(GL_COLOR_MATERIAL);
     initializeOpenGLFunctions();
+    glDrawArraysInstanced = (PFNGLDRAWARRAYSINSTANCEDARBPROC)ui->viewer->context()->getProcAddress("glDrawArraysInstancedARB");
+    if(!glDrawArraysInstanced)
+    {
+        qDebug()<<"glDrawArraysInstancedARB : extension not found. Wireframe mode will be forced.";
+        extension_is_found = false;
+    }
+    else
+        extension_is_found = true;
+
+    glVertexAttribDivisor = (PFNGLVERTEXATTRIBDIVISORARBPROC)ui->viewer->context()->getProcAddress("glVertexAttribDivisorARB");
+    if(!glDrawArraysInstanced)
+    {
+        qDebug()<<"glVertexAttribDivisorARB : extension not found. Wireframe mode will be forced.";
+        extension_is_found = false;
+    }
+    else
+        extension_is_found = true;
+
+    wireframe = !extension_is_found;
     // camera
     // only 2.7 gets an 'f' as VC++ warns if we don't
     ui->viewer->camera()->setPosition(Vec(0.5,0.5,2.7f));
@@ -753,6 +780,7 @@ void Scene::init() {
 
 // Draws the triangulation
 void Scene::draw() {
+    glEnable(GL_DEPTH_TEST);
     if(!are_buffers_initialized)
         initialize_buffers();
     gl_draw_location();
@@ -971,8 +999,11 @@ void Scene::update_position()
     rendering_program_spheres.enableAttributeArray(centerLocation[0]);
     rendering_program_spheres.setAttributeBuffer(centerLocation[0],GL_FLOAT,0,3);
     buffers[5].release();
-    glVertexAttribDivisor(centerLocation[0],1);
-    glVertexAttribDivisor(normalsLocation[1],0);
+    if(extension_is_found)
+    {
+        glVertexAttribDivisor(centerLocation[0],1);
+        glVertexAttribDivisor(normalsLocation[1],0);
+    }
     vao[7].release();
 
     ui->viewer->update();
diff --git a/Periodic_3_triangulation_3/demo/Periodic_3_triangulation_3/Scene.h b/Periodic_3_triangulation_3/demo/Periodic_3_triangulation_3/Scene.h
index 4f0db183696..4c012aa04dc 100644
--- a/Periodic_3_triangulation_3/demo/Periodic_3_triangulation_3/Scene.h
+++ b/Periodic_3_triangulation_3/demo/Periodic_3_triangulation_3/Scene.h
@@ -6,12 +6,12 @@
 #include <fstream>
 #include <QObject>
 #include <QFileDialog>
-#include <QOpenGLFunctions_3_3_Core>
+#include <QOpenGLFunctions_2_1>
 #include <QOpenGLVertexArrayObject>
 #include <QOpenGLBuffer>
 #include <QOpenGLShaderProgram>
 
-class Scene : public QObject, QOpenGLFunctions_3_3_Core
+class Scene : public QObject, QOpenGLFunctions_2_1
 {
   Q_OBJECT
 
@@ -144,9 +144,9 @@ public Q_SLOTS:
     ui->viewer->update();
   }
   void toggle_wireframe(bool on) {
-    wireframe = on;
-    ( on ? glDisable(GL_LIGHTING) : glEnable(GL_LIGHTING) );
-    changed();
+        wireframe = !(!on && extension_is_found);
+        ( on ? glDisable(GL_LIGHTING) : glEnable(GL_LIGHTING) );
+        changed();
   }
   void toggle_in_plane(bool on) {
     in_plane = on;
@@ -287,11 +287,16 @@ private:
       std::vector<float> transfo4_square;
 
       bool are_buffers_initialized;
+      bool extension_is_found;
       QOpenGLBuffer buffers[24];
       QOpenGLVertexArrayObject vao[12];
       QOpenGLShaderProgram rendering_program;
       QOpenGLShaderProgram rendering_program_spheres;
       QOpenGLShaderProgram rendering_program_cylinders;
+      typedef void (APIENTRYP PFNGLDRAWARRAYSINSTANCEDARBPROC) (GLenum mode, GLint first, GLsizei count, GLsizei primcount);
+      typedef void (APIENTRYP PFNGLVERTEXATTRIBDIVISORARBPROC) (GLuint index, GLuint divisor);
+      PFNGLDRAWARRAYSINSTANCEDARBPROC glDrawArraysInstanced;
+      PFNGLVERTEXATTRIBDIVISORARBPROC glVertexAttribDivisor;
       void initialize_buffers();
       void compute_elements();
       void attrib_buffers(QGLViewer*);
diff --git a/Periodic_3_triangulation_3/demo/Periodic_Lloyd_3/Viewer.cpp b/Periodic_3_triangulation_3/demo/Periodic_Lloyd_3/Viewer.cpp
index 7d1b9a93d09..cd59c5dc42f 100644
--- a/Periodic_3_triangulation_3/demo/Periodic_Lloyd_3/Viewer.cpp
+++ b/Periodic_3_triangulation_3/demo/Periodic_Lloyd_3/Viewer.cpp
@@ -27,6 +27,7 @@ Viewer::sceneChanged()
 void
 Viewer::draw()
 {
+    glEnable(GL_DEPTH_TEST);
   if(!are_buffers_initialized)
       initialize_buffers();
   QColor color;
@@ -265,8 +266,8 @@ void Viewer::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
         "uniform highp mat4 mvp_matrix;\n"
         "void main(void)\n"
         "{\n"
@@ -276,7 +277,7 @@ void Viewer::compile_shaders()
     //Fragment source code
     const char fragment_source[] =
     {
-        "#version 330 \n"
+        "#version 120 \n"
         "uniform highp vec4 color; \n"
         "void main(void) { \n"
         "gl_FragColor = color; \n"
diff --git a/Periodic_3_triangulation_3/demo/Periodic_Lloyd_3/Viewer.h b/Periodic_3_triangulation_3/demo/Periodic_Lloyd_3/Viewer.h
index cce393ebe1d..c03df5c5c65 100644
--- a/Periodic_3_triangulation_3/demo/Periodic_Lloyd_3/Viewer.h
+++ b/Periodic_3_triangulation_3/demo/Periodic_Lloyd_3/Viewer.h
@@ -3,14 +3,14 @@
 
 #include "Scene.h"
 #include <QGLViewer/qglviewer.h>
-#include <QOpenGLFunctions_3_3_Core>
+#include <QOpenGLFunctions_2_1>
 #include <QOpenGLVertexArrayObject>
 #include <QOpenGLBuffer>
 #include <QOpenGLShaderProgram>
 #include <CGAL/Qt/CreateOpenGLContext.h>
 
 
-class Viewer : public QGLViewer, QOpenGLFunctions_3_3_Core {
+class Viewer : public QGLViewer, QOpenGLFunctions_2_1 {
 
   typedef qglviewer::Vec Vec;
 
diff --git a/Periodic_3_triangulation_3/include/CGAL/Periodic_3_triangulation_3.h b/Periodic_3_triangulation_3/include/CGAL/Periodic_3_triangulation_3.h
index 6a21b1b4ff5..3bebc4df680 100644
--- a/Periodic_3_triangulation_3/include/CGAL/Periodic_3_triangulation_3.h
+++ b/Periodic_3_triangulation_3/include/CGAL/Periodic_3_triangulation_3.h
@@ -2175,6 +2175,7 @@ Periodic_3_triangulation_3<GT,TDS>::periodic_insert(
 
   // This only holds for Delaunay
   CGAL_triangulation_assertion(lt != VERTEX);
+  CGAL_USE(lt);
 
