599 lines
22 KiB
HTML
599 lines
22 KiB
HTML
<!doctype html public "-//w3c//dtd html 4.0 transitional//en"
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"http://www.w3.org/TR/REC-html40/loose.dtd">
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<html>
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<head>
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<meta http-equiv="Content-Type"
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content="text/html; charset=iso-8859-1">
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<meta name="Author"
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content="David Turner">
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<title>FreeType 2 FAQ</title>
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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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<font size=1>http://www.freetype.org</font><p>
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<h1 align=center>
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<a href="freetype.html">
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<img src="image/freetype.jpg"
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width=550 height=105
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alt="The FreeType Project"
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border=0></a>
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<h1>The FreeType 2 FAQ</h1>
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</h1>
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<center>
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<table width="75%">
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<tr><td>
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<hr><p>
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Document index
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<ul>
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<li><a href="#general">General</a>
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<ul><p>
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<li>
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<a href="#general-dead">I thought the FreeType project was dead.
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Is this true?</a>
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</li>
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<li>
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<a href="#general-long">Why did it take so long to release
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FreeType 2?</a>
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</li>
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<li>
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<a href="#general-unix">Is FreeType 2 a Unix-only
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project?</a>
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</li>
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<li>
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<a href="#general-x11">When will X11 support anti-aliased
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glyphs?</a>
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</li>
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<li>
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<a href="#general-ft1">Is FreeType 2 backwards compatible
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to FreeType 1.x?</a>
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</li>
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<li>
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<a href="#general-edit">Can I use FreeType 2 to edit fonts
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or create new ones?</a>
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</li>
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</p></ul>
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</li>
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<li><a href="#builds">Compilation & Configuration</a>
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<ul><p>
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<li>
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<a href="#builds-compile">How do I compile the FreeType 2
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library?</a>
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</li>
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<li>
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<a href="#builds-config">How do I configure my library build?</a>
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</li>
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<li>
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<a href="#builds-modules">How do I select the modules I need?</a>
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</li>
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<li>
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<a href="#builds-flat">How do I compile all FreeType 2 files
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in a single directory?</a>
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</li>
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</p></ul>
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</li>
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<li>
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<a href="#autohint">The FreeType 2 autohinter</a>
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<ul><p>
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<li>
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<a href="#autohint-license">Under which license is the auto-hinter
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released?</a>
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</li>
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<li>
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<a href="#autohint-work">How does auto-hinting work in
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FreeType 2?</a>
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</li>
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<li>
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<a href="#autohint-cjk">Why doesn't the auto-hinter work well
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with CJK fonts?</a>
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</li>
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</p></ul>
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</li>
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<li>
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<a href="#other">Other questions</a>
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<ul><p>
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<li>
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<a href="#other-antialias">Which anti-aliasing algorithm is
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used in the FreeType 2 renderer?</a>
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</li>
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<li>
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<a href="#other-opentype">When will FreeType 2 support
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OpenType?</a>
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</li>
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</p></ul>
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</li>
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</ul>
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<p><hr></p>
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<table width="100%">
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<tr bgcolor="#CCCCEE"><td>
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<h2 align=center>
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<a name="general">General questions & answers
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</h2>
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</td></tr>
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<tr><td>
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<a name="general-dead">
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<h3>
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I.1 I though the FreeType project was dead. Is this true?
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</h3>
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<p>Well, not exactly :-) It's true that the TrueType patents
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issues 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 open
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source projects (or other products).</p>
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<p>We have thus continued updating FreeType 1.x, and started
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developing FreeType 2 with the idea of providing this time a
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completely patent free font engine. However, we largely preferred not
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to broadly communicate about it until we've got a satisfying
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implementation to show.</p>
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<a name="general-long">
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<h3>
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I.2 Why did it take so long to release FreeType 2?
