2000-10-31 08:36:53 +01:00
|
|
|
<!doctype html public "-//w3c//dtd html 4.0 transitional//en"
|
|
|
|
|
"http://www.w3.org/TR/REC-html40/loose.dtd">
|
2000-10-30 19:55:47 +01:00
|
|
|
<html>
|
2000-10-31 08:36:53 +01:00
|
|
|
<head>
|
|
|
|
|
<meta http-equiv="Content-Type"
|
|
|
|
|
content="text/html; charset=iso-8859-1">
|
|
|
|
|
<meta name="Author"
|
|
|
|
|
content="David Turner">
|
2000-11-10 23:39:21 +01:00
|
|
|
<title>The design of FreeType 2</title>
|
2000-10-30 19:55:47 +01:00
|
|
|
</head>
|
2000-10-31 08:36:53 +01:00
|
|
|
|
|
|
|
|
<body text="#000000"
|
2000-11-10 23:39:21 +01:00
|
|
|
bgcolor="#FFFFFF"
|
|
|
|
|
link="#0000EF"
|
|
|
|
|
vlink="#51188E"
|
|
|
|
|
alink="#FF0000">
|
2000-10-31 08:36:53 +01:00
|
|
|
|
|
|
|
|
<h1 align=center>
|
|
|
|
|
The design of FreeType 2
|
|
|
|
|
</h1>
|
|
|
|
|
|
2000-11-10 23:39:21 +01:00
|
|
|
<h3 align=center>
|
|
|
|
|
Copyright 1998-2000 David Turner (<a
|
|
|
|
|
href="mailto:david@freetype.org">david@freetype.org</a>)<br>
|
|
|
|
|
Copyright 2000 The FreeType Development Team (<a
|
|
|
|
|
href="mailto:devel@freetype.org">devel@freetype.org</a>)
|
|
|
|
|
</h3>
|
|
|
|
|
|
2000-10-31 08:36:53 +01:00
|
|
|
<center>
|
2000-11-10 23:39:21 +01:00
|
|
|
<table width="65%">
|
2000-10-31 08:36:53 +01:00
|
|
|
<tr><td>
|
|
|
|
|
|
2000-11-10 23:39:21 +01:00
|
|
|
<center>
|
|
|
|
|
<table width="100%"
|
|
|
|
|
border=0
|
|
|
|
|
cellpadding=5>
|
|
|
|
|
<tr bgcolor="#CCFFCC"
|
|
|
|
|
valign=center>
|
|
|
|
|
<td align=center
|
|
|
|
|
width="30%">
|
|
|
|
|
<a href="design-4.html">Previous</a>
|
|
|
|
|
</td>
|
|
|
|
|
<td align=center
|
|
|
|
|
width="30%">
|
|
|
|
|
<a href="index.html">Contents</a>
|
|
|
|
|
</td>
|
|
|
|
|
<td align=center
|
|
|
|
|
width="30%">
|
|
|
|
|
<a href="design-6.html">Next</a>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
</table>
|
|
|
|
|
</center>
|
|
|
|
|
|
|
|
|
|
<p><hr></p>
|
2000-11-09 02:14:31 +01:00
|
|
|
|
2000-10-31 08:36:53 +01:00
|
|
|
<table width="100%">
|
|
|
|
|
<tr bgcolor="#ccccee"><td>
|
|
|
|
|
<h1>
|
|
|
|
|
IV. Module Classes
|
|
|
|
|
</h1>
|
2000-10-30 19:55:47 +01:00
|
|
|
</td></tr>
|
2000-10-31 08:36:53 +01:00
|
|
|
</table>
|
|
|
|
|
|
|
|
|
|
<p>We will now try to explain more precisely the <em>types</em> of modules
|
|
|
|
|
that FreeType 2 is capable of managing. Note that each one of them
|
|
|
|
|
is decribed with more details in the following chapters of this
|
|
|
|
|
document.</p>
|
2000-10-30 19:55:47 +01:00
|
|
|
|
|
|
|
|
<ul>
|
2000-10-31 08:36:53 +01:00
|
|
|
<li>
|
2000-10-31 21:42:18 +01:00
|
|
|
<p><em>Renderer</em> modules are used to manage scalable glyph images.
