diff --git a/AABB_tree/demo/AABB_tree/CMakeLists.txt b/AABB_tree/demo/AABB_tree/CMakeLists.txt
index 2aa8c6dc98b..77b7c395440 100644
--- a/AABB_tree/demo/AABB_tree/CMakeLists.txt
+++ b/AABB_tree/demo/AABB_tree/CMakeLists.txt
@@ -27,15 +27,12 @@ find_package(Qt5 QUIET COMPONENTS Xml Script OpenGL Gui Svg)
 
 include( ${CGAL_USE_FILE} )
 
-# Find OpenGL
-find_package(OpenGL)
-
 # Find QGLViewer
 if(Qt5_FOUND)
   find_package(QGLViewer)
 endif(Qt5_FOUND)
 
-if(CGAL_FOUND AND CGAL_Qt5_FOUND AND Qt5_FOUND AND OPENGL_FOUND AND QGLVIEWER_FOUND)
+if(CGAL_FOUND AND CGAL_Qt5_FOUND AND Qt5_FOUND AND QGLVIEWER_FOUND)
 
   include_directories ( ${QGLVIEWER_INCLUDE_DIR} )
 
@@ -71,7 +68,7 @@ if(CGAL_FOUND AND CGAL_Qt5_FOUND AND Qt5_FOUND AND OPENGL_FOUND AND QGLVIEWER_FO
   include(${CGAL_MODULES_DIR}/CGAL_add_test.cmake)
   cgal_add_compilation_test(AABB_demo)
 
-else (CGAL_FOUND AND CGAL_Qt5_FOUND AND Qt5_FOUND AND OPENGL_FOUND AND QGLVIEWER_FOUND)
+else (CGAL_FOUND AND CGAL_Qt5_FOUND AND Qt5_FOUND AND QGLVIEWER_FOUND)
 
   set(AABB_MISSING_DEPS "")
 
@@ -87,14 +84,10 @@ else (CGAL_FOUND AND CGAL_Qt5_FOUND AND Qt5_FOUND AND OPENGL_FOUND AND QGLVIEWER
     set(AABB_MISSING_DEPS "Qt5, ${AABB_MISSING_DEPS}")
   endif()
 
-  if(NOT OPENGL_FOUND)
-    set(AABB_MISSING_DEPS "OpenGL, ${AABB_MISSING_DEPS}")
-  endif()
-
   if(NOT QGLVIEWER_FOUND)
     set(AABB_MISSING_DEPS "QGLViewer, ${AABB_MISSING_DEPS}")
   endif()
 
   message(STATUS "NOTICE: This demo requires ${AABB_MISSING_DEPS}and will not be compiled.")
 
-endif (CGAL_FOUND AND CGAL_Qt5_FOUND AND Qt5_FOUND AND OPENGL_FOUND AND QGLVIEWER_FOUND)
+endif (CGAL_FOUND AND CGAL_Qt5_FOUND AND Qt5_FOUND AND QGLVIEWER_FOUND)
diff --git a/AABB_tree/demo/AABB_tree/Scene.cpp b/AABB_tree/demo/AABB_tree/Scene.cpp
index 19b07ee9b6f..09277853f80 100644
--- a/AABB_tree/demo/AABB_tree/Scene.cpp
+++ b/AABB_tree/demo/AABB_tree/Scene.cpp
@@ -595,6 +595,7 @@ void Scene::draw(QGLViewer* viewer)
         initGL();
     if(!are_buffers_initialized)
         initialize_buffers();
+    gl->glEnable(GL_DEPTH_TEST);
     QColor color;
     QMatrix4x4 fMatrix;
     fMatrix.setToIdentity();
@@ -663,7 +664,7 @@ void Scene::draw(QGLViewer* viewer)
 
