docs/glyphs/glyphs-1.html - third_party/freetype2 - Git at Google

 <!doctype html public "-//w3c//dtd html 4.0 transitional//en">
 <html>
 <head>
    <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
    <meta name="Author" content="blob">
    <meta name="GENERATOR" content="Mozilla/4.5 [fr] (Win98; I) [Netscape]">
    <title>FreeType Glyph Conventions</title>
 </head>
 <body>

 <body text="#000000"
       bgcolor="#FFFFFF"
       link="#0000EF"
       vlink="#51188E"
       alink="#FF0000">

 <center><h1>
 FreeType Glyph Conventions
 </h1></center>

 <center><h2>
 version 2.1
 </h2></center>

 <center><h3>
 Copyright 1998-2000 David Turner (<a href="mailto:david@freetype.org">david@freetype.org</a>)<br>
 Copyright 2000 The FreeType Development Team (<a href="devel@freetype.org">devel@freetype.org</a>)
 </h3></center>

 <center><table width=650><tr><td>

 <center><table width="100%" border=0 cellpadding=5><tr bgcolor="#CCFFCC" valign=center>
 <td align=center width="30%">
 &nbsp;
 </td>
 <td align=center width="30%">
 <a href="index.html">Contents</a>
 </td>
 <td align=center width="30%">
 <a href="glyphs-2.html">Next</a>
 </td>
 </tr></table></center>

 <table width="100%" cellpadding=5><tr bgcolor="#CCCCFF" valign=center><td>
 <h2>
 I. Basic typographic concepts
 </h2>
 </td></tr></table>

 <a name="section-1"><h3>
 1. Font files, format and information
 </h3><blockquote>

 <p>
 A font is a collection of various character images that can
 be used to display or print text. The images in a single font share some
 common properties, including look, style, serifs, etc.. Typographically
 speaking, one has to distinguish between a <b>font family</b> and its
 multiple <b>font faces</b>, which usually differ in style though come
 from the same template.</p>

 For example, "<i>Palatino Regular</i>" and "<i>Palatino Italic</i>" are
 two distinct <i>faces</i> from the same famous <i>family</i>, called
 "<i>Palatino</i>" itself.</p>

 <p>The single term font is nearly always used in ambiguous ways to refer
 to either a given family or given face, depending on the context. For example,
 most users of word-processors use "font" to describe a font family (e.g.
 Courier, Palatino, etc..); however most of these families are implemented
 through several data files depending on the file format : for TrueType,
 this is usually one per face (i.e. ARIAL.TFF for "Arial Regular", ARIALI.TTF
 for "Arial Italic", etc..). The file is also called a "font" but really
 contains a font face.
 </p>

 <p>A <i>digital font</i> is thus a data file that may contain <i>one or
 more font faces</i>. For each of these, it contains character images,
 character metrics, as well as other kind of information important to the
 layout of text and the processing of specific character encodings. In some
 awkward formats, like Adobe Type1, a single font face is described through
 several files (i.e. one contains the character images, another one the
 character metrics). We will ignore this implementation issue in most of
 this document and consider digital fonts as single files, though FreeType
 2.0 is able to support multiple-files fonts correctly.
 </p>

 <p>As a convenience, a font file containing more than one face is called
 a font collection. This case is rather rare but can be seen in many asian
 fonts, which contain images for two or more scripts for a given language.
 </p>


 </blockquote><h3><a name="section-2">
 2. Character images and mappings :
 </h3><blockquote>


 <p>The character images are called <b>glyphs</b>. A single character
 can have several distinct images, i.e. several glyphs, depending on script,
 usage or context. Several characters can also take a single glyph (good
 examples are roman ligatures like "oe" and "fi" which can be represented
 by a single glyph). The relationships between characters
 and glyphs can be a very complex one but won't be detailed in this document.
 Moreover, some formats use more or less awkward schemes to store and access
 the glyphs. For the sake of clarity, we'll only retain the following notions
 when working with FreeType :</p>

