 evaluation
            shading stages if the corresponding shader executable does
            not write to gl_PointSize. It is also undefined after the geometry processing stage if the geometry shader executable calls
            <a class="citerefentry" href="EmitVertex"><span class="citerefentry"><span class="refentrytitle">EmitVertex</span></span></a> without having
            written <code class="varname">gl_PointSize</code> since the last call to <a class="citerefentry" href="EmitVertex"><span class="