be greater than a fixed value defined by the &lsquo;FT_MAX_GRAY_SPANS&rsquo; configuration macro in &lsquo;ftoption.h&rsquo;. By default, this value is set to&nbsp;32, which means that if there are more than 32&nbsp;spans on a given scanline, the callback is called several times with the same &lsquo;y&rsquo; parameter in order to draw all callbacks.</p>
<p>Otherwise, the callback is only called once per scan-line, and only for those scanlines that do have &lsquo;gray&rsquo; pixels on them.</p>
</td></tr></t