title: how to use gl_polygon to draw 3d cylinder
body: <p>i am new opengl learner. i know there is build in function to draw cylinder in glut something like </p>
  
  <pre><code>GLUquadricObj *quadratic;
  quadratic=gluNewQuadric();
  gluCylinder(quadratic,0.6f,0.6f,1.5f,20,20);
  </code></pre>
  
  <p>However, is there any other way to draw cylinder using glBegin(GL_POLYGON) and glvertex3d, i am not quite clear about the algorithm behind, please help.</p>