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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>Shaping operations: 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="shaping-concepts.html" title="Shaping concepts"> <link rel="prev" href="complex-scripts.html" title="Complex scripts"> <link rel="next" href="unicode-character-categories.html" title="Unicode character categories"> <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="shaping-concepts.html"><img src="up.png" width="16" height="16" border="0" alt="Up"></a></td> <td><a accesskey="p" href="complex-scripts.html"><img src="left.png" width="16" height="16" border="0" alt="Prev"></a></td> <td><a accesskey="n" href="unicode-character-categories.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="shaping-operations"></a>Shaping operations</h2></div></div></div> <p> Shaping a complex-script text run involves transforming the input sequence of Unicode codepoints with some combination of operations that is specified in the shaping model for the script. </p> <p> The specific conditions that trigger a given operation for a text run varies from script to script, as do the order that the operations are performed in and which codepoints are affected. However, the same general set of shaping operations is common to all of the complex-script shaping models. </p> <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"> <p> A <span class="emphasis"><em>reordering</em></span> operation moves a glyph from its original ("logical") position in the sequence to some other ("visual") position. </p> <p> The shaping model for a given complex script might involve more than one reordering step. </p> </li> <li class="listitem"><p> A <span class="emphasis"><em>joining</em></span> operation replaces a glyph with an alternate form that is designed to connect with one or more of the adjacent glyphs in the sequence. </p></li> <li class="listitem"> <p> A contextual <span class="emphasis"><em>substitution</em></span> operation replaces either a single glyph or a subsequence of several glyphs with an alternate glyph. This substitution is performed when the original glyph or subsequence of glyphs occurs in a specified position with respect to the surrounding sequence. For example, one substitution might be performed only when the target glyph is the first glyph in the sequence, while another substitution is performed only when a different target glyph occurs immediately after a particular string pattern. </p> <p> The shaping model for a given complex script might involve multiple contextual-substitution operations, each applying to different target glyphs and patterns, and which are performed in separate steps. </p> </li> <li class="listitem"> <p> A contextual <span class="emphasis"><em>positioning</em></span> operation moves the horizontal and/or vertical position of a glyph. This positioning move is performed when the glyph occurs in a specified position with respect to the surrounding sequence. </p> <p> Many contextual positioning operations are used to place <span class="emphasis"><em>mark</em></span> glyphs (such as diacritics, vowel signs, and tone markers) with respect to <span class="emphasis"><em>base</em></span> glyphs. However, some complex scripts may use contextual positioning operations to correctly place base glyphs as well, such as when the script uses <span class="emphasis"><em>stacking</em></span> characters. </p> </li> </ul></div> </div> <div class="footer"> <hr>Generated by GTK-Doc V1.32</div> </body> </html>
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