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| author | Werner Lemberg <wl@gnu.org> | 2021-05-17 07:05:08 +0200 |
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| committer | Werner Lemberg <wl@gnu.org> | 2021-05-17 07:05:08 +0200 |
| commit | 38c51fccf2934a8e32e5175bbbd93aff002d5684 (patch) | |
| tree | 56d8782c724e16028ccd7eb625c81d9b8d04021b | |
| parent | a011888c912afebe6ba08b889aaf68f39dc3a5ca (diff) | |
ft2faq.html: Completely revised.
This commit updates the layout from FreeType 1 to FreeType 2 design, removes
outdated information and (slightly) updates the questions.
| -rw-r--r-- | freetype2/docs/ft2faq.html | 1216 |
1 files changed, 559 insertions, 657 deletions
diff --git a/freetype2/docs/ft2faq.html b/freetype2/docs/ft2faq.html index aac9fa3..af8da36 100644 --- a/freetype2/docs/ft2faq.html +++ b/freetype2/docs/ft2faq.html @@ -1,717 +1,619 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" - "http://www.w3.org/TR/html4/loose.dtd"> +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" + "http://www.w3.org/TR/html4/loose.dtd"> -<html> +<html lang="en"> <head> <meta http-equiv="Content-Type" - content="text/html; charset=US-ASCII"> + content="text/html; charset=utf-8"> + <meta http-equiv="Content-Style-Type" + content="text/css"> + <meta http-equiv="Content-Script-Type" + content="text/javascript"> <meta name="description" - content="FreeType FAQ"> + content="FreeType Documentation"> + <meta name="Author" + content="David Turner"> + + <link rel="icon" + href="../../image/favicon_-90.ico"> + <link rel="shortcut icon" + href="../../image/favicon_-90.ico"> <link rel="stylesheet" - href="../../css/freetype.css"> - <title>FreeType 2 FAQ</title> + type="text/css" + href="../../css/freetype2_-90.css"> + + <script type="text/javascript" + src="../../js/jquery-1.11.0.min.js"> + </script> + <script type="text/javascript" + src="../../js/jquery.ba-resize.min.js"> + </script> + <script type="text/javascript" + src="../../js/freetype2.js"> + </script> + + <title>FreeType FAQ</title> </head> -<body text="#000000" - bgcolor="#FFFFFF" - link="#0000EF" - vlink="#51188E" - alink="#FF0000"> - -<table width="100%" - border="0" - cellspacing="0" - cellpadding="5"> - <tr> - <td bgcolor="#06425F"> - <a href="../../index.html"> - <img src="../../image/fond3.jpg" - align="right" - border="0" - hspace="0" - vspace="0" - alt="FreeType Homepage"> - </a> - </td> - </tr> - - <tr> - <td bgcolor="#06425F"> - <h1 class="intro">FREETYPE 2 FAQ</h1> - </td> - </tr> - - <tr> - <td bgcolor="#669999"> - <a href="#general" - class="index">General</a> - <a href="#builds" - class="index">Compilation & - Configuration</a> - <a href="#autohint" - class="index">The FreeType 2 - auto-hinter</a> - <a href="#other" - class="index">Other</a> - <font color="#FFFFFF">|</font> - <a href="documentation.html" - class="index">FreeType 2 - documentation</a> - </td> - </tr> -</table> - -<table align="center" - width="80%"> - <tr> - <td> - <h1 class="section">Table of Contents</h1> - - <ul> - <li><a href="#general">General questions</a> + +<body> + +<div id="top" + class="bar"> + <h1><a href="../../index.html">FreeType</a> FAQ</h1> +</div> + + +<div id="wrapper"> + +<div class="colmask leftmenu"> + <div class="colright"> + <div class="col1wrap"> + <div class="col1"> + + + <!-- ************************************************** --> + + <div id="contents"> + <h3><a href="#general">General questions</a></h3> <ul> <li> - <a href="#general-what">What is FreeType 2?</a> + <a href="#general-what">What is FreeType?</a> </li> <li> - <a href="#general-uses">What can I do with - FreeType 2?</a> + <a href="#general-uses">What can I do with FreeType?</a> </li> <li> <a href="#general-donts">What can I not do with - FreeType 2?</a> + FreeType?</a> </li> <li> <a href="#general-portability">How portable is - FreeType 2?</a> + FreeType?</a> </li> <li> - <a href="#general-freetype1">What are the differences between - FreeType 1.x and FreeType 2?</a> + <a href="#general-edit">Can I use FreeType to edit fonts + or create new ones?</a> + </li> + </ul> + + <h3><a href="#builds">Compilation & + configuration</a></h3> + <ul> + <li> + <a href="#builds-compile">How do I compile the FreeType + library?</a> </li> <li> - <a href="#general-ft1">Is FreeType 2 backwards compatible - to FreeType 1.x?</a> + <a href="#builds-config">How do I configure my build of + the library?</a> </li> <li> - <a href="#general-edit">Can I use FreeType 2 to edit - fonts or create new ones?</a> + <a href="#builds-differences">Why does FreeType render + differently on different platforms?</a> </li> </ul> - </li> - <li><a href="#builds">Compilation & Configuration</a> + <h3><a href="#autohint">The FreeType auto-hinter</a></h3> <ul> <li> - <a href="#builds-compile">How do I compile the FreeType 2 - library?</a> + <a href="#autohint-work">How does the auto-hinter + work?</a> </li> <li> - <a href="#builds-config">How do I configure my library - build?</a> + <a href="#autohint-other-scripts">Why doesn't the + auto-hinter work well with my script?