diff --git a/Arrangement_on_surface_2/demo/earth/Main_widget.cpp b/Arrangement_on_surface_2/demo/earth/Main_widget.cpp
index 5c434e3c0b7..1a9fc44f1e7 100644
--- a/Arrangement_on_surface_2/demo/earth/Main_widget.cpp
+++ b/Arrangement_on_surface_2/demo/earth/Main_widget.cpp
@@ -472,6 +472,19 @@ void Main_widget::paintGL()
   const auto projection = m_camera.get_projection_matrix();
   const auto mvp = projection * view * model;
 
+  // compute the cutting plane
+// remember that we are passing the local vertex positions of the sphere 
+// between the vertex and fragment shader stages, so we need to convert
+// the camera-pos in world coords to sphere's local coords!
+  auto c = model.inverted() * m_camera.get_pos();
+  const auto d = c.length();
+  const auto r = 1.0f;
+  const auto sin_alpha = r / d;
+  const auto n = (c / d); // plane unit normal vector
+  const auto cos_beta = sin_alpha;
+  const auto p = (r * cos_beta) * n;
+  QVector4D plane(n.x(), n.y(), n.z(), -QVector3D::dotProduct(p, n));
+
   // Clear color and depth buffer
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   // SPHERE
@@ -481,8 +494,9 @@ void Main_widget::paintGL()
     auto& sp = m_sp_smooth;
     sp.use();
     sp.set_uniform("u_mvp", mvp);
-    QVector4D sphere_color(167. / 255, 205. / 255, 242. / 255, 1);
+    auto sphere_color = QVector4D(167, 205, 242, 255) / 255;
     sp.set_uniform("u_color", sphere_color);
+    sp.set_uniform("u_plane", QVector4D(0,0,0,0));
     //sp.set_uniform("u_color", m_sphere->get_color());
     
     //glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
@@ -494,6 +508,7 @@ void Main_widget::paintGL()
       glDisable(GL_DEPTH_TEST);
       QVector4D face_color(1, .5, 0, 1);
       sp.set_uniform("u_color", face_color);
+      sp.set_uniform("u_plane", plane);
       //glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
       g_face_triangles->draw();
 
@@ -525,18 +540,6 @@ void Main_widget::paintGL()
     sp.use();
     sp.set_uniform("u_mvp", mvp);
 
-    // compute the cutting plane
-    // remember that we are passing the local vertex positions of the sphere 
-    // between the vertex and fragment shader stages, so we need to convert
-    // the camera-pos in world coords to sphere's local coords!
-    auto c =  model.inverted() * m_camera.get_pos();
-    const auto d = c.length();
-    const auto r = 1.0f;
-    const auto sin_alpha = r / d;
-    const auto n = (c / d); // plane unit normal vector
-    const auto cos_beta = sin_alpha;
-    const auto p = (r * cos_beta) * n;
-    QVector4D plane(n.x(), n.y(), n.z(), -QVector3D::dotProduct(p, n));
     const QVector4D arc_color(0, 0.5, 1, 1);
     glLineWidth(5);
     sp.set_uniform("u_plane", plane);
diff --git a/Arrangement_on_surface_2/demo/earth/shaders/smooth_fs.glsl b/Arrangement_on_surface_2/demo/earth/shaders/smooth_fs.glsl
index 16e116c79d1..dee9a5b16ac 100644
--- a/Arrangement_on_surface_2/demo/earth/shaders/smooth_fs.glsl
+++ b/Arrangement_on_surface_2/demo/earth/shaders/smooth_fs.glsl
@@ -2,7 +2,9 @@
 #version 330
 
 uniform vec4 u_color;
+uniform vec4 u_plane;
 
+in vec3 v_pos;
 in vec3 v_normal;
 
 out vec4 out_color;
@@ -10,6 +12,9 @@ out vec4 out_color;
 
 void main()
 {
+	if( dot(u_plane, vec4(v_pos, 1)) < 0 )
+		discard;
+
 	const vec3 lightDir = normalize(vec3(1,.5,.5));
 
 	//float c = clamp(dot(lightDir,triNormal), 0, 1);
diff --git a/Arrangement_on_surface_2/demo/earth/shaders/smooth_vs.glsl b/Arrangement_on_surface_2/demo/earth/shaders/smooth_vs.glsl
index 50a1842fed1..e5d39bc2b0f 100644
--- a/Arrangement_on_surface_2/demo/earth/shaders/smooth_vs.glsl
+++ b/Arrangement_on_surface_2/demo/earth/shaders/smooth_vs.glsl
@@ -5,14 +5,14 @@ layout (location = 0) in vec3 a_pos;
 layout (location = 1) in vec3 a_normal;
 
 //out vec4 v_col;
-//out vec3 v_pos;
+out vec3 v_pos;
 out vec3 v_normal;
 
 uniform mat4 u_mvp; 
 
 void main()
 {
-	//v_pos = a_pos;
+	v_pos = a_pos;
   v_normal = a_normal;
 	gl_Position = u_mvp * vec4(a_pos.xyz, 1);
   //gl_Position = vec4(pos.xyz, 1);