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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>What HarfBuzz doesn't do: HarfBuzz Manual</title> <meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> <link rel="home" href="index.html" title="HarfBuzz Manual"> <link rel="up" href="what-is-harfbuzz.html" title="What is HarfBuzz?"> <link rel="prev" href="ch01s03.html" title="What does HarfBuzz do?"> <link rel="next" href="why-is-it-called-harfbuzz.html" title="Why is it called HarfBuzz?"> <meta name="generator" content="GTK-Doc V1.32 (XML mode)"> <link rel="stylesheet" href="style.css" type="text/css"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table class="navigation" id="top" width="100%" summary="Navigation header" cellpadding="2" cellspacing="5"><tr valign="middle"> <td width="100%" align="left" class="shortcuts"></td> <td><a accesskey="h" href="index.html"><img src="home.png" width="16" height="16" border="0" alt="Home"></a></td> <td><a accesskey="u" href="what-is-harfbuzz.html"><img src="up.png" width="16" height="16" border="0" alt="Up"></a></td> <td><a accesskey="p" href="ch01s03.html"><img src="left.png" width="16" height="16" border="0" alt="Prev"></a></td> <td><a accesskey="n" href="why-is-it-called-harfbuzz.html"><img src="right.png" width="16" height="16" border="0" alt="Next"></a></td> </tr></table> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="what-harfbuzz-doesnt-do"></a>What HarfBuzz doesn't do</h2></div></div></div> <p> HarfBuzz will take a Unicode string, shape it, and give you the information required to lay it out correctly on a single horizontal (or vertical) line using the font provided. That is the extent of HarfBuzz's responsibility. </p> <p> It is important to note that if you are implementing a complete text-layout engine you may have other responsibilities that HarfBuzz will <span class="emphasis"><em>not</em></span> help you with. For example: </p> <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"> <p> HarfBuzz won't help you with bidirectionality. If you want to lay out text that includes a mix of Hebrew and English, you will need to ensure that each buffer provided to HarfBuzz has all of its characters in the same order and that the directionality of the buffer is set correctly. This may mean segmenting the text before it is placed into HarfBuzz buffers. In other words, the user will hit the keys in the following sequence: </p> <pre class="programlisting"> A B C [space] ג ב א [space] D E F </pre> <p> but will expect to see in the output: </p> <pre class="programlisting"> ABC אבג DEF </pre> <p> This reordering is called <span class="emphasis"><em>bidi processing</em></span> ("bidi" is short for bidirectional), and there's an algorithm as an annex to the Unicode Standard which tells you how to process a string of mixed directionality. Before sending your string to HarfBuzz, you may need to apply the bidi algorithm to it. Libraries such as <a class="ulink" href="http://icu-project.org/" target="_top">ICU</a> and <a class="ulink" href="http://fribidi.org/" target="_top">fribidi</a> can do this for you. </p> </li> <li class="listitem"> <p> HarfBuzz won't help you with text that contains different font properties. For instance, if you have the string "a <span class="emphasis"><em>huge</em></span> breakfast", and you expect "huge" to be italic, then you will need to send three strings to HarfBuzz: <code class="literal">a</code>, in your Roman font; <code class="literal">huge</code> using your italic font; and <code class="literal">breakfast</code> using your Roman font again. </p> <p> Similarly, if you change the font, font size, script, language, or direction within your string, then you will need to shape each run independently and output them independently. HarfBuzz expects to shape a run of characters that all share the same properties. </p> </li> <li class="listitem"> <p> HarfBuzz won't help you with line breaking, hyphenation, or justification. As mentioned above, HarfBuzz lays out the string along a <span class="emphasis"><em>single line</em></span> of, notionally, infinite length. If you want to find out where the potential word, sentence and line break points are in your text, you could use the ICU library's break iterator functions. </p> <p> HarfBuzz can tell you how wide a shaped piece of text is, which is useful input to a justification algorithm, but it knows nothing about paragraphs, lines or line lengths. Nor will it adjust the space between words to fit them proportionally into a line. </p> </li> </ul></div> <p> As a layout-engine implementor, HarfBuzz will help you with the interface between your text and your font, and that's something that you'll need—what you then do with the glyphs that your font returns is up to you. </p> </div> <div class="footer"> <hr>Generated by GTK-Doc V1.32</div> </body> </html>