 <ul>
 <p><li>
 A font file contains a set of glyphs, each one can be stored as a bitmap,
 a vector representation or any other scheme (e.g. most scalable formats
 use a combination of math representation and control data/programs). These
 glyphs can be stored in any order in the font file, and is typically accessed
 through a simple glyph index.
 </li></p>

 <p><li>
 The font file contains one (or more) table, called a character map (or
 charmap in short), which is used to convert character codes for a given
 encoding (e.g. ASCII, Unicode, DBCS, Big5, etc..) into glyph indexes
 relative to the font file. A single font face may contain several charmaps.
 For example, most TrueType fonts contain an Apple-specific charmap as well
 as a Unicode charmap, which makes them usable on both Mac and Windows
 platforms.
 </li></p>
 </ul>


 </blockquote><h3><a name="section-3">
 3. Character and font metrics :
 </h3><blockquote>

 <p>Each glyph image is associated to various metrics which are used to
 describe the way it must be placed and managed when rendering text. Though
 they are described in more details in section III, they relate to glyph
 placement, cursor advances as well as text layouts. They are extremely
 important to compute the flow of text when rendering string of text.
 </p>

 <p>Each scalable format also contains some global metrics, expressed in
 notional units, used to describe some properties of all glyphs in a same
 face. For example : the maximum glyph bounding box, the ascender, descender
 and text height for the font.
 </p>

 <p>Though these metrics also exist for non-scalable formats, they only
 apply for a set of given character dimensions and resolutions, and they're
 usually expressed in pixels then.</p>

 <center><table width="100%" border=0 cellpadding=5><tr bgcolor="#CCFFCC" valign=center>
 <td align=center width="30%">
 &nbsp;
 </td>
 <td align=center width="30%">
 <a href="index.html">Contents</a>
 </td>
 <td align=center width="30%">
 <a href="glyphs-2.html">Next</a>
 </td>
 </tr></table></center>

 </td></tr></table></center>


 </body>
 </html>
	<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
	<html>
	<head>
	<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
	<meta name="Author" content="blob">
	<meta name="GENERATOR" content="Mozilla/4.5 [fr] (Win98; I) [Netscape]">
	<title>FreeType Glyph Conventions</title>
	</head>
	<body>

	<body text="#000000"
	bgcolor="#FFFFFF"
	link="#0000EF"
	vlink="#51188E"
	alink="#FF0000">

	<center><h1>
	FreeType Glyph Conventions
	</h1></center>

	<center><h2>
	version 2.1
	</h2></center>

	<center><h3>
	Copyright 1998-2000 David Turner (<a href="mailto:david@freetype.org">david@freetype.org</a>)<br>
	Copyright 2000 The FreeType Development Team (<a href="devel@freetype.org">devel@freetype.org</a>)
	</h3></center>

	<center><table width=650><tr><td>

	<center><table width="100%" border=0 cellpadding=5><tr bgcolor="#CCFFCC" valign=center>
	<td align=center width="30%">

	</td>
	<td align=center width="30%">
	<a href="index.html">Contents</a>
	</td>
	<td align=center width="30%">
	<a href="glyphs-2.html">Next</a>
	</td>
	</tr></table></center>

	<table width="100%" cellpadding=5><tr bgcolor="#CCCCFF" valign=center><td>
	<h2>
	I. Basic typographic concepts
	</h2>
	</td></tr></table>

	<a name="section-1"><h3>
	1. Font files, format and information
	</h3><blockquote>

	<p>
	A font is a collection of various character images that can
	be used to display or print text. The images in a single font share some
	common properties, including look, style, serifs, etc.. Typographically
	speaking, one has to distinguish between a <b>font family</b> and its
	multiple <b>font faces</b>, which usually differ in style though come
	from the same template.</p>

