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<!doctype html public "-//w3c//dtd html 4.0 transitional//en"
"http://www.w3.org/TR/REC-html40/loose.dtd">
<html>
<head><title>The Design of FreeType 2 - Introduction</title>
<basefont face="Georgia, Arial, Helvetica, Geneva">
<style content="text/css">
P { text-align=justify }
H1 { text-align=center }
H2 { text-align=center }
LI { text-align=justify }
</style>
<head>
<meta http-equiv="Content-Type"
content="text/html; charset=iso-8859-1">
<meta name="Author"
content="David Turner">
<title>The Design of FreeType 2 - Introduction</title>
</head>
<body text=#000000 bgcolor=#ffffff>
<center><table width="500"><tr><td>
<center><h1>The Design of FreeType 2</h1></center>
<table width="100%" cellpadding=5><tr bgcolor="#ccccee"><td>
<h1>Introduction</h1>
</td></tr></table>
<p>This document provides details on the design and implementation
of the FreeType 2 library. Its goal is to allow developers to
better understand the way FT2 is organized, in order to let them
extend, customize and debug it.</p>
<p>Before anything else, it is important to understand the <em>purpose</em>
of this library, i.e. why it has been written:</p>
<ul>
<li><p>first of all, to allow client applications to <em>access font files
easily</em>, wherever they could be stored, and as independently
of font format as possible.</p></li>
<li><p>to allow easy <em>retrieval of global font data</em> most commonly
found in normal font formats (i.e. global metrics,
encoding/charmaps, etc..)</p></li>
<li><p>to allow easy <em>retrieval of individual glyph data</em>
(metrics, images, name, anything else)</p></li>
<li><p>to allow <em>access to font format-specific "features"</em>
whenever possible (e.g. SFNT tables, Multiple Masters,
OpenType Layout tables, etc..)</p></li>
</ul>
<p>its design has also severely been influenced by the following
requirements:</p>
<ul>
<li><p><b>high portability</b>, as the library must be able to run
on any kind of environment. this requirement introduces a few
drastic choices that are part of FreeType 2's low-level system
interface.</p></li>
<li><p><b>extendibility</b>, as new features should be added with
the least modifications in the library's code base. this
requirements induces an extremely simple design where nearly
all operations are provided by modules.
</p></li>
<li><p><b>customization</b>, it should be easy to build a version
of the library that only contains the features needed by a
specific project. This really is important when you need to
integrate it in a font server for embedded graphics libraries.</p></li>
<li><p><b>compactness</b> and <b>efficiency</b>, given that the
primary target for this library is embedded systems with low
cpu and memory resources.</p></li>
</ul>
<p>The rest of this document is divided in several sections. First, a
few chapters will present the library's basic design as well as the
objects/data managed internally by FreeType 2.</p>
<p>A later section is then dedicated to library customization, relating
such topics as system-specific interfaces, how to write your own
module and how to tailor library initialisation & compilation
to your needs.</p>
</td></tr></table></center>
<body text="#000000"
bgcolor="#ffffff">
<h1 align=center>
The Design of FreeType&nbsp;2
</h1>
<center>
<table width="75%">
<tr><td>
<table width="100%">
<tr bgcolor="#ccccee"><td>
<h1>
Introduction
</h1>
</td></tr>
</table>
<p>This document provides details on the design and implementation of the
FreeType&nbsp;2 library. Its goal is to allow developers to better
understand the way how FreeType&nbsp;2 is organized, in order to let them
extend, customize, and debug it.</p>
<p>Before anything else, it is important to understand the
<em>purpose</em> of this library, i.e., why it has been written:</p>
<ul>
<li>
<p>It allows client applications to <em>access font files easily</em>,
wherever they could be stored, and as independently of the font format
as possible.</p>
</li>
<li>
<p>Easy <em>retrieval of global font data</em> most commonly found in
normal font formats (i.e. global metrics, encoding/charmaps,
etc.).</p>
</li>
<li>
<p>It allows easy <em>retrieval of individual glyph data</em>
(metrics, images, name, anything else).</p>
</li>
<li>
<p><em>Access to font format-specific "features"</em> whenever
possible (e.g. SFNT tables, Multiple Masters, OpenType Layout tables,
etc.).</p>
</li>
</ul>
<p>Its design has also severely been influenced by the following
requirements:</p>
<ul>
<li>
<p><em>High portability</em>. The library must be able to run on any
kind of environment. This requirement introduces a few drastic
choices that are part of FreeType&nbsp;2's low-level system
interface.</p>
</li>
<li>
<p><em>Extendability</em>. New features should be added with the
least modifications in the library's code base. This requirement
induces an extremely simple design where nearly all operations are
provided by modules.</p>
</li>
<li>
<p><em>Customization</b>. It should be easy to build a version of the
library that only contains the features needed by a specific project.