   // Choose the periodic copy of tester.point() that is inside c.
   Offset current_off = get_location_offset(tester, c);
diff --git a/Polyhedron/demo/Polyhedron/CGAL_demo/Viewer_interface.h b/Polyhedron/demo/Polyhedron/CGAL_demo/Viewer_interface.h
index 10eb01aa7c8..fe99eda60b2 100644
--- a/Polyhedron/demo/Polyhedron/CGAL_demo/Viewer_interface.h
+++ b/Polyhedron/demo/Polyhedron/CGAL_demo/Viewer_interface.h
@@ -4,7 +4,7 @@
 #include <QGLViewer/qglviewer.h>
 #include <QWidget>
 #include <QPoint>
-#include <QOpenGLFunctions_3_3_Core>
+#include <QOpenGLFunctions_2_1>
 #include <CGAL/Qt/CreateOpenGLContext.h>
 // forward declarations
 class QWidget;
@@ -14,7 +14,7 @@ class QKeyEvent;
 
 #include "../Viewer_config.h" // for VIEWER_EXPORT
 
-class VIEWER_EXPORT Viewer_interface : public QGLViewer, public QOpenGLFunctions_3_3_Core {
+class VIEWER_EXPORT Viewer_interface : public QGLViewer, public QOpenGLFunctions_2_1 {
 
   Q_OBJECT
 
@@ -30,6 +30,11 @@ public:
   static QString dumpFrame(const qglviewer::Frame&);
 
   virtual bool inFastDrawing() const = 0;
+  typedef void (APIENTRYP PFNGLDRAWARRAYSINSTANCEDARBPROC) (GLenum mode, GLint first, GLsizei count, GLsizei primcount);
+  typedef void (APIENTRYP PFNGLVERTEXATTRIBDIVISORARBPROC) (GLuint index, GLuint divisor);
+  PFNGLDRAWARRAYSINSTANCEDARBPROC glDrawArraysInstanced;
+  PFNGLVERTEXATTRIBDIVISORARBPROC glVertexAttribDivisor;
+  bool extension_is_found;
   GLfloat pickMatrix_[16];
 
 Q_SIGNALS:
@@ -47,6 +52,7 @@ public Q_SLOTS:
   virtual QString dumpCameraCoordinates() = 0;
   virtual bool moveCameraToCoordinates(QString, 
                                        float animation_duration = 0.5f) = 0;
+
 }; // end class Viewer_interface
 
 #endif // VIEWER_INTERFACE_H
diff --git a/Polyhedron/demo/Polyhedron/MainWindow.cpp b/Polyhedron/demo/Polyhedron/MainWindow.cpp
index e56572adff8..8a06dd6344e 100644
--- a/Polyhedron/demo/Polyhedron/MainWindow.cpp
+++ b/Polyhedron/demo/Polyhedron/MainWindow.cpp
@@ -959,7 +959,7 @@ QList<int> MainWindow::getSelectedSceneItemIndices() const
 
 void MainWindow::selectionChanged()
 {
-  scene->setSelectedItem(getSelectedSceneItemIndex());
+  scene->setSelectedItemIndex(getSelectedSceneItemIndex());
   scene->setSelectedItemsList(getSelectedSceneItemIndices());
   Scene_item* item = scene->item(getSelectedSceneItemIndex());
   if(item != NULL && item->manipulatable()) {
diff --git a/Polyhedron/demo/Polyhedron/Polyhedron_demo_advancing_front_plugin.ui b/Polyhedron/demo/Polyhedron/Polyhedron_demo_advancing_front_plugin.ui
index a699faed2b8..917d82a299a 100644
--- a/Polyhedron/demo/Polyhedron/Polyhedron_demo_advancing_front_plugin.ui
+++ b/Polyhedron/demo/Polyhedron/Polyhedron_demo_advancing_front_plugin.ui
@@ -30,7 +30,7 @@
       <double>0.000000000000000</double>
      </property>
      <property name="maximum">
-      <double>30.000000000000000</double>
+      <double>999999999.000000000000000</double>
      </property>
      <property name="value">
       <double>0.000000000000000</double>
diff --git a/Polyhedron/demo/Polyhedron/Polyhedron_demo_hole_filling_plugin.cpp b/Polyhedron/demo/Polyhedron/Polyhedron_demo_hole_filling_plugin.cpp
index 8c30ec50cb2..43a9325e747 100644
--- a/Polyhedron/demo/Polyhedron/Polyhedron_demo_hole_filling_plugin.cpp
+++ b/Polyhedron/demo/Polyhedron/Polyhedron_demo_hole_filling_plugin.cpp
@@ -35,6 +35,7 @@
 #include "Kernel_type.h"
 
 #include <boost/function_output_iterator.hpp>
+#include <QMap>
 
 // Class for visualizing holes in a polyhedron
 // provides mouse selection functionality
@@ -307,13 +308,7 @@ public:
   void init(QMainWindow* mainWindow, Scene_interface* scene_interface, Messages_interface* m);
 
   Scene_hole_visualizer* get_hole_visualizer(Scene_polyhedron_item* poly_item) {
-    // did not use a map to assoc Scene_polyhedron_item with Scene_hole_visualizer to prevent crowded code
-    for(Scene_interface::Item_id i = 0, end = scene->numberOfEntries(); i < end; ++i) {
-      Scene_hole_visualizer* hole_visualizer = qobject_cast<Scene_hole_visualizer*>(scene->item(i));
-      if(hole_visualizer && hole_visualizer->poly_item == poly_item) 
-      { return hole_visualizer; }
-    }
-    return NULL;
+      return visualizers[poly_item];
   }
 
 public Q_SLOTS:
@@ -353,6 +348,9 @@ private:
   QDockWidget* dock_widget;
   Ui::HoleFilling ui_widget;
 
+  //Maintains a reference between all the visualizers and their poly_item
+  // to ease the management of the visualizers
+  QMap<Scene_polyhedron_item*, Scene_hole_visualizer*> visualizers;
   // hold created facet for accept reject functionality
   std::vector<Polyhedron::Facet_handle> new_facets; 
   Scene_polyhedron_item* last_active_item; // always keep it NULL while not active-reject state
@@ -427,11 +425,18 @@ void Polyhedron_demo_hole_filling_plugin::item_about_to_be_destroyed(Scene_item*
   if(poly_item) {
     // erase assoc polylines item
     scene->erase( scene->item_id( get_hole_visualizer(poly_item) ) );
+    visualizers.remove(poly_item);
     // close accept-reject dialog if it is open
     if(last_active_item == poly_item) {
       on_Accept_button();
     }
   }
+  else {
+    Scene_hole_visualizer* visu_item = qobject_cast<Scene_hole_visualizer*>(scene_item);
+    if(visu_item) {
+        visualizers.remove(visu_item->poly_item);
+    }
+  }
 }
 // removes Scene_hole_visualizer items
 void Polyhedron_demo_hole_filling_plugin::dock_widget_closed() {
@@ -460,10 +465,12 @@ void Polyhedron_demo_hole_filling_plugin::on_Visualize_holes_button() {
   }
 
   Scene_hole_visualizer* hole_visualizer = new Scene_hole_visualizer(poly_item, mw);
+  visualizers[poly_item] = hole_visualizer;
   connect(hole_visualizer, SIGNAL(itemChanged()), this, SLOT(hole_visualizer_changed()));
 
   if(hole_visualizer->polyline_data_list.empty()) {
     print_message("There is no hole in selected polyhedron item!");
+    visualizers.remove(poly_item);
     delete hole_visualizer;
     return;
   }
@@ -590,6 +597,7 @@ void Polyhedron_demo_hole_filling_plugin::hole_visualizer_changed() {
   Scene_hole_visualizer* hole_visualizer = qobject_cast<Scene_hole_visualizer*>(this->sender());
   if(hole_visualizer && hole_visualizer->polyline_data_list.empty()) {
     scene->erase( scene->item_id(hole_visualizer));
+    visualizers.remove(hole_visualizer->poly_item);
   }
 }
 // helper function for filling holes
diff --git a/Polyhedron/demo/Polyhedron/Polyhedron_demo_mean_curvature_flow_skeleton_plugin.cpp b/Polyhedron/demo/Polyhedron/Polyhedron_demo_mean_curvature_flow_skeleton_plugin.cpp
index e8d3625ef3a..98161cd4b11 100644
--- a/Polyhedron/demo/Polyhedron/Polyhedron_demo_mean_curvature_flow_skeleton_plugin.cpp
+++ b/Polyhedron/demo/Polyhedron/Polyhedron_demo_mean_curvature_flow_skeleton_plugin.cpp
@@ -155,6 +155,9 @@ public:
     connect(ui->pushButton_segment, SIGNAL(clicked()),
             this, SLOT(on_actionSegment()));
 
