#include <GL/glut.h>
#include <math.h>

/* Pi konstans kozelito erteke. */
#define GL_PI 3.1415f

/* A szabalyos sokszog csucspontjainak szama. */
int N = 3;

/* A sokszog kore irhato kor sugara. */
double R = 0.0;

double pos_x = 0.0;
double pos_y = 0.0;

/* Kitoltott vagy korvonalas megjelenites. */
int filled_display = 1;

void DiskApprox(int n, double radius, float x, float y)
{
  /*
    n      - hany oldalu szabalyos sokszoggel kozelitunk (n legalább 3)
    radius - a sokszog kore irhato kor sugara
    x, y   - a sokszog kore irhato kor kozeppontjanak koordinatai
  */

  int i;
  GLfloat angle;

  if(n < 3)
    n = 3;
  
  glBegin(GL_LINES);
  for(i = 0, angle = 0.0; i < n; i++, angle += 2.0 * GL_PI / n)
  {
      glVertex2f(x, y);
      glVertex2f(x + radius * cos(angle), y + radius * sin(angle));
  }
  glEnd();
}

void Timer(int value)
{
  /* Itt változtathatunk a globális változókon. */

  R += 0.25f;

  if(R>20.0f) R = 0.0f;

  glutPostRedisplay();
  glutTimerFunc(50, Timer, value + 1);
}

void RenderScene(void)
{
  /* Ablak torlese az aktualis torloszinnel. */
  glClear(GL_COLOR_BUFFER_BIT);

  /* Poligon megjelenitesi modja. */
  if(filled_display)
    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
  else
    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

  glLineWidth(3.0);

  glLineStipple(1.0, 0x00ff);

  glEnable(GL_LINE_STIPPLE);

  DiskApprox( 32, R, pos_x, pos_y );

  glDisable(GL_LINE_STIPPLE);

  /* Pufferek csereje, uj kep megjelenitese */
  glutSwapBuffers();
}

void SetupRC()
{
  /* Fekete hatter */
  glClearColor(0.0f, 0.0f, 0.0f, 1.0f );

  /* Modellezes szinenek beallitasa */
  glColor3f(1.0, 1.0, 0.0);
}

void SpecialKeys(int key, int x, int y)
{
  if(key == GLUT_KEY_F1)
    filled_display = !filled_display;

  if(key == GLUT_KEY_UP)
      pos_y += 2.0;
  
  if(key == GLUT_KEY_DOWN)
      pos_y -= 2.0;
  
  if(key == GLUT_KEY_LEFT)
      pos_x -= 2.0;
  
  if(key == GLUT_KEY_RIGHT)
      pos_x += 2.0;

  /* Ablak frissitese */
  glutPostRedisplay();
}

void ChangeSize(int w, int h)
{
  GLfloat nRange = 25.0f;
  
  /* Nullaval nem osztunk */
  if(h == 0)
    h = 1;
  
  /* Viewport beallitasa az ablak meretere. */
  glViewport(0, 0, w, h);
  
  /* Projekcios matrix inicializalasa */
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  
  /* Parhuzamos vetites beallitasa */
  if (w <= h) 
    glOrtho (-nRange, nRange, -nRange*h/w, nRange*h/w, -nRange, nRange);
  else 
    glOrtho (-nRange*w/h, nRange*w/h, -nRange, nRange, -nRange, nRange);
  
  /* ModelView matrix inicializalasa */
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

int main(int argc, char* argv[])
{
  /* Inicializalas */
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
  glutCreateWindow("Szabalyos sokszog");

  /* Viszahivhato fuggvenyek beallitasa */
  glutReshapeFunc(ChangeSize);
  glutSpecialFunc(SpecialKeys);
  glutDisplayFunc(RenderScene);

  /* Globalis beallitasok */
  SetupRC();

  glutTimerFunc(50, Timer, 0);

 /* Vezerles atadasa a GLUT-nak */
  glutMainLoop();
  
  return 0;
}