#!/usr/bin/perl -w
use strict;
use warnings;
use OpenGL qw/ :all /;
use OpenGL::Config;   



glutInit();
glutInitDisplayMode(GLUT_RGB|GLUT_SINGLE);
glutInitWindowPosition(100,100);
glutInitWindowSize(400,400);
glutCreateWindow("my  OpenGL program");
glClearColor(0,0,0,255);
glClear(GL_COLOR_BUFFER_BIT);  
glMatrixMode(GL_PROJECTION);
glOrtho(-2,2,-2,2,-2,2);
glMatrixMode(GL_MODELVIEW);
gluLookAt(0.1,0.1,0.1,0.0,0.0,0.0,0.0,0.1,0.0); 
glutDisplayFunc(\&mydis);
glutMainLoop();



 sub mydis()
{
  my $x;
  my $y;
  my $z;
  my $c=3.1415926/180;
 
  glClearColor(0,0,0,255);
  glClear(GL_COLOR_BUFFER_BIT);
  glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

	  
  for (my $phi=-80.00;$phi<=80.00;$phi+=20.00)
  {

      my $phir=$c*$phi;
      my $phir20=$c*($phi+20);     
      glBegin(GL_QUAD_STRIP);      
      for (my $theta=-180.00;$theta<=180.00;$theta+=20.00)
      {
          my $thetar=$c*$theta;
          $x=sin($thetar)*cos($phir);
          $y=cos($thetar)*cos($phir);
          $z=sin($phir);
          glVertex3d($x,$y,$z);	
          $x=sin($thetar)*cos($phir20);
          $y=cos($thetar)*cos($phir20);
          $z=sin($phir20);          
          glVertex3d($x,$y,$z);				  
	  }  
      glEnd();	  
  }
  glFlush();
}