+    QObject* scene_object = dynamic_cast<QObject*>(scene);
+    connect(scene_object, SIGNAL(itemAboutToBeDestroyed(Scene_item*)),
+            this, SLOT(on_actionItemAboutToBeDestroyed(Scene_item*)));
   }
 
   QList<QAction*> actions() const {
@@ -719,10 +722,6 @@ void Polyhedron_demo_mean_curvature_flow_skeleton_plugin::on_actionRun()
     delete temp;
   }
 
-  QObject* scene_object = dynamic_cast<QObject*>(scene);
-  connect(scene_object, SIGNAL(itemAboutToBeDestroyed(Scene_item*)),
-          this, SLOT(on_actionItemAboutToBeDestroyed(Scene_item*)));
-
 //#define DRAW_NON_FIXED_POINTS
 #ifdef DRAW_NON_FIXED_POINTS
   // draw non-fixed points
diff --git a/Polyhedron/demo/Polyhedron/Polyhedron_demo_off_plugin.cpp b/Polyhedron/demo/Polyhedron/Polyhedron_demo_off_plugin.cpp
index 01bc86868bb..30c6e3d0d76 100644
--- a/Polyhedron/demo/Polyhedron/Polyhedron_demo_off_plugin.cpp
+++ b/Polyhedron/demo/Polyhedron/Polyhedron_demo_off_plugin.cpp
@@ -5,6 +5,9 @@
 #include "Polyhedron_demo_io_plugin_interface.h"
 #include <fstream>
 
+#include <CGAL/IO/File_scanner_OFF.h>
+#include <QMessageBox>
+
 class Polyhedron_demo_off_plugin :
   public QObject,
   public Polyhedron_demo_io_plugin_interface
@@ -37,7 +40,12 @@ Polyhedron_demo_off_plugin::load(QFileInfo fileinfo) {
     std::cerr << "Error! Cannot open file " << (const char*)fileinfo.filePath().toUtf8() << std::endl;
     return NULL;
   }
-    
+
+  // to detect isolated vertices
+  CGAL::File_scanner_OFF scanner( in, false);
+  std::size_t total_nb_of_vertices = scanner.size_of_vertices();
+  in.seekg(0);
+
   // Try to read .off in a polyhedron
   Scene_polyhedron_item* item = new Scene_polyhedron_item();
   item->setName(fileinfo.baseName());
@@ -56,6 +64,14 @@ Polyhedron_demo_off_plugin::load(QFileInfo fileinfo) {
     }
     return soup_item;
   }
+  else
+    if( total_nb_of_vertices!= item->polyhedron()->size_of_vertices())
+    {
+      QMessageBox::warning((QWidget*)NULL,
+                     tr("Isolated vertices found"),
+                     tr("%1 isolated vertices ignored")
+                     .arg(total_nb_of_vertices-item->polyhedron()->size_of_vertices()));
+    }
 
   return item;
 }
diff --git a/Polyhedron/demo/Polyhedron/Polyhedron_demo_polyhedron_slicer_plugin.cpp b/Polyhedron/demo/Polyhedron/Polyhedron_demo_polyhedron_slicer_plugin.cpp
index a8825d7659b..7fb2f93a929 100644
--- a/Polyhedron/demo/Polyhedron/Polyhedron_demo_polyhedron_slicer_plugin.cpp
+++ b/Polyhedron/demo/Polyhedron/Polyhedron_demo_polyhedron_slicer_plugin.cpp
@@ -229,6 +229,7 @@ void Polyhedron_demo_polyhedron_slicer_plugin::on_Generate_button_clicked()
   get_base_1_2(bases); // no need to check since we call on_Update_plane_button_clicked
   Epic_kernel::Vector_3 base_1(bases[0], bases[1], bases[2]);
   Epic_kernel::Vector_3 base_2(bases[3], bases[4], bases[5]);
+  const Epic_kernel::Vector_3 normal = CGAL::cross_product(base_1, base_2);
 
   // get distance between planes
   bool to_double_ok = true;
@@ -255,7 +256,7 @@ void Polyhedron_demo_polyhedron_slicer_plugin::on_Generate_button_clicked()
 
     //Epic_kernel::Plane_3 plane(n[0], n[1],  n[2], - n * new_pos);
     Epic_kernel::Point_3 new_pos_cgal(new_pos[0], new_pos[1], new_pos[2]);
-    Epic_kernel::Plane_3 plane(new_pos_cgal, new_pos_cgal + base_1, new_pos_cgal + base_2);
+    Epic_kernel::Plane_3 plane(new_pos_cgal, normal);
 
     if(!CGAL::do_intersect(cgal_bbox, plane)) { 
       if(dir == -1) { break; }
diff --git a/Polyhedron/demo/Polyhedron/Scene.cpp b/Polyhedron/demo/Polyhedron/Scene.cpp
index d3fc928e732..fc573bc5776 100644
--- a/Polyhedron/demo/Polyhedron/Scene.cpp
+++ b/Polyhedron/demo/Polyhedron/Scene.cpp
@@ -288,7 +288,7 @@ Scene::draw_aux(bool with_names, Viewer_interface* viewer)
             ::glPopName();
         }
     }
-
+glDepthFunc(GL_LEQUAL);
     // Wireframe OpenGL drawing
     for(int index = 0; index < m_entries.size(); ++index)
     {
@@ -353,6 +353,7 @@ Scene::draw_aux(bool with_names, Viewer_interface* viewer)
         }
     }
 
+
     // Points OpenGL drawing
     for(int index = 0; index < m_entries.size(); ++index)
     {
@@ -381,6 +382,8 @@ Scene::draw_aux(bool with_names, Viewer_interface* viewer)
             ::glPopName();
         }
     }
+    glDepthFunc(GL_LESS);
+
 }
 
 int 
diff --git a/Polyhedron/demo/Polyhedron/Scene.h b/Polyhedron/demo/Polyhedron/Scene.h
index 2777b23715c..a8990104a01 100644
--- a/Polyhedron/demo/Polyhedron/Scene.h
+++ b/Polyhedron/demo/Polyhedron/Scene.h
@@ -115,6 +115,11 @@ public Q_SLOTS:
   void itemChanged(int i); 
   void itemChanged(Scene_item*);
 
+  void setSelectedItemIndex(int i)
+  {
+    selected_item = i;
+  }
+
   void setSelectedItem(int i )
   {
     selected_item = i;
diff --git a/Polyhedron/demo/Polyhedron/Scene_edit_polyhedron_item.cpp b/Polyhedron/demo/Polyhedron/Scene_edit_polyhedron_item.cpp
index e0aaecaf4bb..c1a2ec5a506 100644
--- a/Polyhedron/demo/Polyhedron/Scene_edit_polyhedron_item.cpp
+++ b/Polyhedron/demo/Polyhedron/Scene_edit_polyhedron_item.cpp
@@ -73,7 +73,7 @@ Scene_edit_polyhedron_item::Scene_edit_polyhedron_item
 
     const char vertex_shader_source_bbox[] =
     {
-
+        "#version 120 \n"
         "attribute highp vec3 vertex; \n"
         "attribute highp vec3 colors; \n"
 
@@ -92,6 +92,7 @@ Scene_edit_polyhedron_item::Scene_edit_polyhedron_item
     };
     const char fragment_shader_source[]=
     {
+        "#version 120 \n"
         "varying vec3 fColors; \n"
         " \n"
         "void main(void) \n"
@@ -214,8 +215,11 @@ void Scene_edit_polyhedron_item::initialize_buffers(Viewer_interface *viewer =0)
         program->setAttributeBuffer("center",GL_DOUBLE,0,3);
         buffers[8].release();
 
