  plane-equation coefficients. If the dot product of the eye coordinates of
    a vertex with the stored plane equation components is positive or zero,
    the vertex is <code class="constant">in</code> with respect to that clipping plane.
    Otherwise, it is <code class="constant">out</code>.</p><p>To enable and disable clipping planes, call <a class="citerefentry" href="glEnable"><span class="citerefentry"><span class="refentrytitle">glEnable</span></span></a> and <code class="function">glDisable</code> 