title: GL_QUAD draws triangle
body: <p>I am trying to fill quad that is generated by 4 lines with <code>GL_LINES</code>. However, when I try to fill the quad it only fills with triangle. This is the code that draws the lines: </p>
  
  <pre><code>def SurfaceContour(self, vertices, edges):
       glBegin(GL_LINES)
       for edge in edges:
           for vertex in edge:
               glColor3fv((1.0, 0.0, 0.0))
               glVertex3fv(vertices[vertex])
       glEnd()
  </code></pre>
  
  <p>This is the code that draws fills the quad: </p>
  
  <pre><code>def Surfaces(self,  vertices):
       glBegin(GL_QUADS)
       for i in range(4):
          glColor4f(1, 1, 1, 0.3)
          glVertex3fv(vertices[i ,:])
       glEnd()
  </code></pre>
  
  <p>This is the vertices matrix that I pass into: </p>
  
  <pre><code>[[   0.    -20.23    7.  ]
   [   0.    -20.23   -7.  ]
   [ 100.    -10.      5.  ]
   [ 100.    -10.     -5.  ]]
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/fChi7.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fChi7.jpg" alt="This is the result that i get: "></a></p>