|
2000-10-31 08:36:53 +01:00
|
|
|
This means <em>transforming</em> them, computing their <em>bounding
|
|
|
|
|
box</em>, and <em>converting</em> them to either <em>monochrome</em>
|
|
|
|
|
or <em>anti-aliased</em> bitmaps</em>.</p>
|
|
|
|
|
|
|
|
|
|
<p>Note that FreeType 2 is capable of dealing with <em>any</em>
|
2000-10-31 21:42:18 +01:00
|
|
|
kind of glyph images, as long as a renderer module is provided for it.
|
2000-10-31 08:36:53 +01:00
|
|
|
The library comes by default with two renderers:</p>
|
|
|
|
|
|
|
|
|
|
<p><table cellpadding=8>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>raster</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>Supports the conversion of vectorial outlines (described by a
|
|
|
|
|
<tt>FT_Outline</tt> object) to <em>monochrome</em> bitmaps.
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>smooth</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>Supports the conversion of the same outlines to high-quality
|
|
|
|
|
<em>anti-aliased</em> pixmaps (using 256 levels of gray). Note
|
|
|
|
|
that this renderer also supports direct span generation.</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
</table></p>
|
|
|
|
|
|
|
|
|
|
<li>
|
|
|
|
|
<p><em>Font driver</em> modules are used to support one or more
|
|
|
|
|
specific font format. By default, FreeType 2 comes with the
|
|
|
|
|
following font drivers:</p>
|
|
|
|
|
|
|
|
|
|
<p><table cellpadding=8>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>truetype</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>supports TrueType font files</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>type1</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>supports Postscript Type 1 fonts, both in binary
|
|
|
|
|
(<tt>.pfb</tt>) or ASCII (<tt>.pfa</tt>) formats, including
|
|
|
|
|
Multiple Master fonts.</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>cid</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>supports Postscript CID-keyed fonts</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>cff</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>supports OpenType, CFF as well as CEF fonts (CEF is a
|
|
|
|
|
derivative of CFF used by Adobe in its SVG viewer)</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>winfonts</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>supports Windows bitmap fonts (i.e. <tt>.fon</tt> and
|
|
|
|
|
<tt>.fnt</tt>)</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
</table></p>
|
|
|
|
|
|
|
|
|
|
<p>Note that font drivers can support bitmapped or scalable glyph
|
|
|
|
|
images. A given font driver that supports Bézier outlines
|
|
|
|
|
through <tt>FT_Outline</tt> can also provide its own hinter, or rely
|
|
|
|
|
on FreeType's <tt>autohinter</tt> module.</p>
|
|
|
|
|
</li>
|
|
|
|
|
|
|
|
|
|
<li>
|
|
|
|
|
<p><em>Helper</em> modules are used to hold shared code that is often
|
|
|
|
|
used by several font drivers, or even other modules. Here are the
|
|
|
|
|
default helpers:</p>
|
|
|
|
|
|
|
|
|
|
<p><table cellpadding=8>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>sfnt</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
used to support font formats based on the <tt>SFNT</tt> storage
|
|
|
|
|
scheme: TrueType & OpenType fonts as well as other variants (like
|
|
|
|
|
TrueType fonts that only contain embedded bitmaps)
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>psnames</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
used to provide various useful functions related to glyph names
|
|
|
|
|
ordering and Postscript encodings/charsets. For example, this
|
|
|
|
|
module is capable of automatically synthetizing a Unicode charmap
|
|
|
|
|
from a Type 1 glyph name dictionary.
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>psaux</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
used to provide various useful functions related to Type 1
|
|
|
|
|
charstring decoding, as this "feature" is needed by the
|
|
|
|
|
<tt>type1</tt>, <tt>cid</tt>, and <tt>cff</tt> drivers.