This really is important when you need to integrate it in a font
server for embedded graphics libraries.</p>
</li>
<li>
<p><em>Compactness</em> and <em>efficiency</em>. The primary target
for this library are embedded systems with low cpu and memory
resources.</p>
</li>
</ul>
<p>The rest of this document is divided in several sections. First, a few
chapters will present the library's basic design as well as the
objects/data managed internally by FreeType&nbsp;2.</p>
<p>A later section is then dedicated to library customization, relating
such topics as system-specific interfaces, how to write your own module
and how to tailor library initialization & compilation to your needs.</p>
</td></tr>
</table>
</center>
</body>
</html>

233
docs/design/design-2.html
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<!doctype html public "-//w3c//dtd html 4.0 transitional//en"
"http://www.w3.org/TR/REC-html40/loose.dtd">
<html>
<head><title>The Design of FreeType 2 - Basic Design</title>
<basefont face="Georgia, Arial, Helvetica, Geneva">
<style content="text/css">
P { text-align=justify }
H1 { text-align=center }
H2 { text-align=center }
LI { text-align=justify }
</style>
<head>
<meta http-equiv="Content-Type"
content="text/html; charset=iso-8859-1">
<meta name="Author"
content="David Turner">
<title>The Design of FreeType 2 - Basic Design</title>
</head>
<body text=#000000 bgcolor=#ffffff>
<center><table width="500"><tr><td>
<center><h1>The Design of FreeType 2</h1></center>
<table width="100%" cellpadding=5><tr bgcolor="#ccccee"><td>
<h1>I. Components and APIs</h1>
</td></tr></table>
<p>It's better to describe FreeType 2 as a collection of
<em>components</em>. Each one of them is a more or less abstract
part of the library that is in charge of one specific task. We will
now explicit the connections and relationships between them.</p>
<p>A first brief description of this system of components could be:</p>
<ul>
<li><p>
client applications typically call the FreeType 2 <b>high-level
API</b>, whose functions are implemented in a single component
called the <em>Base Layer</em>.
</p></li>
<li><p>
depending on the context or the task, the base
layer then calls one or more <em>module</em> components to
perform the work. In most cases, the client application doesn't
need to know what module was called.
</p></li>
<li><p>
the base layer also contains a set of routines that are
used for generic things like memory allocation, list
processing, i/o stream parsing, fixed point computation,
etc.. these functions can also be called by a module
at any time, and they form what is called the <b>low-level
base API</b>.
</p></li>
</ul>
<p>This is illustrated by the following graphics (note that component
entry points are represented as colored triangles):</p>
<center><img src="basic-design.png" width="394" height="313"></center>
<p>Now, a few additional things must be added to complete this picture:</p>
<ul>
<li><p>some parts of the base layer can be replaced for specific builds
of the library, and can thus be considered as components themselves.
this is the case for the <b>ftsystem</b> component, which is in
charge of implementing memory management & input stream access,
as well as the <b>ftinit</b>, which is in charge of library
initialisation (i.e. implementing <tt>FT_Init_FreeType</tt>).
