forked from minhngoc25a/freetype2
503 lines
21 KiB
HTML
503 lines
21 KiB
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<title>FreeType 2 FAQ</title>
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alink="#FF0000">
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<font size=1>http://www.freetype.org</font><p>
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<center>
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<a href="freetype.html">
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<img src="image/freetype.jpg" width=550 height=105 alt="The FreeType Project" border=0></a>
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<h1>The FreeType 2 FAQ</h1>
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<center><table width=750 cellspacing=10 cellpadding=30><tr><td>
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<hr><p>
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DOCUMENT INDEX:<br>
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<ul>
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<li><p><a href="#general">General</a>
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<ul>
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<li><a href="#general-dead">I thought the FreeType project was dead. It this true?</a></li>
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<li><a href="#general-long">Why did it take so long to release FreeType 2?</a></li>
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<li><a href="#general-unix">Is FreeType 2 a Unix-only project?</a></li>
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<li><a href="#general-x11">When will X11 support anti-aliased glyphs?</a></li>
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<li><a href="#general-ft1">Is FreeType 2 backwards compatible with 1.x?</a></li>
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<li><a href="#general-edit">Can I use FreeType 2 to edit fonts or create new ones?</a></li>
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</ul></p>
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</li>
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<li><p><a href="#builds">Compilation & Configuration</a>
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<ul>
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<li><a href="#builds-compile">How do I compile the FreeType 2 library?</a></li>
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<li><a href="#builds-config">How do I configure my library build?</a></li>
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<li><a href="#builds-modules">How do I select the modules I need?</a></li>
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<li><a href="#builds-flat">How do I compile all FreeType 2 files in a single directory?</a></li>
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</ul>
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</p></li>
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<li><p><a href="#library">Using the FreeType 2 library</a></p></li>
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<li><p><a href="#autohint">The FreeType 2 Autohinter</a>
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<ul>
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<li><a href="#autohint-license">Under which license is the auto-hinter released ?</a></li>
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<li><a href="#autohint-work">How does auto-hinting work in FreeType 2 ?</a></li>
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<li><a href="#autohint-cjk">Why doesn't the auto-hinter work well with CJK fonts ?</a></li>
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</ul>
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</p></li>
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<li><p><a href="#other">Other questions</a>
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<ul>
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<li><a href="#other-antialias">What is the anti-aliasing algorithm used in the FreeType 2 renderer?</a></li>
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<li><a href="#other-opentype">When will FreeType 2 support OpenType ?</a></li>
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</ul></p>
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</li>
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</ul><p>
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<hr><p>
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<table width="100%" cellspacing=5><tr bgcolor="#CCCCEE"><td>
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<h2 align=center><a name="general">General questions & answers</h2>
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</td></tr><tr><td>
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<a name="general-dead">
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<h3>I.1. I though the FreeType project was dead. Is this true?</h3>
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<ul>
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<p>Well, not exactly :-) It's true that the TrueType patents issues
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have been less than a graceful event to handle but it didn't not
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really killed the project per se, as Apple hasn't made an official
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statement yet regarding the use of the patented "technology" in
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open source projects (or other products).</p>
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<p>We have thus continued updating FreeType 1.x, and started developping
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FreeType 2 with the idea of providing this time a completely patent
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free font engine. However, we largely preferred not to broadly
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communicate about it until we've got a satisfying implementation
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to show.</p>
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</ul>
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<a name="general-long">
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<h3>I.2. Why did it take so long to release FreeType 2?</h3>
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<ul>
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<p>Several factors come to mind. The first one is that FreeType 2 is
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a much more complex and dense project that was mostly developed
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on non-working hours. And surely some important changes in the
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life (like marriage, new jobs and kids) of some the FreeType
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developers cannot be ignored :-)</p>
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<p>A second one is that a first version of the library was designed
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one year ago (and already worked with a multitude of font drivers),
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though with a design that was judged by its authors as well as
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beta testers as not enough flexible or consistent. In short, it worked
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well but we were not exactly proud of it (call us perfectionists).
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It has then be significantly reworked to become what we're now
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distributing as FreeType 2</p>
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<p>Finally, it would have been hard to distribute such a library without
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an alternative technology to replace the patented bytecode interpreter.
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This involved significant research work that could only be performed
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correctly full-time, and we had to found a company to fund such a
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development and still make it available under a BSD-like license.
