kmx git

Commit 31fa0bdcd8ad8bf6f6c29f25d13817d7b45f837e

2000-10-30T18:55:47
added page 5 of design documentation
diff --git a/docs/design/design-5.html b/docs/design/design-5.html
new file mode 100644
index 0000000..3e366ab
--- /dev/null
+++ b/docs/design/design-5.html
@@ -0,0 +1,324 @@
+<html>
+<head><title>FreeType 2 - Modules</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>
+<body text=#000000 bgcolor=#ffffff>
+
+<center><table width="500"><tr><td>
+
+<center><h1>FreeType 2 Design - Modules Classes</h1></center>
+
+<table width="100%" cellpadding=5><tr bgcolor="#ccccee"><td>
+<h1>IV. Module Classes</h1>
+</td></tr></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>
+
+<ul>
+  <li><p>
+  <b>renderer</b> modules are used to manage scalable glyph images. This
+     means <em>transforming</em> them, computing their <em>bounding box</em>,
+     and <em>converting</em> them to either <em>monochrome or anti-aliased
+     bitmaps</em>.</p>
+
+  <p>Note that FreeType 2 is capable of dealing with <em>any</em> kind of
+     glyph images, as long as a renderer module is provided for it. The
+     library comes by default with two renderers:</p>
+
+  <center><table cellpadding=5><tr valign=top><td>
+  <p><b><tt>raster</tt></b></p>
+  </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></p>
+
+  <p><b><tt>smooth</tt></b></p>
+  </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></center>
+
+
+  <li><p>
+  <b>font driver</b> modules are used to support one or more specific
+  font format. By default, FT2 comes with the following font drivers:</p>
+
+  <center><table cellpadding=5><tr valign=top><td>
+  <p><tt><b>truetype</b></tt></p>
+  </td><td>
+  <p>supports TrueType font files</p>
+  </td></tr><tr valign=top><td>
+
+  <p><tt><b>type1</b></tt></p>
+  </td><td>
+  <p>supports Postscript Type 1 fonts, both in binary (.pfb) or ASCII
+  (.pfa) formats, including Multiple Master fonts.</p>
+  </td></tr><tr valign=top><td>
+
+  <p><tt><b>cid</b></tt></p>
+  </td><td>
+  <p>supports Postscript CID-keyed fonts</p>
+  </td></tr><tr valign=top><td>
+
+  <p><tt><b>cff</b></tt></p>
+  </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>
+
+  <p><tt><b>winfonts</b></tt></p>
+  </td><td>
+  <p>supports Windows bitmap fonts (i.e. ".FON" and ".FNT").</p>
+  </td></tr>
+
+  </td></tr></table></center>
+
+  <p>Note that font drivers can support bitmapped or scalable glyph
+     images. A given font driver that supports bezier outlines through
+     the <tt>FT_Outline</tt> can also provide its own hinter, or rely
+     on FreeType's <b>autohinter</b> module.
+  </p></li>
+
+  <li><p>
+  <b>helper</b> 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>
+
+  <table cellpadding=5><tr valign=top><td>
+  <b><tt>sfnt</tt></b>
+  </td><td>
+  used to support font formats based on the "<tt>SFNT</tt>"
+  storage scheme. This means TrueType & OpenType fonts as
+  well as other variants (like TrueType fonts that only
+  contain embedded bitmaps).
+  </td></tr><tr valign=top><td>
+  
+  <b><tt>psnames</tt></b>
+  </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>
+
+  <b><tt>psaux</tt></b>
+  </td><td>
+  used to provide various useful functions related to Type 1
+  charstring decoding, as this "feature" is needed by the
+  <b>type1</b>, <b>cid</b> and <b>cff</b> drivers.
+  </td></tr></table></center>
+  </p></li>
+
+
+  <li><p>
+  finally, the <b>autohinter</b> 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>
+</ul>
+
+<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 initialisation 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's take a look at this function's declaration:</p>
+
+<pre><font color="blue">
+    extern FT_Error  FT_Add_Module( FT_Library              library,
+                                    const FT_Module_Class*  clazz );
+</font></pre>
+