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</h3>
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<p>Several factors come to mind. The first one is that FreeType 2
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is a much more complex and dense project that was mostly developed
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during non-working hours. And surely some important changes in the life
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(like marriage, new jobs and kids) of some the FreeType developers
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cannot be ignored :-)</p>
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<p>A second one is that a first version of the library was designed one
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year ago (and already worked with a multitude of font drivers), though
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with a design that was judged by its authors as well as beta testers as
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not enough flexible or consistent. In short, it worked well but we were
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not exactly proud of it (call us perfectionists). It has then be
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significantly reworked to become what we are now distributing as
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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. Huge
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thanks to <a href="http://www.catharon.com">Catharon Productions,
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Inc.</a> for their commitment to this project.</p>
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<p>And of course, we added support for more font files, and we will
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continue to as long as the specifications are available and that we find
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an 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 Adobe
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"CEF" font format.</p>
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<a name="general-unix">
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<h3>
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I.3 Is FreeType 2 a Unix-only project?
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</h3>
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<p>Absolutely not, even though many people still seem to think
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so :-) FreeType 2, just like version 1.x, can be compiled
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on any platform with an ANSI compiler. Some beta versions of the
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library are even heavily used in brand new OSes (see the <a
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href="http://www.atheos.cx">AtheOS</a> screenshots for examples).</p>
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<p>The library is itself mainly developed on several platforms (Windows
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& Linux, though a great deal has also been achieved on OS/2) and the
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code is highly generic and modular to adapt even the most strict
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environments like low-memory embedded systems.</p>
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<a name="general-x11">
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<h3>
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I.4 When will X11/XFree support anti-aliased text?
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</h3>
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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 have 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.
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The 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
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specifically:</p>
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<ul>
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<li>
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X11 assumes that all glyph images are monochrome bitmaps, hence the
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X font library and server are unable to send anything else to
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the X server.
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</li>
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<li>
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Even if the X font library/server was able to generate
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anti-aliased bitmaps (and this has been already done through
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extensions), the X rendering model doesn't allow translucent
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composition of "gray" pixmaps onto an arbitrary drawable.
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</li>
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</ul>
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<p>As both the font and rendering models of X11 are limited, it is
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basically impossible to draw anti-aliased glyphs without performing
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<em>huge</em> hacks within the server.</p>
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<p>Note that Keith Packard, from XFree fame, has recently started
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working on a new rendering model for X11 in order to support new
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features (mainly transparency and anti-aliased fonts). This will be
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provided through protocol extensions. The question of knowing whether
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legacy X applications will be able to display anti-aliased text is still
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very uncertain.</p>
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<a name="general-ft1">
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<h3>
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I.5 Is FreeType 2 backwards compatible with FreeType 1.x?
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</h3>
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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 independently on any system
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(read: no namespace conflicts).</p>
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<p>The FreeType 2 API is a lot simpler than the one in 1.x
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while being much more powerful. We thus encourage you to adapt your
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source code to it as this should not involve much work.</p>
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<a name="general-edit">
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<h3>
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I.6 Can I use FreeType 2 to edit fonts or create new ones?
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</h3>
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<p>The answer is a definitive <b>no</b>, because the library was
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specifically designed to <em>read</em> font files with small code size
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and very low memory usage.</p>
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<p>We thus do not plan to support editing or creation in the font engine
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in any way, as this would imply a complete rewrite. This doesn't mean
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that we won't introduce a font editing/creation library in the future,
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as this really depends on how many people are asking for it (or how much
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they would be willing to pay for it), as well as the time of the
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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 axes 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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</td></tr>
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</table>
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<br>
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<table width="100%">
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<tr bgcolor="#CCCCEE"><td>
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<h2 align=center>
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<a name="builds">Compilation & Configuration
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</h2>
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</td></tr>
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<tr><td>
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<a name="builds-compile">
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<h3>
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II.1 How do I compile the FreeType 2 library?
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</h3>
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<p>The library can be compiled in various ways, and a detailed
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documentation is available in the file <tt>freetype2/docs/BUILD</tt>.
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However, we will summarize the process to a few cases:</p>
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<h4>
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a. Using the command-line 2 build system
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</h4>
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<p>The engine comes with a sophisticated build system that is used to
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configure and compile a build of the library. You will need <em>GNU
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Make</em> installed on your platform (<b>Note:</b> It will
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<em>not</em> work with other Make tools).</p>
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<p>Basically, you will need to invoke <tt>make</tt> a first time in
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the top-level FreeType 2 directory in order to set up the build.