</p></li>
<li><p>
FreeType 2 comes also with a set of <em>optional components</em>,
which can be used either as a convenience for client applications
(e.g. the <b>ftglyph</b> component, used to provide a simple API
to manage glyph images independently of their internal representation),
or to access format-specific features (e.g. the <b>ftmm</b> component
used to access and manage Multiple Masters data in Type 1 fonts)
</p></li>
<li><p>
Finally, a module is capable of calling functions provided by
another module. This is very useful to share code and tables
between several font driver modules (for example, the <tt>truetype</tt>
and <tt>cff</tt> both use the routines provided by the <tt>sfnt</tt>
module).
</p></li>
</ul>
<p>Hence, a more complete picture would be:</p>
<center><img src="detailed-design.png" width="390" height="429"></center>
<p>Please take note of the following important points:</p>
<ul>
<li><p>
an optional component can use either the high-level or base
API. This is the case of <b>ftglyph</b> in the above picture.
</p></li>
<li><p>
some optional component can use module-specific interfaces
ignored by the base layer. In the above example, <b>ftmm</b>
directly accesses the Type 1 module to set/query data
</p></li>
<li><p>
a replacable component can provide a function of the high-level
API. For example, <b>ftinit</b> provides <tt>FT_Init_FreeType</tt>
to client applications.
</p></li>
</ul>
</td></tr></table></center>
<body text="#000000"
bgcolor="#ffffff">
<h1 align=center>
The Design of FreeType&nbsp;2
</h1>
<center>
<table width="75%">
<tr><td>
<table width="100%">
<tr bgcolor="#ccccee"><td>
<h1>
I. Components and APIs
</h1>
</td></tr>
</table>
<p>It's better to describe FreeType&nbsp;2 as a collection of
<em>components</em>. Each one of them is a more or less abstract part of
the library that is in charge of one specific task. We will now explicit
the connections and relationships between them.</p>
<p>A first brief description of this system of components could be:</p>
<ul>
<li>
<p>Client applications typically call the FreeType&nbsp;2
<b>high-level API</b>, whose functions are implemented in a single
component called the <em>Base Layer</em>.</p>
</li>
<li>
<p>Depending on the context or the task, the base layer then calls one
or more <em>module</em> components to perform the work. In most
cases, the client application doesn't need to know which module was
called.</p>
</li>
<li>
<p>The base layer also contains a set of routines that are used for
generic things like memory allocation, list processing, i/o stream
parsing, fixed point computation, etc. these functions can also be
called by a module at any time, and they form what is called the
<b>low-level base API</b>.</p>
</li>
</ul>
<p>This is illustrated by the following graphics (note that component
entry points are represented as colored triangles):</p>
<center>
<img src="basic-design.png"
width="394" height="313"
alt="Basic FreeType design">
</center>
<p>Now, a few additional things must be added to complete this
picture:</p>
<ul>
<li>
<p>Some parts of the base layer can be replaced for specific builds of
the library, and can thus be considered as components themselves.
This is the case for the <tt>ftsystem</tt> component, which is in
charge of implementing memory management & input stream access, as
well as <tt>ftinit</tt>, which is in charge of library initialization
(i.e. implementing the <tt>FT_Init_FreeType()</tt> function).</p>
</li>
<li>
<p>FreeType&nbsp;2 comes also with a set of <em>optional
components</em>, which can be used either as a convenience for client
applications (e.g. the <tt>ftglyph</tt> component, used to provide a
simple API to manage glyph images independently of their internal
representation), or to access format-specific features (e.g. the
<tt>ftmm</tt> component used to access and manage Multiple Masters
data in Type&nbsp;1 fonts).</p>
</li>
<li>
<p>Finally, a module is capable of calling functions provided by
another module. This is very useful to share code and tables between
several font driver modules (for example, the <tt>truetype</tt> and
<tt>cff</tt> modules both use the routines provided by the
<tt>sfnt</tt> module).</p>
</li>
</ul>
<p>Hence, a more complete picture would be:</p>
<center>
<img src="detailed-design.png"
width="390" height="429"
alt="Detailed FreeType design">
</center>
<p>Please take note of the following important points:</p>
<ul>
<li>
<p>An optional component can use either the high-level or base API.
