development.html

<h1>Relationship to the <span class="caps">GSUB</span> and <span class="caps">GPOS</span> Specification</h1>


	<p>The Compositor <span class="caps">GSUB</span> and <span class="caps">GPOS</span> tables adhere as closely as possible to the <span class="caps">GSUB</span> and <span class="caps">GPOS</span> specification. Every effort has been made to keep terminology consistent. All known deviations from the spec are documented. (The deviations are generally trivial. For example, most the of the subtables don&#8217;t implement the <em>Count</em> attributes. This is done because the Python iterator provides a more convenient and faster way to deal with iteration than creating a range. Therefore, the <em>Count</em> objects are not needed.)</p>


	<h1>Object Loading</h1>


	<p>For performance reasons, when a new font is loaded, all of the <span class="caps">GSUB</span> and <span class="caps">GPOS</span> data is extracted from the font with fontTools. The data is placed into compositor objects. These objects are then used to process text. This initial loading can be relatively expensive, but the processing speed of the objects is worth the initial expense.</p>