3 <title>FreeType 2 FAQ</title>
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20 <font size=1>http://www.freetype.org</font><p>
23 <a href="freetype.html">
24 <img src="image/freetype.jpg" width=550 height=105 alt="The FreeType Project" border=0></a>
25 <h1>The FreeType 2 FAQ</h1>
28 <center><table width=750 cellspacing=10 cellpadding=30><tr><td>
33 <li><p><a href="#general">General</a>
35 <li><a href="#general-dead">I thought the FreeType project was dead. It this true?</a></li>
36 <li><a href="#general-long">Why did it take so long to release FreeType 2?</a></li>
37 <li><a href="#general-unix">Is FreeType 2 a Unix-only project?</a></li>
38 <li><a href="#general-x11">When will X11 support anti-aliased glyphs?</a></li>
39 <li><a href="#general-ft1">Is FreeType 2 backwards compatible with 1.x?</a></li>
40 <li><a href="#general-edit">Can I use FreeType 2 to edit fonts or create new ones?</a></li>
43 <li><p><a href="#builds">Compilation & Configuration</a>
45 <li><a href="#builds-compile">How do I compile the FreeType 2 library?</a></li>
46 <li><a href="#builds-config">How do I configure my library build?</a></li>
47 <li><a href="#builds-modules">How do I select the modules I need?</a></li>
48 <li><a href="#builds-flat">How do I compile all FreeType 2 files in a single directory?</a></li>
51 <li><p><a href="#library">Using the FreeType 2 library</a></p></li>
52 <li><p><a href="#autohint">The FreeType 2 Autohinter</a>
54 <li><a href="#autohint-license">Under which license is the auto-hinter released ?</a></li>
55 <li><a href="#autohint-work">How does auto-hinting work in FreeType 2 ?</a></li>
56 <li><a href="#autohint-cjk">Why doesn't the auto-hinter work well with CJK fonts ?</a></li>
59 <li><p><a href="#other">Other questions</a>
61 <li><a href="#other-antialias">What is the anti-aliasing algorithm used in the FreeType 2 renderer?</a></li>
62 <li><a href="#other-opentype">When will FreeType 2 support OpenType ?</a></li>
70 <table width="100%" cellspacing=5><tr bgcolor="#CCCCEE"><td>
71 <h2 align=center><a name="general">General questions & answers</h2>
74 <a name="general-dead">
75 <h3>I.1. I though the FreeType project was dead. Is this true?</h3>
77 <p>Well, not exactly :-) It's true that the TrueType patents issues
78 have been less than a graceful event to handle but it didn't not
79 really killed the project per se, as Apple hasn't made an official
80 statement yet regarding the use of the patented "technology" in
81 open source projects (or other products).</p>
83 <p>We have thus continued updating FreeType 1.x, and started developping
84 FreeType 2 with the idea of providing this time a completely patent
85 free font engine. However, we largely preferred not to broadly
86 communicate about it until we've got a satisfying implementation
91 <a name="general-long">
92 <h3>I.2. Why did it take so long to release FreeType 2?</h3>
94 <p>Several factors come to mind. The first one is that FreeType 2 is
95 a much more complex and dense project that was mostly developed
96 on non-working hours. And surely some important changes in the
97 life (like marriage, new jobs and kids) of some the FreeType
98 developers cannot be ignored :-)</p>
100 <p>A second one is that a first version of the library was designed
101 one year ago (and already worked with a multitude of font drivers),
102 though with a design that was judged by its authors as well as
103 beta testers as not enough flexible or consistent. In short, it worked
104 well but we were not exactly proud of it (call us perfectionists).
105 It has then be significantly reworked to become what we're now
106 distributing as FreeType 2</p>
108 <p>Finally, it would have been hard to distribute such a library without
109 an alternative technology to replace the patented bytecode interpreter.
110 This involved significant research work that could only be performed
111 correctly full-time, and we had to found a company to fund such a
112 development and still make it available under a BSD-like license.