This is the case of <tt>ftglyph</tt> in the above picture.</p>
</li>
<li>
<p>Some optional components can use module-specific interfaces ignored
by the base layer. In the above example, <tt>ftmm</tt> directly
accesses the Type&nbsp;1 module to set/query data.</p>
</li>
<li>
<p>A replacable component can provide a function of the high-level
API. For example, <tt>ftinit</tt> provides
<tt>FT_Init_FreeType()</tt> to client applications.</p>
</li>
</ul>
</td></tr>
</table>
</center>
</body>
</html>

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<!doctype html public "-//w3c//dtd html 4.0 transitional//en"
"http://www.w3.org/TR/REC-html40/loose.dtd">
<html>
<head><title>The Design of FreeType 2 - Public Objects</title>
<basefont face="Georgia, Arial, Helvetica, Geneva">
<style content="text/css">
P { text-align=justify }
H1 { text-align=center }
H2 { text-align=center }
LI { text-align=justify }
</style>
<head>
<meta http-equiv="Content-Type"
content="text/html; charset=iso-8859-1">
<meta name="Author"
content="David Turner">
<title>The Design of FreeType 2 - Public Objects</title>
</head>
<body text=#000000 bgcolor=#ffffff>
<center><table width="500"><tr><td>
<body text="#000000"
bgcolor="#ffffff">
<h1 align=center>
The Design of FreeType&nbsp;2
</h1>
<center>
<table width="75%">
<tr><td>
<table width="100%">
<tr bgcolor="#ccccee"><td>
<h1>
II. Public Objects and Classes
</h1>
</td></tr>
</table>
<p>We will now explain the abstractions provided by FreeType&nbsp;2 to
client applications to manage font files and data. As you would normally
expect, these are implemented through objects/classes.</p>
<h2>
1. Object Orientation in FreeType&nbsp;2
</h2>
<p>Though written in ANSI&nbsp;C, the library employs a few techniques,
inherited from object-oriented programming, to make it easy to extend.
Hence, the following conventions apply in the FreeType&nbsp;2 source
code:</p>
<ol>
<li>
<p>Each object type/class has a corresponding <em>structure
type</em> <b>and</b> a corresponding <em>structure pointer
type</em>. The latter is called the <em>handle type</em> for the
type/class.</p>
<p>Consider that we need to manage objects of type "foo" in
FreeType&nbsp;2. We would define the following structure and handle
types as follows:</p>
<font color="blue"><pre>
typedef struct FT_FooRec_* FT_Foo;
typedef struct FT_FooRec_
{
// fields for the "foo" class
...
} FT_FooRec;</pre>
</font>
<p>As a convention, handle types use simple but meaningful
identifiers beginning with <tt>FT_</tt>, as in <tt>FT_Foo</tt>,
while structures use the same name with a <tt>Rec</tt> suffix
appended to it ("Rec" is short for "record"). <em>Note that each
class type has a corresponding handle type</em>.</p>
</li>
<li>
<p>Class derivation is achieved internally by wrapping base class
structures into new ones. As an example, we define a "foobar" class
that is derived from "foo". We would do something like:</p>
<font color="blue"><pre>
typedef struct FT_FooBarRec_* FT_FooBar;
typedef struct FT_FooBarRec_
{
// the base "foo" class fields
FT_FooRec root;
// fields proper to the "foobar" class
...
