forked from minhngoc25a/freetype2
removing obsolete files:
the design of FT2 has evolved considerably since these documents were written, and it's better not to include them in order to avoid confusion among users of the library..
This commit is contained in:
David Turner
parent
8bb45ec8fb
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<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="Author" content="David Turner">
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||||
<meta name="GENERATOR" content="Mozilla/4.5 [fr] (Win98; I) [Netscape]">
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<title>FreeType 2 Internals - I/O Frames</title>
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<basefont face="Georgia, Arial, Helvetica, Geneva">
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<style content="text/css">
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P { text-align=justify }
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||||
H1 { text-align=center }
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||||
H2 { text-align=center }
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||||
LI { text-align=justify }
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||||
</style>
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</head>
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||||
|
||||
<body text="#000000"
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||||
bgcolor="#FFFFFF"
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||||
link="#0000EF"
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||||
vlink="#51188E"
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alink="#FF0000">
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|
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<center>
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<h1>FreeType 2.0 Build System</h1></center>
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|
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<center>
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<h3>
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© 2000 David Turner (<a href="fichier :///david@freetype.org">david@freetype.org</a>)<br>
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© 2000 The FreeType Development Team
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(<a href="mailto:devel@freetype.org">devel@freetype.org</a>)
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</h3></center>
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<center><table width=650><tr><td>
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||||
<p><hr WIDTH="100%"></p>
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<h2>Table of Content</h2>
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<center><table><tr><td>
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<p><font size="+1"><a href="#introduction">Introduction</a></font></p>
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||||
<p><font size="+1"><a href="#features">I. Features & Background</a></font></p>
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<ul>
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<li><a href="#features-1">1. Convenience, not Requirement</a>
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<li><a href="#features-2">2. Compiler and platform independence</a>
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<li><a href="#features-3">3. Uses GNU Make</a>
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||||
<li><a href="#features-4">4. Automatic host platform detection</a>
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<li><a href="#features-5">5. User-selectable builds</a>
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<li><a href="#features-6">6. Robustness</a>
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<li><a href="#features-7">7. Simple modules management</a>
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</ul>
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<p><font size="+1"><a href="#overview">II. Overview of the build process</a></font></p>
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<ul>
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<p><li><a href="#overview-1">1. Build setup</a>
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<ul>
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<li><a href="#overview-1-a">a. Default build setup</a>
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<li><a href="#overview-1-b">b. Selecting another build configuration</a>
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</ul>
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</p>
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<li><a href="#overview-2">2. Library compilation</a>
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</ul>
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<p><font size="+1"><a href="#setup">III. Build setup details</a></font></p>
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<p><font size="+1"><a href="#compilation">IV. Library compilation details</a></font></p>
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<ul>
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<li><a href="#compilation-1">a. Compiling the <tt>ftsystem</tt> component</a>
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<li><a href="#compilation-2">b. Compiling the base layer and optional components</a>
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<li><a href="#compilation-3">c. Compiling the modules</a>
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<li><a href="#compilation-4">d. Compiling the <tt>ftinit</tt> component</a>
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</ul>
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</ul>
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</td></tr></table></center>
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<hr><a name="introduction">
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<h2>Introduction:</h2>
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<p>This document describes the new build system that was introduced
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with FreeType 2.</p>
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<p><hr></p>
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<a name="features">
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<h2>I. Features and Background:</h2>
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<p>The FreeType 2 build system is a set of Makefiles and sub-Makefiles that
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are used to build the library on a very large variety of systems easily.
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One of its main features are the following:</p>
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<a name="features-1">
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<h3>1. Convenience, not Requirement</h3>
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<ul>
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<p>Even though the build system is rather sophisticated, it simply is a
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convenience that was written simply to allow the compilation of the
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FreeType 2 library on as many platforms as possible, as easily as
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possible. However, it is not a requirement and the library can be
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compiled manually or in a graphical IDE without using it, with minimal
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efforts</p>
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<p>(for more information on this topic, see the <tt>BUILD</tt>
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document that comes with your release of FreeType, in its <em>Detailed
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Compilation Guide</em> section).</p>
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</ul>
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|
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<a name="features-2">
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<h3>2. Compiler and platform independence</h3>
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<ul>
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<p>The FreeType 2 build system can be used with any compiler, on any platform.
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It is independent of object file suffix, executable file suffix, directory
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separator convention (i.e. "/" or "\"), and compiler flags for path
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inclusion, macro definition, output naming, ansi compliance, etc..</p>
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|
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<p>Supporting a new compiler is trivial and only requires writing a minimal
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configuration sub-makefile that contains several Makefile variables
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definitions that are later used by the rest of the build system. This is
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described in details later in the document.</p>
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</ul>
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|
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<a name="features-3">
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<h3>3. Uses GNU Make</h3>
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<ul>
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<p>The build system works <em>exclusively</em> with <b>GNU Make</b>. Reason
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is that it is the only make utility that has all the features required to
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implement the build system as described below. Moreover, it is already
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ported to hundreds of various distinct platforms and is widely and
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freely available.</p>
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<p>It also uses the native command line shell. <em>You thus
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don't need a Unix-like shell on your platform</em>.
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For example, FreeType 2 already compiles on Unix, Dos, Windows
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and OS/2 right "out of the box" (assuming you have GNU Make
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installed).</p>
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|
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<p>Finally, note that the build system is <em>specifically</em> designed
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for gnu make and will <em>fail</em> with any other make tool. We have
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<em>no plans</em> to support a different tools, as you'll rapidly
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understand by reading this document or looking at the sub-makefiles
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themselves.</p>
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</ul>
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|
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<a name="features-4">
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<h3>4. Automatic host platform detection</h3>
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<ul>
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<p>When you launch the build system for the first time, by simply invoking
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GNU make in the top-level directory, it automatically tries to detect
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your current platform in order to choose the best configuration
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sub-makefile available. It then displays what it found. If everything
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is ok, you can then launch compilation of the library, by invoking make
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a second time.</p>
|
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|
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<p>The following platforms are currently automatically detected:</p>
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<ul>
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<li>Dos (plain-dos, windows in Dos mode, or Dos session under OS/2)
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<li>Windows 95, 98 + Windows NT (a.k.a win32)
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<li>OS/2
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<li>Unix (uses Autoconf/Automake)
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</ul>
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<p>Note that adding support for a new platform requires writing a minimal
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number of very small files, and simply putting them in a new sub-directory
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of <tt>freetype2/config</tt>.</p>
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</ul>
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|
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<a name="features-5">
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<h3>5. User-selectable builds</h3>
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<ul>
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<p>The platform auto-detection rules try to setup the build for a default
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compiler (<em>gcc</em> for most platforms), with default build options
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for the library (which normally is
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<em>"all features enable, no debugging"</em>), as well as the default
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list of modules (which is <em>"all modules in <tt>freetype2/src</tt>"</em>)</p>
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|
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<p>There are cases where it is important to specify a different compiler,
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different build options or simply a different module list. The FreeType 2
|
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build system is designed in such a way that all of this is easily possible
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from the command line, <em>without having to touch a single file</em>.
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The latter is crucial when dealing with projects that need specific
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builds of the library without modifying a single file from the FreeType
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distribution.</p>
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|
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<p>The exact mechanism and implementation to do this is described later in
|
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this document. It allows, for example, to compile FreeType with any of
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the following compilers on Win32: gcc, Visual C++, Win32-LCC.</p>
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||||
</ul>
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|
||||
<a name="features-6">
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||||
<h3>6. Robustness</h3>
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||||
<ul>
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<p>The build system uses a single top-level Makefile that includes
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one or more sub-makefiles to build the entire library (base layer
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plus all modules).
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<font color="red">
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To understand why this is important, we <em>strongly</em> recommend
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||||
the following article to all of our readers:</font></p>
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||||
<p>
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||||
<center>
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||||
<font size="+2"><a href="http://www.pcug.org.au/~millerp/rmch/recu-make-cons-harm.html">
|
||||
Recursive Make Considered Dangerous
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</a>
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||||
</font>
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</center>
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||||
</p>
|
||||
|
||||
<p>As an example, here's a short list of files that make up the
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build system. Note that each sub-makefile contains rules corresponding
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to a very specific purpose, and that they all use the "<tt>.mk</tt>"
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suffix:</p>
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||||
<ul>
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<li><tt>freetype2/Makefile</tt>
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<li><tt>freetype2/config/detect.mk</tt>
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<li><tt>freetype2/config/freetype.mk</tt>
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<li><tt>freetype2/config/<em><system></em>/detect.mk</tt>
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||||
<li><tt>freetype2/src/<em><module></em>/rules.mk</tt>
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<li><tt>freetype2/src/<em><module></em>/module.mk</tt>
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||||
</ul>
|
||||
|
||||
</ul>
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|
||||
<a name="features-7">
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<h3>7. Simple Module Management</h3>
|
||||
<ul>
|
||||
<p>FreeType 2 has a very modular design, and is made of a core
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<em>base layer</em> that provides its high-level API as well as
|
||||
generic services used by one or more <em>modules</em>.
|
||||
|
||||
Most modules are used to support a specific font format (like TrueType
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or Type 1), and they are called <em>font drivers</em>. However, some of
|
||||
them do not support font files directly, but rather provide helper
|
||||
services to the font drivers.</p>
|
||||
|
||||
<p>FreeType 2 is designed so that adding modules at run-time is possible
|
||||
and easy. Similarly, we expect many more modules to come in the near
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||||
future and wanted a build system that makes such additions to the
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source package itself dead easy.
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||||
|
||||
Indeed, all source code (base + modules) is located in the
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<tt>freetype2/src</tt> directory hierarchy. And the build system is
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||||
capable of re-generating automatically the list of known modules
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from the contents of this directory. Hence, adding a new font driver
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to the FreeType sources simply requires to:</p>
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||||
|
||||
<ul>
|
||||
<li><p>Add a new sub-directory to <tt>freetype2/src</tt>
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||||
<li><p>Re-launch the build system</p>
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||||
</ul>
|
||||
|
||||
<p>There is thus no need to edit a source file</p>
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||||
</ul>
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||||
<p><hr><p>
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||||
<a name="overview">
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<h2>II. Overview of the build process(es):</h2>
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||||
|
||||
<p>Before describing in details how the build system works, it is essential
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||||
to give a few examples of how it's used. This section presents
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||||
what's the build process is to the typical developer:</p>
|
||||
|
||||
<p>Compiling the library is normally done in two steps: the first one
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||||
configures the build according to the current platform and possible
|
||||
additional parameters, while the second simply compiles the library with
|
||||
the information gathered in the configuration step.</p>
|
||||
|
||||
<a name="overview-1">
|
||||
<h3>1. Build Setup</h3>
|
||||
|
||||
<a name="overview-1-a">
|
||||
<h4>a. Default build setup</h4>
|
||||
<ul>
|
||||
<p>To configure the build, simply invoke gnu make from the top-level FreeType
|
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directory. This will launch a series of rules that will detect your current
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||||
host platform, and choose a configuration file for you. It will then display
|
||||
what it found. For example, here's the output of typing the command "make"
|
||||
on a win32 platform (assuming this calls GNU make):</p>
|
||||
|
||||
<pre><font color="blue">
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||||
<font color="purple">C:\FreeType> make</font>
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||||
|
||||
FreeType build system -- automatic system detection
|
||||
|
||||
The following settings are used:
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||||
|
||||
platform win32
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||||
compiler gcc
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||||
configuration directory ./config/win32
|
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configuration rules ./config/win32/w32-gcc.mk
|
||||
|
||||
If this does not correspond to your system or settings please remove the file
|
||||
'config.mk' from this directory then read the INSTALL file for help.
|
||||
|
||||
Otherwise, simply type 'make' again to build the library.
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||||
|
||||
<font color="purple">C:\FreeType></font>
|
||||
</font></pre>
|
||||
|
||||
<p>Note that this step copies the selected configuration file (here
|
||||
<tt>./config/win32/w32-gcc.mk</tt>) to <em>the current directory</em>, under
|
||||
the name <tt><b>config.mk</b></tt>. This file contains data that is used
|
||||
to drive the library compilation of the second step. It correspond to
|
||||
the platform and compiler selected by the auto-detection phase.</p>
|
||||
|
||||
<p>Note that you can re-generate the <tt><b>config.mk</b></tt> file anytime
|
||||
by invoking <tt>make setup</tt> whenever you need it, even when the file is
|
||||
already present in the current directory.</p>
|
||||
|
||||
<p>Finally, if your platform is not correctly detected, the build system will
|
||||
display and use configuration information for the virtual "ansi" platform.
|
||||
</p>
|
||||
</ul>
|
||||
<a name="overview-1-b">
|
||||
<h4>b. Selecting another build configuration</h4>
|
||||
<ul>
|
||||
<p>You may not be really satisfied by the configuration file selected by the
|
||||
auto-detection routines. Typically, you might be using a compiler that is
|
||||
not the default one for your platform. It is however possible to re-launch
|
||||
the build setup phase with an additional argument, used to specify a
|
||||
different compiler/config file. For example, you can type the following
|
||||
commands on Win32 systems:</p>
|
||||
|
||||
<p align=center><table width="80%" cellpadding=10><tr valign=top><td>
|
||||
<p><b><tt>make setup</tt></b></p>
|
||||
</td><td>
|
||||
<p>re-run the platform detection phase, and select the default compiler for it.
|
||||
On Win32, this is <em>gcc</em>.</p>
|
||||
</td></tr><tr valign=top><td>
|
||||
<p><b><tt>make setup visualc</tt></b></p>
|
||||
</td><td>
|
||||
<p>re-run the platform detection phase, and select a config file that
|
||||
corresponds to the <em>Visual C++</em> compiler</p>
|
||||
</td></tr><tr valign=top><td>
|
||||
<p><b><tt>make setup lcc</tt></b></p>
|
||||
</td><td>
|
||||
<p>re-run the platform detection phase, and select a config file that
|
||||
corresponds to the <em>Win32-LCC</em> compiler</p>
|
||||
</td></tr></table>
|
||||
</p>
|
||||
|
||||
<p>Note that a specific configuration is selected with a command that
|
||||
looks like : <tt><b>make setup <em>compiler</em></b></tt>,
|
||||
where the <em><tt>compiler</tt></em> keywords depends on the platform.
|
||||
Moreover, each one of them corresponds to a specific configuration
|
||||
sub-makefile that is copied as <b><tt>config.mk</tt></b> in the current
|
||||
directory.</p>
|
||||
</ul>
|
||||
|
||||
|
||||
<a name="overview-2">
|
||||
<h3>2. Library compilation</h3>
|
||||
|
||||
<p>Once you're satisfied with the version of <b><tt>config.mk</tt></b> that
|
||||
has been copied to your current directory, you can simply re-invoke
|
||||
gnu make <em>with no arguments</em>. The top-level Makefile will
|
||||
automatically detect the config sub-makefile in the current directory,
|
||||
and use it to drive the library compilation. The latter can be seen
|
||||
as a series of different steps decribed here:</p>
|
||||
|
||||
<ul>
|
||||
<li><p><b>Compiling the <tt>ftsystem</tt> component</b><br><ul>
|
||||
It encapsulates all low-level operations (memory management +
|
||||
i/o access) for the library. Its default version, located in
|
||||
<tt>./src/base/ftsystem.c</tt> uses the ANSI C library but
|
||||
system-specific implementations are also available to
|
||||
improve performance (e.g. memory-mapped files on Unix).
|
||||
</ul></p>
|
||||
|
||||
<li><p><b>Compiling the <em>base layer</em> and optional components</b><br><ul>
|
||||
They provide the library's high-level API as well as various useful
|
||||
routines for client applications. Many features of the base layer can
|
||||
be activated or not depending on a configuration file named
|
||||
<tt>ftoption.h</tt>
|
||||
</ul></p>
|
||||
|
||||
<li><p><b>Compiling the <em>modules</em></b><br><ul>
|
||||
Each module is used to support a specific font format (it is then
|
||||
called a <em>font driver</em>), or to provide helper services to
|
||||
the drivers (e.g. the auto-hinter). They are all located in
|
||||
sub-directories of <tt>./src</tt>, like <tt>./src/truetype</tt>,
|
||||
<tt>./src/type1</tt>.
|
||||
</ul></p>
|
||||
|
||||
<li><p><b>Compiling the <tt>ftinit</tt> component</b><br><ul>
|
||||
This one is in charge of implementing <tt>FT_Init_FreeType</tt>,
|
||||
the library initialisation routine. It also selects what modules
|
||||
are activated when a new library instance is created.
|
||||
</ul></p>
|
||||
</ul>
|
||||
<p><hr><p>
|
||||
<a name="setup">
|
||||
<h2>II. Details of the build setup.</h2>
|
||||
|
||||
<p>When the top-level <tt>Makefile</tt> is invoked, it looks for a
|
||||
file named <b><tt>config.mk</tt></b> in the <em>current directory</em>.