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Huge thanks to <a href="http://www.catharon.com">Catharon Productions, Inc.</a>
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for their commitment to this project.</p>
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<p>And of course, we added support for more font files, and we'll
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continue to as long as the specs are available and that we find an
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interest in it. For example, FreeType 2 is to date the only
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software library available on the market that supports the new
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Adobe "CEF" font format.</p>
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</ul>
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<a name="general-unix">
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<h3>I.3. Is FreeType 2 a Unix-only project?</h3>
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<ul>
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<p>Absolutely not, even though many people still seem to think so :-)
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FreeType 2, just like version 1.x, can be compiled on any platform with
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an ANSI compiler. Some beta versions of the library are even heavily
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used in brand new OSes (see the <a href="http://www.atheos.cx">AtheOS
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</a> screenshots for examples).</p>
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<p>The library is itself mainly developped on several platforms
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(Windows & Linux, though a great deal has also been achieved on OS/2)
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and the code is highly generic and modular to adapt even the most
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strict environments like low-memory embedded systems.</p>
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</ul>
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<a name="general-x11">
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<h3>I.4. When will X11/XFree support anti-aliased text?</h3>
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<ul>
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<p>This question isn't exactly related to FreeType as we have no direct
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connection to the XFree people, but we've been asked so frequently
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about it that it deserves a prominent place in this FAQ :-)</p>
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<p>FreeType has been capable of anti-aliasing since version 1.0. The
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reason why XFree doesn't support it is directly related to the
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limitations of the design and specification of X11. More specifically:</p>
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<ul>
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<li><p>
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X11 assumes that all glyph images are monochrome bitmaps,
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hence the X font library and server are unable to send anything
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else to the X server.
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</p></li>
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<li><p>
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Even if the X font library/server was able to generate anti-aliased
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bitmaps (and this has been already done through extensions), the X
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rendering model doesn't allow translucent composition of "gray" pixmaps
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onto an arbitrary drawable.
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</p></li>
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</ul>
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<p>As both the font and rendering models of X11 are limited, it's basically
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impossible to draw anti-aliased glyphs without performing <em>huge</em>
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hacks within the server.</p>
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<p>Note that Keith Packard, from XFree fame, has recently started working
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on a new rendering model for X11 in order to support new features
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(mainly transparency and anti-aliased fonts). This will be provided
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through protocol extensions. The question of knowing wether legacy X
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applications will be able to display anti-aliased text is still very
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uncertain.
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</p>
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</ul>
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<a name="general-ft1">
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<h3>I.5. Is FreeType 2 backwards compatible with FreeType 1.x?</h3>
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<ul>
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<p>Not directly, though we had the project to provide an optional binary
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compatibility layer on top of it in order to easily re-link applications
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with the new version. However, this idea has been dropped as it is
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possible to install and use the two versions independtly on any
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system (read: no namespace conflicts).</p>
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<p>The FreeType 2 API is a lot simpler than the one in 1.x while being
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much more powerful. We thus encourage you to adapt your source code
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to it as this should not involve much work.</p>
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</ul>
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<a name="general-edit">
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<h3>I.6. Can I use FreeType 2 to edit fonts or create new ones?</h3>
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<ul>
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<p>The answer is a definitive NO, because the library was specifically
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designed to <em>read</em> font files with small code size and very
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low memory usage.</p>
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<p>We thus do not plan to support editing or creation in the font
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engine in any way, as this would imply a complete rewrite. This
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doesn't mean that we won't introduce a font editing/creation library
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in the future, as this really depends on how many people are asking
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for it (or how much they would be willing to pay for it), as well as
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the time of the FreeType developers.</p>
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<p>Do not expect anything in this direction until we officially announce
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something though. There are other axis of development for this project
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(like text-layout capabilities, glyph caching, etc..) that may be more
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important to us at the moment..</p>
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</ul>
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</td></tr></table>
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<table width="100%" cellspacing=5><tr bgcolor="#CCCCEE"><td>
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<h2 align=center><a name="builds">Compilation & Configuration</h2>
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</td></tr><tr><td>
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<a name="builds-compile">
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<h3>II.1. How do I compile the FreeType 2 library?</h3>