113 Huge thanks to <a href="http://www.catharon.com">Catharon Productions, Inc.</a>
114 for their commitment to this project.</p>
116 <p>And of course, we added support for more font files, and we'll
117 continue to as long as the specs are available and that we find an
118 interest in it. For example, FreeType 2 is to date the only
119 software library available on the market that supports the new
120 Adobe "CEF" font format.</p>
123 <a name="general-unix">
124 <h3>I.3. Is FreeType 2 a Unix-only project?</h3>
126 <p>Absolutely not, even though many people still seem to think so :-)
127 FreeType 2, just like version 1.x, can be compiled on any platform with
128 an ANSI compiler. Some beta versions of the library are even heavily
129 used in brand new OSes (see the <a href="http://www.atheos.cx">AtheOS
130 </a> screenshots for examples).</p>
132 <p>The library is itself mainly developped on several platforms
133 (Windows & Linux, though a great deal has also been achieved on OS/2)
134 and the code is highly generic and modular to adapt even the most
135 strict environments like low-memory embedded systems.</p>
139 <a name="general-x11">
140 <h3>I.4. When will X11/XFree support anti-aliased text?</h3>
142 <p>This question isn't exactly related to FreeType as we have no direct
143 connection to the XFree people, but we've been asked so frequently
144 about it that it deserves a prominent place in this FAQ :-)</p>
146 <p>FreeType has been capable of anti-aliasing since version 1.0. The
147 reason why XFree doesn't support it is directly related to the
148 limitations of the design and specification of X11. More specifically:</p>
152 X11 assumes that all glyph images are monochrome bitmaps,
153 hence the X font library and server are unable to send anything
154 else to the X server.
158 Even if the X font library/server was able to generate anti-aliased
159 bitmaps (and this has been already done through extensions), the X
160 rendering model doesn't allow translucent composition of "gray" pixmaps
161 onto an arbitrary drawable.
165 <p>As both the font and rendering models of X11 are limited, it's basically
166 impossible to draw anti-aliased glyphs without performing <em>huge</em>
167 hacks within the server.</p>
169 <p>Note that Keith Packard, from XFree fame, has recently started working
170 on a new rendering model for X11 in order to support new features
171 (mainly transparency and anti-aliased fonts). This will be provided
172 through protocol extensions. The question of knowing wether legacy X
173 applications will be able to display anti-aliased text is still very
178 <a name="general-ft1">
179 <h3>I.5. Is FreeType 2 backwards compatible with FreeType 1.x?</h3>
181 <p>Not directly, though we had the project to provide an optional binary
182 compatibility layer on top of it in order to easily re-link applications
183 with the new version. However, this idea has been dropped as it is
184 possible to install and use the two versions independtly on any
185 system (read: no namespace conflicts).</p>
187 <p>The FreeType 2 API is a lot simpler than the one in 1.x while being
188 much more powerful. We thus encourage you to adapt your source code
189 to it as this should not involve much work.</p>
193 <a name="general-edit">
194 <h3>I.6. Can I use FreeType 2 to edit fonts or create new ones?</h3>
196 <p>The answer is a definitive NO, because the library was specifically
197 designed to <em>read</em> font files with small code size and very
198 low memory usage.</p>
200 <p>We thus do not plan to support editing or creation in the font
201 engine in any way, as this would imply a complete rewrite. This
202 doesn't mean that we won't introduce a font editing/creation library
203 in the future, as this really depends on how many people are asking
204 for it (or how much they would be willing to pay for it), as well as
205 the time of the FreeType developers.</p>
207 <p>Do not expect anything in this direction until we officially announce
208 something though. There are other axis of development for this project
209 (like text-layout capabilities, glyph caching, etc..) that may be more
210 important to us at the moment..</p>
215 <table width="100%" cellspacing=5><tr bgcolor="#CCCCEE"><td>
216 <h2 align=center><a name="builds">Compilation & Configuration</h2>
219 <a name="builds-compile">
220 <h3>II.1. How do I compile the FreeType 2 library?</h3>
222 <p>The library can be compiled in various ways, and a detailed documentation
223 is available in the file "<tt>freetype2/docs/BUILD</tt>". However, we'll
224 summarize the process to a few cases:</p>
226 <h3>a. by using the command-line 2 build system</h3>
228 <p>The engine comes with a sophisticated build system that is used
229 to configure and compile a build of the library. You'll need
230 <em>GNU Make</em> installed on your platform (NOTE: It will <b>not</b>
231 work with other Make tools).</p>
233 <p>Basically, you'll need to invoke <tt>make</tt> a first time in the
234 top-level FreeType 2 directory in order to setup the build. This will
235 detect your current platform and choose a configuration sub-makefile to
236 drive the build. A specific compiler can be selected on some platforms
237 by providing an additional target. For example, on Win32:</p>
240 <li><b><tt>make visualc</tt></b> will select the Visual C++ compiler</li>
241 <li><b><tt>make lcc</tt></b> will select the Win32-lcc compiler</li>
244 <p>Note that on Unix, the first time make is called, a configure script
245 located in "<tt>freetype2/builds/unix</tt>" will be run in order to
246 automatically detect the platform & compiler.</p>
248 <p>A summary will be displayed showing the detected platform and compiler
249 selected. You'll then be able to start the build by invoking <tt>make</tt>
250 a second time. In case of problem, consult the <tt>BUILD</tt> document.</p>
253 <h3>b. by direct compilation</h3>
255 <p>You can also directly compile the library from the command line by
256 using these simple rules:</p>
260 You should place the directories "<tt>freetype2/include</tt>" and
261 "<tt>freetype2/src</tt>" in your include path in order to compile
262 any component of the library. You can also add the system-specific
263 build directory (i.e. "<tt>builds/<em>system</em>/</tt>") in the
264 case where an alternate implementation of some of the components
265 is available there (e.g. the memory-mapped i/o implementation
266 on some Unix systems).