-        viewer->glVertexAttribDivisor(program->attributeLocation("center"), 1);
-        viewer->glVertexAttribDivisor(program->attributeLocation("colors"), 1);
+        if(viewer->extension_is_found)
+        {
+            viewer->glVertexAttribDivisor(program->attributeLocation("center"), 1);
+            viewer->glVertexAttribDivisor(program->attributeLocation("colors"), 1);
+        }
         vaos[3]->release();
     }
     //vao for the BBOX
@@ -292,8 +296,11 @@ void Scene_edit_polyhedron_item::initialize_buffers(Viewer_interface *viewer =0)
         program->setAttributeBuffer("center",GL_DOUBLE,0,3);
         buffers[16].release();
 
-        viewer->glVertexAttribDivisor(program->attributeLocation("center"), 1);
-        viewer->glVertexAttribDivisor(program->attributeLocation("colors"), 1);
+        if(viewer->extension_is_found)
+        {
+            viewer->glVertexAttribDivisor(program->attributeLocation("center"), 1);
+            viewer->glVertexAttribDivisor(program->attributeLocation("colors"), 1);
+        }
         vaos[6]->release();
     }
     //vao for the axis
@@ -501,7 +508,7 @@ void Scene_edit_polyhedron_item::draw_ROI_and_control_vertices(Viewer_interface*
   color.set_rgb_color(0, 1.f, 0);
   if(ui_widget->ShowROICheckBox->isChecked()) {
 
-        if(!ui_widget->ShowAsSphereCheckBox->isChecked()) {
+        if(!ui_widget->ShowAsSphereCheckBox->isChecked() || !viewer->extension_is_found) {
 
             vaos[1]->bind();
             program = getShaderProgram(PROGRAM_WITHOUT_LIGHT);
@@ -524,7 +531,7 @@ void Scene_edit_polyhedron_item::draw_ROI_and_control_vertices(Viewer_interface*
     }
   }
 
-    if(!ui_widget->ShowAsSphereCheckBox->isChecked()) {
+    if(!ui_widget->ShowAsSphereCheckBox->isChecked() || !viewer->extension_is_found) {
         vaos[5]->bind();
         program = getShaderProgram(PROGRAM_WITHOUT_LIGHT);
         attrib_buffers(viewer,PROGRAM_WITHOUT_LIGHT);
diff --git a/Polyhedron/demo/Polyhedron/Scene_polylines_item.cpp b/Polyhedron/demo/Polyhedron/Scene_polylines_item.cpp
index 9314bdbcdea..93a8be66aea 100644
--- a/Polyhedron/demo/Polyhedron/Scene_polylines_item.cpp
+++ b/Polyhedron/demo/Polyhedron/Scene_polylines_item.cpp
@@ -51,40 +51,63 @@ Scene_polylines_item::initialize_buffers(Viewer_interface *viewer = 0) const
     }
    //vao for the spheres
     {
-        program = getShaderProgram(PROGRAM_INSTANCED, viewer);
-        program->bind();
+        if(viewer->extension_is_found)
+        {
+            program = getShaderProgram(PROGRAM_INSTANCED, viewer);
+            program->bind();
 
-        vaos[1]->bind();
-        buffers[1].bind();
-        buffers[1].allocate(positions_spheres.data(), 
-                            static_cast<int>(positions_spheres.size()*sizeof(float)));
-        program->enableAttributeArray("vertex");
-        program->setAttributeBuffer("vertex",GL_FLOAT,0,3);
-        buffers[1].release();
+            vaos[1]->bind();
+            buffers[1].bind();
+            buffers[1].allocate(positions_spheres.data(),
+                                static_cast<int>(positions_spheres.size()*sizeof(float)));
+            program->enableAttributeArray("vertex");
+            program->setAttributeBuffer("vertex",GL_FLOAT,0,3);
+            buffers[1].release();
 
-        buffers[2].bind();
-        buffers[2].allocate(normals_spheres.data(),
-                            static_cast<int>(normals_spheres.size()*sizeof(float)));
-        program->enableAttributeArray("normals");
-        program->setAttributeBuffer("normals",GL_FLOAT,0,3);
-        buffers[2].release();
+            buffers[2].bind();
+            buffers[2].allocate(normals_spheres.data(),
+                                static_cast<int>(normals_spheres.size()*sizeof(float)));
+            program->enableAttributeArray("normals");
+            program->setAttributeBuffer("normals",GL_FLOAT,0,3);
+            buffers[2].release();
 
-        buffers[3].bind();
-        buffers[3].allocate(color_spheres.data(),
-                            static_cast<int>(color_spheres.size()*sizeof(float)));
-        program->enableAttributeArray("colors");
-        program->setAttributeBuffer("colors",GL_FLOAT,0,3);
-        buffers[3].release();
+            buffers[3].bind();
+            buffers[3].allocate(color_spheres.data(),
+                                static_cast<int>(color_spheres.size()*sizeof(float)));
+            program->enableAttributeArray("colors");
+            program->setAttributeBuffer("colors",GL_FLOAT,0,3);
+            buffers[3].release();
 
-        buffers[4].bind();
-        buffers[4].allocate(positions_center.data(),
-                            static_cast<int>(positions_center.size()*sizeof(float)));
-        program->enableAttributeArray("center");
-        program->setAttributeBuffer("center",GL_FLOAT,0,3);
-        buffers[4].release();
+            buffers[4].bind();
+            buffers[4].allocate(positions_center.data(),
+                                static_cast<int>(positions_center.size()*sizeof(float)));
+            program->enableAttributeArray("center");
+            program->setAttributeBuffer("center",GL_FLOAT,0,3);
+            buffers[4].release();
 
-        viewer->glVertexAttribDivisor(program->attributeLocation("center"), 1);
-        viewer->glVertexAttribDivisor(program->attributeLocation("colors"), 1);
+            viewer->glVertexAttribDivisor(program->attributeLocation("center"), 1);
+            viewer->glVertexAttribDivisor(program->attributeLocation("colors"), 1);
+        }
+        else
+        {
+            program = getShaderProgram(PROGRAM_WITHOUT_LIGHT, viewer);
+            program->bind();
+
+            vaos[1]->bind();
+            buffers[1].bind();
+            buffers[1].allocate(positions_center.data(),
+                                static_cast<int>(positions_center.size()*sizeof(float)));
+            program->enableAttributeArray("vertex");
+            program->setAttributeBuffer("vertex",GL_FLOAT,0,3);
+            buffers[1].release();
+
+            buffers[2].bind();
+            buffers[2].allocate(color_spheres.data(),
+                                static_cast<int>(color_spheres.size()*sizeof(float)));
+            program->enableAttributeArray("colors");
+            program->setAttributeBuffer("colors",GL_FLOAT,0,3);
+            buffers[2].release();
+        }
         vaos[1]->release();
 
         program->release();
@@ -92,39 +115,51 @@ Scene_polylines_item::initialize_buffers(Viewer_interface *viewer = 0) const
 
 //vao for the wired spheres
     {
-        program = getShaderProgram(PROGRAM_INSTANCED_WIRE, viewer);
-        program->bind();
+        if(viewer->extension_is_found)
+        {
+            program = getShaderProgram(PROGRAM_INSTANCED_WIRE, viewer);
+            program->bind();
 
-        vaos[2]->bind();
-        buffers[5].bind();
-        buffers[5].allocate(positions_wire_spheres.data(),
-                            static_cast<int>(positions_wire_spheres.size()*sizeof(float)));
-        program->enableAttributeArray("vertex");
-        program->setAttributeBuffer("vertex",GL_FLOAT,0,3);
-        buffers[5].release();
-        QColor temp = this->color();
-        program->setAttributeValue("colors", temp);
+            vaos[2]->bind();
+            buffers[5].bind();
+            buffers[5].allocate(positions_wire_spheres.data(),
+                                static_cast<int>(positions_wire_spheres.size()*sizeof(float)));
+            program->enableAttributeArray("vertex");
+            program->setAttributeBuffer("vertex",GL_FLOAT,0,3);
+            buffers[5].release();
 