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<ul>
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<p>The library can be compiled in various ways, and a detailed documentation
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is available in the file "<tt>freetype2/docs/BUILD</tt>". However, we'll
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summarize the process to a few cases:</p>
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<h3>a. by using the command-line 2 build system</h3>
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<p>The engine comes with a sophisticated build system that is used
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to configure and compile a build of the library. You'll need
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<em>GNU Make</em> installed on your platform (NOTE: It will <b>not</b>
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work with other Make tools).</p>
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<p>Basically, you'll need to invoke <tt>make</tt> a first time in the
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top-level FreeType 2 directory in order to setup the build. This will
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detect your current platform and choose a configuration sub-makefile to
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drive the build. A specific compiler can be selected on some platforms
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by providing an additional target. For example, on Win32:</p>
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<ul>
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<li><b><tt>make visualc</tt></b> will select the Visual C++ compiler</li>
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<li><b><tt>make lcc</tt></b> will select the Win32-lcc compiler</li>
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</ul>
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<p>Note that on Unix, the first time make is called, a configure script
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located in "<tt>freetype2/builds/unix</tt>" will be run in order to
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automatically detect the platform & compiler.</p>
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<p>A summary will be displayed showing the detected platform and compiler
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selected. You'll then be able to start the build by invoking <tt>make</tt>
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a second time. In case of problem, consult the <tt>BUILD</tt> document.</p>
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<h3>b. by direct compilation</h3>
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<p>You can also directly compile the library from the command line by
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using these simple rules:</p>
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<ul>
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<li><p>
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You should place the directories "<tt>freetype2/include</tt>" and
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"<tt>freetype2/src</tt>" in your include path in order to compile
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any component of the library. You can also add the system-specific
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build directory (i.e. "<tt>builds/<em>system</em>/</tt>") in the
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case where an alternate implementation of some of the components
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is available there (e.g. the memory-mapped i/o implementation
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on some Unix systems).
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</p></li>
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<li><p>
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The components of the library are located in sub-directories of
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"<tt>src</tt>", for example: "<tt>src/base</tt>",
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"<tt>src/truetype</tt>", etc..
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</p></li>
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<li><p>
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Each component is normally compiled through a single C file that
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"wraps" other sources in the component's directory. For example,
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your should compile the TrueType font driver by compiling the
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file "<tt>src/truetype/truetype.c</tt>". The list of C files to
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compile for a feature-complete build of the library is given in
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the <tt>BUILD</tt> document.
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</p></li>
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</ul>
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<h3>c. in a graphical IDE</h3>
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<ul>
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<p>Well, the process is vastly similar to the one described in b.,
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except that you need to set the include paths, source code paths,
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etc.. in dialog boxes before running the compilation.
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</p>
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</ul>
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</ul>
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<a name="builds-config">
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<h3>II.2. How do I configure my build of the library?</h3>
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<ul>
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<p>Each build of the library is configured through two header files
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located in "<tt>include/freetype/config</tt>":</p>
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<ul>
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<li><p><b><tt>ftoption.h</tt></b><br>
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This file contains various configuration macros whose definition
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can be toggled on a per-build basis. Each macro is heavily
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commented in this file's comment, and we invite you to refer
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to it directly.</p></li>
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<li><p><b><tt>ftmodule.h</tt></b><br>
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This file contains the list of all the modules that are initially
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registered (added) when the function <b><tt>FT_Init_FreeType</tt></b>
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is called. See the next answer to know how to change it and
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why it may be important.</p></li>
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</ul>
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<p>Alternatively, some specific implementations of some FT2 components
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can be provided in a "<tt>builds/<em>system</em>/</tt>" directory
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(e.g. the Unix-specific <tt>ftsystem.c</tt> that uses memory-mapped
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file for i/o).</p>
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</ul>
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<a name="builds-modules">
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<h3>II.3. How do I select the modules I need in my build?</h3>
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<ul>
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<p>The function <tt><b>FT_Init_FreeType</b></tt> creates a new instance
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of the FT2 library and registers a set of "default" modules before
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returning to the calling application. Its default implementation
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is in the file "<tt>src/base/ftinit.c</tt>".</p>
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<p>The list of default modules used by <tt>ftinit.c</tt> is located in
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the configuration file "<tt>include/freetype/config/ftmodule.h</tt>".