|
||||
If this file is found, it is used directly to build the library
|
||||
(skip to <a href="library">Section III</a> for details then).</p>
|
||||
|
||||
<p>Otherwise, the file <b><tt>./config/detect.mk</tt></b> is included
|
||||
by the top-level <tt>Makefile</tt> and parsed. Its purpose is to drive the
|
||||
platform-detection phase, by:</p>
|
||||
|
||||
<ul>
|
||||
<li><p>Defining the <tt>PLATFORM</tt> variable, which indicates
|
||||
what the currently detected platform is. It is initially
|
||||
set to the default value "<tt><b>ansi</b></tt>".
|
||||
</p>
|
||||
|
||||
<li><p>Searching for a <tt>detect.mk</tt> file in <em>all
|
||||
subdirectories</em> of <b><tt>./config</tt></b>.
|
||||
Each such file is included and parsed. Each of these files must
|
||||
try to detect if the host platform is a system it knows
|
||||
about. If so, it changes the value of the <tt>PLATFORM</tt> variable
|
||||
accordingly.</p>
|
||||
|
||||
<li><p>Copying the selected configuration submakefile to the current directory
|
||||
under the name <tt><b>config.mk</b></tt>.</p>
|
||||
</ul>
|
||||
<p>This is illustrated by the following graphics :</p>
|
||||
<p><center>
|
||||
<img src="platform-detection.png" border=0>
|
||||
</center></p>
|
||||
|
||||
<p>Each system-specific <b><tt>detect.mk</tt></b> works as follows:</p>
|
||||
<ul>
|
||||
<li><p>It checks that the value of <tt>PLATFORM</tt> is currently set
|
||||
to <b>ansi</b>, which indicates that no platform was detected
|
||||
for now. If this isn't true, it doesn't do anything</p>
|
||||
|
||||
<li><p>Otherwise, it runs a series of test to see wether it is on a
|
||||
system it knows about. Here are a few examples of tests:</p>
|
||||
|
||||
<p><center><table width="80%" cellpadding=5><tr valign=top><td>
|
||||
<em><b>Unix</b></em>
|
||||
</td><td>
|
||||
<p>checks for a file named <tt>/sbin/init</tt>, and runs, when it found
|
||||
it, a 'configure' script to generate the relevant config sub-makefile</p>
|
||||
</td></tr><tr valign=top><td>
|
||||
<em><b>Dos</b></em>
|
||||
</td><td>
|
||||
<p>checks for the <tt>COMSPEC</tt> environment variable, then tries to
|
||||
run the "<tt>ver</tt>" command on the current shell to check that there
|
||||
is a "Dos" substring in its output; if not, it tries to find the
|
||||
substring "<tt>MDOS\COMMAND</tt>" in <tt>COMSPEC</tt>, which indicates
|
||||
a Dos session under OS/2.</p>
|
||||
</td></tr><tr valign=top><td>
|
||||
<em><b>Win32</b></em>
|
||||
</td><td>
|
||||
<p>if the environment variable <tt>OS</tt> is defined and has the value
|
||||
<tt>Windows_NT</tt>, or if <tt>COMSPEC</tt> is defined and the
|
||||
"<tt>ver</tt>" returns a string that contains <tt>Windows</tt> in it,
|
||||
we're on a Win32 system.</p>
|
||||
</td></tr></table></center>
|
||||
</p>
|
||||
|
||||
<li><p>It sets the value of <tt>PLATFORM</tt> to a new value corresponding
|
||||
to its platform.</p>
|
||||
|
||||
<li><p>It then tries to select a configuration
|
||||
sub-makefile, depending on the current platform and any optional
|
||||
make target (like "visualc" or "devel", etc..). Note that it can
|
||||
even generate the file, as on Unix through Autoconf/Automake.</p>
|
||||
|
||||
<li><p>It copies the selected configuration sub-makefile to the current
|
||||
directory, under the name <tt><b>config.mk</b></tt>
|
||||
</ul>
|
||||
|
||||
<p>If one wants to support a new platform in the build system, it simply needs
|
||||
to provide:</p>
|
||||
|
||||
<ul>
|
||||
<li>A new subdirectory, in <tt>./config</tt>, with a file named
|
||||
<tt>detect.mk</tt> in it, containing relevant checks for the system.
|
||||
|
||||
<li>One or more configuration sub-makefiles that will get copied to
|
||||
<tt>config.mk</tt> at build setup time. You can use the one in
|
||||
<tt>./config/ansi/config.mk</tt> as a template.
|
||||
</ul>
|
||||
|
||||
<p>Similary, supporting a new compiler on an existing system simply means:</p>
|
||||
<ul>
|
||||
<li>Writing a new config sub-makefile that contains definitions used to
|
||||
specify the compiler and flags for the build.
|
||||
|
||||
<li>Change your <tt>./config/<em>system</em>/detect.mk</tt> to recognize
|
||||
a new optional build target that will copy your new config sub-makefile
|
||||
instead of the default one.
|
||||
</ul>
|
||||
|
||||
|
||||
<p><hr><p>
|
||||
<h2>III. Details of the library compilation.</h2>
|
||||
|
||||
<p>When the top-level Makefile is invoked, it looks for a file named
|
||||
<tt>config.mk</tt> in the current directory. If one is found, it
|
||||
defines the <tt>BUILD_FREETYPE</tt> variable, then includes and parses it.
|
||||
The structure of this file is the following:
|
||||
</p>
|
||||
|
||||
<ul>
|
||||
<li><p>First, it defines a series of Make variables that describe
|
||||
the host environment, like the compiler, compilation flags,
|
||||
object file suffix, the directory where all object files are
|
||||
placed, etc..</p>
|
||||
|
||||
<li><p>If <tt>BUILD_FREETYPE</tt> is defined, it includes the file
|
||||
<tt><b>./config/freetype.mk</b></tt>, which is in charge of
|
||||
defining all the rules used to build the library object files.
|
||||
(The test is useful to use the <tt>config.mk</tt> file to
|
||||
compile other projects that rely on FreeType 2, like its
|
||||
demonstration programs).</p>
|
||||
|
||||
<li><p>Finally, it defines the rule(s) used to link FreeType 2 object files
|
||||
into a library file (e.g. <tt>libfreetype.a</tt>, <tt>freetype.lib</tt>,
|
||||
<tt>freetype.dll</tt>, ...). Unfortunately, the command line interface of link tools is
|
||||
a <em>lot less</em> standardized than those of compilers, which
|
||||
explains why this rule must be defined in the system-specific
|
||||
<tt>config.mk</tt>.</p>
|
||||
</ul>
|
||||
|
||||
<p>The following is an explanation of what <tt><b>./config/freetype.mk</b></tt>
|
||||
does to build the library objects:
|
||||
</p>
|
||||
|
||||
<h4>a. Include paths</h4>
|
||||
<ul>
|
||||
<p>To avoid namespace pollution, the <tt><em>freetype</em></tt> directory prefix
|
||||
is used to include all public header files of the library. This means
|
||||
that a client application will typically use lines like:</p>
|
||||
|
||||
<pre><font color="blue">
|
||||
#include <freetype/freetype.h>
|
||||
#include <freetype/ftglyph.h>
|
||||
</font></pre>
|
||||
|
||||
<p>to include one the FreeType 2 public header files. <tt>freetype.mk</tt>
|
||||
uses a variable named <tt><b>INCLUDES</b></tt> to hold the inclusion
|
||||
paths list, and thus starts by adding <tt>./include</tt> to it. However,
|
||||
nothing prevents
|
||||
|
||||
<p><tt>freetype.mk</tt> uses a variable named <tt><b>INCLUDES</b></tt>
|
||||
to hold directory inclusion-path to be used when compiling the library.
|
||||
It always add <tt>./include</tt> to this variable, which means
|
||||
|
||||
</ul>
|
||||
|
||||
<h4>b. Configuration header files:</h4>
|
||||
<ul>
|
||||
<p>Three header files used to configure the compilation of the
|
||||
FreeType 2 library. Their default versions are all located in the
|
||||
directory <tt><b>./include/freetype/config/</b></tt>, even though
|
||||
project specific versions can be provided on a given build, as
|
||||
described later:</p>
|
||||
|
||||
<ul>
|
||||
<p><b><tt>#include <freetype/config/ftoption.h></tt></b><br><ul>
|
||||
This file contains a set of configuration macro definitions that
|
||||
can be toggled to activate or deactivate certain features of the
|
||||
library. By changing one of these definitions, it is possible to
|
||||
compile <em>only the features that are needed</em> for a specific
|
||||
project. Note that by default, all options are enabled.
|
||||
<br><br>
|
||||
You might need to provide an alternative version of <tt>ftoption.h</tt>
|
||||
for one of your own projects.
|
||||
</ul></p>
|
||||
|
||||
<p><b><tt>#include <freetype/config/ftconfig.h></tt></b><br><ul>
|
||||
This file includes <tt>ftoption.h</tt> but also contains some automatic
|
||||
macro definitions used to indicate some important system-specific
|
||||
features (e.g: word size in bytes, DLL export prefix macros, etc..).
|
||||
<br><br>
|
||||
You shouldn't normally need to change or provide an alternative
|
||||
version of this file.
|
||||
</ul></p>
|
||||
|
||||
|
||||
<p><b><tt>#include <freetype/config/ftmodule.h></tt></b><br><ul>
|
||||
This file is very special, as it is normally machine-generated, and
|
||||
used by the <tt>ftinit</tt> component that is described below. To
|
||||
understand it, one must reminds that FreeType 2 has an extremely
|
||||
modular design and that it's possible to change, <em>at run-time</em>,
|
||||
the modules it's using. The <tt>ftmodule.h</tt> file simply contains
|
||||
the list of modules that are registered with each new instance of
|
||||
the library.
|
||||
<br><br>
|
||||
Note that the file can be re-generated automatically by invoking
|
||||
<tt>make setup</tt> from the top-level directory. The re-generated
|
||||
list contains all the modules that were found in subdirectories of
|
||||
<tt>./src</tt>.
|
||||
</ul></p>
|
||||
</ul>
|
||||
|
||||
<p>Note that we strongly advise you to avoid modifying the config files
|
||||
within the FreeType 2 source directory hierarchy. Rather, it's possible
|
||||
to specify alternative versions through the help of a build-specific
|
||||
include path that is include before <tt>./include</tt> in the inclusion
|
||||
path.</p>
|
||||
|
||||
<p>For example, imagine that your platform, named <em>foo</em>, needs a
|
||||
specific version of <tt>ftoption.h</tt>
|
||||
</ul>
|
||||
|
||||
<h4>a. Compiling the <b><tt>ftsystem</tt></b> component:</h4>
|
||||
<ul>
|
||||
<p>FreeType 2 encapsulates all low-level operations (i.e. memory management
|
||||
and i/o access) within a single component called <tt><b>ftsystem</b></tt>.
|
||||
Its default implementation uses the <em>ANSI C Library</em> and is located
|
||||
in <tt>./src/base/ftsystem.c</tt>.</p>
|
||||
|
||||
<p>However, some alternate, system-specific, implementations of
|
||||
<tt>ftsystem</tt> are provided with the library in order to support more
|
||||
efficient and advanced features. As an example, the file
|
||||
<tt>./config/unix/ftsystem.c</tt> is an implementation that
|
||||
uses memory-mapped files rather than the slow ANSI <tt>fopen</tt>,
|
||||
<tt>fread</tt> and <tt>fseek</tt>, boosting performance significantly.</p>
|
||||
|
||||
<p>The build system is thus capable of managing alternate implementations
|
||||
of <tt>ftsystem</tt></p>
|
||||
</ul>
|
||||
|
||||
<h4>b. Compiling the base layer and optional components:</h4>
|
||||
<ul>
|
||||
<p>The high-level API of the library is provided by a component called the
|
||||
<em>base layer</em>, whose source is located in <tt>./src/base</tt>. This
|
||||
directory also contains one or more components that are optional, i.e.
|
||||
that are not required by the library but provide valuable routines to
|
||||
client applications.</p>
|
||||
|
||||
<p>The features of the base library and other components are selected through
|
||||
a single configuration file named
|
||||
<tt><b>./include/freetype/config/ftoption.h</b></tt>. It contains a list
|
||||
of commented configuration macro definitions, that can be toggled to
|
||||
activate or de-activate a certain feature or component at build time.</p>
|
||||
|
||||
<p>For example, the code in <tt>./src/base/ftdebug.c</tt> will be compiled
|
||||
only if one of these two macros are defined in <tt>ftoption.h</tt>:
|
||||
<tt>FT_DEBUG_LEVEL_ERROR</tt> or <tt>FT_DEBUG_LEVEL_TRACE</tt></p>
|
||||
</ul>
|
||||
|
||||
<h4>c. Compiling the modules:</h4>
|
||||
<ul>
|
||||
<p>Once the base layer is completed, the build system starts to compile each
|
||||
additional module independently. These are simply defined as all source
|
||||
code located in a sub-directory of <tt>./src</tt> that contains a file
|
||||
named <tt><b>rules.</b></tt>, for example:
|
||||
<tt>src/sfnt</tt>, <tt>src/truetype</tt>, <tt>src/type1</tt>, ...</p>
|
||||
|
||||
<p>The <tt><b>rules.</b></tt> file simply contains directives used by the
|
||||
build system to compile the corresponding module into a single object
|
||||
file.</p>
|
||||
</ul>
|
||||
|
||||
<h4>d. Compiling the <b><tt>ftinit</tt></b> component:</h4>
|
||||
<ul>
|
||||
<p>The file <tt><b>./src/base/ftinit.c</b></tt> is special because it is used
|
||||
to implement the library initialisation function <tt>FT_Init_FreeType</tt>.
|
||||
</p>
|
||||
</ul>
|
||||
|
||||
<p>Typically, you will end up with all object files, as well as the
|
||||
corresponding library file, residing in the <tt>freetype2/obj</tt>
|
||||
directory.</p>
|
||||
|
||||
|
||||
<h3>1. Purpose of the configuration sub-makefile</h3>
|
||||
|
||||
<h3>2. Managing module dependencies</h3>
|
||||
|
||||
<h3>3. </h3>
|
||||
|
||||
<p><hr><p>
|
||||
<a name="modules">
|
||||
<h2>IV. Managing the modules list</h2>
|
||||
|
||||
<p><hr><p>
|
||||
The build system features some important points, which are all detailed
|
||||
in the following sections:<p>
|
||||
<ul>
|
||||
<li><b>Automatic host platform detection</b><br>
|
||||
The first time the top <tt>Makefile</tt> is invoked, it will
|
||||
run a series of rules to detect your platform. It will then
|
||||
create a system-specific configuration sub-Makefile in the
|
||||
current directory, called <b><tt>config.mk</tt></b>. You can now
|
||||
invoke the top <tt>Makefile</tt> a second time to compile the
|
||||
library directly.
|
||||
<p>
|
||||
The configuration sub-makefile can be regenerated any time
|
||||
by invoking "<tt>make setup</tt>", which will re-run the
|
||||
detection rules even if a <tt>config.mk</tt> is already present.
|
||||
<p>
|
||||
|
||||
|
||||
<li><b>User-selectable builds</b><br>
|
||||
<p>
|
||||
|
||||
|
||||
|
||||
<li><b>Automatic detection of font drivers</b><br>
|
||||
FreeType is made of a "base" layer that invokes several
|
||||
separately-compiled modules. Each module is a given
|
||||
font driver, in charge of supporting a given font format.
|
||||
<p>
|
||||
The list of font drivers is located in the file
|
||||
"<tt>freetype2/config/<em>system</em>/ftmodule.h</tt>", however
|
||||
it can be regenerated on-demand. Adding a new module to the
|
||||
FreeType source tree is thus as easy as:<p>
|
||||
<ul>
|
||||
<li>create a new directory in "<tt>freetype2/src</tt>" and
|
||||
put the new driver's source code and sub-makefiles there.
|
||||
<p>
|
||||
|
||||
<li>invoke the top <tt>Makefile</tt> with target
|
||||
"<tt>modules</tt>" (as in "<tt>make modules</tt>"),
|
||||
as this will automatically regenerate the list of
|
||||
available drivers by detecting the new directory and
|
||||
its content.
|
||||
</ul>
|
||||
<p>
|
||||
</ul>
|
||||
</ul>
|
||||
|
||||
<p><hr><p>
|
||||
|
||||
<h2>II. Host Platform Detection</h2>
|
||||
<ul>
|
||||
When the top-level <tt>Makefile</tt> is invoked, it looks for a
|
||||
file named <tt>config.mk</tt> in the current directory. If this
|
||||
file is found, it is used to build the library
|
||||
(see <a href="library">Section III</a>).
|
||||
<p>
|
||||
Otherwise, the file <tt>freetype2/config/detect.mk</tt> is included
|
||||
and parsed. Its purpose is to:<p>
|
||||
<ul>
|
||||
<li>Define the <tt>PLATFORM</tt> variable, which indicates
|
||||
what is the currently detected platform. It is initially
|
||||
set to the default value "<tt>ansi</tt>".
|
||||
<p>
|
||||
|
||||
<li>It searches for a <tt>detect.mk</tt> file in all
|
||||
subdirectories of <tt>freetype2/config</tt>. Each such
|
||||
file is included and parsed. Each of these files must
|
||||
try to detect if the host platform is a system it knows
|
||||
about. If so, it changes the value of the <tt>PLATFORM</tt>
|
||||
accordingly.