</a> </li> + </ul> + + <h3><a href="#other">Other questions</a></h3> + <ul> <li> - <a href="#builds-differences">Why does FreeType render - differently on different platforms?</a> + <a href="#other-depth">Can I use FreeType to draw text + on a pixmap with arbitrary depth?</a> + </li> + <li> + <a href="#other-color">How can I set the colour of text + rendered by FreeType?</a> + </li> + <li> + <a href="#other-size">I set the pixel size to 8×8, + but the resulting glyphs are larger (or smaller) 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 + before?</a> + </li> + <li> + <a href="#other-antialias">Which anti-aliasing algorithm + is used by FreeType?</a> + </li> + <li> + <a href="#other-opentype">When will FreeType support + OpenType?</a> + </li> + </ul> + </div> + + + <!-- ************************************************** --> + + <div id="faq"> + <a name="general"></a> + <h1>General questions</h1> + + <a name="general-what"></a> + <h3>What is FreeType?</h3> + + <p>It is a software library that can be used by all kinds of + applications to access the contents 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, and others.</p> + </li> + + <li> + <p>It supports high-speed, anti-aliased glyph bitmap + generation with 256 gray levels.</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 + 30kByte.</p> </li> </ul> - </li> - <li> - <a href="#autohint">The FreeType 2 auto-hinter</a> + <a name="general-uses"></a> + <h3>What can I do with FreeType?</h3> + + <p>FreeType is already used in many products. For example, + it serves as a font rendering engine</p> + <ul> <li> - <a href="#autohint-work">How does the auto-hinter work?</a> + in graphics subsystem and libraries to display text + (Android OS, Apple's iOS, and others), </li> <li> - <a href="#autohint-other-scripts">Why doesn't the auto-hinter - work well with my script?</a> + in text layout and pagination services to measure and + eventually render text, + </li> + <li> + in font inspection and conversion tools. </li> </ul> - </li> - <li> - <a href="#other">Other questions</a> + <p>Generally speaking, the library allows you to access and + manage the contents of font files in a very easy way.</p> + + <a name="general-donts"></a> + <h3>What can I not do with FreeType?</h3> + + <p>FreeType 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 features are not supported + directly by the library, even though they can be more or + less implemented on top of it, or by using it.</p> + <ul> <li> - <a href="#other-depth">Can I use FreeType to draw text on a - pixmap with arbitrary depth?</a> + <p><b>rendering glyphs to arbitrary surfaces</b><br> + + FreeType doesn't try to be a graphics library and thus + only supports a very small number of pixel formats + when rendering glyphs, in particular monochrome 1-bit + bitmaps and 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 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> - <a href="#other-color">How can I set the colour of text - rendered by FreeType?</a> + <p><b>glyph caching</b><br> + + Each time you request a glyph image from a font, + FreeType does it by parsing the relevant portion of + the font file or font stream and interpreting it + according to its font format. This can be very slow + for certain formats, including scalable ones like + TrueType or CFF.</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 caching sub-system with + FreeType. However, it might not suit your + needs.</em></p> </li> + <li> - <a href="#other-size">I set the pixel size to 8×8, but - the resulting glyphs are larger (or smaller) than that. - Why?</a> + <p><b>text layout</b><br> + + The library doesn't support text layout operations. + Sophisticated features like glyph substitution, + positioning (kerning), justification, bi-directional + ordering, etc., are not part of a + <em>font service</em> in itself. They must be handled + (at least) one level higher.</p> </li> + </ul> + + <a name="general-portability"></a> + <h3>How portable is FreeType?</h3> + + <p>FreeType's source code is <em>extremely</em> portable for + the following reasons.</p> + + <ul> <li> - <a href="#other-bbox">How can I compute the bounding box of a - text string without loading its glyphs before?</a> + <p>Everything is written in standard ANSI C.</p> </li> <li> - <a href="#other-antialias">Which anti-aliasing algorithm is - used by FreeType 2?</a> + <p>We are very pedantic to avoid any kinds of compiler + warnings. The current source code has been compiled + with many compilers without producing a single + warning.</p> </li> <li> - <a href="#other-opentype">When will FreeType 2 support - OpenType?</a> + <p>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). It + is completely thread-safe too.</p> </li> </ul> - </li> - </ul> - - <p><a href="#top" - class="index"> - <img src="../../image/top.gif" - width="35" - height="19" - align="right" - border="0" - hspace="0" - vspace="0" - alt="Top"></a></p> - - <hr> - - <h1 class="section"> - <a name="general"> - General questions - </a> - </h1> - - <a name="general-what"></a> - <h3> - What is FreeType 2? - </h3> - - <p>It is a software library that can be used by all kinds of - applications to access the contents 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, and - others.