-        program->setAttributeValue("normals",QVector3D(0.0,0.0,0.0));
 
-        buffers[6].bind();
-        buffers[6].allocate(color_spheres.data(),
-                            static_cast<int>(color_spheres.size()*sizeof(float)));
-        program->enableAttributeArray("colors");
-        program->setAttributeBuffer("colors",GL_FLOAT,0,3);
-        buffers[6].release();
+            buffers[3].bind();
+            program->enableAttributeArray("colors");
+            program->setAttributeBuffer("colors",GL_FLOAT,0,3);
+            buffers[3].release();
 
-        buffers[7].bind();
-        buffers[7].allocate(positions_center.data(),
-                            static_cast<int>(positions_center.size()*sizeof(float)));
-        program->enableAttributeArray("center");
-        program->setAttributeBuffer("center",GL_FLOAT,0,3);
-        buffers[7].release();
+            buffers[2].bind();
+            program->enableAttributeArray("normals");
+            program->setAttributeBuffer("normals",GL_FLOAT,0,3);
+            buffers[2].release();
 
-        viewer->glVertexAttribDivisor(program->attributeLocation("center"), 1);
-        viewer->glVertexAttribDivisor(program->attributeLocation("colors"), 1);
-        vaos[2]->release();
-        program->release();
+            buffers[6].bind();
+            buffers[6].allocate(color_spheres.data(),
+                                static_cast<int>(color_spheres.size()*sizeof(float)));
+            program->enableAttributeArray("colors");
+            program->setAttributeBuffer("colors",GL_FLOAT,0,3);
+            buffers[6].release();
+
+            buffers[7].bind();
+            buffers[7].allocate(positions_center.data(),
+                                static_cast<int>(positions_center.size()*sizeof(float)));
+            program->enableAttributeArray("center");
+            program->setAttributeBuffer("center",GL_FLOAT,0,3);
+            buffers[7].release();
+
+
+            viewer->glVertexAttribDivisor(program->attributeLocation("center"), 1);
+            viewer->glVertexAttribDivisor(program->attributeLocation("colors"), 1);
+
+            vaos[2]->release();
+            program->release();
+        }
     }
 
    are_buffers_filled = true;
@@ -283,7 +318,7 @@ Scene_polylines_item::Scene_polylines_item()
     ,d(new Scene_polylines_item_private())
     ,nbSpheres(0)
 {
-    setRenderingMode(Flat);
+    setRenderingMode(FlatPlusEdges);
     changed();
 
 }
@@ -363,8 +398,7 @@ Scene_polylines_item::toolTip() const {
 bool
 Scene_polylines_item::supportsRenderingMode(RenderingMode m) const {
     return (m == Wireframe ||
-            m == Flat ||
-            m == Flat ||
+            m == FlatPlusEdges ||
             m == Points);
 }
 
@@ -376,26 +410,30 @@ Scene_polylines_item::draw(Viewer_interface* viewer) const {
         initialize_buffers(viewer);
     if(d->draw_extremities)
     {
-        vaos[1]->bind();
-        program = getShaderProgram(PROGRAM_INSTANCED);
-        attrib_buffers(viewer, PROGRAM_INSTANCED);
-        program->bind();
-        viewer->glDrawArraysInstanced(GL_TRIANGLES, 0,
-                                    static_cast<GLsizei>(positions_spheres.size()/3), nbSpheres);
-        program->release();
-        vaos[1]->release();
-    }
-    if(renderingMode() == Flat)
-    {
-        vaos[0]->bind();
-        attrib_buffers(viewer, PROGRAM_WITHOUT_LIGHT);
-        program = getShaderProgram(PROGRAM_WITHOUT_LIGHT);
-        program->bind();
-        QColor temp = this->color();
-        program->setAttributeValue("colors", temp);
-        viewer->glDrawArrays(GL_LINES, 0, static_cast<GLsizei>(positions_lines.size()/4));
-        program->release();
-        vaos[0]->release();
+        if(viewer->extension_is_found)
+        {
+            vaos[1]->bind();
+            program = getShaderProgram(PROGRAM_INSTANCED);
+            attrib_buffers(viewer, PROGRAM_INSTANCED);
+            program->bind();
+            viewer->glDrawArraysInstanced(GL_TRIANGLES, 0,
+                                          static_cast<GLsizei>(positions_spheres.size()/3), nbSpheres);
+            program->release();
+            vaos[1]->release();
+        }
+        else
+        {
+            vaos[1]->bind();
+            program = getShaderProgram(PROGRAM_WITHOUT_LIGHT);
+            attrib_buffers(viewer, PROGRAM_WITHOUT_LIGHT);
+            glPointSize(8.0f);
+            glEnable(GL_POINT_SMOOTH);
+            program->bind();
+            viewer->glDrawArrays(GL_POINTS, 0, static_cast<GLsizei>(positions_center.size()/3));
+            glDisable(GL_POINT_SMOOTH);
+            program->release();
+            vaos[1]->release();
+        }
     }
 }
 
@@ -409,21 +447,23 @@ Scene_polylines_item::draw_edges(Viewer_interface* viewer) const {
     attrib_buffers(viewer, PROGRAM_WITHOUT_LIGHT);
     program = getShaderProgram(PROGRAM_WITHOUT_LIGHT);
     program->bind();
-    QColor temp = this->color();
-    program->setAttributeValue("colors", temp);
+    program->setAttributeValue("colors", this->color());
     viewer->glDrawArrays(GL_LINES, 0, static_cast<GLsizei>(positions_lines.size()/4));
     program->release();
     vaos[0]->release();
     if(d->draw_extremities)
     {
-        vaos[2]->bind();
-        attrib_buffers(viewer, PROGRAM_INSTANCED_WIRE);
-        program = getShaderProgram(PROGRAM_INSTANCED_WIRE);
-        program->bind();
-        viewer->glDrawArraysInstanced(GL_LINES, 0,
-                                    static_cast<GLsizei>(positions_wire_spheres.size()/3), nbSpheres);
-        program->release();
-        vaos[2]->release();
+        if(viewer->extension_is_found)
+        {
+            vaos[2]->bind();
+            attrib_buffers(viewer, PROGRAM_INSTANCED_WIRE);
+            program = getShaderProgram(PROGRAM_INSTANCED_WIRE);
+            program->bind();
+            viewer->glDrawArraysInstanced(GL_LINES, 0,
+                                          static_cast<GLsizei>(positions_wire_spheres.size()/3), nbSpheres);
+            program->release();
+            vaos[2]->release();
+        }
     }
 
 }
diff --git a/Polyhedron/demo/Polyhedron/Viewer.cpp b/Polyhedron/demo/Polyhedron/Viewer.cpp
index 78e08c6dee0..7da7c0d194f 100644
--- a/Polyhedron/demo/Polyhedron/Viewer.cpp
+++ b/Polyhedron/demo/Polyhedron/Viewer.cpp
@@ -105,6 +105,25 @@ void Viewer::initializeGL()
 {
   QGLViewer::initializeGL();
   initializeOpenGLFunctions();
+  glDrawArraysInstanced = (PFNGLDRAWARRAYSINSTANCEDARBPROC)this->context()->getProcAddress("glDrawArraysInstancedARB");
+  if(!glDrawArraysInstanced)
+  {
+      qDebug()<<"glDrawArraysInstancedARB : extension not found. Spheres will be displayed as points.";
+      extension_is_found = false;
+  }
+  else
+      extension_is_found = true;
+
+  glVertexAttribDivisor = (PFNGLVERTEXATTRIBDIVISORARBPROC)this->context()->getProcAddress("glVertexAttribDivisorARB");
+  if(!glDrawArraysInstanced)
+  {
+      qDebug()<<"glVertexAttribDivisorARB : extension not found. Spheres will be displayed as points.";
+      extension_is_found = false;
+  }
+  else
+      extension_is_found = true;
+
+
   setBackgroundColor(::Qt::white);
   d->scene->initializeGL();
 