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This will detect your current platform and choose a configuration
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sub-makefile to drive the build. A specific compiler can be selected
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on some platforms by providing an additional target. For example, on
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Win32:</p>
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<ul>
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<li>
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<b><tt>make visualc</tt></b> will select the Visual C++
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compiler
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</li>
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<li>
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<b><tt>make lcc</tt></b> will select the Win32-lcc compiler
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</li>
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</ul>
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<p>Note that on Unix, when the first time make is called, a configure
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script located in <tt>freetype2/builds/unix</tt> will be run in order
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to automatically detect the platform & compiler.</p>
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<p>A summary will be displayed showing the detected platform and
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compiler selected. You will then be able to start the build by
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invoking <tt>make</tt> a second time. In case of problem, consult the
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<tt>BUILD</tt> document.</p>
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<h4>
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b. Direct compilation
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</h4>
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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>
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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
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system-specific build directory (i.e.
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<tt>builds/<em>system</em>/</tt>) in the case where an alternate
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implementation of some of the components is available there (e.g.
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the memory-mapped i/o implementation on some Unix systems).
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</li>
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<li>
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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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</li>
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<li>
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Each component is normally compiled through a single C file that
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<em>wraps</em> other sources in the component's directory. For
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example, you should build the TrueType font driver by compiling
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the file <tt>src/truetype/truetype.c</tt>. The list of
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C files to compile for a feature-complete build of the
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library is given in the <tt>BUILD</tt> document.
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</li>
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</ul>
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<h4>
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c. Using a graphical IDE
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</h4>
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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, etc.
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in dialog boxes before running the compilation.</p>
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<a name="builds-config">
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<h3>
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II.2 How do I configure my build of the library?
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</h3>
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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>
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<tt>ftoption.h</tt>
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<br>
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This file contains various configuration macros whose definition can
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be toggled on a per-build basis. Each macro is heavily commented in
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this file's comment, and we invite you to refer to it directly.
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</li>
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<li>
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<tt>ftmodule.h</tt>
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<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 <tt>FT_Init_FreeType()</tt> is
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called. See the next answer to know how to change it and why it may
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be important.
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</li>
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</ul>
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<p>Alternatively, some specific implementations of some FreeType 2
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components can be provided in a <tt>builds/<em>system</em>/</tt>
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directory (e.g. the Unix-specific <tt>ftsystem.c</tt> that uses
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memory-mapped file for i/o).</p>
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<a name="builds-modules">
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<h3>
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II.3 How do I select the modules I need in my build?
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</h3>
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<p>The function <tt>FT_Init_FreeType()</tt> creates a new instance of
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the FreeType 2 library and registers a set of "default" modules
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before 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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Normally, it is automatically generated by the build system by invoking
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the "<tt><b>make modules</b></tt>" command in the top level
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FreeType 2 directory (Note: this only works with GNU Make; you can
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edit the file by hand otherwise). It does so by parsing all
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sub-directories of <tt>src</tt> that contain a file named
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<tt>module.mk</tt>.</p>
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<p>Note that a specific port or project is free to provide its own
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implementation of <tt>ftinit.c</tt> in order to ensure a different
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initialization sequence. For example, one could do something like:</p>
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<ul>
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<li>
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Compile each module as a shared library (DLL or <tt>.so</tt>) with a
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common "entry point" to retrieve a pointer to its module class
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(there is already some code that allows this when compiling each
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module).
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</li>
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<li>
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Place these modules in a directory like
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<tt>/usr/lib/freetype2/modules/</tt>.
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</li>
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<li>
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Provide an implementation of <tt>ftinit.c</tt> that would scan the
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directory for valid modules.
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</li>
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</ul>
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<p>This example only emphasizes the flexibility that is left to
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developers when building the library.</p>
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<a name="builds-flat">
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<h3>
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II.4 How do I compile all FreeType 2 files in a single
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directory?