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
</table></p>
|
|
|
|
|
</li>
|
|
|
|
|
|
|
|
|
|
<li>
|
|
|
|
|
<p>Finally, the <em>autohinter</em> module has a specific role in
|
|
|
|
|
FreeType 2, as it can be used automatically during glyph loading
|
|
|
|
|
to process individual glyph outlines when a font driver doesn't
|
|
|
|
|
provide it's own hinting engine.</p>
|
|
|
|
|
|
|
|
|
|
<p>This module's purpose and design is also heavily described on the
|
|
|
|
|
FreeType web site.</p>
|
|
|
|
|
</li>
|
2000-10-30 19:55:47 +01:00
|
|
|
</ul>
|
2000-10-31 08:36:53 +01:00
|
|
|
|
|
|
|
|
<p>We will now study how modules are described, then managed by the
|
|
|
|
|
library.</p>
|
|
|
|
|
|
|
|
|
|
<h3>
|
|
|
|
|
1. The <tt>FT_Module_Class</tt> structure
|
|
|
|
|
</h3>
|
|
|
|
|
|
|
|
|
|
<p>As described later in this document, library initialization is
|
|
|
|
|
performed by calling the <tt>FT_Init_FreeType()</tt> function. The
|
|
|
|
|
latter is in charge of creating a new "empty" <tt>FT_Library</tt>
|
|
|
|
|
object, then register each "default" module by repeatedly calling the
|
|
|
|
|
<tt>FT_Add_Module()</tt> function.</p>
|
|
|
|
|
|
|
|
|
|
<p>Similarly, client applications can call <tt>FT_Add_Module()</tt> any
|
|
|
|
|
time they wish in order to register a new module in the library. Let us
|
|
|
|
|
take a look at this function's declaration:</p>
|
|
|
|
|
|
|
|
|
|
<font color="blue"><pre>
|
|
|
|
|
extern FT_Error FT_Add_Module(
|
|
|
|
|
FT_Library library,
|
|
|
|
|
const FT_Module_Class* clazz );</pre>
|
|
|
|
|
</font>
|
|
|
|
|
|
|
|
|
|
<p>As one can see, this function expects a handle to a library object,
|
|
|
|
|
as well as a pointer to a <tt>FT_Module_Class</tt> structure. It
|
|
|
|
|
returns an error code. In case of success, a new module object is
|
|
|
|
|
created and added to the library. Note by the way that the module isn't
|
|
|
|
|
returned directly by the call!</p>
|
|
|
|
|
|
|
|
|
|
<p>Here the definition of <tt>FT_Module_Class</tt>, with some
|
|
|
|
|
explanation. The following code is taken from
|
|
|
|
|
<tt><freetype/ftmodule.h></tt>:</p>
|
|
|
|
|
|
|
|
|
|
<font color="blue"><pre>
|
|
|
|
|
typedef struct FT_Module_Class_
|
|
|
|
|
{
|
|
|
|
|
FT_ULong module_flags;
|
|
|
|
|
FT_Int module_size;
|
|
|
|
|
const FT_String* module_name;
|
|
|
|
|
FT_Fixed module_version;
|
|
|
|
|
FT_Fixed module_requires;
|
|
|
|
|
|
|
|
|
|
const void* module_interface;
|
|
|
|
|
|
|
|
|
|
FT_Module_Constructor module_init;
|
|
|
|
|
FT_Module_Destructor module_done;
|
|
|
|
|
FT_Module_Requester get_interface;
|
|
|
|
|
|
|
|
|
|
} FT_Module_Class;</pre>
|
|
|
|
|
</font>
|
|
|
|
|
|
|
|
|
|
<p>A description of its fields:</p>
|
|
|
|
|
|
|
|
|
|
<p><table cellpadding=8>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>module_flags</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>A set of bit flags used to describe the module's category. Valid
|
|
|
|
|
values are:</p>
|
|
|
|
|
|
|
|
|
|
<ul>
|
|
|
|
|
<li>
|
|
|
|
|
<tt>ft_module_font_driver</tt> if the module is a font driver
|
|
|
|
|
</li>
|
|
|
|
|
<li>
|
|
|
|
|
<tt>ft_module_renderer</tt> if the module is a renderer
|
|
|
|
|
</li>
|
|
|
|
|
<li>
|
|
|
|
|