} FT_FooBarRec;</pre>
</font>
<p>As you can see, we ensure that a "foobar" object is also a "foo"
object by placing a <tt>FT_FooRec</tt> at the start of the
<tt>FT_FooBarRec</tt> definition. It is called <b>root</b> by
convention.</p>
<p>Note that a <tt>FT_FooBar</tt> handle also points to a "foo"
object and can be typecasted to <tt>FT_Foo</tt>. Similarly, when
the library returns a <tt>FT_Foo</tt> handle to client applications,
the object can be really implemented as a <tt>FT_FooBar</tt> or any
derived class from "foo".</p>
</li>
</ol>
<p>In the following sections of this chapter, we will refer to "the
<tt>FT_Foo</tt> class" to indicate the type of objects handled through
<tt>FT_Foo</tt> pointers, be they implemented as "foo" or "foobar".</p>
<hr>
<h2>
2. The <tt>FT_Library</tt> class
</h2>
<p>This type corresponds to a handle to a single instance of the
library. Note that the corresponding structure <tt>FT_LibraryRec</tt>
is not defined in public header files, making client applications unable
to access its internal fields.</p>
<p>The library object is the <em>parent</em> of all other objects in
FreeType&nbsp;2. You need to create a new library instance before doing
anything else with the library. Similarly, destroying it will
automatically destroy all its children (i.e. faces and modules).</p>
<p>Typical client applications should call <tt>FT_Init_FreeType()</tt>
in order to create a new library object, ready to be used for further
actions.</p>
<p>Another alternative is to create a fresh new library instance by
calling the function <tt>FT_New_Library()</tt>, defined in the
<tt>&lt;freetype/ftmodule.h&gt;</tt> public header file. This function
will however return an "empty" library instance with no module
registered in it. You can "install" modules in the instance by calling
<tt>FT_Add_Module()</tt> manually.</p>
<p>Calling <tt>FT_Init_FreeType()</tt> is a lot more convenient, because
this function basically registers a set of default modules into each new
library instance. The way this list is accessed and/or computed is
determined at build time, and depends on the content of the
<tt>ftinit</tt> component. This process is explained in details later
in this document.</p>
<p>For now, one should consider that library objects are created with
<tt>FT_Init_FreeType()</tt>, and destroyed along with all children with
<tt>FT_Done_FreeType()</tt>.</p>
<hr>
<h2>
3. The <tt>FT_Face</tt> class
</h2>
<p>A face object corresponds to a single <em>font face</em>, i.e., a
specific typeface with a specific style. For example, "Arial" and
"Arial Italic" correspond to two distinct faces.</p>
<p>A face object is normally created through <tt>FT_New_Face()</tt>.
This function takes the following parameters: an <tt>FT_Library</tt>
handle, a C file pathname used to indicate which font file to open, an
index used to decide which face to load from the file (a single file may
contain several faces in certain cases), and the address of a
<tt>FT_Face</tt> handle. It returns an error code:</p>
<font color="blue"><pre>
FT_Error FT_New_Face( FT_Library library,
const char* filepathname,
FT_Long face_index,
FT_Face* face );</pre>
</font>
<p>In case of success, the function will return&nbsp;0, and the handle
pointed to by the <tt>face</tt> parameter will be set to a non-NULL
value.</p>
<p>Note that the face object contains several fields used to describe
global font data that can be accessed directly by client applications.
For example, the total number of glyphs in the face, the face's family
name, style name, the EM size for scalable formats, etc. For more
details, look at the <tt>FT_FaceRec</tt> definition in the
FreeType&nbsp;2 API Reference.</p>
<hr>
<h2>
4. The <tt>FT_Size</tt> class
</h2>
<p>Each <tt>FT_Face</tt> object <em>has</em> one or more
<tt>FT_Size</tt> objects. A <em>size object</em> is used to store data
specific to a given character width and height. Each newly created face
object has one size, which is directly accessible as
<tt>face-&gt;size</tt>.</p>
<p>The contents of a size object can be changed by calling either
<tt>FT_Set_Pixel_Sizes()</tt> or <tt>FT_Set_Char_Size()</tt>.</p>
<p>A new size object can be created with <tt>FT_New_Size()</tt>, and
destroyed manually with </tt>FT_Done_Size()</tt>. Note that typical
applications don't need to do this normally: they tend to use the
default size object provided with each <tt>FT_Face</tt>.</p>
<p>The public fields of <tt>FT_Size</tt> objects are defined in a very