|
||||
</ul>
|
||||
<p>
|
||||
This is illustrated by the following graphics :<p>
|
||||
<center>
|
||||
<img src="platform-detection.png" border=0>
|
||||
</center>
|
||||
<p>
|
||||
Note that each system-specific <tt>detect.mk</tt> is in charge
|
||||
of copying a valid configuration makefile to the current directory
|
||||
(i.e. the one where <tt>make</tt> was invoked), depending on the
|
||||
current targets. For example, the Win32 <tt>detect.mk</tt> will
|
||||
be able to detect a "<tt>visualc</tt>" or "<tt>lcc</tt>" target,
|
||||
as described in section I. Similarly, the OS/2 <tt>detect.mk</tt>
|
||||
can detect targets like "<tt>borlandc</tt>", "<tt>watcom</tt>"
|
||||
or "<tt>visualage</tt>", etc..
|
||||
</ul>
|
||||
|
||||
<p><hr><p>
|
||||
|
||||
<h2>III. Building the library</h2>
|
||||
<ul>
|
||||
When the top-level <tt>Makefile</tt> is invoked and that it finds
|
||||
a <tt>config.mk</tt> file in the current directory, it defines
|
||||
the variable <tt>BUILD_FREETYPE</tt>, then includes and parses the
|
||||
configuration sub-makefile.
|
||||
<p>
|
||||
The latter defines a number of important variables that describe
|
||||
the compilation process to the build system. Among other things:<p>
|
||||
<ul>
|
||||
<li>the extension to be used for object files and library files
|
||||
(i.e. <tt>.o</tt> and <tt>.a</tt> on Unix, <tt>.obj</tt>
|
||||
and <tt>.lib</tt> on Dos-Windows-OS/2, etc..).
|
||||
<p>
|
||||
|
||||
<li>the directory where all object files will be stored
|
||||
(usually <tt>freetype2/obj</tt>), as well as the one
|
||||
containing the library file (usually the same as for
|
||||
objects).
|
||||
<p>
|
||||
|
||||
<li>the command line compiler, and its compilation flags for
|
||||
indicating a new include path (usually "<tt>-I</tt>"),
|
||||
a new macro declaration (usually "<tt>-D</tt>") or
|
||||
the target object file (usually "<tt>-o </tt>")
|
||||
</ul>
|
||||
<p>
|
||||
Once these variable are defined, <tt>config.mk</tt> test for the
|
||||
definition of the <tt>BUILD_FREETYPE</tt> variable. If it exists,
|
||||
the makefile then includes "<tt>freetype2/config/freetype.mk</tt>"
|
||||
which contains the rules required to compile the library.
|
||||
<p>
|
||||
Note that <tt>freetype.mk</tt> also scans the subdirectories of
|
||||
"<tt>freetype2/src</tt>" for a file called "<tt>rules.mk</tt>".
|
||||
Each <tt>rules.mk</tt> contains, as it names suggests, the rules
|
||||
required to compile a given font driver or module.
|
||||
<p>
|
||||
Once all this parsing is done, the library can be compiled. Usually,
|
||||
each font driver is compiled as a standalone object file (e.g.
|
||||
<tt>sfnt.o</tt>, <tt>truetype.o</tt> and <tt>type1.o</tt>).
|
||||
<p>
|
||||
This process can be illustrated by the following graphics:<p>
|
||||
<center>
|
||||
<img src="library-compilation.png" border=0>
|
||||
</center>
|
||||
<p>
|
||||
</ul>
|
||||
|
||||
<p><hr><p>
|
||||
|
||||
<h2>IIV. Managing the list of modules</h2>
|
||||
<ul>
|
||||
The makefile <tt>freetype.mk</tt> only determines how to compile
|
||||
each one of the modules that are located in the sub-directories of
|
||||
<tt>freetype2/src</tt>.
|
||||
<p>
|
||||
However, when the function <tt>FT_Init_FreeType</tt> is invoked at
|
||||
the start of an application, it must create a new <tt>FT_Library</tt>
|
||||
object, and registers all <em>known</em> font drivers to it by
|
||||
repeatly calling <tt>FT_Add_Driver</tt>.
|
||||
<p>
|
||||
The list of <em>known</em> drivers is located in the file
|
||||
"<tt>freetype2/config/<em>system</em>/ftmodule.h</tt>", and is used
|
||||
exclusively by the internal function <tt>FT_Default_Drivers</tt>. The
|
||||
list in <tt>ftmodule.h</tt> must be re-generated each time you add
|
||||
or remove a module from <tt>freetype2/src</tt>.
|
||||
<p>
|
||||
This is normally performed by invoking the top-level <tt>Makefile</tt>
|
||||
with the <tt>modules</tt> target, as in:<p>
|
||||
<ul>
|
||||
<tt>make modules</tt>
|
||||
</ul>
|
||||
<p>
|
||||
This will trigger a special rule that will re-generate
|
||||
<tt>ftmodule.h</tt>. To do so, the Makefile will parse all module
|
||||
directories for a file called "<tt>module.mk</tt>". Each
|
||||
<tt>module.mk</tt> is a tiny sub-Makefile used to add a single
|
||||
module to the driver list.
|
||||
<p>
|
||||
This is illustrated by the following graphics:<p>
|
||||
<center>
|
||||
<img src="drivers-list.png" border=0>
|
||||
</center>
|
||||
<p>
|
||||
Note that the new list of modules is displayed in a very human-friendly
|
||||
way after a "<tt>make modules</tt>". Here's an example with the current
|
||||
source tree (on 11 Jan 2000):<p>
|
||||
<ul><pre>
|
||||
Regenerating the font drivers list in ./config/unix/ftmodule.h
|
||||
* driver: sfnt ( pseudo-driver for TrueType & OpenType formats )
|
||||
* driver: truetype ( Windows/Mac font files with extension *.ttf or *.ttc )
|
||||
* driver: type1 ( Postscript font files with extension *.pfa or *.pfb )
|
||||
-- done --
|
||||
</pre></ul>
|
||||
|
||||
</ul>
|
||||
|
||||
<p><hr><p>
|
||||
|
||||
<h2>V. Building the demonstration programs</h2>
|
||||
<ul>
|
||||
Several demonstration programs are located in the
|
||||
"<tt>freetype2/demos</tt>" directory hierarchy. This directory also
|
||||
includes a tiny graphics sub-system that is able to blit glyphs to
|
||||
a great variety of surfaces, as well as display these in various
|
||||
graphics libraries or windowed environments.
|
||||
<p>
|
||||
This section describes how the demonstration programs are compiled,
|
||||
using the configuration <tt>freetype2/config.mk</tt> and their own
|
||||
<tt>freetype2/demos/Makefile</tt>.
|
||||
<p>
|
||||
To compile the demonstration programs, <em>after the library</em>,
|
||||
simply go to <tt>freetype2/demos</tt> then invoke GNU make with no
|
||||
arguments.
|
||||
<p>
|
||||
The top-level Makefile will detect the <tt>config.mk</tt> in the
|
||||
<em>upper</em> directory and include it. Because it doesn't define
|
||||
the <tt>BUILD_FREETYPE</tt> variable, this will not force the
|
||||
inclusion of <tt>freetype2/config/freetype.mk</tt> as described in
|
||||
the previous section.
|
||||
<p>
|
||||
the <tt>Makefile</tt> will then include the makefile called
|
||||
"<tt>freetype2/demos/graph/rules.mk</tt>". The graphics <tt>rules.mk</tt>
|
||||
defines the rules required to compile the graphics sub-system.
|
||||
<p>
|
||||
Because the graphics syb-system is also designed modularly, it is able
|
||||
to use any number of "modules" to display surfaces on the screen.
|
||||
The graphics modules are located in the subdirectories of
|
||||
<tt>freetype2/demos/config</tt>. Each such directory contains a file
|
||||
named <tt>rules.mk</tt> which is in charge of:<p>
|
||||
<ul>
|
||||
<li>detecting wether the corresponding graphics library is
|
||||
available at the time of compilation.
|
||||
<p>
|
||||
<li>if it is, alter the compilation rules to include the graphics
|
||||
module in the build of the <tt>graph</tt> library.
|
||||
</ul>
|
||||
<p>
|
||||
When the <tt>graph</tt> library is built in <tt>demos/obj</tt>, the
|
||||
demonstration programs executables are generated by the top-level
|
||||
Makefile.
|
||||
<p>
|
||||
This is illustrated by the following graphics:<p>
|
||||
<center>
|
||||
<img src="demo-programs.png" border="0">
|
||||
</center>
|
||||
</ul>
|
||||
|
||||
<p><hr>
|
||||
</td></tr></table></center>
|
||||
</body>
|
||||
</html>
|
||||
|
||||
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|
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|
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|
|
@ -1,791 +0,0 @@
|
|||
<!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="David Turner">
|
||||
<meta name="GENERATOR" content="Mozilla/4.5 [fr] (Win98; I) [Netscape]">
|
||||
<title>FreeType 2 Internals</title>
|
||||
</head>
|
||||
<body>
|
||||
|
||||
<body text="#000000"
|
||||
bgcolor="#FFFFFF"
|
||||
link="#0000EF"
|
||||
vlink="#51188E"
|
||||
alink="#FF0000">
|
||||
|
||||
<center>
|
||||
<h1>
|
||||
FreeType 2.0 Internals</h1></center>
|
||||
|
||||
<center>
|
||||
<h2>
|
||||
Version 1.2</h2></center>
|
||||
|
||||
<center>
|
||||
<h3>
|
||||
© 1999-2000 David Turner (<a href="fichier :///david@freetype.org">david@freetype.org</a>)<br>
|
||||
© 1999-2000 The FreeType Development Team (<a href="fichier :///devel@freetype.org">devel@freetype.org</a>)</h3></center>
|
||||
|
||||
<p><br>
|
||||
<hr WIDTH="100%">
|
||||
<br>
|
||||
<h2>Introduction:</h2>
|
||||
|
||||
<p>This document describes in great deatils the internals of FreeType 2.
|
||||
It is a must read for porters and developers alike. Its purpose is to
|
||||
|
||||
present the
|
||||
<blockquote>This document describes in great details the internals of the
|
||||
FreeType 2.0 library. It is a must read for porters and developers alike.
|
||||
Its purpose is to present the engine's objects, their roles and interactions.
|
||||
It is assumed that the <b><i>FreeType Glyph Conventions</i></b> document
|
||||
has been read.
|
||||
<p>We advise porters to also read the <b><i>FreeType Porting Guide</i></b>
|
||||
after this document. Would-be hackers and maintainers are of course encouraged
|
||||
to read the <b><i>FreeType Coding Conventions</i></b> document too. The
|
||||
development of a new driver is described in more details in the <b><i>FreeType
|
||||
Driver HowTo</i></b> document.</blockquote>
|
||||
|
||||
<p><br>
|
||||
<hr WIDTH="100%">
|
||||
<h2>
|
||||
I. Overview :</h2>
|
||||
|
||||
<blockquote>
|
||||
<h3>
|
||||
1. Features (and what's new) :</h3>
|
||||
|
||||
<blockquote>FreeType 2.0 has a number of important new features that were
|
||||
not found in the 1.x releases :
|
||||
<br>
|
||||
<blockquote><b>font-format independent API</b>
|
||||
<br>FreeType 2.0 is able to support any kind of font format, be it fixed
|
||||
or scalable, through the use of pluggable "font drivers". These drivers
|
||||
can be added or replaced at run time, while applications use a new font
|
||||
format-independent API.
|
||||
<p><b>advanced stream caching</b>
|
||||
<br>2.0 is able to control the number of concurrently opened streams when
|
||||
using fonts. It is thus possible to open dozens or hundreds of font faces
|
||||
without running out of system resources.
|
||||
<p><b>real reentrancy support</b>
|
||||
<br>It is now possible to use FreeType as a shared library with no static
|
||||
data in a multi-threaded environment. The synchronization model has also
|
||||
been simplified in order to make font driver writing easier. Of course,
|
||||
you can build FreeType with no thread support to get a smaller library.
|
||||
<p><b>support for cubic beziers and 17-levels anti-aliasing</b>
|
||||
<br>The FreeType scan-line converter (a.k.a. raster) now supports cubic
|
||||
bezier arcs seamlessly. It also provides a new anti-aliasing mode which
|
||||
uses a palette of 17 levels of grays.
|
||||
<br> </blockquote>
|
||||
It also features the following :
|
||||
<blockquote><b>performance improvements :</b>
|
||||
<br>The FreeType raster has been optimized, and the generation of anti-aliased
|
||||
pixmaps is now 60% faster than in the 1.x release. Moreover, the TrueType
|
||||
bytecode interpreter has been profiled and greatly optimised.
|
||||
<p><b>easier portability</b>
|
||||
<br>Porting and configuring FreeType is now much easier. A single file
|
||||
must be provided for system-specific operations (like memory, i/o, thread
|
||||
management), and a single configuration header is used to select the build
|
||||
you need.
|
||||
<br> </blockquote>
|
||||
</blockquote>
|
||||
|
||||
<h3>
|
||||
2. Architecture :</h3>
|
||||
|
||||
<blockquote>The engine is now split in several parts, which are :
|
||||
<h4>
|
||||
a. The base layer :</h4>
|
||||
|
||||
<blockquote>This part contains all the font-format independent features
|
||||
of the engine which are :
|
||||
<ul>
|
||||
<li>
|
||||
computations/scaling</li>
|
||||
|
||||
<li>
|
||||
list processing</li>
|
||||
|
||||
<li>
|
||||
outline processing</li>
|
||||
|
||||
<li>
|
||||
scan-line converter</li>
|
||||
|
||||
<li>
|
||||
stream manager</li>
|
||||
|
||||
<li>
|
||||
base object classes</li>
|
||||
|
||||
<li>
|
||||
debugging & traces</li>
|
||||
|
||||
<li>
|
||||
high-level API functions</li>
|
||||
|
||||
<li>
|
||||
low-level system object (memory, i/o, threads)</li>
|
||||
</ul>
|
||||
</blockquote>
|
||||
|
||||
<h4>
|
||||
b. The font drivers :</h4>
|
||||
|
||||
<blockquote>Each font format is managed with the use of a single font driver
|
||||
object. The base layer is able to manage several drivers, and these can
|
||||
be easily added, removed or upgraded at runtime. Each driver has the following
|
||||
features and functions :
|
||||
<ul>
|
||||
<li>
|
||||
auto-check font format when opening a font resource (i.e. file)</li>
|
||||
|
||||
<li>
|
||||
access, load and/or extract all tables and data from the font file</li>
|
||||
|
||||
<li>
|
||||
grid-fit/hint the glyph outlines (in the case of scalable formats like
|
||||
TrueType or Type1)</li>
|
||||
|
||||
<li>
|
||||
provide extensions to access font format-specific data and tables from
|
||||
the font file</li>
|
||||
</ul>
|
||||
Note that FreeType 2.0 is a font service. Its purpose is to provide a unified
|
||||
API for all kinds of fonts and extract individual glyph images and metrics.
|
||||
However, it does not render text itself, as this operation is left to the
|
||||
developer, or to higher-level libraries built on top of FreeType. Here
|
||||
are a few features that are thus not implemented :
|
||||
<blockquote>1) Text string rendering
|
||||
<br>2) Glyph bitmap/outline caching for improved performance
|
||||
<br>3) Synthetic fonts (i.e. italicising, emboldening, underlining)
|
||||
<br>4) Contextual glyph substitution and other advanced layout processes</blockquote>
|
||||
Note that features 1 through 3 should be provided by the SemTex library,
|
||||
which may soon become part of the standard FreeType distribution.</blockquote>
|
||||
</blockquote>
|
||||
</blockquote>
|
||||
|
||||
<p><br>
|
||||
<hr WIDTH="100%">
|
||||
<h2>
|
||||
II. Design :</h2>
|
||||
|
||||
<blockquote>
|
||||
<h3>
|
||||
1. Objects :</h3>
|
||||
|
||||
<blockquote>They are several kinds of objects in FreeType, which can be
|
||||
described as follows :
|
||||
<blockquote><b>Base objects</b>
|
||||
<br>These objects do not relate directly to font data, but to the way it
|
||||
is organised and managed. It is the basic core and provides functions that
|
||||
are heavily used by each font driver. Examples are the resource objects,
|
||||
used to describe font files, the system object used to manage low-level
|
||||
system operations, or the raster object, used to convert vector outlines
|
||||
into bitmaps or anti-aliased pixmaps. Most of the base objects are not
|
||||
directly visible for client applications of FreeType.
|
||||
<p><b>Font objects</b>
|
||||
<br>The font objects directly model the data as it is found in font files.
|
||||
The root classes implemented in the base layer like <tt>FT_Face</tt>, <tt>FT_Size</tt>,
|
||||
<tt>FT_GlyphSlot</tt>,
|
||||
must be derived in each font driver.</blockquote>
|
||||
Objects are defined in the files "<tt>base/freetype.h</tt>" and "<tt>base/ftobjs.h</tt>".
