4.20 How to render a star sytem model in OpenGL?

In OpenGL, we can also draw a simple start system model like our solar system. To simpify a story, we assume an imaginary star system which consists of a single sun-like sphere star and some planet-like spheres rotating on circular oribits around the sun star , and furthermore, to avoid confusion, we do not care the light direction and reflection light problem of sun and the planets. We have used the following classes:

OpenGLCircle to describe a circular orbit for the planets.

OpenGLSolidSphere to draw the sun and the planets.

OpenGLTimerThread to move the planets.

The following StarSystemModel is a simple example to draw a star system model.

/*
 * StarSystemModel.cpp 
 * Copyright (c) 2015 Antillia.com TOSHIYUKI ARAI. ALL RIGHTS RESERVED. 
 */


#include <sol/opengl/OpenGLMainView.h>
#include <sol/opengl/OpenGLView.h>
#include <sol/opengl/OpenGLGC.h>
#include <sol/opengl/OpenGLLight.h>
#include <sol/opengl/OpenGLMaterial.h>
#include <sol/opengl/OpenGLSolidSphere.h>
#include <sol/opengl/OpenGLCircle.h>
#include <sol/opengl/OpenGLTimerThread.h>

namespace SOL {

class MainView :public OpenGLMainView {
private:
  static const int NUMBER_OF_PLANETS = 4;
  
private:
  //Inner class starts
  class SimpleView: public OpenGLView {
  private:
    SmartPtr<OpenGLGC>      gc;
    SmartPtr<OpenGLSolidSphere>  sun;    
    SmartPtr<OpenGLSolidSphere>  planets[NUMBER_OF_PLANETS];
    SmartPtr<OpenGLCircle>  orbits[NUMBER_OF_PLANETS];
    float                   angles[NUMBER_OF_PLANETS];
    SmartPtr<OpenGLTimerThread> timerThread;
    int                     renderingInterval;
    float angle;
    static const int CIRCLE_ANGLE = 360;
    static const int INCREMENT    = 1;
    CriticalSection    criticalSection;

  public:
    virtual void display()
    {
      criticalSection.enter();
      
      if (angle <(CIRCLE_ANGLE - INCREMENT) ) {
          angle += INCREMENT;
      } else {
        angle = INCREMENT;
      }
        
      static const float INCREMENT[NUMBER_OF_PLANETS] = { 1.0f, 0.7f, 0.5f, 0.2f };
      for (int i = 0; i < NUMBER_OF_PLANETS; i++) {
          if (angles[i] < CIRCLE_ANGLE - INCREMENT[i]) {
            angles[i] += INCREMENT[i];
          }
          else {
            angles[i] = INCREMENT[i];
          }
      }
      
      if (gc && sun) {

        gc -> clear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        gc -> loadIdentity();
        gc -> lookAt(-1.0, 8.0, 17.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

        gc -> clearColor(0.0, 0.0, 0.0, 1.0);
        gc -> enable(GL_CULL_FACE); 
        gc -> enable(GL_LIGHTING);

        gc->color(1.0f, 1.0f, 1.0f); 

        sun-> draw(gc, 0.0f, 0.0f, 0.0f);
        
        OpenGLLight light(GL_LIGHT0);
        GLfloat lightPosition[] = {-2.0f, 0.0f, -1.0f, 1.0};  
        light.position(lightPosition);

        for (int i = 0; i<NUMBER_OF_PLANETS; i++) {
          Vertex3 pos = orbits[i]->getOrbitPosition(angles[i]);
          planets[i]-> draw(gc, pos.x, pos.y, pos.z);
        }
      }
      criticalSection.leave();
    }

    virtual void resize(int w, int h)
    {
      if (w == 0 || h == 0) {
          return;
      }
      if (gc) {
        gc -> matrixMode(GL_PROJECTION);
        gc -> loadIdentity();
        gc -> perspective(16.0, (double)w / (double)h, 0.5, 40.0); 

        gc -> matrixMode(GL_MODELVIEW);
      }
    }


    virtual void initialize()
    {
      gc = new OpenGLGC();
                