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</h3>
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<p>Some projects may need, for the sake of simplicity or ease of
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building, to compile the FreeType 2 library with all source files
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copied to a single directory. This is possible.</p>
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<p>To do so, you have to copy all source files located under
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<tt>src</tt> to your own directory (you must retain the include files in
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a distinct hierarchy though), then compile each of the FreeType 2
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component with the macro <tt>FT_FLAT_COMPILE</tt>. This will change the
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way <tt>#include</tt> works during the build.</p>
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</td></tr>
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</table>
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<br>
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<table width="100%">
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<tr bgcolor="#CCCCEE"><td>
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<h2 align=center>
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<a name="autohint">The FreeType 2 auto-hinter
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</h2>
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</td></tr>
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<tr><td>
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<a name="autohint-license">
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<h3>
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III.1 Under which license is the FreeType 2 auto-hinter released?
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</h3>
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<p>The auto-hinter was initially designed and implemented under contract
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for <a href="http://www.catharon.com">Catharon Productions, Inc</a>
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which gladly accepted to released it under an open-source license
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compatible with the FreeType one.</p>
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<p>This license can be found in
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<tt>src/autohint/CatharonLicense.txt</tt> and requires that you cite
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Catharon Productions in your documentation (just like you do with
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FreeType) when using the auto-hinting module.</p>
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<p>Other than that, you still have the same freedom than with the good
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old FreeType license. Enjoy!</p>
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<a name="autohint-work">
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<h3>
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III.2 How does the auto-hinter work?
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</h3>
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<p>Well, a complete description would be difficult. Have a look at the
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dedicated <a href="autohinting/index.html">auto-hinter pages</a> on the
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FreeType site, as they describe most of its details with graphics and
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explanations. You could also look at the source code if you want
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to :-)</p>
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<p>To give a few details, the auto-hinter is used to perform
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grid-fitting on scalable font formats that use Bézier outlines as
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their primary glyph image format (this means nearly all scalable font
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|
formats today). If a given font driver doesn't provide its own hinter,
|
|
the auto-hinter is used by default. If a format-specific hinter is
|
|
provided, it is still possible to use the auto-hinter using the
|
|
<tt>FT_LOAD_FORCE_AUTOHINT</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>
|
|
|
|
<a name="autohint-cjk">
|
|
<h3>
|
|
III.3 Why does the auto-hinter doesn't work correctly with CJK
|
|
fonts?
|
|
</h3>
|
|
|
|
<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 in the near future. Please be
|
|
patient.</p>
|
|
</td></tr>
|
|
</table>
|
|
|
|
<br>
|
|
|
|
<table width="100%">
|
|
<tr bgcolor="#CCCCEE"><td>
|
|
<h2 align=center>
|
|
<a name="other">Other questions
|
|
</h2>
|
|
</td></tr>
|
|
<tr><td>
|
|
|
|
<a name="other-antialias">
|
|
<h3>
|
|
IV.1 Which anti-aliasing algorithm is used by FreeType 2?</h3>
|
|
|
|
<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 no 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 FreeType 2 anti-aliasing renderer is indeed <em>faster</em>
|
|
than the monochrome renderer for small character sizes (typically
|
|
<20 pixels). The reason is that the monochrome renderer must
|
|
perform two passes on the outline in order to perform drop-out control
|
|
according to the TrueType specification (we could drop this requirement
|
|
later though).</p>
|
|
|
|
<p>We will try to document its design in a later document, though this
|
|
is not a priority for now.</p>
|
|
|
|
<a name="other-opentype">
|
|
<h3>
|
|
IV.2 When will FreeType 2 support OpenType?
|
|
</h3>
|
|
|
|
<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>" to show its capabilities.</p>
|
|
|
|
<p>For FreeType 2, we have decided that the layout operations
|
|
provided through these tables are better placed in a specific
|
|
text-layout library, (many people having asked for such a thing). This
|
|
new engine will not depend on FreeType2 explicitly 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>
|
|
|
|
</td></tr>
|
|
</table>
|
|
|
|
<p><hr></p>
|
|
|
|
<a href="index.html">Back to FreeType homepage</a><p>
|
|
|
|
</td></tr>
|
|
</table>
|
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