@@ -202,6 +221,8 @@ void Viewer_impl::draw_aux(bool with_names, Viewer* viewer)
     scene->drawWithNames(viewer);
   else
     scene->draw(viewer);
+   ::glDisable(GL_POLYGON_OFFSET_FILL);
+  ::glPolygonMode(GL_FRONT_AND_BACK,GL_FILL);
 }
 
 void Viewer::drawWithNames()
diff --git a/Polyhedron/demo/Polyhedron/resources/shader_instanced.v b/Polyhedron/demo/Polyhedron/resources/shader_instanced.v
index 0f7d6ff4740..d353c8d9949 100644
--- a/Polyhedron/demo/Polyhedron/resources/shader_instanced.v
+++ b/Polyhedron/demo/Polyhedron/resources/shader_instanced.v
@@ -1,4 +1,4 @@
-#version 330
+#version 120
 attribute highp vec4 vertex;
 attribute highp vec3 normals;
 attribute highp vec3 colors;
diff --git a/Polyhedron/demo/Polyhedron/resources/shader_with_light.f b/Polyhedron/demo/Polyhedron/resources/shader_with_light.f
index 9fa9b65352f..8d958ab4085 100644
--- a/Polyhedron/demo/Polyhedron/resources/shader_with_light.f
+++ b/Polyhedron/demo/Polyhedron/resources/shader_with_light.f
@@ -1,4 +1,4 @@
-#version 330
+#version 120
 varying highp vec4 color;
 varying highp vec4 fP; 
 varying highp vec3 fN; 
diff --git a/Polyhedron/demo/Polyhedron/resources/shader_with_light.v b/Polyhedron/demo/Polyhedron/resources/shader_with_light.v
index cad171b3084..fa04afac9df 100644
--- a/Polyhedron/demo/Polyhedron/resources/shader_with_light.v
+++ b/Polyhedron/demo/Polyhedron/resources/shader_with_light.v
@@ -1,4 +1,4 @@
-#version 330
+#version 120
 attribute highp vec4 vertex;
 attribute highp vec3 normals;
 attribute highp vec3 colors;
diff --git a/Polyhedron/demo/Polyhedron/resources/shader_with_texture.f b/Polyhedron/demo/Polyhedron/resources/shader_with_texture.f
index 2c90da7dba8..4d9bc7ca323 100644
--- a/Polyhedron/demo/Polyhedron/resources/shader_with_texture.f
+++ b/Polyhedron/demo/Polyhedron/resources/shader_with_texture.f
@@ -1,4 +1,4 @@
-#version 330
+#version 120
 varying highp vec3 fColors;
 varying highp vec2 f_texCoord; 
 uniform sampler2D s_texture; 
diff --git a/Polyhedron/demo/Polyhedron/resources/shader_with_texture.v b/Polyhedron/demo/Polyhedron/resources/shader_with_texture.v
index 09ced2cacaf..bfecbfc3b74 100644
--- a/Polyhedron/demo/Polyhedron/resources/shader_with_texture.v
+++ b/Polyhedron/demo/Polyhedron/resources/shader_with_texture.v
@@ -1,4 +1,4 @@
-#version 330
+#version 120
 attribute highp vec4 vertex;
 attribute highp vec3 normal;
 attribute highp vec3 color_facets;
diff --git a/Polyhedron/demo/Polyhedron/resources/shader_with_textured_edges.f b/Polyhedron/demo/Polyhedron/resources/shader_with_textured_edges.f
index ef0d574d1bc..888152005a4 100644
--- a/Polyhedron/demo/Polyhedron/resources/shader_with_textured_edges.f
+++ b/Polyhedron/demo/Polyhedron/resources/shader_with_textured_edges.f
@@ -1,4 +1,4 @@
-#version 330
+#version 120
 varying highp vec3 fColors;
 varying highp vec2 f_texCoord; 
 uniform highp sampler2D s_texture; 
diff --git a/Polyhedron/demo/Polyhedron/resources/shader_with_textured_edges.v b/Polyhedron/demo/Polyhedron/resources/shader_with_textured_edges.v
index 7d3010a1ca1..7770cc309fe 100644
--- a/Polyhedron/demo/Polyhedron/resources/shader_with_textured_edges.v
+++ b/Polyhedron/demo/Polyhedron/resources/shader_with_textured_edges.v
@@ -1,4 +1,4 @@
-#version 330
+#version 120
  attribute highp vec4 vertex;
  attribute highp vec2 v_texCoord; 
  uniform highp vec3 color_lines; 
diff --git a/Polyhedron/demo/Polyhedron/resources/shader_without_light.f b/Polyhedron/demo/Polyhedron/resources/shader_without_light.f
index 6a14655a5a7..32b3ebd0455 100644
--- a/Polyhedron/demo/Polyhedron/resources/shader_without_light.f
+++ b/Polyhedron/demo/Polyhedron/resources/shader_without_light.f
@@ -1,4 +1,4 @@
-#version 330
+#version 120
 varying highp vec4 color;
 void main(void) 
 { 
diff --git a/Polyhedron/demo/Polyhedron/resources/shader_without_light.v b/Polyhedron/demo/Polyhedron/resources/shader_without_light.v
index 6f9e362709b..69e5741f510 100644
--- a/Polyhedron/demo/Polyhedron/resources/shader_without_light.v
+++ b/Polyhedron/demo/Polyhedron/resources/shader_without_light.v
@@ -1,12 +1,12 @@
-  #version 330
-  attribute highp vec4 vertex;
-  attribute highp vec3 colors;
-  uniform highp mat4 mvp_matrix;
-  uniform highp mat4 f_matrix;
-  varying highp vec4 color; 
-  void main(void)
-  {
-     color = vec4(colors, 1.0); 
-     gl_Position = mvp_matrix * f_matrix * vertex;
-  }
+#version 120
+attribute highp vec4 vertex;
+attribute highp vec3 colors;
+uniform highp mat4 mvp_matrix;
+uniform highp mat4 f_matrix;
+varying highp vec4 color; 
+void main(void)
+{
+   color = vec4(colors, 1.0); 
+   gl_Position = mvp_matrix * f_matrix * vertex;
+}
  
diff --git a/Triangulation_3/demo/Triangulation_3/Viewer.cpp b/Triangulation_3/demo/Triangulation_3/Viewer.cpp
index 2262eeab95f..495e52b8e4b 100644
--- a/Triangulation_3/demo/Triangulation_3/Viewer.cpp
+++ b/Triangulation_3/demo/Triangulation_3/Viewer.cpp
@@ -18,6 +18,25 @@ using namespace std;
 void Viewer::init()
 {
     initializeOpenGLFunctions();
+    glDrawArraysInstanced = (PFNGLDRAWARRAYSINSTANCEDARBPROC)this->context()->getProcAddress("glDrawArraysInstancedARB");
+    if(!glDrawArraysInstanced)
+    {
+        qDebug()<<"glDrawArraysInstancedARB : extension not found. Spheres will be displayed as points.";
+        extension_is_found = false;
+    }
+    else
+        extension_is_found = true;
+
+    glVertexAttribDivisor = (PFNGLVERTEXATTRIBDIVISORARBPROC)this->context()->getProcAddress("glVertexAttribDivisorARB");
+    if(!glDrawArraysInstanced)
+    {
+        qDebug()<<"glVertexAttribDivisorARB : extension not found. Spheres will be displayed as points.";
+        extension_is_found = false;
+    }
+    else
+        extension_is_found = true;
+//    extension_is_found = false;
+
     /* Initial timer for playing incremental construction */
     m_pTimer = new QTimer(this);
     connect(m_pTimer, SIGNAL(timeout()), this, SLOT(incremental_insert()));
@@ -162,8 +181,8 @@ void Viewer::compile_shaders()
     //Vertex source code
     const char vertex_source[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
         "uniform highp mat4 mvp_matrix;\n"
         "void main(void)\n"
         "{\n"
@@ -173,7 +192,7 @@ void Viewer::compile_shaders()
     //Fragment source code
     const char fragment_source[] =
     {
-        "#version 330 \n"
+        "#version 120 \n"
         "uniform highp vec4 color; \n"
         "void main(void) { \n"
         "gl_FragColor = color; \n"
@@ -210,15 +229,15 @@ void Viewer::compile_shaders()
     //Vertex source code
     const char vertex_source_spheres[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
-        "in highp vec3 normal;\n"
-        "in highp vec4 center;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
+        "attribute highp vec3 normal;\n"
+        "attribute highp vec4 center;\n"
 