small structure named <tt>FT_SizeRec</tt>. However, it is important to
understand that some font drivers define their own derivatives of
<tt>FT_Size</tt> to store important internal data that is re-computed
each time the character size changes. Most of the time, these are
size-specific <em>font hints</em>./p>
<p>For example, the TrueType driver stores the scaled CVT table that
results from the execution of the "cvt" program in a <tt>TT_Size</tt>
structure, while the Type&nbsp;1 driver stores scaled global metrics
(like blue zones) in a <tt>T1_Size</tt> object. Don't worry if you
don't understand the current paragraph; most of this stuff is highly
font format specific and doesn't need to be explained to client
developers&nbsp;:-)</p>
<hr>
<h2>
5. The <tt>FT_GlyphSlot</tt> class
</h2>
<p>The purpose of a glyph slot is to provide a place where glyph images
can be loaded one by one easily, independently of the glyph image format
(bitmap, vector outline, or anything else).</p>
<p>Ideally, once a glyph slot is created, any glyph image can be loaded
into it without additional memory allocation. In practice, this is only
possible with certain formats like TrueType which explicitly provide
data to compute a slot's maximum size.</p>
<p>Another reason for glyph slots is that they are also used to hold
format-specific hints for a given glyphs as well as all other data
necessary to correctly load the glyph.</p>
<p>The base <tt>FT_GlyphSlotRec</tt> structure only presents glyph
metrics and images to client applications, while actual implementation
may contain more sophisticated data.</p>
<p>As an example, the TrueType-specific <tt>TT_GlyphSlotRec</tt>
structure contains additional fields to hold glyph-specific bytecode,
transient outlines used during the hinting process, and a few other
things.
The Type&nbsp;1-specific <tt>T1_GlyphSlotRec</tt> structure holds glyph
hints during glyph loading, as well as additional logic used to properly
hint the glyphs when a native Type&nbsp;1 hinter is used.</p>
<p>Finally, each face object has a single glyph slot that is directly
accessible as <tt>face-&gt;glyph</tt>.</p>
<hr>
<h2>
6. The <tt>FT_CharMap</tt> class
</h2>
<p>The <tt>FT_CharMap</tt> type is used as a handle to character map
objects, or <em>charmaps</em>. A charmap is simply some sort of table
or dictionary which is used to translate character codes in a given
encoding into glyph indices for the font.</p>
<p>A single face may contain several charmaps. Each one of them
corresponds to a given character repertoire, like Unicode, Apple Roman,
Windows codepages, and other encodings.</p>
<p>Each <tt>FT_CharMap</tt> object contains a "platform" and an
"encoding" field used to identify precisely the character repertoire
corresponding to it.</p>
<p>Each font format provides its own derivative of
<tt>FT_CharMapRec</tt> and thus needs to implement these objects.</p>
<hr>
<h2>
7. Objects relationships
</h2>
<center><h1>The Design of FreeType 2</h1></center>
<p>The following diagram summarizes what we have just said regarding the
public objects managed by the library, as well as explicitely describes
their relationships</p>
<table width="100%" cellpadding=5><tr bgcolor="#ccccee"><td>
<h1>II. Public Objects and Classes</h1>
</td></tr></table>
<center>
<image alt="to be added">
</center>
<p>We will now detail the abstractions provided by FreeType 2 to
client applications to manage font files and data. As you would
normally expect, these are implemented through objects/classes.</p>
<h2>1. Object Orientation in FreeType 2:</h2>
<p>Though written in ANSI C, the library employs a few
techniques, inherited from object-oriented programming, to make
it easy to extend. Hence, the following conventions apply in
the FT2 source code:</p>
<ol>
<li><p>
each object type/class has a corresponding <em>structure type</em> <b>and</b>
a corresponding <em>structure pointer type</em>. the latter is called the
<em>handle type</em> for the type/class.</p>
<p>Consider that we need to manage objects of type "foo" in FT2.
We would define the following structure and handle types as
follow:</p>
<pre><font color="blue">
typedef struct FT_FooRec_* FT_Foo;
typedef struct FT_FooRec_
{
// fields for the "foo" class
...
} FT_FooRec;
</font></pre>
<p>As a convention, handle types use simple but meaningful identifiers
beginning with "FT_", as in "FT_Foo", while structures use the same
name with a "Rec" suffix appended to it ('Rec' is short for "record").
<em>Note that each class type has a corresponding handle type</em>.