|
||||
The former contains all the public object definitions usable by client
|
||||
applications. The latter contains private definitions used by the rest
|
||||
of the base layer and each font driver.</blockquote>
|
||||
|
||||
<h3>
|
||||
2. List management</h3>
|
||||
|
||||
<blockquote>The "<tt>base/ftlist.c</tt>" component a very simple doubly-linked
|
||||
list facility which is used by the rest of the engine to create and process
|
||||
lists, including iteration and finalisation. The definition of the list
|
||||
node and functions are placed in the "<tt>base/freetype.h</tt>" to let
|
||||
client applications access listed objects as they like.
|
||||
<p>The base list type is <tt>FT_List</tt>, which links nodes of type <tt>FT_ListNode</tt>
|
||||
together.
|
||||
<br> </blockquote>
|
||||
|
||||
<h3>
|
||||
3. Limited encapsulation</h3>
|
||||
|
||||
<blockquote>Unlike what happened in the 1.x releases, the <tt>FT_Face</tt>,
|
||||
<tt>FT_Size</tt>,
|
||||
<tt>FT_GlyphSlot</tt> and <tt>FT_CharMap</tt> types are no longer blind
|
||||
pointers to opaque types. Rather, the corresponding structures are now
|
||||
public (and defined in "<tt>base/freetype.h</tt>", see <tt>FT_FaceRec</tt>,
|
||||
<tt>FT_SizeRec</tt>,
|
||||
etc..) in order to let client applications read directly the various object
|
||||
attributes they're interested in.
|
||||
<p>This breaks encapsulation of implementation, famed by OOP, but was chosen
|
||||
because:
|
||||
<br>
|
||||
<ul>
|
||||
<li>
|
||||
it simplifies a lot the work of client applications and libraries which
|
||||
don't need to perform a function call everytime they want to read one important
|
||||
object attribute (nor does it force them to cache these attributes in their
|
||||
own structures).</li>
|
||||
</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
It reduces greatly the API, as many <tt>FT_Get_XXX</tt> functions are avoided.</li>
|
||||
</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
Higher-level libraries are able to access data directly. When it
|
||||
is used frequently, they don't need to cache it in their own structures.</li>
|
||||
</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
It is possible to tightly link FreeType objects with higher-level ones,
|
||||
in a clearer and more efficient way. This is very important when one wants
|
||||
to write a C++ wrapper or a text rendering library on top of FreeType (actually,
|
||||
both projects were performed in an earlier version of FreeType 2.0 which
|
||||
featured classic encapsulation through get/set methods. The resulting code
|
||||
was ugly and slow. Moving to a limited encapsulation approach simplified
|
||||
so many things that the compiled code size was reduced by a factor of two
|
||||
!).</li>
|
||||
</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
Finally, the API and font object structures were designed after the creation
|
||||
of two scalable font drivers and one bitmap font driver. They are now very
|
||||
stable and the public (visible) attributes are not going to change.</li>
|
||||
</ul>
|
||||
</blockquote>
|
||||
</blockquote>
|
||||
|
||||
<p><br>
|
||||
<hr WIDTH="100%">
|
||||
<h2>
|
||||
III. Base objects :</h2>
|
||||
|
||||
<blockquote>This section describes the FreeType base object classes :
|
||||
<br>
|
||||
<h3>
|
||||
1. System objects :</h3>
|
||||
|
||||
<blockquote>The system class is in charge of managing all low-level and
|
||||
system-specific operations. This means simply memory management, i/o access
|
||||
and thread synchronisation. It is implemented by the "<tt>ftsys.c</tt>"
|
||||
component, whose source must be located in the configuration directory
|
||||
when building FreeType. (e.g. "<tt>lib/arch/ansi/ftsys.c</tt>" for an ANSI
|
||||
build, "<tt>lib/arch/unix/ftsys.c</tt>" for a Unix one, etc..).
|
||||
<p>Porting FreeType 2.0 really means providing a new implementation of
|
||||
<tt>ftsys</tt>
|
||||
(along with a few configuration file changes). Note however that its interface
|
||||
is common to all ports, and located in "<tt>base/ftsys.h</tt>".</blockquote>
|
||||
|
||||
<h3>
|
||||
2. Resources and Streams:</h3>
|
||||
|
||||
<blockquote>The concepts of files as storages, and files as streams has
|
||||
been separated for FreeType 2.0. The "<b><i>resource</i></b>" concept was
|
||||
introduced while the "<b><i>stream</i></b>" one has been redefined. Here
|
||||
is how they work together :
|
||||
<ul>
|
||||
<li>
|
||||
a "<b>resource</b>" is an object which models a file, seen as a storage.
|
||||
There are several classes of resources, which differ usually in two ways
|
||||
: the way their data is accessed by applications, and the way they're named
|
||||
within the system.</li>
|
||||
</ul>
|
||||
|
||||
<ul>For example, when parsing files with the ANSI C library, data has to
|
||||
be read (through fseek/fread) into intermediate buffers before it can be
|
||||
decoded. This scheme is highly portable, but rather inefficient; when using
|
||||
it, we'll describe the file as a disk-based resource.
|
||||
<p>As most modern operating systems now provide memory-mapped files, which
|
||||
allow direct access while improving performance and reducing memory usage.
|
||||
Because data can be read directly in memory, we'll speak of a memory-based
|
||||
resource in this case. For embedded systems (like printers, PDAs, etc..),
|
||||
ROM-fonts fit into this category as well.
|
||||
<p>Regarding naming, most systems use a string to name files in their storage
|
||||
hierarchy. Though a typical pathname is an ASCII string (<tt>'c:\windows\fonts\times.ttf'</tt>
|
||||
on Windows, <tt>'/home/fonts/times.ttf'</tt> on Unix), some OSes use different
|
||||
schemes, varying from Unicode character strings to file i-node numbers.
|
||||
These details are platform-specific and must be hidden to the rest of the
|
||||
library in resource objects.
|
||||
<p>A resource encapsulates the lowest details regarding a file, though
|
||||
it should have NO STATE. Note that the nature or type of a resource (i.e.
|
||||
disk or memory based) is important to the "stream" component only. The
|
||||
rest of the library and font drivers work transparently from their implementation.
|
||||
<p>Note also that it is perfectly possible to mix resources of distinct
|
||||
natures in a single build</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
a "<b>stream</b>" is an object which is used to extract bytes from a resource.
|
||||
Only resource objects can create streams, through its <i><tt>Open_Stream()</tt></i>
|
||||
method. A stream has state, which typically consist of a file "cursor",
|
||||
some intermediate buffers, a "current frame" and, of course, methods used
|
||||
to extract the data from streams, resolving endianess and alignement issues.</li>
|
||||
</ul>
|
||||
Data can be extracted from streams through direct reads, or through the
|
||||
use of <b>frames</b>. A frame models <i>a run of contiguous bytes</i> starting
|
||||
from the current stream position, and of liberal size.
|
||||
<p>Methods exist to extract successive integers of any sizes, while resolving
|
||||
endianess and alignement issues. Rather than a long rethorical explanation,
|
||||
here's how frames are typically used :
|
||||
<blockquote><tt>{</tt>
|
||||
<br><tt> …</tt>
|
||||
<br><tt> FT_Error error;</tt>
|
||||
<p><tt> error = FT_Access_Frame( stream, 14 );</tt>
|
||||
<br><tt> if (error) goto Fail;</tt>
|
||||
<p><tt> val1 = FT_Get_Short(stream);</tt>
|
||||
<br><tt> val2 = FT_Get_Long(stream);</tt>
|
||||
<br><tt> val3 = FT_Get_Long(stream);</tt>
|
||||
<br><tt> val4 = FT_Get_Long(stream);</tt>
|
||||
<p><tt> FT_Forget_Frame(stream);</tt>
|
||||
<br><tt> …</tt>
|
||||
<br><tt>}</tt></blockquote>
|
||||
This code does the following :
|
||||
<blockquote>
|
||||
<ol>
|
||||
<li>
|
||||
first, it "loads" the next 14 bytes from the current cursor position
|
||||
into the stream's frame, using the <tt>FT_Access_Frame</tt> API. An error
|
||||
is returned if, for example, less than 14 bytes are left in the stream
|
||||
when the call occurs..</li>
|
||||
</ol>
|
||||
|
||||
<ol>
|
||||
<li>
|
||||
it extract four integers (one 16-bit short, three 32-bit longs) from
|
||||
the frame using <tt>FT_Get_Short</tt> and <tt>FT_Get_Long</tt>. These function
|
||||
increment the frame's cursor finally, it "releases" the stream's frame.</li>
|
||||
</ol>
|
||||
|
||||
<ol>
|
||||
<li>
|
||||
Each stream has its own frame which can be accessed independently,
|
||||
however, nested frame accesses are not allowed. Note also that the bytes
|
||||
are effectively read from the stream on the call to <tt>FT_Access_Frame</tt>.
|
||||
Any subsequent read will occur after these 14 bytes, even if less are extracted
|
||||
through <tt>FT_Get_xxxx</tt> functions.</li>
|
||||
</ol>
|
||||
</blockquote>
|
||||
The implementation of the resource class is located in the system component
|
||||
(i.e. "<tt>arch/<i><system></i>/ftsys.c</tt>") and can thus be tailored
|
||||
for a specific port of the engine.
|
||||
<p>A resource can be created through the <tt>FT_New_Resource</tt> API;
|
||||
however this function only accepts an 8-bit pathname to name the target
|
||||
font file, which may be inappropriate for systems using a different naming
|
||||
scheme (e.g. UTF-16 pathname, i-node number, etc..). It's up to the porter
|
||||
then to provide its own resource creation function (like. <tt>FT_New_UTF16_Resource</tt>,
|
||||
for example) in its version of "<tt>ftsys.c</tt>".
|
||||
<p>Note that <tt>FT_New_Resource</tt> will fail and return an error code
|
||||
if the font file cannot be found, or when its font format isn't recognized
|
||||
by one of the drivers installed in the library. The list or resources created
|
||||
for a given library instance is thus the list of "installed font files".
|
||||
<br> </blockquote>
|
||||
|
||||
<h3>
|
||||
3. Stream Manager :</h3>
|
||||
|
||||
<blockquote>As said before, resources do not bear states, while streams
|
||||
do. Stream creation is also a very lengthy process, depending on the target
|
||||
operating system (e.g. "<tt>fopen</tt>" is usually very slow).
|
||||
<p>Because a typical font driver will want to use a new stream on each
|
||||
access to individual glyphs, being able to cache the most recently used
|
||||
streams is a requirement in order to avoid considerable performance penalties.
|
||||
<p>Stream caching is thus implemented in the "<tt>ftstream</tt>" component.
|
||||
It maintains a simple LRU list of the least recently used streams. Each
|
||||
stream in the cache is still opened and available for immediate processing.
|
||||
When a resource is destroyed, the stream cache is parsed to remove all
|
||||
related cached streams.
|
||||
<p>Stream caching can also be disabled with a configuration macro when
|
||||
using only ROM based resources (where stream opening is really quick).
|
||||
It is implemented through a Stream Manager object (see <tt>ftstream.c</tt>).
|
||||
<br> </blockquote>
|
||||
|
||||
<h3>
|
||||
4. Raster :</h3>
|
||||
|
||||
<blockquote>The raster is the component is charge of generating bitmaps
|
||||
and anti-aliased pixmaps from vectorial outline definitions. It is also
|
||||
sometimes called the scan-line converter. It has been completely rewritten
|
||||
for FreeType 2.0 in order to support third-order bezier arcs, 17-levels
|
||||
anti-aliasing (through 4x4 sub-sampling), improved performance, as well
|
||||
as stand-alone compilation (in order to include it in other graphics package
|
||||
without requiring the rest of the FreeType engine).
|
||||
<p>Because it was designed for easy re-use and embedded systems, the raster
|
||||
is a rtaher 'unusual' piece of code, because it doesn't perform a single
|
||||
memory allocation, nor contain any static or global variable. Rather, it
|
||||
is up to client applications to allocate a raster object in their own heap
|
||||
or memory space.
|
||||
<p>Each raster object also needs a rather large block of memory called
|
||||
its render pool. The pool is used during rendering (and only during it)
|
||||
in order to perform the scan-line conversion. Because it accesses and manages
|
||||
data directly within the pool, the raster yelds impressive performance
|
||||
as well as bounded memory consumption. It can also automatically decompose
|
||||
large requests into smaller individual sub-tasks.
|
||||
<p>Finally, it never creates bitmaps or pixmaps, but simply renders into
|
||||
them (providing clipping too). These must be described to the raster with
|
||||
the help of a <tt>FT_Raster_Map</tt> structure (a very simple bitmap/pixmap
|
||||
descriptor).
|
||||
<p>Note that when rendering anti-aliased pixmaps, the raster doesn't use
|
||||
an intermediate bitmap buffer, as filtering is part of the scan-line conversion
|
||||
process.
|
||||
<br> </blockquote>
|
||||
|
||||
<h3>
|
||||
5. Library objects :</h3>
|
||||
|
||||
<blockquote>A library object models a single instance of the FreeType engine.
|
||||
This is useful when FreeType is compiled as a shared object (DLL), as it
|
||||
can then be used by several applications, each with its own resources and
|
||||
objects.
|
||||
<p>The <tt>FT_Library</tt> type is an opaque handle to a library object.
|
||||
Such an object is created through a call to <tt>FT_Init_FreeType</tt>.
|
||||
Once you don't need it anymore, one can destroy a library object through
|
||||
<tt>FT_Done_FreeType</tt>.
|
||||
<p>Note that in reentrant builds, several threads can access a single library
|
||||
object concurrently. Such a build can be chosen by switching one configuration
|
||||
macro in the file '<tt>arch/<i><system></i>/ftconfig.h</tt>'</blockquote>
|
||||
|
||||
<h3>
|
||||
6. Driver objects :</h3>
|
||||
|
||||
<blockquote>A driver object models an instance of a given font driver,
|
||||
i.e. an element of FreeType code in charge of handling a given font format,
|
||||
like TrueType, Type1, FNT, PCF, etc..
|
||||
<p>Each library object contains a given set of driver objects when it is
|
||||
created through FT_Init_FreeType, this set being determined at compile
|
||||
time (see the file 'base/ftapi.c'). However, removing or adding drivers
|
||||
is possible at run-time, in order to make upgrades easy.</blockquote>
|
||||
|
||||
<h3>
|
||||
7. Diagram</h3>
|
||||
|
||||
<blockquote>This diagram show the object relationships for the sole base
|
||||
layer. The library object is the root of the object graph :
|
||||
<center>
|
||||
<p><img SRC="objects_diagram.png" height=300 width=562></center>
|
||||
|
||||
<p>It can be read as follows :
|
||||
<br>
|
||||
<ul>
|
||||
<li>
|
||||
Each library object has one system, one raster and one stream manager objects.
|
||||
These objects can only belong to one given library.</li>
|
||||
</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
Each library contains one list of 0 or more resources, as well as one list
|
||||
of 0 or more driver objects.</li>
|
||||
</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
Each stream manager holds a bounded list ("0..n" where 'n' is the stream
|
||||
cache's size) of stream objects. Each stream is related to one given resource
|
||||
object. Each resource may be related to zero or one stream.</li>
|
||||
</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
Each resource is related to one driver object. A driver is related to 0
|
||||
or more resources.</li>
|
||||
</ul>
|
||||
</blockquote>
|
||||
</blockquote>
|
||||
|
||||
<p><br>
|
||||
<hr WIDTH="100%">
|
||||
<h2>
|
||||
IV. Font objects :</h2>
|
||||
|
||||
<blockquote>Font objects are used to directly map the information found
|
||||
in font files into several categories :
|
||||
<br>
|
||||
<h3>
|
||||
1. Face objects :</h3>
|
||||
|
||||
<blockquote>Face objects are used to model individual font faces. They
|
||||
encapsulate data which isn't related to a specific character size, or a
|
||||
specific glyph or glyph set. Usually, this means :
|
||||
<ul>
|
||||
<li>
|
||||
the font face's family and style names (e.g. "Palatino" + "Regular")</li>
|
||||
|
||||
<li>
|
||||
some flags indicating which kind of font this is (scalable or fixed ? fixed-width
|
||||
or proportional ? horizontal or vertical ? etc…)</li>
|
||||
|
||||
<li>
|
||||
the number of glyphs, charmaps and eventually fixed character sizes (for
|
||||
bitmap formats) found in the font face.</li>
|
||||
|
||||
<li>
|
||||
for scalable formats, some important metrics like the ascender, descender,
|
||||
global font bounding box, maximum advance width, etc.. expressed in notional
|
||||
font/grid units (as well as the number of units on the EM grid).</li>
|
||||
</ul>
|
||||
A face is created from a resource object, with the <tt>FT_New_Face</tt>
|
||||
API. Each driver contains a list of opened face objects for the resources
|
||||
it manages. When a driver is removed or destroyed, all its child faces
|
||||
are discarded automatically with it.</blockquote>
|
||||
|
||||
<h3>
|
||||
2. Size objects :</h3>
|
||||
|
||||
<blockquote>Size objects are used to model a given character dimension
|
||||
for a given device resolution (which really means a given character pixel
|
||||
dimensions).
|
||||
<p>Each size object is created from a parent face object. The object can
|
||||
be reset to new dimensions at any time. Each face object holds a list of
|
||||
all its child sizes, these are destroyed automatically when the face object
|
||||
is discarded.
