// 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>
#include <QKeyEvent>
#include <QTimer>


#include <GL/glu.h>

class Renderer : protected QOpenGLFunctions_2_0{

public:
  float t;

public:
  Renderer()  : t(0.0) {}

public:
  void display() {    
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    // camera orbits in the y=10 plane
    // and looks at origin
    double rad = M_PI / 180.0f * t;
    gluLookAt(10.0*cos(rad), 10.0 , 10.0*sin(rad), // eye
              0.0, 0.0, 0.0, // look at
              0.0, 1.0, 0.0); // up

    //draw model at origin
    //drawCube();
    drawCubeHierarchy(0, 4);
  }

  void init() {
    initializeOpenGLFunctions();
    glEnable(GL_DEPTH_TEST);
  }

  void resize(int w, int h) {
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective (30.0, (float)w/(float)h, 2.0, 20.0);
  }

  void dispose() {
  }

private:
  void drawCube() {
    glColor3f(1.0,0.0,0.0);
    glBegin(GL_POLYGON);
    glVertex3f(-1.0f, 1.0f, 1.0f);
    glVertex3f(-1.0f,-1.0f, 1.0f);
    glVertex3f( 1.0f,-1.0f, 1.0f);
    glVertex3f( 1.0f, 1.0f, 1.0f);
    glEnd();
    glColor3f(0.0,1.0,0.0);
    glBegin(GL_POLYGON);
    glVertex3f( 1.0f, 1.0f,-1.0f);
    glVertex3f( 1.0f,-1.0f,-1.0f);
    glVertex3f(-1.0f,-1.0f,-1.0f);
    glVertex3f(-1.0f, 1.0f,-1.0f);
    glEnd();
    glColor3f(0.0,0.0,1.0);
    glBegin(GL_POLYGON);
    glVertex3f( 1.0f, 1.0f, 1.0f);
    glVertex3f( 1.0f,-1.0f, 1.0f);
    glVertex3f( 1.0f,-1.0f,-1.0f);
    glVertex3f( 1.0f, 1.0f,-1.0f);
    glEnd();
    glColor3f(1.0,1.0,0.0);
    glBegin(GL_POLYGON);
    glVertex3f(-1.0f, 1.0f,-1.0f);
    glVertex3f(-1.0f,-1.0f,-1.0f);
    glVertex3f(-1.0f,-1.0f, 1.0f);
    glVertex3f(-1.0f, 1.0f, 1.0f);
    glEnd();
    glColor3f(1.0,1.0,1.0);
    glBegin(GL_POLYGON);
    glVertex3f( 1.0f, 1.0f,-1.0f);
    glVertex3f(-1.0f, 1.0f,-1.0f);
    glVertex3f(-1.0f, 1.0f, 1.0f);
    glVertex3f( 1.0f, 1.0f, 1.0f);
    glEnd();
    glColor3f(0.0,1.0,1.0);
    glBegin(GL_POLYGON);
    glVertex3f( 1.0f, -1.0f, 1.0f);
    glVertex3f(-1.0f, -1.0f, 1.0f);
    glVertex3f(-1.0f, -1.0f,-1.0f);
    glVertex3f( 1.0f, -1.0f,-1.0f);  
    glEnd();
  }

  void drawCubeHierarchy(int depth, int neighbors) {
    drawCube(); // draw parent
    depth +=1;
    if (depth < 6){
      for (int n = 0; n < neighbors; n++){
        glPushMatrix();
        glRotatef(n*90.0f-90.0f, 0.0f, 0.0f, 1.0f);
        glTranslatef(2.5f, 0.0f, 0.0f );
        glScalef(0.5f, 0.5f, 0.5f);
        drawCubeHierarchy(depth, 3); // draw children
        glPopMatrix();
      }
    }
  }
};

class MyWidget : public QOpenGLWidget {

private:
  Renderer *renderer;
  QTimer *timer;

public:
  MyWidget(QWidget *parent = NULL) : QOpenGLWidget(parent) {
    this->setWindowTitle("Demo for gluLookAt and chains of local transformations");
    this->resize(320, 320);
    renderer = new Renderer();
    timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(update()));
    timer->start(30);
  }

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

protected:
  void initializeGL() { renderer->init(); }
  void resizeGL(int w, int h){ renderer->resize(w, h); }
  void paintGL() {
      float offset = 1.0f;
      renderer->t += offset;
      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
}