// This code example is created for educational purpose
// by Thorsten Thormaehlen (contact: www.thormae.de).
// It is distributed without any warranty.

#include <QApplication>
#include <QOpenGLWidget>
#include <QOpenGLFunctions_2_0>

class Renderer : protected QOpenGLFunctions_2_0 {

public:
  void init() {
    initializeOpenGLFunctions();
  }
  void resize(int w, int h) {
    glViewport(0, 0, w, h);
  }
  void display() {
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    glLoadIdentity();
    glOrtho(-1.0f, 1.0f, -1.0f, 1.0f, -1.0f, 1.0f);
    glColor3f(1.0f, 1.0f, 1.0f);
    glBegin(GL_TRIANGLES);
    glVertex3f(-0.5f, -0.5f, 0.0f); // vertex on the left
    glVertex3f( 0.5f, -0.5f, 0.0f); // vertex on the right
    glVertex3f( 0.0f,  0.5f, 0.0f); // vertex at the top of the triangle
    glEnd();
  }
  void dispose() {}
};

class MyWidget : public QOpenGLWidget {

private:
  Renderer* renderer;

public:
  MyWidget(QWidget* parent = NULL) : QOpenGLWidget(parent) {
    this->setWindowTitle("OpenGL with Qt");
    this->resize(320, 320);
    renderer = new Renderer();
  }

  ~MyWidget() {
    makeCurrent();
    renderer->dispose();
    doneCurrent();
    delete renderer;
  }

protected:
  void initializeGL() { renderer->init(); }
  void resizeGL(int w, int h) { renderer->resize(w, h); }
  void paintGL() { renderer->display(); }
};

int main(int argc, char* argv[]) {
  // create a QApplication object that handles initialization,
  // finalization, and the main event loop
  QApplication appl(argc, argv);
  MyWidget widget;  // create a widget
  widget.show(); //show the widget and its children
  return appl.exec(); // execute the application
}