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<!doctype html public "-//w3c//dtd html 4.0 transitional//en" "http://www.w3.org/TR/REC-html40/loose.dtd"><html><head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <meta name="Author" content="David Turner"> <title>FreeType 2 FAQ</title></head><body text="#000000" bgcolor="#FFFFFF" link="#0000EF" vlink="#51188E" alink="#FF0000"><font size=1>http://www.freetype.org</font><p><h1 align=center> <a href="freetype.html"> <img src="image/freetype.jpg" width=550 height=105 alt="The FreeType Project" border=0></a> <h1>The FreeType 2 FAQ</h1></h1><center><table width="75%"><tr><td> <hr><p> Document index <ul> <li><a href="#general">General</a> <ul><p> <li> <a href="#general-what">What is FreeType 2 ?</a> </li> <li> <a href="#general-uses">What can I do with FreeType 2 ?</a> </li> <li> <a href="#general-donts">What can't I do with FreeType 2 ?</a> </li> <li> <a href="#general-portability">How portable is FreeType 2 ?</a> </li> <li> <a href="#general-freetype1">What are the differences between FreeType 1.x and FreeType 2 ?</a> </li> <li> <a href="#general-truetype">What about the TrueType patents ?</a> </li> <li> <a href="#general-ft1">Is FreeType 2 backwards compatible to FreeType 1.x?</a> </li> <li> <a href="#general-edit">Can I use FreeType 2 to edit fonts or create new ones?</a> </li> </p></ul> </li> <li><a href="#builds">Compilation & Configuration</a> <ul><p> <li> <a href="#builds-compile">How do I compile the FreeType 2 library?</a> </li> <li> <a href="#builds-problems">I've tried to compile FreeType 2, but I'm having problems. What can I do ?</a> </li> <li> <a href="#builds-config">How do I configure my library build?</a> </li> <li> <a href="#builds-modules">How do I select the modules I need?</a> </li> <li> <a href="#builds-flat">How do I compile all FreeType 2 files in a single directory?</a> </li> </p></ul> </li> <li> <a href="#autohint">The FreeType 2 autohinter</a> <ul><p> <li> <a href="#autohint-license">Under which license is the auto-hinter released?</a> </li> <li> <a href="#autohint-work">How does auto-hinting work in FreeType 2?</a> </li> <li> <a href="#autohint-cjk">Why doesn't the auto-hinter work well with CJK fonts?</a> </li> </p></ul> </li> <li> <a href="#other">Other questions</a> <ul><p> <li> <a href="#other-bbox">How can I compute the dimensions of glyphs before rendering them ?</a> </li> <li> <a href="#other-ascent">How can I determine the ascent, descent or "x-height" of glyphs before rendering them ?</a> </li> <li> <a href="#other-color">How can I set the color of text rendered by FreeType?</a> </li> <li> <a href="#other-depth">Can I use FreeType to draw text on a pixmap with arbitrary depth?</a> </li> <li> <a href="#other-size">I set the pixel size to 8x8, but the resulting glyphs are larger than that. Why?</a> </li> <li> <a href="#other-bbox">How can I compute the bounding box of a text string without loading its glyphs?</a> </li> <li> <a href="#other-antialias">Which anti-aliasing algorithm is used in the FreeType 2 renderer?</a> </li> <li> <a href="#other-opentype">When will FreeType 2 support OpenType?</a> </li> </p></ul> </li> </ul> <p><hr></p> <table width="100%"> <tr bgcolor="#CCCCEE"><td> <h2 align=center> <a name="general">General questions & answers </h2> </td></tr> <tr><td> <p> <a name="general-what"> <h3> I.1 What is FreeType 2 ? </h3> <p>It's a software library that can be used by all kinds of applications to access the content of font files. Most notably, it supports the following "features":</p> <ul> <li><p> It provides a uniform interface to access font files. It supports both bitmap and scalable formats, including TrueType, OpenType, Type1, CID, CFF, Windows FON/FNT, X11 PCF. </p></li> <li><p> It supports high-speed anti-aliased glyph bitmap generation with 256 levels of gray. </p></li> <li><p> It is extremely modular, each font format being supported by a specific module. A build of the library can be tailored to support only the formats you need, thus reducing code size (a minimal anti-aliasing build of FreeType can be less than 30 Kb) </p></li> </ul> <hr><a name="general-uses"> <h3> I.2 What can I do with FreeType 2 ? </h3> <p>FreeType 2 is already used in countless product. For example:</p> <ul> <li>in graphics subsystem and libraries to display text</li> <li>in text layout and pagination services to measure and eventually render text</li> <li>in font inspection and conversion tools</li> </ul> <p>Generally speaking, the library allows you to access and manage the content of font files in a very easy way.</p> <hr><a name="general-donts"> <h3> I.3 What can't I do with FreeType 2 ? </h3> <p>FreeType 2 doesn't try to perform a number of sophisticated things, because it focuses on being an excellent <em>font service</em>.</p> <p>This means that the following are not supported directly by the library, even though they can be more or less be implemented on top of it, or by using it:</p> <ul> <li><p><b>rendering glyphs to arbitrary surfaces</b><br> FT2 doesn't try to be a graphics library and thus only supports two pixel formats when rendering glyphs: monochrome 1-bit bitmaps, or 8-bit gray-level pixmaps.