|
||||
<p>The metrics contains metrics, expressed in pixels, for the ascender,
|
||||
descender, maximum advance width, etc..
|
||||
<br> </blockquote>
|
||||
|
||||
<h3>
|
||||
3. Glyph Slot objects :</h3>
|
||||
|
||||
<blockquote>A glyph slot is a container where one can load individual glyphs,
|
||||
be they in vector of bitmap format. Each slot also contains metrics for
|
||||
the glyph it contains.
|
||||
<p>Each face object contains one or more glyph slot object : the first
|
||||
glyph slot is created automatically with its parent face, and it is possible
|
||||
to add new glyph slots (this is rarely used outside of debugging purposes).
|
||||
<br> </blockquote>
|
||||
|
||||
<h3>
|
||||
4. CharMap objects :</h3>
|
||||
|
||||
<blockquote>A charmap object is a sort of dictionary whose task is to translate
|
||||
character codes in a given character encoding (like ShiftJIS, Unicode,
|
||||
ANSI, etc..) into glyph indexes in a given font face.
|
||||
<p>A face object contains one or more charmap objects. All charmap objects
|
||||
are created when the parent face is created, though they're not directly
|
||||
visible to client applications (rather, they can be enumerated through
|
||||
FT_Get_First_CharMap and FT_Get_Next_CharMap, or more simply picked adequately
|
||||
with FT_Find_CharMap for a set of given encodings).
|
||||
<br> </blockquote>
|
||||
|
||||
<h3>
|
||||
5. Diagram</h3>
|
||||
|
||||
<blockquote>The following diagram illustrates the relationships between
|
||||
font objects :
|
||||
<center>
|
||||
<p><img SRC="objects_diagram2.png" height=327 width=561></center>
|
||||
|
||||
<p>Which can be read as :
|
||||
<br>
|
||||
<ul>
|
||||
<li>
|
||||
each resource may have zero or more child face objects "opened" for it.
|
||||
The number of faces is bounded by the number of font faces within the font
|
||||
resource.</li>
|
||||
</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
each driver holds a list of all the faces opened for the resources it manages.
|
||||
When the driver is removed, its child faces are discarded automatically.</li>
|
||||
</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
each face object has one single parent resource, and one single driver.</li>
|
||||
</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
each face has one or more charmaps, and one or more glyph slots</li>
|
||||
</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
each face holds a list of zero or more child size objects</li>
|
||||
</ul>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
each charmap, glyph slot and size is related to one given parent face.
|
||||
These objects are destroyed automatically when the parent face is discarded.</li>
|
||||
</ul>
|
||||
</blockquote>
|
||||
</blockquote>
|
||||
|
||||
<p><br>
|
||||
<hr WIDTH="100%">
|
||||
<h2>
|
||||
V. Driver Interface :</h2>
|
||||
|
||||
<blockquote>A font driver is added to a given library object through the
|
||||
<tt>FT_Add_Driver</tt>
|
||||
API. This function receives a structure known as a <tt>FT_DriverInterface</tt>,
|
||||
which describes the driver's basic properties.
|
||||
<p>The <tt>FT_DriverInterface</tt> contains a set of function pointers
|
||||
used for the base FreeType functionalities. However, each driver can also
|
||||
provide a font-format-specific extended interface to allow client applications
|
||||
to use more advanced features.
|
||||
<br>
|
||||
<h3>
|
||||
1. Common Interface</h3>
|
||||
|
||||
<blockquote>The structure of <tt>FT_DriverInterface</tt> is rather simple,
|
||||
and defined in "<tt>base/ftdriver.h</tt>". It must be well known by any
|
||||
developer who wants to write a new driver for the engine. We advise reading
|
||||
the <b><i>FreeType Driver HowTo</i></b> as well as the source code of existing
|
||||
drivers. Source comments.</blockquote>
|
||||
|
||||
<h3>
|
||||
2. Driver-specific extensions</h3>
|
||||
|
||||
<blockquote>The field of the <tt>FT_DriverInterface</tt> structure is a
|
||||
typeless pointer to a format-specific interface. This extended interface
|
||||
is usually a structure containing function pointers as well as other kind
|
||||
of information related to the driver.
|
||||
<p>It is assumed that client applications that wish to use the driver-specific
|
||||
extensions are able to <tt>#include</tt> the relevant header files to understand
|
||||
the format-specific interface structure.</blockquote>
|
||||
</blockquote>
|
||||
|
||||
<hr WIDTH="100%">
|
||||
<h2>
|
||||
VI. Configuration:</h2>
|
||||
|
||||
<blockquote>This section relates to the configuration of the FreeType library.
|
||||
By configuration, we mean selection of build options as well as the choice
|
||||
of font drivers to be used for each new library object.
|
||||
<br>
|
||||
<h3>
|
||||
1. Configuration files :</h3>
|
||||
|
||||
<blockquote>A single file is used to configure the FreeType base engine.
|
||||
As it is considered system-specific, it is located in the architecture
|
||||
directories of the library, under the name "arch/<system>/ftconfig.h".
|
||||
Note that the same directory should also contain a platform-specific implementation
|
||||
of "ftsys.c".
|
||||
<p>The configuration files is a simple C header which is included by the
|
||||
engine's sources during compilation. It is not included in "freetype.h",
|
||||
and hence doesn't need to be copied when installing the FreeType headers
|
||||
on your system.
|
||||
<p>It is made of a series of #define or #undef statements, which are used
|
||||
to select or turn off a specific option. Each option is documented with
|
||||
heavy comments, and some of them are explained below.</blockquote>
|
||||
|
||||
<h3>
|
||||
2. Building and Makefiles :</h3>
|
||||
|
||||
<blockquote>FreeType 2.0 is more complex than its 1.x release. In order
|
||||
to facilitate maintenance, as well as ease considerably the writing of
|
||||
new font drivers, <b><i>only GNU Make is supported with FreeType 2.0</i></b>.
|
||||
However, it is possible to use any compiler, as well as any object or library
|
||||
prefix (<tt>.o, .obj, .a, .lib</tt> etc..) with them.
|
||||
<p>To build FreeType 2.0, one has to be in the library directory, then
|
||||
invoke its platform-specific makefile. For a Unix system, this would be
|
||||
:
|
||||
<blockquote>
|
||||
<blockquote><tt>% cd freetype2/lib</tt>
|
||||
<br><tt>% make -f arch/unix/Makefile</tt>
|
||||
<p>where '<tt>make</tt>' is really GNU Make !</blockquote>
|
||||
</blockquote>
|
||||
The system-specific <tt>Makefile</tt> located in '<tt>arch/<i><system></i></tt>'
|
||||
is a tiny file used to define several variables. It then includes the file
|
||||
<tt>freetype2/lib/Makefile.lib</tt>,
|
||||
which contains all the gory details about library compilation. The system-specific
|
||||
<tt>Makefile</tt> can be very easily modified to accomodate a new compiler/platform
|
||||
(see the comments within one of these files).
|
||||
<p>Each font driver is located in a directory like "<tt>freetype2/lib/drivers/<i><formatdir></i></tt>".
|
||||
For example, the TrueType driver is located in "<tt>drivers/truetype</tt>".
|
||||
Each driver directory must contain a <tt>Makefile</tt> which will be included
|
||||
by <tt>Makefile.lib</tt>. The former is used to define and build driver
|
||||
object files.
|
||||
<br>
|
||||
<p><br>
|
||||
<center>
|
||||
<p><img SRC="build_diagram.png" height=284 width=559></center>
|
||||
</blockquote>
|
||||
|
||||
<h3>
|
||||
3. Make options :</h3>
|
||||
|
||||
<blockquote>The base layer, as well as each font driver, are made up of
|
||||
several C sources. Traditionally, one compiles each source (i.e. '<tt>.c</tt>'
|
||||
file) into an object ('<tt>.o</tt>' or '<tt>.obj</tt>') file, and all of
|
||||
them are grouped into a library file (i.e. '<tt>.a</tt>' or '<tt>.lib</tt>').
|
||||
<p>By default, FreeType takes a slightly different approach when it comes
|
||||
to compiling each part of the engine. Usually, a single tiny source is
|
||||
compiled, which includes all other component sources. This results in a
|
||||
single object files, with the benefits or reduced code size, usually better
|
||||
compilation as well as a drastic reduction of the number of symbols exported
|
||||
by the library. Of course, it is made possible through the use of specific
|
||||
declaration macros in the FreeType source (see the definition of <tt>LOCAL_DEF</tt>
|
||||
and <tt>LOCAL_FUNC</tt> in <tt>ftconfig.h</tt> for details).
|
||||
<p>For a concrete example, see the source code in "<tt>base/ftbase.c</tt>"
|
||||
which generates the whole base layer in a single object file. The same
|
||||
build process is applied to font drivers, in order to generate one single
|
||||
object file per given font format (e.g. <tt>truetype.o</tt>, <tt>type1.o</tt>,
|
||||
etc..).
|
||||
<p>Compiling the library and drivers in "normal" mode is possible, through
|
||||
the use of the '<tt>multi</tt>' target (which really means « multiple
|
||||
objects »). For example, calling :
|
||||
<blockquote><tt>% make -f arch/ansi/Makefile multi</tt></blockquote>
|
||||
Will build the FreeType library by compiling each source file to an individual
|
||||
object, then linking them together. You'll notice that the library is significantly
|
||||
bigger in this case. Creating a shared dll from a 'multi' build is certainly
|
||||
a very poor idea, as this will export a huge quantity of symbols that aren't
|
||||
useful to any client application.</blockquote>
|
||||
|
||||
<h3>
|
||||
4. Adding a driver at compile time</h3>
|
||||
|
||||
<blockquote>A driver can be included very easily in the build process by
|
||||
including its <tt>Makefile</tt> in <tt>Makefile.lib</tt>. For example,
|
||||
the TrueType driver is simply included with the following lines (see <tt>Makefile.lib</tt>):
|
||||
<blockquote><tt># TrueType driver rules</tt>
|
||||
<br><tt>#</tt>
|
||||
<br><tt>include $(DRIVERS_DIR)/truetype/Makefile</tt></blockquote>
|
||||
|
||||
<p><br>Where <tt>DRIVERS_DIR</tt> really is "<tt>freetype2/lib/drivers</tt>",
|
||||
though this can be redefined. You can, of course specify a different path
|
||||
if you want to place your driver sources in another location.
|
||||
<p>Note that this only adds the driver's object files to the generated
|
||||
library file. A few more steps are needed to make your <tt>FT_Library</tt>
|
||||
objects use the driver. They consist in modifying the file "<tt>base/ftinit.c</tt>",
|
||||
whose sole purpose is to define the set of driver objects that are to be
|
||||
created with each new library object.
|
||||
<br> </blockquote>
|
||||
|
||||
<h3>
|
||||
5. Adding a driver at run time</h3>
|
||||
|
||||
<blockquote>New driver objects can be added at run-time through the <tt>FT_Add_Driver</tt>
|
||||
API. This function takes a handle to an existing library object, as well
|
||||
as a pointer to a given driver interface. This interface is used to create
|
||||
a new driver object and register it within the library.
|
||||
<p>Similarly, a single driver can be removed from a library anytime through
|
||||
<tt>FT_Remove_Driver</tt>.
|
||||
This will automatically discard the resources and face objects managed
|
||||
by the driver.</blockquote>
|
||||
|
||||
<h3>
|
||||
6. Custom library objects :</h3>
|
||||
|
||||
<blockquote>Finally, it is possible to build custom library objects. You
|
||||
need to pass a handle to a valid <tt>FT_System</tt> object to the <tt>FT_Build_Library</tt>
|
||||
API. The function will return a handle to the new fresh library object.
|
||||
Note that the library has no registered drivers after the call, developers
|
||||
have to add them by hand with <tt>FT_Add_Driver</tt>.
|
||||
<p>It is thus possible to create two distinct library objects with distinct
|
||||
<tt>FT_System</tt>
|
||||
implementations in the same session, which can be useful for debugging
|
||||
purpose.</blockquote>
|
||||
|
||||
<br> </blockquote>
|
||||
|
||||
</body>
|
||||
</html>
|
||||
|
|
@ -1,343 +0,0 @@
|
|||
<!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="David Turner">
|
||||
<title>FreeType 2 Internals - I/O Frames</title>
|
||||
</head>
|
||||
|
||||
<body text="#000000"
|
||||
bgcolor="#FFFFFF"
|
||||
link="#0000EF"
|
||||
vlink="#51188E"
|
||||
alink="#FF0000">
|
||||
|
||||
<h1 align=center>
|
||||
FreeType 2.0 I/O Frames
|
||||
</h1>
|
||||
|
||||
<h3 align=center>
|
||||
© 2000 David Turner
|
||||
(<a href="mailto:david@freetype.org">david@freetype.org</a>)<br>
|
||||
© 2000 The FreeType Development Team
|
||||
(<a href="http://www.freetype.org">www.freetype.org</a>)
|
||||
</h3>
|
||||
|
||||
<center>
|
||||
<table width="70%">
|
||||
<tr><td>
|
||||
|
||||
<hr>
|
||||
|
||||
<h2>
|
||||
Introduction
|
||||
</h2>
|
||||
|
||||
<p>This document explains the concept of I/O <b>frames</b> as used in the
|
||||
FreeType 2 source code. It also enumerates the various functions and
|
||||
macros that can be used to read them.</p>
|
||||
|
||||
<p>It is targeted to FreeType hackers, or more simply to developers who
|
||||
would like a better understanding of the library's source code.</p>
|
||||
|
||||
<hr>
|
||||
|
||||
<h2>
|
||||
I. What frames are
|
||||
</h2>
|
||||
|
||||
<p>Simply speaking, a frame is an array of bytes in a font file that is
|
||||
`preloaded' into memory in order to be rapidly parsed. Frames are useful
|
||||
to ensure that every `load' is checked against end-of-file overruns, and
|
||||
provides nice functions to extract data in a variety of distinct
|
||||
formats.</p>
|
||||
|
||||
<p>But an example is certainly more meaningful than anything else. The
|
||||
following code</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
error = read_short( stream, &str.value1 );
|
||||
if ( error ) goto ...
|
||||
|
||||
error = read_ulong( stream, &str.value2 );
|
||||
if ( error ) goto ...
|
||||
|
||||
error = read_ulong( stream, &str.value3 );
|
||||
if ( error ) goto ...</pre>
|
||||
</font>
|
||||
|
||||
<p>can easily be replaced with</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
error = FT_Access_Frame( stream, 2 + 4 + 4 );
|
||||
if ( error ) goto ...
|
||||
|
||||
str.value1 = FT_Get_Short( stream );
|
||||
str.value2 = FT_Get_ULong( stream );
|
||||
str.value3 = FT_Get_ULong( stream );
|
||||
|
||||
FT_Forget_Frame( stream );</pre>
|
||||
</font>
|
||||
|
||||
<p>Here, the call to <code>FT_Access_Frame()</code> will</p>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
<p>Ensure that there are at least 2+4+4=10 bytes left in the
|
||||
stream.</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>`Preload' (for disk-based streams) 10 bytes from the current
|
||||
stream position.</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>Set the frame `cursor' to the first byte in the frame.</p>
|
||||
</li>
|
||||
</ul>
|
||||
|
||||
<p>Each <code>FT_Get_Short()</code> or <code>FT_Get_ULong()</code> call
|
||||
will read a big-endian integer from the stream (2 bytes for
|
||||
<code>FT_Get_Short()</code>, 4 bytes for <code>FT_Get_ULong</code>)
|
||||
and advance the frame cursor accordingly.</p>
|
||||
|
||||
<p><code>FT_Forget_Frame()</code> `releases' the frame from memory.</p>
|
||||
|
||||
<p>There are several advantages to using frames:</p>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
<p>Single-check when loading tables.</p>
|
||||
</li>
|
||||
<li>
|
||||
<p><em>Making code clearer</em> by providing simple parsing functions
|
||||
<em>while keeping code safe</em> from file over-runs and invalid
|
||||
offsets.</p>
|
||||
</li>
|
||||
</ul>
|
||||
|
||||
<hr>
|
||||
|
||||
<h2>
|
||||
II. Accessing and reading a frame with macros
|
||||
</h2>
|
||||
|
||||
<p>By convention in the FreeType source code, macros are able to use two
|
||||
implicit variables named <var>error</var> and <var>stream</var>. This is
|
||||
useful because these two variables are extremely often used in the
|
||||
library, and doing this only reduces our typing requirements and make the
|
||||
source code much clearer.</p>
|
||||
|
||||
<p>Note that <var>error</var> must be a local variable of type
|
||||
<code>FT_Error</code>, while <var>stream</var> must be a local variable or
|
||||
argument of type <code>FT_Stream</code>.</p>
|
||||
|
||||
<p>The macro used to access a frame is <font
|
||||
color="purple"><code><b>ACCESS_Frame(_size_)</b></code></font>, it will
|
||||
translate to</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
( error = FT_Access_Frame( stream, _size_ ) )
|
||||
!= FT_Err_Ok</pre>
|
||||
</font>
|
||||
|
||||
<p>Similarly, the macro <font
|
||||
color="purple"><b><code>FORGET_Frame()</code></b></font> translates to</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
FT_Forget_Frame( stream )</pre>
|
||||
</font>
|
||||
|
||||
<p>Extracting integers can be performed with the <code>GET_xxx()</code>
|
||||
macros, like</p>
|
||||
|
||||
<table align=center
|
||||
cellpadding=5>
|
||||
<tr valign="top">
|
||||
<th>
|
||||
Macro name
|
||||
</th>
|
||||
<th>
|
||||
Translation
|
||||
</th>
|
||||
<th>
|
||||
Description
|
||||
</th>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<font color="purple"><code><b>GET_Byte()</b></code></font>
|
||||
</td>
|
||||
<td>
|
||||
<font color="blue"><code>FT_Get_Byte(stream)</code></font>
|
||||
</td>
|
||||
<td>
|
||||
<p>Reads an 8-bit unsigned byte.</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<font color="purple"><code><b>GET_Char()</b></code></font>
|
||||
</td>
|
||||
<td>
|
||||
<font color="blue"><code>(FT_Char)<br>
|
||||
FT_Get_Byte(stream)</code></font>
|
||||
</td>
|
||||
<td>
|
||||
<p>Reads an 8-bit <em>signed</em> byte.</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<font color="purple"><code><b>GET_Short()</b></code></font>
|
||||
</td>
|
||||
<td>
|
||||
<font color="blue"><code>FT_Get_Short(stream)</code></font>
|
||||
</td>
|
||||
<td>
|
||||
Reads a 16-bit signed big-endian integer.
