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<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <!doctype html public "-//w3c//dtd html 4.0 transitional//en"
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<meta name="GENERATOR" content="Mozilla/4.5 [fr] (Win98; I) [Netscape]"> <meta name="Author"
<title>FreeType Glyph Conventions</title> content="David Turner">
<title>FreeType Glyph Conventions</title>
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<center><h1> <h1 align=center>
FreeType Glyph Conventions FreeType Glyph Conventions
</h1></center> </h1>
<center><h2> <h2 align=center>
version 2.1 Version&nbsp;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> </h2>
</td></tr></table>
<a name="section-1"><h3> <h3 align=center>
1. Font files, format and information Copyright&nbsp;1998-2000 David Turner (<a
</h3><blockquote> href="mailto:david@freetype.org">david@freetype.org</a>)<br>
Copyright&nbsp;2000 The FreeType Development Team (<a
href="mailto:devel@freetype.org">devel@freetype.org</a>)
</h3>
<p> <center>
A font is a collection of various character images that can <table width="65%">
be used to display or print text. The images in a single font share some <tr><td>
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 <center>
two distinct <i>faces</i> from the same famous <i>family</i>, called <table width="100%"
"<i>Palatino</i>" itself.</p> 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>
<p>The single term font is nearly always used in ambiguous ways to refer <table width="100%">
to either a given family or given face, depending on the context. For example, <tr bgcolor="#CCCCFF"
most users of word-processors use "font" to describe a font family (e.g. valign=center><td>
Courier, Palatino, etc..); however most of these families are implemented <h2>
through several data files depending on the file format : for TrueType, I. Basic typographic concepts
this is usually one per face (i.e. ARIAL.TFF for "Arial Regular", ARIALI.TTF </h2>
for "Arial Italic", etc..). The file is also called a "font" but really </td></tr>
contains a font face. </table>
</p>
<p>A <i>digital font</i> is thus a data file that may contain <i>one or <a name="section-1">
more font faces</i>. For each of these, it contains character images, <h3>
character metrics, as well as other kind of information important to the 1. Font files, format and information
layout of text and the processing of specific character encodings. In some </h3>
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 <p>A font is a collection of various character images that can be used
a font collection. This case is rather rare but can be seen in many asian to display or print text. The images in a single font share some common
fonts, which contain images for two or more scripts for a given language. properties, including look, style, serifs, etc. Typographically
</p> speaking, one has to distinguish between a <em>font family</em> and its
multiple <em>font faces</em>, which usually differ in style though come
from the same template.</p>
For example, "Palatino Regular" and "Palatino Italic" are two distinct
<em>faces</em> from the same famous <em>family</em>, called "Palatino"
itself.</p>
<p>The single term <em>font</em> 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.
<tt>arial.ttf</tt> for "Arial Regular", <tt>ariali.ttf</tt> for "Arial
Italic", etc.). The file is also called a "font" but really contains a
font face.</p>
<p>A <em>digital font</em> is thus a data file that may contain <em>one
or more font faces</em>. 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's Type&nbsp;1, 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 parts of this document and consider
digital fonts as single files, though FreeType&nbsp;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 <em>font collection</em>. This case is rather rare but can be seen in
many Asian fonts, which contain images for two or more representation
forms of a given scripts (usually for horizontal and vertical
layout.</p>
<a name="section-2">
<h3>
2. Character images and mappings
</h3>
</blockquote><h3><a name="section-2"> <p>The character images are called <em>glyphs</em>. A single character
2. Character images and mappings : can have several distinct images, i.e. several glyphs, depending on
</h3><blockquote> script, usage or context. Several characters can also take a single
glyph (good examples are Roman ligatures like "fi" and "fl" which can be
represented by a single glyph). The relationships between characters
and glyphs can be very complex, but won't be discussed in this document.
Moreover, some formats use more or less awkward schemes to store and
access glyphs. For the sake of clarity, we only retain the following
notions when working with FreeType:</p>
<ul>
<li>
<p>A font file contains a set of glyphs; each one can be stored as a
bitmap, a vector representation or any other scheme (most scalable
formats use a combination of mathematical 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.</p>
</li>
<li>
<p>The font file contains one or more tables, called a <em>character
map</em> (or charmap in short), which is used to convert character
codes for a given encoding (e.g. ASCII, Unicode, DBCS, Big5, etc..)
into glyph indices 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.</p>
</li>
</ul>
<a name="section-3">
<h3>
3. Character and font metrics
</h3>
<p>The character images are called <b>glyphs</b>. A single character <p>Each glyph image is associated to various metrics which are used to
can have several distinct images, i.e. several glyphs, depending on script, describe how must be placed and managed when rendering text. Though
usage or context. Several characters can also take a single glyph (good they are described in more details in section&nbsp;III, they relate to
examples are roman ligatures like "oe" and "fi" which can be represented glyph placement, cursor advances as well as text layout. They are
by a single glyph). The relationships between characters extremely important to compute the flow of text when rendering a string
and glyphs can be a very complex one but won't be detailed in this document. of text.</p>
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>Each scalable format also contains some global metrics, expressed in
<p><li> notional units, to describe some properties of all glyphs in the same
A font file contains a set of glyphs, each one can be stored as a bitmap, face. Examples for global metrics are the maximum glyph bounding box,
a vector representation or any other scheme (e.g. most scalable formats the ascender, descender and text height for the font.</p>
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> <p>Though these metrics also exist for non-scalable formats, they only
The font file contains one (or more) table, called a character map (or apply for a set of given character dimensions and resolutions, and
charmap in short), which is used to convert character codes for a given they are usually expressed in pixels then.</p>
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>
<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>
</blockquote><h3><a name="section-3"> </td></tr>
3. Character and font metrics : </table>
</h3><blockquote> </center>
<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>
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