+<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>Let's study the definition of <tt>FT_Module_Class</tt>, and explain it
+   a bit. The following code is taken from
+   <tt>&lt;freetype/ftmodule.h&gt;</tt>:</p>
+
+<pre><font color="blue">
+  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;
+</font></pre>
+
+<p>here's a description of its fields:</p>
+
+<center><table cellpadding=5><tr valign=top><td>
+<p><b>module_flags</b></p>
+</td><td>
+<p>this is a set of bit flags used to describe the module's
+category. Valid values are:</p>
+  <ul>
+    <li><p>
+    <b>ft_module_font_driver</b> if the module is a font driver
+    </p></li>
+
+    <li><p>
+    <b>ft_module_renderer</b> if the module is a renderer
+    </p></li>
+
+    <li><p>
+    <b>ft_module_hinter</b> if the module is an auto-hinter
+    </p></li>
+
+    <li><p>
+    <b>ft_module_driver_scalable</b> if the module is a font
+    driver supporting scalable glyph formats.
+    </p></li>
+
+    <li><p>
+    <b>ft_module_driver_no_outlines</b> if the module is a
+    font driver supporting scalable glyph formats that <em>cannot</em>
+    be described by a <tt>FT_Outline</tt> object
+    </p></li>
+
+    <li><p>
+    <b>ft_module_driver_has_hinter</b> if the module is a font
+    driver that provides its own hinting scheme/algorithm
+    </p></li>
+  </ul>
+</td></tr><tr valign=top><td>
+
+<p><b>module_size</b></p>
+</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 when the module
+needs to sub-class the base <tt>FT_ModuleRec</tt> class.</p>
+</td></tr><tr valign=top><td>
+
+<p><b>module_name</b></p>
+</td><td>
+<p>this is 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 <b>module_version</b> field to detect module upgrades
+and perform them cleanly, even at run-time.</p>
+</td></tr><tr valign=top><td>
+
+<p><b>module_version</b></p>
+</td><td>
+<p>a 16.16 fixed float number giving the module's major and minor
+   version numbers. It is used to determine wether a module needs
+   to be upgraded when calling <tt>FT_Add_Module</tt>.</p>
+</td></tr><tr valign=top><td>
+
+<p><b>module_requires</b></p>
+</td><td>
+<p>a 16.16 fixed float number giving the version of FreeType 2 that
+   is required to install this module. By default, should be 0x20000
+   for FreeType 2.0</p>
+</td></tr><tr valign=top><td>
+
+<p><b>module_requires</b></p>
+</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,
+where there is one. It's 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 <b>get_interface</b> field.</p>
+</td></tr><tr valign=top><td>
+
+<p><b>module_init</b></p>
+</td><td>
+<p>this is a pointer to a function used to initialise 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
+initialise the fields of <tt>FT_ModuleRec</tt> subclasses.</p>
+
+<p>Most module classes set it to NULL to indicate that no extra
+initialisation is necessary</p>
+</td></tr><tr valign=top><td>
+
+<p><b>module_done</b></p>
+</td><td>
+<p>this is a pointer to a function used to finalise 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
+finalisation is necessary</p>
+</td></tr><tr valign=top><td>
+
+<p><b>get_interface</b></p>
+</td><td>
+<p>this is 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><tr valign=top><td>
+
+</td></tr></table></center>
+
+
+<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's not point to look so far
+   in the library's design.</p>
+
+<p>When <tt>FT_Add_Module</tt> is called, it first allocate a new
+   module instance, using the <tt><b>module_size</b></tt> class
+   field to determine its byte size. The function initializes
+   a the root <tt>FT_ModuleRec</tt> fields, then calls
+   the class-specific initializer <tt><b>module_init</b></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 now detail these classes in the next chapters</p>
+
+</td></tr></table></center>
+</body>
+</html>
kc3-lang/freetype

Commit 31fa0bdcd8ad8bf6f6c29f25d13817d7b45f837e
