float width,height;
void RenderScene(void)
{
  glClear(GL_COLOR_BUFFER_BIT);
  glColor3f(0.0f,0.0f,1.0f);
glBegin(GL_LINES);
for(int i=-width/2;i<=width/2; i+=20)
{
glVertex2f(i,height/2);
glVertex2f(i,-height/2);
}
glEnd();

  glFlush();
}
void ChangeSize(GLsizei w, GLsizei h)
{
  GLfloat appect;
  if(h ==0)
   h=1;

  glViewport(0,0,w,h);
     glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  appect = (GLfloat)w /(GLfloat)h;
  if(w<=h)
  {
   glOrtho(-w/2,w/2,(-h/2)/appect,(h/2)/appect,1.0,-1.0);
   height =h/appect;width=w;
  }
  else
  {
   glOrtho((-w/2)*appect,(w/2)*appect,-h/2,h/2,1.0f,-1.0f);
   height =h;width=w*appect;
  }
  glMatrixMode(GL_MODELVIEW);
   
}