</p>
<li><p>
class derivation is achieved internally by wrapping base class
structures into new ones. As an example, let's define a "foobar"
class that is derived from "foo". We would do something like:</p>
<pre><font color="blue">
typedef struct FT_FooBarRec_* FT_FooBar;
typedef struct FT_FooBarRec_
{
// the base "foo" class fields
FT_FooRec root;
// fields proper to the "foobar" class
...
} FT_FooBarRec;
</font></pre>
<p>As you can see, we ensure that a "foobar" object is also a "foo"
object by placing a <tt>FT_FooRec</tt> at the start of the
<tt>FT_FooBarRec</tt> definition. It is called <b>root</b>
by convention.</p>
<p>Note that a <tt>FT_FooBar</tt> handle also points to a "foo" object
and can be typecasted to <tt>FT_Foo</tt>. Similarly, when the
library handles a <tt>FT_Foo</tt> handle to client applications,
the object can be really implemented as a <tt>FT_FooBar</tt> or any
derived class from "foo".</p>
</p></li>
</ul>
<p>Note that in the following sections of this chapter, we will refer
to "the <tt>FT_Foo</tt> class" to indicate the type of objects
handled through <tt>FT_Foo</tt> pointers, be they implemented as
"foo" or "foobar".</p>
<hr>
<h2>2. The <em><b>FT_Library</b></em> class:</h2>
<p>This type corresponds to a handle to a single instance of the
library. Note that the corresponding structure <tt>FT_LibraryRec</tt>
is not defined in public header files, making client applications
unable to access its internal fields.</p>
<p>The library object is the "parent" of all other objects in FreeType 2.
You need to create a new library instance before doing anything else
with the library. Similarly, destroying it will automatically
destroy all its children (i.e. faces and modules).</p>
<p>Typical client applications should call <tt>FT_Init_FreeType</tt>,
in order to create a new library object, ready to be used for
further action.</p>
<p>Another alternative is to create a fresh new library instance
by calling the function <tt>FT_New_Library</tt>, defined in the
<tt>&lt;freetype/ftmodule.h&gt;</tt> public header file. This
function will however return an "empty" library instance with
no module registered in it. You can "install" modules in the
instance by calling <tt>FT_Add_Module</tt> manually.</p>
<p>Calling <tt>FT_Init_FreeType</tt> is a lot more convenient, because
this function basically registers a set of default modules into
each new library instance. The way this list is accessed and/or
computed is determined at build time, and depends on the content
of the <b>ftinit</b> component. This process is explained in
details later in this document.</p>
<p>For now, one should consider that library objects are created
with <tt>FT_Init_FreeType</tt>, and destroyed along with all
children with <tt>FT_Done_FreeType</tt>.</p>
<hr>
<h2>3. The <em><b>FT_Face</b></em> class:</h2>
<p>A face object corresponds to a single <em>font face</em>, i.e.
a specific typeface with a specific style. For example, "Arial"
and "Arial Italic" correspond to two distinct faces.</p>
<p>A face object is normally created through <tt>FT_New_Face</tt>.