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<font color="purple"><code><b>GET_UShort()</b></code></font>
|
||||
</td>
|
||||
<td>
|
||||
<font color="blue"><code>(FT_UShort)<br>
|
||||
FT_Get_Short(stream)</code></font>
|
||||
</td>
|
||||
<td>
|
||||
Reads a 16-bit unsigned big-endian integer.
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<font color="purple"><code><b>GET_Offset()</b></code></font>
|
||||
</td>
|
||||
<td>
|
||||
<font color="blue"><code>FT_Get_Offset(stream)</code></font>
|
||||
</td>
|
||||
<td>
|
||||
Reads a 24-bit signed big-endian integer.
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<font color="purple"><code><b>GET_UOffset()</b></code></font>
|
||||
</td>
|
||||
<td>
|
||||
<font color="blue"><code>(FT_UOffset)<br>
|
||||
FT_Get_Offset(stream)</code></font>
|
||||
</td>
|
||||
<td>
|
||||
Reads a 24-bit unsigned big-endian integer.
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<font color="purple"><code><b>GET_Long()</b></code></font>
|
||||
</td>
|
||||
<td>
|
||||
<font color="blue"><code>FT_Get_Long(stream)</code></font>
|
||||
</td>
|
||||
<td>
|
||||
Reads a 32-bit signed big-endian integer.
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<font color="purple"><code><b>GET_ULong()</b></code></font>
|
||||
</td>
|
||||
<td>
|
||||
<font color="blue"><code>(FT_ULong)<br>
|
||||
FT_Get_Long(stream)</code></font>
|
||||
</td>
|
||||
<td>
|
||||
Reads a 32-bit unsigned big-endian integer.
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
|
||||
<p>(Note that an <b>Offset</b> is an integer stored with 3 bytes on
|
||||
the file.)</p>
|
||||
|
||||
<p>All this means that the following code</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
error = FT_Access_Frame( stream, 2 + 4 + 4 );
|
||||
if ( error ) goto ...
|
||||
|
||||
str.value1 = FT_Get_Short( stream );
|
||||
str.value2 = FT_Get_ULong( stream );
|
||||
str.value3 = FT_Get_ULong( stream );
|
||||
|
||||
FT_Forget_Frame( stream );</pre>
|
||||
</font>
|
||||
|
||||
<p>can be simplified with macros:</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
if ( ACCESS_Frame( 2 +4 + 4 ) ) goto ...
|
||||
|
||||
str.value1 = GET_Short();
|
||||
str.value2 = GET_ULong();
|
||||
str.value3 = GET_ULong();
|
||||
|
||||
FORGET_Frame();</pre>
|
||||
</font>
|
||||
|
||||
<p>Which is clearer. Notice that <var>error</var> and <var>stream</var>
|
||||
must be defined locally though for this code to work!</p>
|
||||
|
||||
<hr>
|
||||
|
||||
<h2>
|
||||
III. Alternatives
|
||||
</h2>
|
||||
|
||||
<p>It is sometimes useful to read small integers from a font file without
|
||||
using a frame. Some functions have been introduced in FreeType 2 to
|
||||
do just that, and they are of the form <font
|
||||
color="blue"><code>FT_Read_xxxx</code></font>.</p>
|
||||
|
||||
<p>For example, <font color="blue"><code>FT_Read_Short(stream,
|
||||
&error)</code></font> reads and returns a 2-byte big-endian integer from a
|
||||
<var>stream</var>, and places an error code in the <var>error</var>
|
||||
variable.</p>
|
||||
|
||||
<p>Thus, reading a single big-endian integer is shorter than using a frame
|
||||
for it.</p>
|
||||
|
||||
<p>Note that there are also macros <font
|
||||
color="purple"><code>READ_xxx()</code></font> which translate to</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
FT_Read_xxx( stream, &error ), error != FT_Err_Ok</pre>
|
||||
</font>
|
||||
|
||||
<p>and can be used as in</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
if ( READ_UShort( variable1 ) ||
|
||||
READ_ULong ( variable2 ) )
|
||||
goto Fail;</pre>
|
||||
</font>
|
||||
|
||||
<p>if <var>error</var> and <var>stream</var> are already defined
|
||||
locally.</p>
|
||||
|
||||
</td></tr>
|
||||
</table>
|
||||
</center>
|
||||
|
||||
</body>
|
||||
</html>
|
||||
Binary file not shown.
|
Before Width: | Height: | Size: 1.7 KiB |
Binary file not shown.
|
Before Width: | Height: | Size: 870 B |
Binary file not shown.
|
Before Width: | Height: | Size: 3.8 KiB |
Binary file not shown.
|
Before Width: | Height: | Size: 3.1 KiB |
Binary file not shown.
|
Before Width: | Height: | Size: 1.7 KiB |
|
|
@ -1,258 +0,0 @@
|
|||
<!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="David Turner">
|
||||
<meta name="GENERATOR" content="Mozilla/4.5 [fr] (Win98; I) [Netscape]">
|
||||
<title>FreeType 2 Internals</title>
|
||||
</head>
|
||||
<body>
|
||||
|
||||
<body text="#000000"
|
||||
bgcolor="#FFFFFF"
|
||||
link="#0000EF"
|
||||
vlink="#51188E"
|
||||
alink="#FF0000">
|
||||
|
||||
<center>
|
||||
<h1>
|
||||
FreeType 2.0 System Interface</h1></center>
|
||||
|
||||
<center>
|
||||
<h3>
|
||||
© 2000 David Turner (<a href="fichier :///david@freetype.org">david@freetype.org</a>)<br>
|
||||
© 2000 The FreeType Development Team (<a href="fichier :///devel@freetype.org">devel@freetype.org</a>)</h3></center>
|
||||
|
||||
<p><br>
|
||||
<hr WIDTH="100%">
|
||||
<br>
|
||||
<h2>Introduction:</h2>
|
||||
<ul>
|
||||
This document explains how the FreeType 2 library performs the low-level and
|
||||
system-specific operations of memory management and i/o access. It is targetted
|
||||
to FreeType hackers, porters and "advanced" developers who want special
|
||||
features like providing their own memory manager or streams.
|
||||
<p>
|
||||
Note that the only system-specific part of the library is a file
|
||||
named "<tt>ftsystem.c</tt>", normally located in the directory
|
||||
"<tt>freetype2/config/<system></tt>" where <tt><system></tt> designates
|
||||
your platform (e.g. "<tt>config/ansi/ftsystem.c</tt>" or
|
||||
"<tt>config/unix/ftsystem.c</tt>").
|
||||
<p>
|
||||
</ul>
|
||||
|
||||
<p>
|
||||
<hr>
|
||||
<p>
|
||||
|
||||
<h2>I. Memory Management</h2>
|
||||
<ul>
|
||||
Memory allocation and releases are performed through a <tt>FT_Memory</tt> object in
|
||||
FreeType. A <tt>FT_Memory</tt> is nothing more than a table of functions plus
|
||||
an arbitrary user data field. It is defined in the file
|
||||
"<tt>freetype2/include/ftsystem.h</tt>" and has the following structure:
|
||||
<p>
|
||||
<ul>
|
||||
<tt>typedef struct</tt><br>
|
||||
<tt>{</tt>
|
||||
<ul>
|
||||
<table>
|
||||
<tr><td><tt><b>void* user</b></tt> <td> // a user-defined pointer. This is zero by default
|
||||
<tr><td><tt><b>void* (*alloc)( FT_System, int)</b></tt> <td> // a function used to allocate a new block
|
||||
<tr><td><tt><b>void* (*realloc)( FT_System, int, int, void* )</b></tt><td> // a function used to reallocate a given block
|
||||
<tr><td><tt><b>void (*free)( FT_System, void*)</b></tt> <td> // a function used to release a given block
|
||||
</table>
|
||||
</ul>
|
||||
<tt>} FT_MemoryRec, *FT_Memory;</tt><br>
|
||||
</ul>
|
||||
<p>
|
||||
You'll notice that:<p>
|
||||
<ul>
|
||||
<li>The <tt>FT_Memory</tt> type is really a pointer to a <tt>FT_MemoryRec</tt>.
|
||||
This is a normal convention for the FreeType code.
|
||||
<li>The <tt>realloc</tt> takes two integer arguments. The first one is the
|
||||
current block size, the second one its new size.
|
||||
</ul>
|
||||
<p>
|
||||
|
||||
All current implementations of "<tt>ftsystem.c</tt>" provide a very simple
|
||||
implementation of the <tt>FT_Memory</tt> interface by calling directly the
|
||||
standard C <tt>alloc</tt>, <tt>realloc</tt> and <tt>free</tt>.
|
||||
<p>
|
||||
The FreeType source code never invokes directly the function pointers. Rather,
|
||||
it calls <tt>FT_Alloc</tt>, <tt>FT_Realloc</tt> and <tt>FT_Free</tt> functions
|
||||
which are defined in "<tt>freetype2/src/base/ftobjs.c</tt>". These will not be
|
||||
discussed here.
|
||||
<p>
|
||||
<b>If you want to use your own memory allocator</b> rather than the one provided
|
||||
by your build of FreeType, follow these simple steps:<p>
|
||||
<ol>
|
||||
<li>Create your own <tt>FT_Memory</tt> object, with pointers that map to
|
||||
your own memory management routines (beware function signatures though).
|
||||
<p>
|
||||
<li>Call <tt>FT_Build_Library(memory,&library)</tt>. This will create a new
|
||||
<tt>FT_Library</tt> object that uses your own <tt>FT_Memory</tt> exclusively.
|
||||
Note however that this library has no font drivers loaded in !!
|
||||
<p>
|
||||
<li>Load the default font drivers into the new library, either by
|
||||
calling <tt>FT_Default_Drivers(library)</tt>, or by adding them manually
|
||||
through repeated calls to <tt>FT_Add_Driver(library,&driver_interface)</tt>
|
||||
<p>
|
||||
</ol>
|
||||
This will replace the <tt>FT_Init_FreeType(&library)</tt> call that an application
|
||||
must do to initialise one library instance.
|
||||
<p>
|
||||
Notice that you <em>don't need to recompile FreeType 2 to use your own memory
|
||||
manager !!</em>.
|
||||
<p>
|
||||
</ul>
|
||||
|
||||
<p>
|
||||
<hr>
|
||||
<p>
|
||||
|
||||
<h2>II. Streams</h2>
|
||||
<ul>
|
||||
<h3>1. Basic Stream Structure</h3>
|
||||
<p>
|
||||
A stream models the array of bytes found in a font file. FreeType 2 separates
|
||||
streams into two families :<p>
|
||||
<ul>
|
||||
<li><b>memory-based streams:</b><br>
|
||||
when the stream's content is entirely found in memory. This is the
|
||||
case for ROM font files, or memory-mapped files.
|
||||
<p>
|
||||
<li><b>disk-based streams:</b><br>
|
||||
when the stream isn't directly accessible in memory. This is the
|
||||
case for local or remote files.
|
||||
<p>
|
||||
</ul>
|
||||
<p>
|
||||
Note that a stream's nature only determines how FreeType accesses its content, not
|
||||
the way it is effectively stored. For example, in the case of a compressed font file,
|
||||
one implementation may choose to uncompress the font in memory, then provide a memory
|
||||
based stream to access it. Another one might chose a disk based stream to perform
|
||||
on-the-fly decompression of the font data. Similarly, the font file can be stored
|
||||
on a local disk, or obtained from a network. This will be completely transparent to
|
||||
FreeType.
|
||||
<p>
|
||||
The stream structure is:
|
||||
<p>
|
||||
<ul>
|
||||
<tt>typedef struct</tt><br>
|
||||
<tt>{</tt><br>
|
||||
<ul><table>
|
||||
<tr><td><tt><b>char* base</b></tt> <td> for memory-based streams, the address
|
||||
of its first byte.
|
||||
|
||||
<tr><td><tt><b>ulong size</b></tt> <td> the stream's size in bytes.
|
||||
|
||||
<tr><td><tt><b>ulong pos</b></tt> <td> the current stream position in the file
|
||||
|
||||
<tr><td><tt><b>descriptor</b></tt><td> a union field used to hold either an
|
||||
integer file descriptor or pointer.
|
||||
This field is not used by FreeType
|
||||
itself, but is left to implementations
|
||||
of "<tt>ftsystem</tt>"
|
||||
<tr><td><tt><b>pathname</b></tt> <td> a union field that can hold either an
|
||||
integer or pointer. It is not used by
|
||||
FreeType itself, but is left to
|
||||
implementations. These can put the
|
||||
file pathname's during debugging for
|
||||
example.
|
||||
|
||||
<tr><td><tt><b>read</b></tt> <td> a pointer to a function used to seek the
|
||||
stream and/or read a run of bytes from it.
|
||||
|
||||
<tr><td><tt><b>close</b></tt><td> a pointer to a function called when the
|
||||
stream is closed.
|
||||
|
||||
<tr><td><tt><b>memory</b></tt> <td> a <tt>FT_Memory</tt> object, which is used
|
||||
to allocate frames for disk-based streams.
|
||||
This field is set and used by FreeType.
|
||||
|
||||
<tr><td><tt><b>cursor</b></tt> <td> a pointer in memory used when accessing
|
||||
frames. This is set and used by FreeType.
|
||||
|
||||
<tr><td><tt><b>limit</b></tt> <td> a pointer in memory used when accessing
|
||||
frames. This is set and used by FreeType.
|
||||
</table></ul>
|
||||
<tt>} FT_StreamRec, *FT_Stream</tt>
|
||||
</ul>
|
||||
<p>
|
||||
|
||||
The following important things must be noticed here:<p>
|
||||
<ul>
|
||||
<li>The <tt>FT_Stream</tt> type is really a pointer to a <tt>FT_StreamRec</tt>.
|
||||
This is a normal convention for the FreeType source.
|
||||
<p>
|
||||
|
||||
<li>When the <tt>read</tt> field is non NULL, the stream is considered to be
|
||||
disk-based. Otherwise, the stream is memory-based, and the <tt>base</tt>
|
||||
field <em>must</em> be set by "<tt>ftsystem.c</tt>" when the stream is
|
||||
created.
|
||||
<p>
|
||||
|
||||
<li>The <tt>base</tt> field must be set to 0 when a disk-based stream is created.
|
||||
However, this field will later be set and used by the FreeType library when
|
||||
accessing frames of bytes within the font file (of course, this doesn't
|
||||
happen with memory-based streams).
|
||||
</ul>
|
||||
|
||||
<h3>2. Stream lifecyles</h3>
|
||||
<p>
|
||||
Each <tt>FT_Face</tt> needs its own stream to access font data. The most common
|
||||
way to create a new <tt>FT_Stream</tt> object is to call the function
|
||||
<tt>FT_New_Face</tt>. This function takes a <em>file pathname</em> argument that
|
||||
is used to create a new stream object.
|
||||
<p>
|
||||
This is possible because each implementation of "<tt>ftsystem.c</tt>" provides
|
||||
a function called <tt>FT_New_Stream</tt> which takes a file pathname and a
|
||||
<tt>FT_Stream</tt> pointer as an argument. The function simply opens the file
|
||||
and initialises the stream structure accordingly. It is called by <tt>FT_New_Face</tt>
|
||||
to create the face's stream object.
|
||||
<p>
|
||||
A stream is only closed when the face is destroyed through <tt>FT_Done_Face</tt>.
|
||||
Its <tt>close</tt> field function will then be called. Note that the function should
|
||||
<em>never</em> destroy the <tt>FT_Stream</tt>.
|
||||
<p>
|
||||
|
||||
|
||||
<h3>3. Using your own streams</h3>
|
||||
<p>
|
||||
There are cases where it is interesting to provide your own stream to create
|
||||
a new face object, rather than rely on the default implementation. For example,
|
||||
a filepathname, which is a C string, might not be useful on a system where files
|
||||
are named with a UTF-16 string or via an i-node number of memory address (for ROM files).
