ader output variable is written to
            <em class="parameter"><code>params</code></em>.  If the active variable is an output for a non-fragment shader,
            the value -1 will be written to <em class="parameter"><code>params</code></em>.
        </p>
        <p>
            For the property <code class="constant">GL_IS_PER_PATCH</code>, a single integer identifying whether the
            input or output is a per-patch attribute.  If the active variable is a
            per-patch attribute (dec