This function takes the following parameters: a <tt>FT_Library</tt>
handle, a C file pathname used to indicate which font file to
open, an index used to decide which face to load from the file
(a single file may contain several faces in certain cases),
as well as the address of a <tt>FT_Face</tt> handle. It returns
an error code:</p>
<pre><font color="blue">
FT_Error FT_New_Face( FT_Library library,
const char* filepathname,
FT_Long face_index,
FT_Face *face );
</font></pre>
<p>in case of success, the function will return 0, and the handle
pointed to by the "face" parameter will be set to a non-NULL value.</p>
<p>Note that the face object contains several fields used to
describe global font data that can be accessed directly by
client applications. For example, the total number of glyphs
in the face, the face's family name, style name, the EM size
for scalable formats, etc.. For more details, look at the
<tt>FT_FaceRec</tt> definition in the FT2 API Reference.</p>
<hr>
<h2>4. The <em><b>FT_Size</b></em> class:</h2>
<p>Each <tt>FT_Face</tt> object <em>has</em> one or more <tt>FT_Size</tt>
objects. A <em>size object</em> is used to store data specific to a
given character width and height. Each newly created face object
has one size, which is directly accessible as <tt>face-&gt;size</tt>.</p>
<p>The content of a size object can be changed by calling either
<tt>FT_Set_Pixel_Sizes</tt> or <tt>FT_Set_Char_Size</tt>.</p>
<p>A new size object can be created with <tt>FT_New_Size</tt>, and
destroyed manually with </tt>FT_Done_Size</tt>. Note that typical
applications don't need to do this normally: they tend to use
the default size object provided with each <tt>FT_Face</tt>.</p>
<p>The public fields of <tt>FT_Size</tt> objects are defined in
a very small structure named <tt>FT_SizeRec</tt>. However, it is
important to understand that some font drivers define their own
derivatives of <tt>FT_Size</tt> to store important internal data
that is re-computed each time the character size changes. Most of
the time, these are size-specific <em>font hints</em>./p>
<p>For example, the TrueType driver stores the scaled CVT table that
results from the execution of the "cvt" program in a <tt>TT_Size</tt>,
while the Type 1 driver stores scaled global metrics (like blue zones)
in a <tt>T1_Size</tt> object. Don't worry if you don't understand
the current paragraph, most of this stuff is highly font format
specific and doesn't need to be explained to client developers :-)</p>
<hr>
<h2>5. The <em><b>FT_GlyphSlot</b></em> class:</h2>
<p>The purpose of a glyph slot is to provide a place where glyph
images can be loaded one by one easily, independently of the
glyph image format (bitmap, vector outline, or anything else).</p>
<p>Ideally, once a glyph slot is created, any glyph image can
be loaded into it without additional memory allocation. In practice,
this is only possible with certain formats like TrueType which
explicitely provide data to compute a slot's maximum size.</p>
<p>Another reason for glyph slots is that they're also used to hold
format-specific hints for a given glyphs has well as all other
data necessary to correctly load the glyph.</p>
<p>The base <tt>FT_GlyphSlotRec</tt> structure only presents glyph
metrics and images to client applications, while actual implementation
may contain more sophisticated data.</p>
<p>As an example, the TrueType-specific <tt>TT_GlyphSlotRec</tt>
structure contains additional fields to hold glyph-specific bytecode,
transient outlines used during the hinting process, and a few other
things.
the Type1-specific <tt>T1_GlyphSlotRec</tt> structure holds
glyph hints during glyph loading, as well as additional logic used
to properly hint the glyphs when a native T1 hinter is used.</p>
<p>Finally, each face object has a single glyph slot, that is directly
accessible as <tt>face-&gt;glyph</tt>.</p>
<hr>
<h2>6. The <em><b>FT_CharMap</b></em> class:</h2>
<p>Finally, the <tt>FT_CharMap</tt> type is used as a handle to
character map objects, or "charmaps" to be brief. A charmap is
simply some sort of table or dictionary which is used to translate
character codes in a given encoding into glyph indices for the
font.</p>
<p>A single face may contain several charmaps. Each one of them
corresponds to a given character repertoire, like Unicode, Apple Roman,
Windows codepages, and other ugly "standards".</p>
<p>Each <tt>FT_CharMap</tt> object contains a "platform" and an "encoding"
field used to identify precisely the character repertoire corresponding
to it.</p>
<p>Each font format provides its own derivative of <tt>FT_CharMapRec</tt>
and thus needs to implement these objects.</p>
<hr>
<h2>7. Objects relationships:</h2>
<p>The following diagram summarizes what we just said regarding the
public objects managed by the library, as well as explicitely
describes their relationships:</p>
<p>Note that this picture will be updated at the end of the next
chapter, related to <em>internal objects</em>.</p>
</td></tr></table></center>
<p>Note that this picture will be updated at the end of the next
chapter, related to <em>internal objects</em>.</p>
</td></tr>
</table>
</center>
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<tr bgcolor="#CCCCEE"><td>
<h2 align=center>
<a name="general">General questions & answers</h2>
<a name="general">General questions & answers
</h2>
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