270 The components of the library are located in sub-directories of
271 "<tt>src</tt>", for example: "<tt>src/base</tt>",
272 "<tt>src/truetype</tt>", etc..
276 Each component is normally compiled through a single C file that
277 "wraps" other sources in the component's directory. For example,
278 your should compile the TrueType font driver by compiling the
279 file "<tt>src/truetype/truetype.c</tt>". The list of C files to
280 compile for a feature-complete build of the library is given in
281 the <tt>BUILD</tt> document.
285 <h3>c. in a graphical IDE</h3>
287 <p>Well, the process is vastly similar to the one described in b.,
288 except that you need to set the include paths, source code paths,
289 etc.. in dialog boxes before running the compilation.
295 <a name="builds-config">
296 <h3>II.2. How do I configure my build of the library?</h3>
298 <p>Each build of the library is configured through two header files
299 located in "<tt>include/freetype/config</tt>":</p>
302 <li><p><b><tt>ftoption.h</tt></b><br>
303 This file contains various configuration macros whose definition
304 can be toggled on a per-build basis. Each macro is heavily
305 commented in this file's comment, and we invite you to refer
306 to it directly.</p></li>
308 <li><p><b><tt>ftmodule.h</tt></b><br>
309 This file contains the list of all the modules that are initially
310 registered (added) when the function <b><tt>FT_Init_FreeType</tt></b>
311 is called. See the next answer to know how to change it and
312 why it may be important.</p></li>
315 <p>Alternatively, some specific implementations of some FT2 components
316 can be provided in a "<tt>builds/<em>system</em>/</tt>" directory
317 (e.g. the Unix-specific <tt>ftsystem.c</tt> that uses memory-mapped
321 <a name="builds-modules">
322 <h3>II.3. How do I select the modules I need in my build?</h3>
324 <p>The function <tt><b>FT_Init_FreeType</b></tt> creates a new instance
325 of the FT2 library and registers a set of "default" modules before
326 returning to the calling application. Its default implementation
327 is in the file "<tt>src/base/ftinit.c</tt>".</p>
329 <p>The list of default modules used by <tt>ftinit.c</tt> is located in
330 the configuration file "<tt>include/freetype/config/ftmodule.h</tt>".
331 It is normally automatically generated by the build system by
332 invoking the "<tt><b>make modules</b></tt>" command in the top
333 level FT2 directory (note: only works with GNU Make, you can
334 edit the file by hand otherwise). It does so by parsing all
335 sub-directories of "<tt>src</tt>" that contain a file named
336 <tt>module.mk</tt>.</p>
338 <p>Note that a specific port or project is free to provide its own
339 implementation of <tt>ftinit.c</tt> in order to ensure a different
340 initialisation sequence. For example, one could do something like:</p>
343 <li><p>compile each module as a shared library (DLL or .so) with
344 a common "entry point" to retrieve a pointer to its
345 module class (there is already some code that allows this
346 when compiling each module).</p></li>
348 <li><p>place these modules in a directory like
349 "<tt>/usr/lib/freetype2/modules/</tt>"</p></li>
351 <li><p>provide an implementation of <tt>ftinit.c</tt> that would
352 scan the directory for valid modules.</p></li>
355 <p>This example only emphasize the flexibility that is left to
356 developers when building the library.</p>
360 <a name="builds-flat">
361 <h3>II.4. How do I compile all FreeType 2 files in a single directory?</h3>
363 <p>Some projects may need, for the sake of simplicity or ease of
364 building, to compile the FT2 library with all source files
365 copied to a single directory. This is possible.</p>
367 <p>To do so, you'll need to copy all source files located under
368 "<tt>src</tt>" to your own directory (you must retain the
369 include files in a distinct hierarchy though), then compile
370 each of the FreeType 2 component with the macro
371 <tt><b>FT_FLAT_COMPILE</b></tt>. This will change the way
372 <tt><b>#include</b></tt> works during the build.</p>
377 <table width="100%" cellspacing=5><tr bgcolor="#CCCCEE"><td>
378 <h2 align=center><a name="library">Using the FreeType 2 library</h2>
383 <table width="100%" cellspacing=5><tr bgcolor="#CCCCEE"><td>
384 <h2 align=center><a name="autohint">The FreeType 2 auto-hinter</h2>
387 <a name="autohint-license">
388 <h3>IV.1. Under which license is the FreeType 2 auto-hinter released</h3>
390 <p>The auto-hinter was initially designed and implemented under contract
391 for <a href="http://www.catharon.com">Catharon Productions, Inc</a>
392 which gladly accepted to released it under an open-source license
393 compatible with the FreeType one.</p>
395 <p>This license can be found in "<tt>src/autohint/CatharonLicense.txt</tt>"
396 and requires that you cite Catharon Productions in your documentation
397 (just like you do with FreeType) when using the auto-hinting module.</p>
399 <p>Other than that, you still have the same freedom than with the good old
400 FreeType license. Enjoy !</p>
403 <a name="autohint-work">
404 <h3>IV.2. How does the auto-hinter works ?</h3>
406 <p>Well, a complete description would be difficult. Have a look at the
407 dedicated <a href="autohinting/index.html">auto-hinter pages</a> on the FreeType
408 site, as they describe most of its details with graphics and explanations.