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 mv_matrix; \n"
-        "out highp vec4 fP; \n"
-        "out highp vec3 fN; \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "void main(void)\n"
         "{\n"
         "   fP = mv_matrix * vertex; \n"
@@ -229,9 +248,9 @@ void Viewer::compile_shaders()
     //Fragment source code
     const char fragment_source_spheres[] =
     {
-        "#version 330 \n"
-        "in highp vec4 fP; \n"
-        "in highp vec3 fN; \n"
+        "#version 120 \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "uniform vec4 color; \n"
         "uniform highp vec4 light_pos;  \n"
         "uniform highp vec4 light_diff; \n"
@@ -288,18 +307,18 @@ void Viewer::compile_shaders()
     //Vertex source code
     const char vertex_source_cylinders[] =
     {
-        "#version 330 \n"
-        "in highp vec4 vertex;\n"
-        "in highp vec3 normal;\n"
-        "in highp vec4 transfo1;\n"
-        "in highp vec4 transfo2;\n"
-        "in highp vec4 transfo3;\n"
-        "in highp vec4 transfo4;\n"
+        "#version 120 \n"
+        "attribute highp vec4 vertex;\n"
+        "attribute highp vec3 normal;\n"
+        "attribute highp vec4 transfo1;\n"
+        "attribute highp vec4 transfo2;\n"
+        "attribute highp vec4 transfo3;\n"
+        "attribute highp vec4 transfo4;\n"
         "mat4 transfo = mat4(transfo1, transfo2, transfo3, transfo4); \n"
         "uniform highp mat4 mvp_matrix;\n"
         "uniform highp mat4 mv_matrix; \n"
-        "out highp vec4 fP; \n"
-        "out highp vec3 fN; \n"
+        "varying highp vec4 fP; \n"
+        "varying highp vec3 fN; \n"
         "void main(void)\n"
         "{\n"
         "   fP = mv_matrix * vertex; \n"
@@ -714,19 +733,24 @@ void Viewer::initialize_buffers()
         rendering_program_spheres.setAttributeBuffer(poly_vertexLocation[1],GL_FLOAT,0,3);
         buffers[13].release();
 
-        glVertexAttribDivisor(centerLocation[0],1);
-        glVertexAttribDivisor(normalsLocation[0],0);
+        if(extension_is_found)
+        {
+            glVertexAttribDivisor(centerLocation[0],1);
+            glVertexAttribDivisor(normalsLocation[0],0);
+        }
         vao[11].release();
 
         //Empty Sphere
         vao[12].bind();
-        buffers[14].bind();
-        buffers[14].allocate(pos_emptySphere->data(), pos_emptySphere->size()*sizeof(float));
-        centerLocation[0] = rendering_program_spheres.attributeLocation("center");
-        rendering_program_spheres.enableAttributeArray(centerLocation[0]);
-        rendering_program_spheres.setAttributeBuffer(centerLocation[0],GL_FLOAT,0,3);
-        buffers[14].release();
-
+        if(extension_is_found)
+        {
+            buffers[14].bind();
+            buffers[14].allocate(pos_emptySphere->data(), pos_emptySphere->size()*sizeof(float));
+            centerLocation[0] = rendering_program_spheres.attributeLocation("center");
+            rendering_program_spheres.enableAttributeArray(centerLocation[0]);
+            rendering_program_spheres.setAttributeBuffer(centerLocation[0],GL_FLOAT,0,3);
+            buffers[14].release();
+        }
         buffers[32].bind();
         buffers[32].allocate(normals_emptySphere->data(), normals_emptySphere->size()*sizeof(float));
         normalsLocation[0] = rendering_program_spheres.attributeLocation("normal");
@@ -741,8 +765,11 @@ void Viewer::initialize_buffers()
         rendering_program_spheres.setAttributeBuffer(poly_vertexLocation[1],GL_FLOAT,0,3);
         buffers[16].release();
 
-        glVertexAttribDivisor(centerLocation[0],1);
-        glVertexAttribDivisor(normalsLocation[0],0);
+        if(extension_is_found)
+        {
+            glVertexAttribDivisor(centerLocation[0],1);
+            glVertexAttribDivisor(normalsLocation[0],0);
+        }
         vao[12].release();
 
         //Vertex Sphere
@@ -767,8 +794,11 @@ void Viewer::initialize_buffers()
         rendering_program_spheres.setAttributeBuffer(poly_vertexLocation[1],GL_FLOAT,0,3);
         buffers[17].release();
 
-        glVertexAttribDivisor(centerLocation[0],1);
-        glVertexAttribDivisor(normalsLocation[0],0);
+        if(extension_is_found)
+        {
+            glVertexAttribDivisor(centerLocation[0],1);
+            glVertexAttribDivisor(normalsLocation[0],0);
+        }
         vao[13].release();
 
         //New point Sphere
@@ -791,8 +821,11 @@ void Viewer::initialize_buffers()
         rendering_program_spheres.setAttributeBuffer(poly_vertexLocation[1],GL_FLOAT,0,3);
         buffers[17].release();
 
-        glVertexAttribDivisor(centerLocation[0],1);
-        glVertexAttribDivisor(normalsLocation[0],0);
+        if(extension_is_found)
+        {
+            glVertexAttribDivisor(centerLocation[0],1);
+            glVertexAttribDivisor(normalsLocation[0],0);
+        }
         vao[14].release();
 
         //Selected point Sphere
@@ -815,8 +848,11 @@ void Viewer::initialize_buffers()
         rendering_program_spheres.setAttributeBuffer(poly_vertexLocation[1],GL_FLOAT,0,3);
         buffers[17].release();
 
-        glVertexAttribDivisor(centerLocation[0],1);
-        glVertexAttribDivisor(normalsLocation[0],0);
+        if(extension_is_found)
+        {
+            glVertexAttribDivisor(centerLocation[0],1);
+            glVertexAttribDivisor(normalsLocation[0],0);
+        }
         vao[15].release();
 
         //Moving point Sphere
@@ -839,8 +875,11 @@ void Viewer::initialize_buffers()
         rendering_program_spheres.setAttributeBuffer(poly_vertexLocation[1],GL_FLOAT,0,3);
         buffers[17].release();
 
-        glVertexAttribDivisor(centerLocation[0],1);
-        glVertexAttribDivisor(normalsLocation[0],0);
+        if(extension_is_found)
+        {
+            glVertexAttribDivisor(centerLocation[0],1);
+            glVertexAttribDivisor(normalsLocation[0],0);
+        }
         vao[16].release();
 
         //Querry point Sphere
@@ -863,8 +902,11 @@ void Viewer::initialize_buffers()
         rendering_program_spheres.setAttributeBuffer(poly_vertexLocation[1],GL_FLOAT,0,3);
         buffers[17].release();
 
-        glVertexAttribDivisor(centerLocation[0],1);
-        glVertexAttribDivisor(normalsLocation[0],0);
+        if(extension_is_found)
+        {
+            glVertexAttribDivisor(centerLocation[0],1);
+            glVertexAttribDivisor(normalsLocation[0],0);
+        }
         vao[17].release();
 