</p> <p>If you need to draw glyphs to other kinds of surfaces (for example, a 24-bit RGB pixmap), you'll need to use your favorite graphics library to do just that.</p> <p><em>Note however that in the case of rendering scalable glyph outlines to anti-aliased pixmaps, an application can also provide its own rendering callback in order to draw or compose directly the anti-aliased glyph on any target surface.</em></p> </li> <li><p><b>glyph caching</b><br> Each time you request a glyph image from a font, FT2 does it by parsing the relevant portion of the font file/stream and interpreting it according to its font format. This can be very slow for certain formats, including scalable ones like TrueType or Type 1.</p> <p>Any decent text-rendering sub-system must thus be capable of caching glyph data in order to reach appropriate rendering speed</p> <p><em>Note that we provide a beta caching sub-system with FreeType 2 since version 2.0.1. Even though you're free to write your own to suit your needs.</em></p> </li> <li><p><b>text layout</b><br> The library doesn't support the text layout operations. Sophisticated operations like glyph substitution, positioning (kerning), justification, bi-directional ordering, etc.. are not part of a <em>font service</em> in itself.</p> </ul> <hr><a name="general-portability"> <h3> I.4 How portable is FreeType 2 ? </h3> <p>The FreeType 2 source code is <em>extremely</em> portable for the following reasons:</p> <ul> <li>Everything is written in standard ANSI C</li> <li>We're very pedantic to avoid any kinds of compiler warnings. The current source code has been compiled with many compilers without producing a single warning.</li> <li>The library doesn't use any static writable data at all, making it an ideal choice on various embedded systems (e.g. it can be run from ROM directly)</li> </ul> <p>Meanwhile, we've made great efforts to ensure that the library is both efficient, compact and customizable.</p> <hr><a name="general-freetype1"> <h3> I.5 What are the differences between FreeType 1.x and FreeType 2 ? </h3> <p>The biggest differences are that:</p> <ul> <li><p> FT1 only supports the TrueType format, while FT2 does a lot more. </p></li> <li><p> The FT2 API is simpler as well as more powerful than the FT1 API, </p></li> <li><p> FT1 includes an extension to support OpenType text layout processing. This support is not part of FT2, but has been moved to a distinct project, called <em>FreeType Layout</em>. ( FT Layout is not currently available though..) </p></li> </ul> <hr><a name="general-ft1"> <h3> I.6 Is FreeType 2 backwards compatible with FreeType 1.x? </h3> <p>Not directly, though we had the project to provide an optional binary compatibility layer on top of it in order to easily re-link applications with the new version. However, this idea has been dropped as it is possible to install and use the two versions independently on any system (read: no namespace conflicts).</p> <p>The FreeType 2 API is a lot simpler than the one in 1.x while being much more powerful. We thus encourage you to adapt your source code to it as this should not involve much work.</p> <hr> <a name="general-edit"> <h3> I.6 Can I use FreeType 2 to edit fonts or create new ones? </h3> <p>The answer is a definitive <b>no</b>, because the library was specifically designed to <em>read</em> font files with small code size and very low memory usage.</p> <p>We thus do not plan to support editing or creation in the font engine in any way, as this would imply a complete rewrite. This doesn't mean that we won't introduce a font editing/creation library in the future, as this really depends on how many people are asking for it (or how much they would be willing to pay for it), as well as the time of the FreeType developers.</p> <p>Do not expect anything in this direction until we officially announce something though. There are other axes of development for this project (like text-layout capabilities, glyph caching, etc.) that may be more important to us at the moment.</p> </td></tr> </table> <br> <table width="100%"> <tr bgcolor="#CCCCEE"><td> <h2 align=center> <a name="builds">Compilation & Configuration </h2> </td></tr> <tr><td> <a name="builds-compile"> <h3> II.1 How do I compile the FreeType 2 library? </h3> <p>The library can be compiled in various ways, and a detailed documentation is available in the file <tt>freetype2/docs/BUILD</tt>. However, we will summarize the process to a few cases:</p> <h4> a. Using the command-line 2 build system </h4> <p>The engine comes with a sophisticated build system that is used to configure and compile a build of the library. You will need <em>GNU Make</em> installed on your platform (<b>Note:</b> It will <em>not</em> work with other Make tools).</p> <p>Basically, you will need to invoke <tt>make</tt> a first time in the top-level FreeType 2 directory in order to set up the build. This will detect your current platform and choose a configuration sub-makefile to drive the build. A specific compiler can be selected on some platforms by providing an additional target. For example, on Win32:</p> <ul> <li> <b><tt>make visualc</tt></b> will select the Visual C++ compiler </li>⌨️ 快捷键说明
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