      Color4  black         = { 0.0, 0.0, 0.0, 1.0 };
      Color4  ambient       = { 0.5, 0.5, 0.5, 1.0 };
      Color4  diffuse       = { 0.2, 0.4, 0.8, 1.0 };
      Color4  greendiffuse  = { 0.0, 1.0, 0.0, 1.0 };
      Color4  reddiffuse    = { 1.0, 0.0, 0.0, 1.0 };
      Color4  bluediffuse   = { 0.0, 0.0, 1.0, 1.0 };
      Color4  silverdiffuse = { 0.8, 0.8, 0.8, 1.0 };

      Color4  specular      = { 1.0, 1.0, 1.0, 1.0 };
      Color4  emission      = { 0.8, 0.2, 0.0, 0.0 };
      GLfloat lowShining    = { 10.0 };
      GLfloat highShining   = {100.0 };
 
      OpenGLMateria sunMateria(GL_FRONT, black,   diffuse, black, emission, highShining);
      
      sun = new OpenGLSolidSphere(sunMateria, 0.5f,  40, 40);

      int index = 0;
      orbits[index++] = new OpenGLCircle(0.0f, 0.0f, 0.0f, 1.0);
      orbits[index++] = new OpenGLCircle(0.0f, 0.0f, 0.0f, 1.6f);
      orbits[index++] = new OpenGLCircle(0.0f, 0.0f, 0.0f, 2.4f);
      orbits[index]   = new OpenGLCircle(0.0f, 0.0f, 0.0f, 2.9f);

      OpenGLMateria planetMateria1(GL_FRONT, ambient, bluediffuse, specular, black, lowShining);
      OpenGLMateria planetMateria2(GL_FRONT, ambient, silverdiffuse, specular, black, lowShining);
      OpenGLMateria planetMateria3(GL_FRONT, ambient, greendiffuse, specular, black, lowShining);
      OpenGLMateria planetMateria4(GL_FRONT, ambient, reddiffuse, specular, black, lowShining);
      
      index = 0;
      planets[index++] = new OpenGLSolidSphere(planetMateria1, 0.10f, 20, 20);
      planets[index++] = new OpenGLSolidSphere(planetMateria2, 0.18f, 20, 20);
      planets[index++] = new OpenGLSolidSphere(planetMateria3, 0.18f, 20, 20);
      planets[index]   = new OpenGLSolidSphere(planetMateria4, 0.12f, 20, 20);

      timerThread  = new OpenGLTimerThread(this, renderingInterval);
      timerThread->start();
    }

  public:
    SimpleView(View* parent, const char* name, Args& args)
    :OpenGLView(parent, name, args),
    renderingInterval(10)
    {
      for (int i = 0; i < NUMBER_OF_PLANETS; i++) {
        angles[i] = 30.0f * i;
      }

      renderingInterval = (const int)args.get(XmNrenderingInterval); 
    } 

    ~SimpleView()
    {
    }
  };
  //Inner class ends
  
private:
  SmartPtr<SimpleView>  view;

 long size(Event& event)
  {
    int width  = 0;
    int height = 0;
    event.getSize(width, height);
    if (view) {
      view -> reshape(0, 0, width, height);
      view -> postResizeRequest(width, height);
    }
    
    return 0L;
  }
  
public:
  MainView(Application& applet, const char* name, Args& args)
  :OpenGLMainView(applet, name, args)
  {
    int interval = args.get(XmNrenderingInterval); 
    Args ar;
    ar.set(XmNrenderingInterval, interval);  //20 millisec
    view = new SimpleView(this, "", ar);
  }
  
  ~MainView()
  {
  }
};

}

//
void Main(int argc, char** argv) 
{
  try {
    glutInit(&argc, argv);
    const char*  name = appName(argv[0]);
    Application applet(name, argc, argv);

    Args args;
    args.set(XmNwidth,  640);
    args.set(XmNheight, 640);
    args.set(XmNrenderingInterval, 20);  //20 millisec

    MainView view(applet, name, args);
    view.realize();

    applet.run();
    
  } catch (Exception& ex) {
    caught(ex);
  }
}