	For example, "<i>Palatino Regular</i>" and "<i>Palatino Italic</i>" are
	two distinct <i>faces</i> from the same famous <i>family</i>, called
	"<i>Palatino</i>" itself.</p>

	<p>The single term font is nearly always used in ambiguous ways to refer
	to either a given family or given face, depending on the context. For example,
	most users of word-processors use "font" to describe a font family (e.g.
	Courier, Palatino, etc..); however most of these families are implemented
	through several data files depending on the file format : for TrueType,
	this is usually one per face (i.e. ARIAL.TFF for "Arial Regular", ARIALI.TTF
	for "Arial Italic", etc..). The file is also called a "font" but really
	contains a font face.
	</p>

	<p>A <i>digital font</i> is thus a data file that may contain <i>one or
	more font faces</i>. For each of these, it contains character images,
	character metrics, as well as other kind of information important to the
	layout of text and the processing of specific character encodings. In some
	awkward formats, like Adobe Type1, a single font face is described through
	several files (i.e. one contains the character images, another one the
	character metrics). We will ignore this implementation issue in most of
	this document and consider digital fonts as single files, though FreeType
	2.0 is able to support multiple-files fonts correctly.
	</p>

	<p>As a convenience, a font file containing more than one face is called
	a font collection. This case is rather rare but can be seen in many asian
	fonts, which contain images for two or more scripts for a given language.
	</p>



	</blockquote><h3><a name="section-2">
	2. Character images and mappings :
	</h3><blockquote>



	<p>The character images are called <b>glyphs</b>. A single character
	can have several distinct images, i.e. several glyphs, depending on script,
	usage or context. Several characters can also take a single glyph (good
	examples are roman ligatures like "oe" and "fi" which can be represented
	by a single glyph). The relationships between characters
	and glyphs can be a very complex one but won't be detailed in this document.
	Moreover, some formats use more or less awkward schemes to store and access
	the glyphs. For the sake of clarity, we'll only retain the following notions
	when working with FreeType :</p>

	<ul>
	<p><li>
	A font file contains a set of glyphs, each one can be stored as a bitmap,
	a vector representation or any other scheme (e.g. most scalable formats
	use a combination of math representation and control data/programs). These
	glyphs can be stored in any order in the font file, and is typically accessed
	through a simple glyph index.
	</li></p>

	<p><li>
	The font file contains one (or more) table, called a character map (or
	charmap in short), which is used to convert character codes for a given
	encoding (e.g. ASCII, Unicode, DBCS, Big5, etc..) into glyph indexes
	relative to the font file. A single font face may contain several charmaps.
	For example, most TrueType fonts contain an Apple-specific charmap as well
	as a Unicode charmap, which makes them usable on both Mac and Windows
	platforms.
	</li></p>
	</ul>



	</blockquote><h3><a name="section-3">
	3. Character and font metrics :
	</h3><blockquote>

	<p>Each glyph image is associated to various metrics which are used to
	describe the way it must be placed and managed when rendering text. Though
	they are described in more details in section III, they relate to glyph
	placement, cursor advances as well as text layouts. They are extremely
	important to compute the flow of text when rendering string of text.
	</p>

	<p>Each scalable format also contains some global metrics, expressed in
	notional units, used to describe some properties of all glyphs in a same
	face. For example : the maximum glyph bounding box, the ascender, descender
	and text height for the font.
	</p>

	<p>Though these metrics also exist for non-scalable formats, they only
	apply for a set of given character dimensions and resolutions, and they're
	usually expressed in pixels then.</p>

	<center><table width="100%" border=0 cellpadding=5><tr bgcolor="#CCFFCC" valign=center>
	<td align=center width="30%">

	</td>
	<td align=center width="30%">
	<a href="index.html">Contents</a>
	</td>
	<td align=center width="30%">
	<a href="glyphs-2.html">Next</a>
	</td>
	</tr></table></center>

	</td></tr></table></center>


	</body>
	</html>