         //Nearest neighbor Sphere
@@ -887,8 +929,11 @@ void Viewer::initialize_buffers()
         rendering_program_spheres.setAttributeBuffer(poly_vertexLocation[1],GL_FLOAT,0,3);
         buffers[17].release();
 
-        glVertexAttribDivisor(centerLocation[0],1);
-        glVertexAttribDivisor(normalsLocation[0],0);
+        if(extension_is_found)
+        {
+            glVertexAttribDivisor(centerLocation[0],1);
+            glVertexAttribDivisor(normalsLocation[0],0);
+        }
         vao[18].release();
 
         //incremental list
@@ -910,8 +955,11 @@ void Viewer::initialize_buffers()
         rendering_program_spheres.setAttributeBuffer(poly_vertexLocation[1],GL_FLOAT,0,3);
         buffers[17].release();
 
-        glVertexAttribDivisor(centerLocation[0],1);
-        glVertexAttribDivisor(normalsLocation[0],0);
+        if(extension_is_found)
+        {
+            glVertexAttribDivisor(centerLocation[0],1);
+            glVertexAttribDivisor(normalsLocation[0],0);
+        }
         vao[25].release();
 
         //incremental next point
@@ -933,8 +981,11 @@ void Viewer::initialize_buffers()
         rendering_program_spheres.setAttributeBuffer(poly_vertexLocation[1],GL_FLOAT,0,3);
         buffers[17].release();
 
-        glVertexAttribDivisor(centerLocation[0],1);
-        glVertexAttribDivisor(normalsLocation[0],0);
+        if(extension_is_found)
+        {
+            glVertexAttribDivisor(centerLocation[0],1);
+            glVertexAttribDivisor(normalsLocation[0],0);
+        }
         vao[26].release();
 
     }
@@ -985,12 +1036,14 @@ void Viewer::initialize_buffers()
         rendering_program_cylinders.setAttributeBuffer(centerLocation[4],GL_FLOAT,0,4);
         buffers[23].release();
 
-
-        glVertexAttribDivisor(centerLocation[1],1);
-        glVertexAttribDivisor(centerLocation[2],1);
-        glVertexAttribDivisor(centerLocation[3],1);
-        glVertexAttribDivisor(centerLocation[4],1);
-        glVertexAttribDivisor(normalsLocation[1],0);
+        if(extension_is_found)
+        {
+            glVertexAttribDivisor(centerLocation[1],1);
+            glVertexAttribDivisor(centerLocation[2],1);
+            glVertexAttribDivisor(centerLocation[3],1);
+            glVertexAttribDivisor(centerLocation[4],1);
+            glVertexAttribDivisor(normalsLocation[1],0);
+        }
 
         vao[19].release();
 
@@ -1035,13 +1088,14 @@ void Viewer::initialize_buffers()
         rendering_program_cylinders.enableAttributeArray(centerLocation[4]);
         rendering_program_cylinders.setAttributeBuffer(centerLocation[4],GL_FLOAT,0,4);
         buffers[27].release();
-
-
-        glVertexAttribDivisor(centerLocation[1],1);
-        glVertexAttribDivisor(centerLocation[2],1);
-        glVertexAttribDivisor(centerLocation[3],1);
-        glVertexAttribDivisor(centerLocation[4],1);
-        glVertexAttribDivisor(normalsLocation[1],0);
+        if(extension_is_found)
+        {
+            glVertexAttribDivisor(centerLocation[1],1);
+            glVertexAttribDivisor(centerLocation[2],1);
+            glVertexAttribDivisor(centerLocation[3],1);
+            glVertexAttribDivisor(centerLocation[4],1);
+            glVertexAttribDivisor(normalsLocation[1],0);
+        }
 
         vao[20].release();
     }
@@ -1139,11 +1193,12 @@ void Viewer::attrib_buffers(QGLViewer* viewer)
 
 void Viewer::draw()
 {
+    glEnable(GL_DEPTH_TEST);
     if(!are_buffers_initialized)
         initialize_buffers();
     QFont fontPrompt("Arial", 8);
     attrib_buffers(this);
-    if(m_isFlat)
+    if(m_isFlat || !extension_is_found)
     {
 
         if(m_showVertex)
@@ -1564,7 +1619,10 @@ void Viewer::draw()
         rendering_program_spheres.bind();
         vao[11].bind();
         rendering_program_spheres.setUniformValue(colorLocation[1], m_colorTrackball);
-        glDrawArraysInstanced(GL_TRIANGLES, 0, points_trackBall->size()/3, 1);
+        if(extension_is_found)
+            glDrawArraysInstanced(GL_TRIANGLES, 0, points_trackBall->size()/3, 1);
+        else
+            glDrawArrays(GL_TRIANGLES, 0, points_trackBall->size()/3);
         vao[11].release();
         rendering_program_spheres.release();
     }
@@ -1573,7 +1631,13 @@ void Viewer::draw()
         rendering_program_spheres.bind();
         vao[12].bind();
         rendering_program_spheres.setUniformValue(colorLocation[1], m_colorEmptySphere);
-        glDrawArraysInstanced(GL_TRIANGLES, 0, points_emptySphere->size()/3, pos_emptySphere->size()/3);
+        if(extension_is_found)
+            glDrawArraysInstanced(GL_TRIANGLES, 0, points_emptySphere->size()/3, pos_emptySphere->size()/3);
+        else if(pos_emptySphere->size()>0)
+        {
+            rendering_program_spheres.setAttributeValue("center", QVector4D(pos_emptySphere->at(0), pos_emptySphere->at(1), pos_emptySphere->at(2), 1.0));
+            glDrawArrays(GL_TRIANGLES, 0, points_emptySphere->size()/3);
+        }
         vao[12].release();
         rendering_program_spheres.release();
     }
diff --git a/Triangulation_3/demo/Triangulation_3/Viewer.h b/Triangulation_3/demo/Triangulation_3/Viewer.h
index ca05da36146..c865f018a41 100644
--- a/Triangulation_3/demo/Triangulation_3/Viewer.h
+++ b/Triangulation_3/demo/Triangulation_3/Viewer.h
@@ -8,7 +8,7 @@
 #include <QSettings>
 #include "PreferenceDlg.h"
 
-#include <QOpenGLFunctions_3_3_Core>
+#include <QOpenGLFunctions_2_1>
 #include <QOpenGLVertexArrayObject>
 #include <QOpenGLBuffer>
 #include <QOpenGLShaderProgram>
@@ -18,7 +18,7 @@ using namespace qglviewer;
 
 class MainWindow;
 
-class Viewer : public QGLViewer, QOpenGLFunctions_3_3_Core {
+class Viewer : public QGLViewer, QOpenGLFunctions_2_1 {
 
   Q_OBJECT
 
@@ -345,6 +345,8 @@ private:
       int lightLocation[5*2];
 
       bool are_buffers_initialized;
+      bool extension_is_found;
+
       std::vector<float> *pos_emptyFacet;
       std::vector<float> *pos_emptySphere;
       std::vector<float> *points_emptySphere;
@@ -385,6 +387,10 @@ private:
       QOpenGLShaderProgram rendering_program;
       QOpenGLShaderProgram rendering_program_spheres;
       QOpenGLShaderProgram rendering_program_cylinders;
+      typedef void (APIENTRYP PFNGLDRAWARRAYSINSTANCEDARBPROC) (GLenum mode, GLint first, GLsizei count, GLsizei primcount);
+      typedef void (APIENTRYP PFNGLVERTEXATTRIBDIVISORARBPROC) (GLuint index, GLuint divisor);
+      PFNGLDRAWARRAYSINSTANCEDARBPROC glDrawArraysInstanced;
+      PFNGLVERTEXATTRIBDIVISORARBPROC glVertexAttribDivisor;
       void initialize_buffers();
       void compute_elements();
       void attrib_buffers(QGLViewer*);