409 You could also look at the source code if you want to :-)</p>
411 <p>To give a few details, the auto-hinter is used to perform grid-fitting
412 on scalable font formats that use bezier outlines as their primary glyph
413 image format (this means nearly all scalable font formats today). When
414 a given font driver doesn't provide its own hinter, the auto-hinter is
415 used by default. When a format-specific hinter is provided, it is still
416 possible to use the auto-hinter using the
417 <tt><b>FT_LOAD_FORCE_AUTOHINT</b></tt> bit flag when calling
418 <tt>FT_Load_Glyph</tt>.</p>
420 <p>The auto-hinter currently doesn't use external hints to do its job,
421 as it automatically computes global metrics (when it "opens" a font
422 for the first time) and glyph "hints" from their outline. Note that
423 we plan the ability to specify external hints, given that it is based
424 on a constraint system. That could be used to support native hints
425 in Type 1/Type 2 fonts, for example.</p>
428 <a name="autohint-cjk">
429 <h3>IV.3. Why does the auto-hinter doesn't work correctly with CJK fonts ?</h3>
431 <p>The auto-hinter was first designed to manage and hint latin-based fonts,
432 as they consist of most of the fonts available today. It doesn't hint
433 asian fonts, as well as a few other complex scripts, because we didn't
434 put enough research on the topic yet. Hinting CJK isn't really more
435 difficult than latin, just different with a set of different constraints
436 (basically, more distortion of glyphs is acceptable as long as certain
437 features like triple-stem positions are respected more strictly..).</p>
439 <p>We thus plan to handle such a case rather rapidly.. Please be patient.</p>
445 <table width="100%" cellspacing=5><tr bgcolor="#CCCCEE"><td>
446 <h2 align=center><a name="other">Other questions</h2>
449 <a name="other-antialias">
450 <h3>V.1. What is the anti-aliasing algorithm used by FreeType 2 ?</h3>
452 <p>The algorithm has been specifically designed for FreeType. It is
453 based on ideas that were originally found in the implementation
454 of the <a href="http://www.levien.com/libart">libArt</a> graphics
455 library to compute the <em>exact pixel coverage</em> of a vector
456 image with absolutely now sub-sampling/filtering.
459 <p>However, these two implementations are radically distinct and use
460 vastly different models. The FreeType 2 renderer is optimized
461 specifically for rendering small complex shapes, like glyphs, at
462 very high speed while using very few memory; while libArt shines
463 at general shape/polygon processing, especially large ones.</p>
465 <p>The FT2 anti-aliasing renderer is indeed <em>faster</em> than the
466 monochrome renderer for small character sizes (typically < 20 pixels).
467 This is explained because the monochrome renderer must perform two
468 passes on the outline in order to perform drop-out control according
469 to the TrueType spec (we could drop this requirement later though).</p>
471 <p>We'll try to document its design in a later document, though this is
472 not a priority for now.</p>
475 <a name="other-opentype">
476 <h3>V.2. When will FreeType 2 support OpenType ?</h3>
478 <p>Well, the engine already reads OpenType/CFF files perfectly. What it
479 doesn't do is handle "OpenType Layout" tables yet.</p>
481 <p>FreeType 1 comes with a set of extensions that are used to load
482 and manage OpenType Layout tables. It even has a demonstration program
483 named "<tt>ftstrtto</tt>" used to demonstrate its capabilities that
484 runs pretty smooth.</p>
486 <p>For FreeType 2, we have decided that the layout operations provided
487 through these tables is better placed in a specific text-layout library,
488 (many people having asked for such a thing). This new engine would not
489 depend on FT2 explicitely and will be developed as a separate project.
490 We plan to announce it in a few weeks with all gory details,
491 once the definitive 2.0 release of FreeType has been made.</p>
498 <a href="index.html">Back to FreeType homepage</a><p>