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It is normally automatically generated by the build system by
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invoking the "<tt><b>make modules</b></tt>" command in the top
|
||
|
|
level FT2 directory (note: only works with GNU Make, you can
|
||
|
|
edit the file by hand otherwise). It does so by parsing all
|
||
|
|
sub-directories of "<tt>src</tt>" that contain a file named
|
||
|
|
<tt>module.mk</tt>.</p>
|
||
|
|
|
||
|
|
<p>Note that a specific port or project is free to provide its own
|
||
|
|
implementation of <tt>ftinit.c</tt> in order to ensure a different
|
||
|
|
initialisation sequence. For example, one could do something like:</p>
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li><p>compile each module as a shared library (DLL or .so) with
|
||
|
|
a common "entry point" to retrieve a pointer to its
|
||
|
|
module class (there is already some code that allows this
|
||
|
|
when compiling each module).</p></li>
|
||
|
|
|
||
|
|
<li><p>place these modules in a directory like
|
||
|
|
"<tt>/usr/lib/freetype2/modules/</tt>"</p></li>
|
||
|
|
|
||
|
|
<li><p>provide an implementation of <tt>ftinit.c</tt> that would
|
||
|
|
scan the directory for valid modules.</p></li>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<p>This example only emphasize the flexibility that is left to
|
||
|
|
developers when building the library.</p>
|
||
|
|
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<a name="builds-flat">
|
||
|
|
<h3>II.4. How do I compile all FreeType 2 files in a single directory?</h3>
|
||
|
|
<ul>
|
||
|
|
<p>Some projects may need, for the sake of simplicity or ease of
|
||
|
|
building, to compile the FT2 library with all source files
|
||
|
|
copied to a single directory. This is possible.</p>
|
||
|
|
|
||
|
|
<p>To do so, you'll need to copy all source files located under
|
||
|
|
"<tt>src</tt>" to your own directory (you must retain the
|
||
|
|
include files in a distinct hierarchy though), then compile
|
||
|
|
each of the FreeType 2 component with the macro
|
||
|
|
<tt><b>FT_FLAT_COMPILE</b></tt>. This will change the way
|
||
|
|
<tt><b>#include</b></tt> works during the build.</p>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
</td></tr></table>
|
||
|
|
|
||
|
|
<table width="100%" cellspacing=5><tr bgcolor="#CCCCEE"><td>
|
||
|
|
<h2 align=center><a name="library">Using the FreeType 2 library</h2>
|
||
|
|
</td></tr><tr><td>
|
||
|
|
|
||
|
|
</td></tr></table>
|
||
|
|
|
||
|
|
<table width="100%" cellspacing=5><tr bgcolor="#CCCCEE"><td>
|
||
|
|
<h2 align=center><a name="autohint">The FreeType 2 auto-hinter</h2>
|
||
|
|
</td></tr><tr><td>
|
||
|
|
|
||
|
|
<a name="autohint-license">
|
||
|
|
<h3>IV.1. Under which license is the FreeType 2 auto-hinter released</h3>
|
||
|
|
<ul>
|
||
|
|
<p>The auto-hinter was initially designed and implemented under contract
|
||
|
|
for <a href="http://www.catharon.com">Catharon Productions, Inc</a>
|
||
|
|
which gladly accepted to released it under an open-source license
|
||
|
|
compatible with the FreeType one.</p>
|
||
|
|
|
||
|
|
<p>This license can be found in "<tt>src/autohint/CatharonLicense.txt</tt>"
|
||
|
|
and requires that you cite Catharon Productions in your documentation
|
||
|
|
(just like you do with FreeType) when using the auto-hinting module.</p>
|
||
|
|
|
||
|
|
<p>Other than that, you still have the same freedom than with the good old
|
||
|
|
FreeType license. Enjoy !</p>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<a name="autohint-work">
|
||
|
|
<h3>IV.2. How does the auto-hinter works ?</h3>
|
||
|
|
<ul>
|
||
|
|
<p>Well, a complete description would be difficult. Have a look at the
|
||
|
|
dedicated <a href="autohinting/index.html">auto-hinter pages</a> on the FreeType
|
||
|
|
site, as they describe most of its details with graphics and explanations.
