bug fix: confirmed that the previous opengl error was due to the inac…

…tive OpenGL context. Fixed it by moving the update function into paintGL(). This causes a delay when updating the approximation, will probably need multithreaded solution (low-priority / future work)

Arrangement_on_surface_2/demo/earth/Main_widget.cpp

@@ -202,7 +202,8 @@ void Main_widget::initializeGL()
   init_geometry();
   init_shader_programs();
 
-  init_country_borders(0.001);
+  m_current_approx_error = 0.001;
+  init_country_borders(m_current_approx_error);
   init_country_selection();
 
   glClearColor(0, 0, 0, 1);
@@ -213,6 +214,7 @@ void Main_widget::initializeGL()
   m_timer.start(12, this);
 }
 
+
 void Main_widget::init_camera()
 {
   m_camera.set_pos(0, 0, 3);
@@ -224,8 +226,9 @@ void Main_widget::init_camera()
   Message_manager::add("zoom_changed", [&] 
     { 
       qDebug() << "ZOOM CHANGED!!!"; 
-      const auto error = compute_backprojected_error(0.5);
-      qDebug() << "new error = " << error;
+      //const auto error = compute_backprojected_error(0.5);
+      //qDebug() << "new error = " << error;
+      m_update_approx_error = true;
       //qDebug() << "re-initializing the country borders..";
       //init_country_borders(error);
     });
@@ -404,9 +407,8 @@ void Main_widget::resizeGL(int w, int h)
   const qreal z_near = 0.1, z_far = 100.0, fov = 45.0;
   m_camera.perspective(fov, aspect, z_near, z_far);
 
-  // compute the world-space error for the given pixel-error
-  const auto err = compute_backprojected_error(0.5f);
-  std::cout << "error = " << err << std::endl;
+  // signal to look into the approximation error
+  m_update_approx_error = true;
 }
 
 template<typename T>
@@ -418,6 +420,19 @@ void draw_safe(T& ptr)
 
 void Main_widget::paintGL()
 {
+  if (m_update_approx_error)
+  {
+    const auto error = compute_backprojected_error(0.5);
+    qDebug() << "new approx error = " << error;
+    qDebug() << "current error = " << m_current_approx_error;
+    if(error < m_current_approx_error)
+    {
+      init_country_borders(error);
+      m_current_approx_error = error;
+    }
+    m_update_approx_error = false;
+  }
+
   QMatrix4x4 model;
   model.rotate(-90, 1,0,0); // this makes z-axes point upwards!
   const auto view = m_camera.get_view_matrix();

Arrangement_on_surface_2/demo/earth/Main_widget.h

@@ -98,6 +98,13 @@ class Main_widget : public QOpenGLWidget, protected OpenGLFunctionsBase
   // view-port 
   int m_vp_width = 0, m_vp_height = 0;
 
+  // After zooming in or making the viewport larger, the approximation-error
+  // needs to be updated and checked against the old value. If a lower approxi-
+  // mation error is needed the necessary graphics-side updates need to be made
+  // INSIDE the paintGL (or whereever the OpenGL context is active)!
+  bool m_update_approx_error = false;
+  float m_current_approx_error;
+
   // Timer for continuous screen-updates
   QBasicTimer m_timer;
 };