<tt>ft_module_hinter</tt> if the module is an auto-hinter
|
|
|
|
|
</li>
|
|
|
|
|
<li>
|
|
|
|
|
<tt>ft_module_driver_scalable</tt> if the module is a font
|
|
|
|
|
driver supporting scalable glyph formats
|
|
|
|
|
</li>
|
|
|
|
|
<li>
|
|
|
|
|
<tt>ft_module_driver_no_outlines</tt> if the module is a font
|
|
|
|
|
driver supporting scalable glyph formats that <em>cannot</em> be
|
|
|
|
|
described by an <tt>FT_Outline</tt> object
|
|
|
|
|
</li>
|
|
|
|
|
<li>
|
|
|
|
|
<tt>ft_module_driver_has_hinter</tt> if the module is a font
|
|
|
|
|
driver that provides its own hinting scheme/algorithm
|
|
|
|
|
</li>
|
|
|
|
|
</ul>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>module_size</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>An integer that gives the size in <em>bytes</em> of a given
|
|
|
|
|
module object. This should <em>never</em> be less than
|
|
|
|
|
<tt>sizeof(FT_ModuleRec)</tt>, but can be more if the module needs
|
|
|
|
|
to sub-class the base <tt>FT_ModuleRec</tt> class.</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>module_name</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>The module's internal name, coded as a simple ASCII
|
|
|
|
|
C string. There can't be two modules with the same name
|
|
|
|
|
registered in a given <tt>FT_Library</tt> object. However,
|
|
|
|
|
<tt>FT_Add_Module()</tt> uses the <tt>module_version</tt> field to
|
|
|
|
|
detect module upgrades and perform them cleanly, even at
|
|
|
|
|
run-time.</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>module_version</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>A 16.16 fixed float number giving the module's major and minor
|
|
|
|
|
version numbers. It is used to determine whether a module needs to
|
|
|
|
|
be upgraded when calling <tt>FT_Add_Module()</tt>.</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>module_requires</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>A 16.16 fixed float number giving the version of FreeType 2
|
|
|
|
|
that is required to install this module. The default value is
|
|
|
|
|
0x20000 for FreeType version 2.0</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>module_requires</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>Most modules support one or more "interfaces", i.e. tables of
|
|
|
|
|
function pointers. This field is used to point to the module's main
|
|
|
|
|
interface, if there is one. It is a short-cut that prevents users
|
|
|
|
|
of the module to call "get_interface()" each time they need to
|
|
|
|
|
access one of the object's common entry points.</p>
|
|
|
|
|
|
|
|
|
|
<p>Note that is is optional, and can be set to NULL. Other
|
|
|
|
|
interfaces can also be accessed through the <tt>get_interface()</tt>
|
|
|
|
|
field.</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>module_init</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>A pointer to a function used to initialize the fields of a fresh
|
|
|
|
|
new <tt>FT_Module</tt> object. It is called <em>after</em> the
|
|
|
|
|
module's base fields have been set by the library, and is generally
|
|
|
|
|
used to initialize the fields of <tt>FT_ModuleRec</tt>
|
|
|
|
|
subclasses.</p>
|
|
|
|
|
|
|
|
|
|