|
||
|
|
You could also look at the source code if you want to :-)</p>
|
||
|
|
|
||
|
|
<p>To give a few details, the auto-hinter is used to perform grid-fitting
|
||
|
|
on scalable font formats that use bezier outlines as their primary glyph
|
||
|
|
image format (this means nearly all scalable font formats today). When
|
||
|
|
a given font driver doesn't provide its own hinter, the auto-hinter is
|
||
|
|
used by default. When a format-specific hinter is provided, it is still
|
||
|
|
possible to use the auto-hinter using the
|
||
|
|
<tt><b>FT_LOAD_FORCE_AUTOHINT</b></tt> bit flag when calling
|
||
|
|
<tt>FT_Load_Glyph</tt>.</p>
|
||
|
|
|
||
|
|
<p>The auto-hinter currently doesn't use external hints to do its job,
|
||
|
|
as it automatically computes global metrics (when it "opens" a font
|
||
|
|
for the first time) and glyph "hints" from their outline. Note that
|
||
|
|
we plan the ability to specify external hints, given that it is based
|
||
|
|
on a constraint system. That could be used to support native hints
|
||
|
|
in Type 1/Type 2 fonts, for example.</p>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<a name="autohint-cjk">
|
||
|
|
<h3>IV.3. Why does the auto-hinter doesn't work correctly with CJK fonts ?</h3>
|
||
|
|
<ul>
|
||
|
|
<p>The auto-hinter was first designed to manage and hint latin-based fonts,
|
||
|
|
as they consist of most of the fonts available today. It doesn't hint
|
||
|
|
asian fonts, as well as a few other complex scripts, because we didn't
|
||
|
|
put enough research on the topic yet. Hinting CJK isn't really more
|
||
|
|
difficult than latin, just different with a set of different constraints
|
||
|
|
(basically, more distortion of glyphs is acceptable as long as certain
|
||
|
|
features like triple-stem positions are respected more strictly..).</p>
|
||
|
|
|
||
|
|
<p>We thus plan to handle such a case rather rapidly.. Please be patient.</p>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
|
||
|
|
</td></tr></table>
|
||
|
|
|
||
|
|
<table width="100%" cellspacing=5><tr bgcolor="#CCCCEE"><td>
|
||
|
|
<h2 align=center><a name="other">Other questions</h2>
|
||
|
|
</td></tr><tr><td>
|
||
|
|
|
||
|
|
<a name="other-antialias">
|
||
|
|
<h3>V.1. What is the anti-aliasing algorithm used by FreeType 2 ?</h3>
|
||
|
|
<ul>
|
||
|
|
<p>The algorithm has been specifically designed for FreeType. It is
|
||
|
|
based on ideas that were originally found in the implementation
|
||
|
|
of the <a href="http://www.levien.com/libart">libArt</a> graphics
|
||
|
|
library to compute the <em>exact pixel coverage</em> of a vector
|
||
|
|
image with absolutely now sub-sampling/filtering.
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<p>However, these two implementations are radically distinct and use
|
||
|
|
vastly different models. The FreeType 2 renderer is optimized
|
||
|
|
specifically for rendering small complex shapes, like glyphs, at
|
||
|
|
very high speed while using very few memory; while libArt shines
|
||
|
|
at general shape/polygon processing, especially large ones.</p>
|
||
|
|
|
||
|
|
<p>The FT2 anti-aliasing renderer is indeed <em>faster</em> than the
|
||
|
|
monochrome renderer for small character sizes (typically < 20 pixels).
|
||
|
|
This is explained because the monochrome renderer must perform two
|
||
|
|
passes on the outline in order to perform drop-out control according
|
||
|
|
to the TrueType spec (we could drop this requirement later though).</p>
|
||
|
|
|
||
|
|
<p>We'll try to document its design in a later document, though this is
|
||
|
|
not a priority for now.</p>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<a name="other-opentype">
|
||
|
|
<h3>V.2. When will FreeType 2 support OpenType ?</h3>
|
||
|
|
<ul>
|
||
|
|
<p>Well, the engine already reads OpenType/CFF files perfectly. What it
|
||
|
|
doesn't do is handle "OpenType Layout" tables yet.</p>
|
||
|
|
|
||
|
|
<p>FreeType 1 comes with a set of extensions that are used to load
|
||
|
|
and manage OpenType Layout tables. It even has a demonstration program
|
||
|
|
named "<tt>ftstrtto</tt>" used to demonstrate its capabilities that
|
||
|
|
runs pretty smooth.</p>
|
||
|
|
|
||
|
|
<p>For FreeType 2, we have decided that the layout operations provided
|
||
|
|
through these tables is better placed in a specific text-layout library,
|
||
|
|
(many people having asked for such a thing). This new engine would not
|
||
|
|
depend on FT2 explicitely and will be developed as a separate project.
|
||
|
|
We plan to announce it in a few weeks with all gory details,
|
||
|
|
once the definitive 2.0 release of FreeType has been made.</p>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
</td></tr></table>
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
<p>
|
||
|
|
<a href="index.html">Back to FreeType homepage</a><p>
|
||
|
|
|
||
|
|
</td></tr></table>
|
||
|
|
</body>
|
||
|
|
</html>
|