|
||||
<p>
|
||||
For this purpose, the <tt>FT_Open_Face</tt> is defined. It simply takes a
|
||||
<tt>FT_Stream</tt> pointer as its second argument, instead of a file pathname (the
|
||||
stream must be allocated and initialised by you, so be careful).
|
||||
<p>
|
||||
Actually, the only thing that <tt>FT_New_Face</tt> does is create a new stream
|
||||
through <tt>FT_New_Stream</tt>, then call <tt>FT_Open_Face</tt> to create the
|
||||
face with it.
|
||||
<p>
|
||||
Note also that you can use the function <tt>FT_New_Memory_Face</tt> to create
|
||||
a new font face for a memory-based font file, whose address and size can be passed
|
||||
as arguments. The function automatically creates the corresponding memory-based
|
||||
stream and use it to create the face.
|
||||
<p>
|
||||
|
||||
</ul>
|
||||
|
||||
|
||||
<p>
|
||||
<hr>
|
||||
<p>
|
||||
|
||||
<h2>III. Thread synchronisation</h2>
|
||||
<ul>
|
||||
The FreeType library uses no static data. It can be used concurrently by two
|
||||
thread as long as each one uses its own <tt>FT_Library</tt> instance. Otherwise,
|
||||
one can very simply synchronize access to a single library instance by using a
|
||||
mutex to protect each call to one of FreeType's API functions.
|
||||
<p>
|
||||
</ul>
|
||||
|
||||
|
||||
|
|
@ -1,871 +0,0 @@
|
|||
<!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="David Turner">
|
||||
<title>FreeType 2 Tutorial</title>
|
||||
</head>
|
||||
|
||||
<body text="#000000"
|
||||
bgcolor="#FFFFFF"
|
||||
link="#0000EF"
|
||||
vlink="#51188E"
|
||||
alink="#FF0000">
|
||||
|
||||
<h1 align=center>
|
||||
FreeType 2.0 Tutorial
|
||||
</h1>
|
||||
|
||||
<h3 align=center>
|
||||
© 2000 David Turner
|
||||
(<a href="mailto:david@freetype.org">david@freetype.org</a>)<br>
|
||||
© 2000 The FreeType Development Team
|
||||
(<a href="http://www.freetype.org">www.freetype.org</a>)
|
||||
</h3>
|
||||
|
||||
<center>
|
||||
<table width="70%">
|
||||
<tr><td>
|
||||
|
||||
<hr>
|
||||
|
||||
<h2>
|
||||
Introduction
|
||||
</h2>
|
||||
|
||||
<p>This short tutorial will teach you how to use the FreeType 2
|
||||
library in your own applications.</p>
|
||||
|
||||
<hr>
|
||||
|
||||
<h3>
|
||||
1. Header files
|
||||
</h3>
|
||||
|
||||
<p>To include the main FreeType header file, simply say</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
#include <freetype/freetype.h></pre>
|
||||
</font>
|
||||
|
||||
<p>in your application code. Note that other files are available in the
|
||||
FreeType include directory, most of them being included by
|
||||
<tt>"freetype.h"</tt>. They will be described later in this
|
||||
tutorial.</p>
|
||||
|
||||
<hr>
|
||||
|
||||
<h3>
|
||||
2. Initialize the library
|
||||
</h3>
|
||||
|
||||
<p>Simply create a variable of type <tt>FT_Library</tt> named, for
|
||||
example, <tt>library</tt>, and call the function
|
||||
<tt>FT_Init_FreeType()</tt> as in</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
#include <freetype/freetype.h>
|
||||
|
||||
FT_Library library;
|
||||
|
||||
...
|
||||
|
||||
{
|
||||
...
|
||||
error = FT_Init_FreeType( &library );
|
||||
if ( error )
|
||||
{
|
||||
... an error occurred during library initialization ...
|
||||
}
|
||||
}</pre>
|
||||
</font>
|
||||
|
||||
<p>This function is in charge of the following:</p>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
<p>Creating a new instance of the FreeType 2 library, and set
|
||||
the handle <tt>library</tt> to it.</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>Load each modules that FreeType knows about in the library.
|
||||
This means that by default, your new <tt>library</tt> object is able
|
||||
to handle TrueType, Type 1, CID-keyed & OpenType/CFF fonts
|
||||
gracefully.</p>
|
||||
</li>
|
||||
</ul>
|
||||
|
||||
<p>As you can see, the function returns an error code, like most others
|
||||
in the FreeType API. An error code of 0 <em>always</em> means that
|
||||
the operation was successful; otherwise, the value describes the error,
|
||||
and <tt>library</tt> is set to NULL.</p>
|
||||
|
||||
<hr>
|
||||
|
||||
<h3>
|
||||
3. Load a font face
|
||||
</h3>
|
||||
|
||||
<h4>
|
||||
a. From a font file
|
||||
</h4>
|
||||
|
||||
<p>Create a new <em>face</em> object by calling <tt>FT_New_Face</tt>.
|
||||
A <em>face</em> describes a given typeface and style. For example,
|
||||
"Times New Roman Regular" and "Times New Roman Italic" correspond to
|
||||
two different faces.</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
FT_Library library; /* handle to library */
|
||||
FT_Face face; /* handle to face object */
|
||||
|
||||
error = FT_Init_FreeType( &library );
|
||||
if ( error ) { ... }
|
||||
|
||||
error = FT_New_Face( library,
|
||||
"/usr/share/fonts/truetype/arial.ttf",
|
||||
0,
|
||||
&face );
|
||||
if ( error == FT_Err_Unknown_File_Format )
|
||||
{
|
||||
... the font file could be opened and read, but it appears
|
||||
... that its font format is unsupported
|
||||
}
|
||||
else if ( error )
|
||||
{
|
||||
... another error code means that the font file could not
|
||||
... be opened or read, or simply that it is broken...
|
||||
}</pre>
|
||||
</font>
|
||||
|
||||
<p>As you can certainly imagine, <tt>FT_New_Face</tt> opens a font
|
||||
file, then tries to extract one face from it. Its parameters are</p>
|
||||
|
||||
<table cellpadding=5>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>library</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>handle to the FreeType library instance where the face object
|
||||
is created</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>filepathname</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>the font file pathname (standard C string).</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>face_index</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>Certain font formats allow several font faces to be embedded
|
||||
in a single file.</p>
|
||||
|
||||
<p>This index tells which face you want to load. An error will
|
||||
be returned if its value is too large.</p>
|
||||
|
||||
<p>Index 0 always work though.</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>face</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>A <em>pointer</em> to the handle that will be set to describe
|
||||
the new face object.</p>
|
||||
|
||||
<p>It is set to NULL in case of error.</p>
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
|
||||
<p>To know how many faces a given font file contains, simply load its
|
||||
first face (use <tt>face_index</tt>=0), then see the value of
|
||||
<tt>face->num_faces</tt> which indicates how many faces are embedded
|
||||
in the font file.</p>
|
||||
|
||||
<h4>
|
||||
b. From memory
|
||||
</h4>
|
||||
|
||||
<p>In the case where you have already loaded the font file in memory,
|
||||
you can similarly create a new face object for it by calling
|
||||
<tt>FT_New_Memory_Face</tt> as in</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
FT_Library library; /* handle to library */
|
||||
FT_Face face; /* handle to face object */
|
||||
|
||||
error = FT_Init_FreeType( &library );
|
||||
if ( error ) { ... }
|
||||
|
||||
error = FT_New_Memory_Face( library,
|
||||
buffer, /* first byte in memory */
|
||||
size, /* size in bytes */
|
||||
0, /* face_index */
|
||||
&face );
|
||||
if ( error ) { ... }</pre>
|
||||
</font>
|
||||
|
||||
<p>As you can see, <tt>FT_New_Memory_Face()</tt> simply takes a
|
||||
pointer to the font file buffer and its size in bytes instead of a
|
||||
file pathname. Other than that, it has exactly the same semantics as
|
||||
<tt>FT_New_Face()</tt>.</p>
|
||||
|
||||
<h4>
|
||||
c. From other sources (compressed files, network, etc.)
|
||||
</h4>
|
||||
|
||||
<p>There are cases where using a file pathname or preloading the file
|
||||
in memory is simply not enough. With FreeType 2, it is possible
|
||||
to provide your own implementation of i/o routines.</p>
|
||||
|
||||
<p>This is done through the <tt>FT_Open_Face()</tt> function, which
|
||||
can be used to open a new font face with a custom input stream, select
|
||||
a specific driver for opening, or even pass extra parameters to the
|
||||
font driver when creating the object. We advise you to refer to the
|
||||
FreeType 2 reference manual in order to learn how to use it.</p>
|
||||
|
||||
<p>Note that providing a custom stream might also be used to access a
|
||||
TrueType font embedded in a Postscript Type 42 wrapper.</p>
|
||||
|
||||
<hr>
|
||||
|
||||
<h3>
|
||||
4. Accessing face content
|
||||
</h3>
|
||||
|
||||
<p>A <em>face object</em> models all information that globally describes
|
||||
the face. Usually, this data can be accessed directly by dereferencing
|
||||
a handle, like</p>
|
||||
|
||||
<table cellpadding=5>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>face->num_glyphs</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>Gives the number of <em>glyphs</em> available in the font face.
|
||||
A glyph is simply a character image. It doesn't necessarily
|
||||
correspond to a <em>character code</em> though.</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>face->flags</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>A 32-bit integer containing bit flags used to describe some
|
||||
face properties. For example, the flag
|
||||
<tt>FT_FACE_FLAG_SCALABLE</tt> is used to indicate that the face's
|
||||
font format is scalable and that glyph images can be rendered for
|
||||
all character pixel sizes. For more information on face flags,
|
||||
please read the <a href="#">FreeType 2 API Reference</a>.</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>face->units_per_EM</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>This field is only valid for scalable formats (it is set to 0
|
||||
otherwise). It indicates the number of font units covered by the
|
||||
EM.</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>face->num_fixed_sizes</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>This field gives the number of embedded bitmap <em>strikes</em>
|
||||
in the current face. A <em>strike</em> is simply a series of
|
||||
glyph images for a given character pixel size. For example, a
|
||||
font face could include strikes for pixel sizes 10, 12
|
||||
and 14. Note that even scalable font formats can have
|
||||
embedded bitmap strikes!</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>face->fixed_sizes</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>this is a pointer to an array of <tt>FT_Bitmap_Size</tt>
|
||||
elements. Each <tt>FT_Bitmap_Size</tt> indicates the horizontal
|
||||
and vertical <em>pixel sizes</em> for each of the strikes that are
|
||||
present in the face.</p>
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
|
||||
<p>For a complete listing of all face properties and fields, please read
|
||||
the <a href="#">FreeType 2 API Reference</a>.<p>
|
||||
|
||||
<hr>
|
||||
|
||||
<h3>
|
||||
5. Setting the current pixel size
|
||||
</h3>
|
||||
|
||||
<p>FreeType 2 uses "<em>size objects</em>" to model all
|
||||
information related to a given character size for a given face.
|
||||
For example, a size object will hold the value of certain metrics
|
||||
like the ascender or text height, expressed in 1/64th of a pixel,
|
||||
for a character size of 12 points.</p>
|
||||
|
||||
<p>When the <tt>FT_New_Face</tt> function is called (or one of its
|
||||
cousins), it <b>automatically</b> creates a new size object for
|
||||
the returned face. This size object is directly accessible as
|
||||
<b><tt>face->size</tt></b>.</p>
|
||||
|
||||
<p><em>NOTA BENE: a single face object can deal with one or more size
|
||||
objects at a time, however, this is something that few programmers
|
||||
really need to do. We have thus have decided to simplify the API for
|
||||
the most common use (i.e. one size per face), while keeping this
|
||||
feature available through additional fuctions.</em></p>
|
||||
|
||||
<p>When a new face object is created, its size object defaults to the
|
||||
character size of 10 pixels (both horizontally and vertically) for
|
||||
scalable formats. For fixed-sizes formats, the size is more or less
|
||||
undefined, which is why you must set it before trying to load a
|
||||
glyph.</p>
|
||||
|
||||
<p>To do that, simply call <tt>FT_Set_Char_Size()</tt>. Here is an
|
||||
example where the character size is set to 16pt for a 300x300 dpi
|
||||
device:</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
error = FT_Set_Char_Size(
|
||||
face, /* handle to face object */
|
||||
0, /* char_width in 1/64th of points */
|
||||
16*64, /* char_height in 1/64th of points */
|
||||
300, /* horizontal device resolution */
|
||||
300 ); /* vertical device resolution */</pre>
|
||||
</font>
|
||||
|
||||
<p>You will notice that:</p>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
<p>The character width and heights are specified in 1/64th of
|
||||
points. A point is a <em>physical</em> distance, equaling 1/72th
|
||||
of an inch, it's not a pixel..<p>
|
||||
</li>
|
||||
<li>
|
||||
<p>The horizontal and vertical device resolutions are expressed in
|
||||
<em>dots-per-inch</em>, or <em>dpi</em>. You can use 72 or
|
||||
96 dpi for display devices like the screen. The resolution
|
||||
is used to compute the character pixel size from the character
|
||||
point size.</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>A value of 0 for the character width means "<em>same as
|
||||
character height</em>", a value of 0 for the character height
|
||||
means "<em>same as character width</em>". Otherwise, it is possible
|
||||
to specify different char widths and heights.</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>Using a value of 0 for the horizontal or vertical resolution means
|
||||
72 dpi, which is the default.</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>The first argument is a handle to a face object, not a size
|
||||
object. That's normal, and must be seen as a convenience.</p>
|
||||
</li>
|
||||
</ul>
|
||||
|
||||
<p>This function computes the character pixel size that corresponds to
|
||||
the character width and height and device resolutions. However, if you
|
||||
want to specify the pixel sizes yourself, you can simply call
|
||||
<tt>FT_Set_Pixel_Sizes()</tt>, as in</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
error = FT_Set_Pixel_Sizes(
|
||||
face, /* handle to face object */
|
||||
0, /* pixel_width */
|
||||
16 ); /* pixel_height */</pre>
|
||||
</font>
|
||||
|
||||
<p>This example will set the character pixel sizes to 16x16 pixels.
|
||||
As previously, a value of 0 for one of the dimensions means
|
||||
"<em>same as the other</em>".</p>
|
||||
|
||||
<p>Note that both functions return an error code. Usually, an error
|
||||
occurs with a fixed-size font format (like FNT or PCF) when trying to
|
||||
set the pixel size to a value that is not listed in the
|
||||
<tt><b>face->fixed_sizes</b></tt> array.</p>
|
||||
|
||||
<hr>
|
||||
|
||||
<h3>
|
||||
6. Loading a glyph image
|
||||
</h3>
|
||||
|
||||
<h4>
|
||||
a. Converting a character code into a glyph index
|
||||
</h4>
|
||||
|
||||
<p>Usually, an application wants to load a glyph image based on its
|
||||
<em>character code</em>, which is a unique value that defines the
|
||||
character for a given <em>encoding</em>. For example, the character
|
||||
code 65 represents the `A' in ASCII encoding.</p>
|
||||
|
||||
<p>A face object contains one or more tables, called
|
||||
<em>charmaps</em>, that are used to convert character codes to glyph
|
||||
indices. For example, most TrueType fonts contain two charmaps. One
|
||||
is used to convert Unicode character codes to glyph indices, the other
|
||||
is used to convert Apple Roman encoding into glyph indices. Such
|
||||
fonts can then be used either on Windows (which uses Unicode) and
|
||||
Macintosh (which uses Apple Roman, bwerk). Note also that a given
|
||||
charmap might not map to all the glyphs present in the font.</p>
|
||||
|
||||
<p>By default, when a new face object is created, it lists all the
|
||||
charmaps contained in the font face and selects the one that supports
|
||||
Unicode character codes if it finds one. Otherwise, it tries to find
|
||||
support for Latin-1, then ASCII.</p>
|
||||
|
||||
<p>We will describe later how to look for specific charmaps in a face.
