title: glBegin(GL_TRIANGLES) doesn't render anything
body: <p>I am trying to import .obj files but cant even get a triangle rendered.  Here is what I'm trying to do just to test if it can show something.</p>
  
  <pre><code>glBegin(GL_TRIANGLES);
      glColor3f(0.5, 0.5, 0.5);
      glVertex3f(0, 0, 0);
      glVertex3f(1, 1, 1);
      glVertex3f(2, 2, 2);
  glEnd();
  </code></pre>
  
  <p>This doesn't display anything.  However when I change GL_TRIANGLES for GL_LINES it displays the line.</p>
  
  <p>How can I get the triangle to display?</p>
  
  <p>Language: C++</p>
  
  <p>OS: Mac 10.7.3</p>