in_upper_left</code> identifier. The values returned can also be
            shifted by half a pixel in both x and y by <code class="function">pixel_center_integer</code> so it
            appears the pixels are centered at whole number pixel offsets. This moves the (x, y) value returned by
            <code class="varname">gl_FragCoord</code> of (0.5, 0.5) by default to (0.0, 0.0) with
            <code class="function">pixel_center_integer</code>.
        </p>
        <p>
            If <code class="varna