             //cutting_segments
             fMatrix.setToIdentity();
-            ::glLineWidth(2.0f);
+            gl->glLineWidth(2.0f);
             vao[3].bind();
             attrib_buffers(viewer);
             rendering_program.bind();
@@ -671,7 +672,7 @@ void Scene::draw(QGLViewer* viewer)
             rendering_program.setUniformValue(colorLocation, color);
             rendering_program.setUniformValue(fLocation, fMatrix);
             gl->glDrawArrays(GL_LINES, 0, static_cast<GLsizei>(pos_cut_segments.size()/3));
-            ::glLineWidth(1.0f);
+            gl->glLineWidth(1.0f);
             rendering_program.release();
             vao[3].release();
             //grid
@@ -690,8 +691,8 @@ void Scene::draw(QGLViewer* viewer)
             //cutting_plane
             // for(int i=0; i< 16 ; i++)
             //     fMatrix.data()[i] =  m_frame->matrix()[i];
-            ::glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
-            ::glEnable(GL_BLEND);
+            gl->glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
+            gl->glEnable(GL_BLEND);
             vao[4].bind();
             attrib_buffers(viewer);
             rendering_program.bind();
@@ -699,7 +700,7 @@ void Scene::draw(QGLViewer* viewer)
             rendering_program.setUniformValue(colorLocation, color);
             rendering_program.setUniformValue(fLocation, fMatrix);
             gl->glDrawArrays(GL_TRIANGLES, 0, static_cast<GLsizei>(pos_plane.size()/3));
-            ::glDisable(GL_BLEND);
+            gl->glDisable(GL_BLEND);
             rendering_program.release();
             vao[4].release();
 
diff --git a/AABB_tree/demo/AABB_tree/Viewer.cpp b/AABB_tree/demo/AABB_tree/Viewer.cpp
index 2f411def1df..56de4c959eb 100644
--- a/AABB_tree/demo/AABB_tree/Viewer.cpp
+++ b/AABB_tree/demo/AABB_tree/Viewer.cpp
@@ -18,7 +18,6 @@ void Viewer::setScene(Scene* pScene)
 
 void Viewer::draw()
 {
-  glEnable(GL_DEPTH_TEST);
   QGLViewer::draw();
   if(m_pScene != NULL)
   {
diff --git a/Alpha_shapes_3/demo/Alpha_shapes_3/CMakeLists.txt b/Alpha_shapes_3/demo/Alpha_shapes_3/CMakeLists.txt
index a22bad2c9e1..1e0ec6c25ec 100644
--- a/Alpha_shapes_3/demo/Alpha_shapes_3/CMakeLists.txt
+++ b/Alpha_shapes_3/demo/Alpha_shapes_3/CMakeLists.txt
@@ -21,10 +21,9 @@ include(${CGAL_USE_FILE})
 
 find_package(Qt5 QUIET COMPONENTS Xml Script OpenGL Svg)
 
-find_package(OpenGL)
 find_package(QGLViewer)
 
-if ( CGAL_FOUND AND CGAL_Qt5_FOUND AND Qt5_FOUND AND OPENGL_FOUND AND QGLVIEWER_FOUND )
+if ( CGAL_FOUND AND CGAL_Qt5_FOUND AND Qt5_FOUND AND QGLVIEWER_FOUND )
 
   add_definitions(-DQT_NO_KEYWORDS)
 
@@ -55,6 +54,6 @@ if ( CGAL_FOUND AND CGAL_Qt5_FOUND AND Qt5_FOUND AND OPENGL_FOUND AND QGLVIEWER_
 
 else()
 
-  message(STATUS "NOTICE: This demo requires CGAL, the QGLViewer, OpenGL and Qt5, and will not be compiled.")
+  message(STATUS "NOTICE: This demo requires CGAL, the QGLViewer, and Qt5, and will not be compiled.")
 
 endif()
diff --git a/Alpha_shapes_3/demo/Alpha_shapes_3/Viewer.cpp b/Alpha_shapes_3/demo/Alpha_shapes_3/Viewer.cpp
index a5a0dd2f222..69d8df641a2 100644
--- a/Alpha_shapes_3/demo/Alpha_shapes_3/Viewer.cpp
+++ b/Alpha_shapes_3/demo/Alpha_shapes_3/Viewer.cpp
@@ -335,7 +335,7 @@ Viewer::draw()
     rendering_program_points.bind();
     color.setRgbF(1.0f, 0.0f, 0.0f);
     glPointSize(5);
-    ::glEnable(GL_POINT_SMOOTH);
+    glEnable(GL_POINT_SMOOTH);
     rendering_program_points.setUniformValue(colorLocation_points, color);
     glDrawArrays(GL_POINTS, 0, static_cast<GLsizei>(pos_points.size()/3));
     rendering_program_points.release();