<p>Most module classes set it to NULL to indicate that no extra
|
|
|
|
|
initialization is necessary.</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>module_done</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>A pointer to a function used to finalize the fields of a given
|
|
|
|
|
<tt>FT_Module</tt> object. Note that it is called <em>before</em>
|
|
|
|
|
the library unsets the module's base fields, and is generally used
|
|
|
|
|
to finalize the fields of <tt>FT_ModuleRec</tt> subclasses.</p>
|
|
|
|
|
|
|
|
|
|
<p>Most module classes set it to NULL to indicate that no extra
|
|
|
|
|
finalization is necessary</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
<tr valign=top>
|
|
|
|
|
<td>
|
|
|
|
|
<tt>get_interface</tt>
|
|
|
|
|
</td>
|
|
|
|
|
<td>
|
|
|
|
|
<p>A pointer to a function used to request the address of a given
|
|
|
|
|
module interface. Set it to NULL if you don't need to support
|
|
|
|
|
additional interfaces but the main one.</p>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
</table></p>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<h3>
|
|
|
|
|
2. The <tt>FT_Module</tt> type
|
|
|
|
|
</h3>
|
|
|
|
|
|
|
|
|
|
<p>The <tt>FT_Module</tt> type is a handle (i.e. a pointer) to a given
|
|
|
|
|
module object/instance, whose base structure is given by the internal
|
|
|
|
|
<tt>FT_ModuleRec</tt> type. We will intentionally <em>not</em> describe
|
|
|
|
|
this structure here, as there is no point to look so far into the
|
|
|
|
|
library's design.</p>
|
|
|
|
|
|
|
|
|
|
<p>When <tt>FT_Add_Module</tt> is called, it first allocates a new
|
|
|
|
|
module instance, using the <tt>module_size</tt> class field to determine
|
|
|
|
|
its byte size. The function initializes the root <tt>FT_ModuleRec</tt>
|
|
|
|
|
field, then calls the class-specific initializer <tt>module_init</tt>
|
|
|
|
|
when this field is not set to NULL.</p>
|
|
|
|
|
|
|
|
|
|
<p>Note that the library defines several sub-classes of
|
|
|
|
|
<tt>FT_ModuleRec</tt>, which are, as you could have guessed:</p>
|
|
|
|
|
|
|
|
|
|
<ul>
|
|
|
|
|
<li><p><tt>FT_Renderer</tt> for renderer modules</p>
|
|
|
|
|
<li><p><tt>FT_Driver</tt> for font driver modules</p>
|
|
|
|
|
<li><p><tt>FT_AutoHinter</tt> for the auto-hinter</p>
|
|
|
|
|
</ul>
|
|
|
|
|
|
|
|
|
|
<p>Helper modules use the base <tt>FT_ModuleRec</tt> type. We will
|
|
|
|
|
describe these classes in the next chapters.</p>
|
|
|
|
|
|
2000-11-10 23:39:21 +01:00
|
|
|
<p><hr></p>
|
|
|
|
|
|
|
|
|
|
<center>
|
|
|
|
|
<table width="100%"
|
|
|
|
|
border=0
|
|
|
|
|
cellpadding=5>
|
|
|
|
|
<tr bgcolor="#CCFFCC" valign=center>
|
|
|
|
|
<td align=center
|
|
|
|
|
width="30%">
|
|
|
|
|
<a href="design-4.html">Previous</a>
|
|
|
|
|
</td>
|
|
|
|
|
<td align=center
|
|
|
|
|
width="30%">
|
|
|
|
|
<a href="index.html">Contents</a>
|
|
|
|
|
</td>
|
|
|
|
|
<td align=center
|
|
|
|
|
width="30%">
|
|
|
|
|
<a href="design-6.html">Next</a>
|
|
|
|
|
</td>
|
|
|
|
|
</tr>
|
|
|
|
|
</table>
|
|
|
|
|
</center>
|
2000-11-09 02:14:31 +01:00
|
|
|
|
2000-10-31 08:36:53 +01:00
|
|
|
</td></tr>
|
|
|
|
|
</table>
|
|
|
|
|
</center>
|
2000-11-10 23:39:21 +01:00
|
|
|
|
2000-10-30 19:55:47 +01:00
|
|
|
</body>
|
|
|
|
|
</html>
|