|
||||
For now, we will assume that the face contains at least a Unicode
|
||||
charmap that was selected during <tt>FT_New_Face()</tt>. To convert a
|
||||
Unicode character code to a font glyph index, we use
|
||||
<tt>FT_Get_Char_Index()</tt> as in</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
glyph_index = FT_Get_Char_Index( face, charcode );</pre>
|
||||
</font>
|
||||
|
||||
<p>This will look the glyph index corresponding to the given
|
||||
<tt>charcode</tt> in the charmap that is currently selected for the
|
||||
face. If charmap is selected, the function simply returns the
|
||||
charcode.</p>
|
||||
|
||||
<p>Note that this is one of the rare FreeType functions that do not
|
||||
return an error code. However, when a given character code has no
|
||||
glyph image in the face, the value 0 is returned. By convention,
|
||||
it always correspond to a special glyph image called the <b>missing
|
||||
glyph</b>, which usually is represented as a box or a space.</p>
|
||||
|
||||
<h4>
|
||||
b. Loading a glyph from the face
|
||||
</h4>
|
||||
|
||||
<p>Once you have a glyph index, you can load the corresponding glyph
|
||||
image. Note that the glyph image can be in several formats. For
|
||||
example, it will be a bitmap for fixed-size formats like FNT, FON, or
|
||||
PCF. It will also be a scalable vector outline for formats like
|
||||
TrueType or Type 1. The glyph image can also be stored in an
|
||||
alternate way that is not known at the time of writing this
|
||||
documentation.</p>
|
||||
|
||||
<p>The glyph image is always stored in a special object called a
|
||||
<em>glyph slot</em>. As its name suggests, a glyph slot is simply a
|
||||
container that is able to hold one glyph image at a time, be it a
|
||||
bitmap, an outline, or something else. Each face object has a single
|
||||
glyph slot object that can be accessed as
|
||||
<b><tt>face->glyph</tt></b>.</p>
|
||||
|
||||
<p>Loading a glyph image into the slot is performed by calling
|
||||
<tt>FT_Load_Glyph()</tt> as in</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
error = FT_Load_Glyph(
|
||||
face, /* handle to face object */
|
||||
glyph_index, /* glyph index */
|
||||
load_flags ); /* load flags, see below */</pre>
|
||||
</font>
|
||||
|
||||
<p>The <tt>load_flags</tt> value is a set of bit flags used to
|
||||
indicate some special operations. The default value
|
||||
<tt>FT_LOAD_DEFAULT</tt> is 0.</p>
|
||||
|
||||
<p>This function will try to load the corresponding glyph image
|
||||
from the face. Basically, this means that:</p>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
<p>If a bitmap is found for the corresponding glyph and pixel
|
||||
size, it will in the slot (embedded bitmaps are always
|
||||
favored over native image formats, because we assume that
|
||||
they are higher-quality versions of the same image. This
|
||||
can be ignored by using the FT_LOAD_NO_BITMAP flag)</p>
|
||||
</li>
|
||||
|
||||
<li>
|
||||
<p>Otherwise, a native image for the glyph will be loaded.
|
||||
It will also be scaled to the current pixel size, as
|
||||
well as hinted for certain formats like TrueType and
|
||||
Type1.</p>
|
||||
</li>
|
||||
</ul>
|
||||
|
||||
<p>The field <tt><b>glyph->format</b></tt> describe the format
|
||||
used to store the glyph image in the slot. If it is not
|
||||
<tt>ft_glyph_format_bitmap</tt>, one can immediately
|
||||
convert it to a bitmap through <tt>FT_Render_Glyph</tt>,
|
||||
as in:</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
error = FT_Render_Glyph(
|
||||
face->glyph, /* glyph slot */
|
||||
render_mode ); /* render mode */
|
||||
</pre>
|
||||
</font>
|
||||
|
||||
<p>The parameter <tt>render_mode</tt> is a set of bit flags used
|
||||
to specify how to render the glyph image. Set it to 0 to render
|
||||
a monochrome bitmap, or to <tt>ft_render_mode_antialias</tt> to
|
||||
generate a high-quality (256 gray levels) anti-aliased bitmap
|
||||
from the glyph image.</p>
|
||||
|
||||
<p>Once you have a bitmap glyph image, you can access it directly
|
||||
through <tt><b>glyph->bitmap</b></tt> (a simple bitmap descriptor),
|
||||
and position it through <tt><b>glyph->bitmap_left</b></tt> and
|
||||
<tt><b>glyph->bitmap_top</b></tt>.</p>
|
||||
|
||||
<p>Note that <tt>bitmap_left</tt> is the horizontal distance from the
|
||||
current pen position to the left-most border of the glyph bitmap,
|
||||
while <tt>bitmap_top</tt> is the vertical distance from the
|
||||
pen position (on the baseline) to the top-most border of the
|
||||
glyph bitmap. <em>It is positive to indicate an upwards
|
||||
distance</em>.</p>
|
||||
|
||||
<p>The next section will detail the content of a glyph slot and
|
||||
how to access specific glyph information (including metrics).</p>
|
||||
|
||||
<h4>
|
||||
c. Using other charmaps
|
||||
</h4>
|
||||
|
||||
<p>As said before, when a new face object is created, it will look for
|
||||
a Unicode, Latin-1, or ASCII charmap and select it. The currently
|
||||
selected charmap is accessed via <b><tt>face->charmap</tt></b>. This
|
||||
field is NULL when no charmap is selected, which typically happens
|
||||
when you create a new <tt>FT_Face</tt> object from a font file that
|
||||
doesn't contain an ASCII, Latin-1, or Unicode charmap (rare
|
||||
stuff).</p>
|
||||
|
||||
<p>There are two ways to select a different charmap with FreeType 2.
|
||||
The easiest is when the encoding you need already has a corresponding
|
||||
enumeration defined in <tt><freetype/freetype.h></tt>, as
|
||||
<tt>ft_encoding_big5</tt>. In this case, you can simply call
|
||||
<tt>FT_Select_CharMap</tt> as in:</p>
|
||||
|
||||
<font color="blue"><pre>
|
||||
error = FT_Select_CharMap(
|
||||
face, /* target face object */
|
||||
ft_encoding_big5 ); /* encoding.. */
|
||||
</pre></font>
|
||||
|
||||
<p>Another way is to manually parse the list of charmaps for the
|
||||
face, this is accessible through the fields
|
||||
<tt><b>num_charmaps</b></tt> and <tt><b>charmaps</b></tt>
|
||||
(notice the 's') of the face object. As you could expect,
|
||||
the first is the number of charmaps in the face, while the
|
||||
second is <em>a table of pointers to the charmaps</em>
|
||||
embedded in the face.</p>
|
||||
|
||||
<p>Each charmap has a few visible fields used to describe it more
|
||||
precisely. Mainly, one will look at
|
||||
<tt><b>charmap->platform_id</b></tt> and
|
||||
<tt><b>charmap->encoding_id</b></tt> that define a pair of
|
||||
values that can be used to describe the charmap in a rather
|
||||
generic way.</p>
|
||||
|
||||
<p>Each value pair corresponds to a given encoding. For example,
|
||||
the pair (3,1) corresponds to Unicode. Their list is
|
||||
defined in the TrueType specification but you can also use the
|
||||
file <tt><freetype/ftnameid.h></tt> which defines several
|
||||
helpful constants to deal with them..</p>
|
||||
|
||||
<p>To look for a specific encoding, you need to find a corresponding
|
||||
value pair in the specification, then look for it in the charmaps
|
||||
list. Don't forget that some encoding correspond to several
|
||||
values pair (yes it's a real mess, but blame Apple and Microsoft
|
||||
on such stupidity..). Here's some code to do it:</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
FT_CharMap found = 0;
|
||||
FT_CharMap charmap;
|
||||
int n;
|
||||
|
||||
for ( n = 0; n < face->num_charmaps; n++ )
|
||||
{
|
||||
charmap = face->charmaps[n];
|
||||
if ( charmap->platform_id == my_platform_id &&
|
||||
charmap->encoding_id == my_encoding_id )
|
||||
{
|
||||
found = charmap;
|
||||
break;
|
||||
}
|
||||
}
|
||||
|
||||
if ( !found ) { ... }
|
||||
|
||||
/* now, select the charmap for the face object */
|
||||
error = FT_Set_CharMap( face, found );
|
||||
if ( error ) { ... }</pre>
|
||||
</font>
|
||||
|
||||
<p>Once a charmap has been selected, either through
|
||||
<tt>FT_Select_CharMap</tt> or <tt>FT_Set_CharMap</tt>,
|
||||
it is used by all subsequent calls to
|
||||
<tt>FT_Get_Char_Index()</tt>.</p>
|
||||
|
||||
|
||||
<h4>
|
||||
d. Glyph Transforms:
|
||||
</h4>
|
||||
|
||||
<p>It is possible to specify an affine transformation to be applied
|
||||
to glyph images when they're loaded. Of course, this will only
|
||||
work for scalable (vectorial) font formats.</p>
|
||||
|
||||
<p>To do that, simply call <tt>FT_Set_Transform</tt>, as in:</p>
|
||||
|
||||
<font color="blue"><pre>
|
||||
error = FT_Set_Transform(
|
||||
face, /* target face object */
|
||||
&matrix, /* pointer to 2x2 matrix */
|
||||
&delta ); /* pointer to 2d vector */
|
||||
</pre></font>
|
||||
|
||||
<p>This function will set the current transform for a given face
|
||||
object. Its second parameter is a pointer to a simple
|
||||
<tt>FT_Matrix</tt> structure that describes a 2x2 affine matrix.
|
||||
The third parameter is a pointer to a <tt>FT_Vector</tt> structure
|
||||
that describe a simple 2d vector.</p>
|
||||
|
||||
<p>Note that the matrix pointer can be set to NULL, (in which case
|
||||
the identity transform will be used). Coefficients of the matrix
|
||||
are in 16.16 fixed float units.</p>
|
||||
|
||||
<p>The vector pointer can also be set to NULL (in which case a delta
|
||||
of (0,0) will be used). The vector coordinates are expressed in
|
||||
1/64th of a pixel (also known as 26.6 fixed floats).</p>
|
||||
|
||||
<p><em>NOTA BENE: The transform is applied every glyph that is loaded
|
||||
through <tt>FT_Load_Glyph</tt>. Note that loading a glyph bitmap
|
||||
with a non-trivial transform will produce an error..</em></p>
|
||||
|
||||
<hr>
|
||||
|
||||
<h3>
|
||||
7. Accessing glyph image data
|
||||
</h3>
|
||||
|
||||
<p>Glyph image data is accessible through <tt><b>face->glyph</b></tt>.
|
||||
See the definition of the <tt>FT_GlyphSlot</tt> type for more details.
|
||||
As stated previously, each face has a single glyph slot, where
|
||||
<em>one</em> glyph image <em>at a time</em> can be loaded. Each time
|
||||
you call <tt>FT_Load_Glyph()</tt>, you erase the content of the glyph
|
||||
slot with a new glyph image.</p>
|
||||
|
||||
<p>Note however that the glyph slot object itself doesn't change, only
|
||||
its content, which means that you can perfectly create a "shortcut" to
|
||||
access it as in</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
{
|
||||
/* shortcut to glyph slot */
|
||||
FT_GlyphSlot glyph = face->glyph;
|
||||
|
||||
for ( n = 0; n < face->num_glyphs; n++ )
|
||||
{
|
||||
... load glyph n ...
|
||||
... access glyph data as glyph->xxxx
|
||||
}
|
||||
}</pre>
|
||||
</font>
|
||||
|
||||
<p>The <tt>glyph</tt> variable will be valid until its parent
|
||||
<tt>face</tt> is destroyed. Here are a few important fields of the
|
||||
glyph slot:<p>
|
||||
|
||||
<table cellpadding=5>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>glyph->format</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>Indicates the type of the loaded glyph image. Can be either
|
||||
<tt>ft_glyph_format_bitmap</tt>, <tt>ft_glyph_format_outline</tt>,
|
||||
or other values.</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>glyph->metrics</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>A simple structure used to hold the glyph image's metrics.
|
||||
Note that <em>most distances are expressed in 1/64th of
|
||||
pixels!</em> See the API reference or the user guide for a
|
||||
description of the <tt>FT_Glyph_Metrics</tt> structure.</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>glyph->bitmap</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>If the glyph slot contains a bitmap, a simple
|
||||
<tt>FT_Bitmap</tt> that describes it. See the API reference or
|
||||
user guide for a description of the <tt>FT_Bitmap</tt>
|
||||
structure.</p>
|
||||
</td>
|
||||
</tr>
|
||||
<tr valign="top">
|
||||
<td>
|
||||
<tt><b>glyph->outline</b></tt>
|
||||
</td>
|
||||
<td>
|
||||
<p>When the glyph slot contains a scalable outline, this structure
|
||||
describes it. See the definition of the <tt>FT_Outline</tt>
|
||||
structure.</p>
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
|
||||
<h3>
|
||||
8. Rendering glyph outlines into bitmaps
|
||||
</h3>
|
||||
|
||||
<p>You can easily test the format of the glyph image by inspecting the
|
||||
<tt>face->glyph->format</tt> variable. If its value is
|
||||
<tt>ft_glyph_format_bitmap</tt>, the glyph image that was loaded is a
|
||||
bitmap that can be directly blit to your own surfaces through your
|
||||
favorite graphics library (FreeType 2 doesn't provide bitmap
|
||||
blitting routines, as you may imagine :-)</p>
|
||||
|
||||
<p>If the format is <tt>ft_glyph_format_outline</tt> or something else,
|
||||
the library provides a means to convert such glyph images to bitmaps
|
||||
through what are called <b>rasters</b>.</p>
|
||||
|
||||
<p>On the other hand, if the image is a scalable outline or something
|
||||
else, FreeType provides a function to convert the glyph image into a
|
||||
pre-existing bitmap that you will handle to it, named
|
||||
<tt>FT_Get_Glyph_Bitmap</tt>. Here's a <em>simple</em> example code
|
||||
that renders an outline into a <b>monochrome</b> bitmap:</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
{
|
||||
FT_GlyphSlot glyph;
|
||||
|
||||
... load glyph ...
|
||||
|
||||
glyph = face->glyph; /* shortcut to glyph data */
|
||||
if ( glyph->format == ft_glyph_format_outline )
|
||||
{
|
||||
FT_Bitmap bit;
|
||||
|
||||
/* set-up a bitmap descriptor for our target bitmap */
|
||||
bit.rows = bitmap_height;
|
||||
bit.width = bitmap_width;
|
||||
bit.pitch = bitmap_row_bytes;
|
||||
/* render into a mono bitmap */
|
||||
bit.pixel_mode = ft_pixel_mode_mono;
|
||||
bit.buffer = bitmap_buffer;
|
||||
|
||||
/* render the outline directly into the bitmap */
|
||||
error = FT_Get_Glyph_Bitmap( face, &bit );
|
||||
if ( error ) { ... }
|
||||
}
|
||||
}</pre>
|
||||
</font>
|
||||
|
||||
<p>You should note that <b><em><tt>FT_Get_Glyph_Bitmap()</tt> doesn't
|
||||
create the bitmap</em></b>. It only needs a descriptor, of type
|
||||
<tt>FT_Bitmap</tt>, and writes directly into it.</p>
|
||||
|
||||
<p>Note that the FreeType scan-converter for outlines can also generate
|
||||
anti-aliased glyph bitmaps with 128 level of grays. For now, it is
|
||||
restricted to rendering to 8-bit gray-level bitmaps, though this may
|
||||
change in the future. Here is some code to do just that:</p>
|
||||
|
||||
<font color="blue">
|
||||
<pre>
|
||||
{
|
||||
FT_GlyphSlot glyph;
|
||||
|
||||
... load glyph ...
|
||||
|
||||
glyph = face->glyph; /* shortcut to glyph data */
|
||||
if ( glyph->format == ft_glyph_format_outline )
|
||||
{
|
||||
FT_Bitmap bit;
|
||||
|
||||
/* set-up a bitmap descriptor for our target bitmap */
|
||||
bit.rows = bitmap_height;
|
||||
bit.width = bitmap_width;
|
||||
bit.pitch = bitmap_row_bytes;
|
||||
/* 8-bit gray-level bitmap */
|
||||
bit.pixel_mode = ft_pixel_mode_gray;
|
||||
/* MUST be 128 for now */
|
||||
bit.grays = 128;
|
||||
bit.buffer = bitmap_buffer;
|
||||
|
||||
/* clean the bitmap - IMPORTANT */
|
||||
memset( bit.buffer, 0, bit.rows*bit.pitch );
|
||||
|
||||
/* render the outline directly into the bitmap */
|
||||
error = FT_Get_Glyph_Bitmap( face, &bit );
|
||||
if ( error ) { ... }
|
||||
}
|
||||
}</pre>
|
||||
</font>
|
||||
|
||||
<p>You will notice that</p>
|
||||
|
||||
<ul>
|
||||
<li>
|
||||
<p>As previously, <tt>FT_Get_Glyph_Bitmap()</tt> doesn't generate
|
||||
the bitmap, it simply renders to it.</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>The target bitmap must be cleaned before calling the function.
|
||||
This is a limitation of our current anti-aliasing algorithm and is
|
||||
EXTREMELY important.</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>The anti-aliaser uses 128 levels of grays exclusively for
|
||||
now (this will probably change in a near future). This means that
|
||||
you <b>must</b> set <tt>bit.grays</tt> to 128. The generated
|
||||
image uses values from 0 (back color) to 127 (foreground color).</p>
|
||||
</li>
|
||||
<li>
|
||||
<p>It is <b>not</b> possible to render directly an anti-aliased
|
||||
outline into a pre-existing gray-level bitmap, or even any
|
||||
colored-format one (like RGB16 or paletted 8-bits). We will not
|
||||
discuss this issue in great details here, but the reason is that we
|
||||
do not want to deal with graphics composition (or alpha-blending)
|
||||
within FreeType.<p/>
|
||||
</li>
|
||||
</ul>
|
||||
</td></tr>
|
||||
</table>
|
||||
</center>
|
||||
|
||||
</body>
|
||||
</html>
|
||||
Loading…
Reference in New Issue