</p> - </li> - - <li> - <p>It supports high-speed anti-aliased glyph bitmap generation - with 256 gray levels.</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 30KB)</p> - </li> - </ul> - - <hr> - - <a name="general-uses"></a> - <h3> - What can I do with FreeType 2? - </h3> - - <p>FreeType 2 is already used in many products. For example, it - serves as a font rendering engine</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 contents of font files in a very easy way.</p> - - <hr> - - <a name="general-donts"></a> - <h3> - What can I not 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 features are not supported directly - by the library, even though they can be more or less implemented on - top of it, or by using it:</p> - - <ul> - <li> - <p><b>rendering glyphs to arbitrary surfaces</b><br> - FreeType 2 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 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, FreeType 2 - does it by parsing the relevant portion of the font file or font - 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 caching sub-system with - FreeType 2 since version 2.0.1 which has become quite stable - at the time of this writing (version 2.2.1). However, it might - not suit your needs.</em></p> - </li> - - <li> - <p><b>text layout</b><br> - The library doesn't support text layout operations. Sophisticated - features like glyph substitution, positioning (kerning), - justification, bi-directional ordering, etc.m are not part of a - <em>font service</em> in itself. They must be handled one level - higher.</p> - </li> - </ul> - - <hr> - - <a name="general-portability"></a> - <h3> - How portable is FreeType 2? - </h3> - - <p>The FreeType 2 source code is <em>extremely</em> portable for the - following reasons:</p> - - <ul> - <li> - <p>Everything is written in standard ANSI C.</p> - </li> - <li> - <p>We are very pedantic to avoid any kinds of compiler warnings. - The current source code has been compiled with many compilers - without producing a single warning.</p> - </li> - <li> - <p>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). It is completely thread-safe too.</p> - </li> - </ul> - - <p>We have made great efforts to ensure that the library is efficient, - compact, and customizable.</p> - - <hr> - - <a name="general-freetype1"></a> - <h3> - What are the differences between FreeType 1.x and - FreeType 2? - </h3> - - <p>The biggest differences are as follows.</p> - - <ul> - <li> - <p>FreeType 1 only supports the TrueType format, while - FreeType 2 supports a lot more.</p> - </li> - - <li> - <p>The FreeType 2 API is simpler as well as more powerful - than the FreeType 1 API.</p> - </li> - - <li> - <p>FreeType 1 includes an extension to support OpenType text - layout processing. This support hasn't become part of - FreeType 2; a much improved version is now part of the <a - href="http://www.pango.org">Pango</a> library.</p> - </li> - </ul> - - <hr> - - <a name="general-ft1"></a> - <h3> - Is FreeType 2 backwards compatible with FreeType 1.x? - </h3> - - <p>Short answer: No. However, transition from 1.x to 2 should be - rather straightforward.</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"></a> - <h3> - Can I use FreeType 2 to edit fonts or create new ones? - </h3> - - <p>No. The library has been specifically designed to <em>read</em> - font files with small code size and very low memory usage.</p> - - <p>A good, freely available font editor is <a - href="https://fontforge.github.io">FontForge</a>.</p> - - <p><a href="#top" - class="index"> - <img src="../../image/top.gif" - width="35" - height="19" - align="right" - border="0" - hspace="0" - vspace="0" - alt="Top"></a></p> - - <hr> - - <h1 class="section"> - <a name="builds"> - Compilation & Configuration - </a> - </h1> - - <a name="builds-compile"></a> - <h3> - How do I compile the FreeType 2 library? - </h3> - - <p>The library can be compiled in various ways, and detailed - documentation is available in documentation directory of the - FreeType 2 source tree.</p> - - <p>For compilation on the command line, GNU make is necessary; other - build tools won't work. The source bundle also comes with project - files for some graphical IDEs like Visual C; note, however, that those - files are sometimes not up to date since it is contributed code not - used by the core developers.</p> - - <hr> - - <a name="builds-config"></a> - <h3> - How do I configure my build of the library? - </h3> - - <p>This is fully described in the file <tt>CUSTOMIZATION</tt> in - FreeType's documentation directory. Basically, you have to edit the - header file <tt>ftoption.h</tt> for compile-time options and to select - the modules with the file <tt>modules.cfg</tt>. Finally, it is - possible to replace the standard system interface (dealing with memory - allocation and stream I/O) with a custom one.</p> - - <hr> - - <a name="builds-differences"></a> - <h3> - Why does FreeType render differently on different platforms? - </h3> - - <p>Different distributions compile FreeType with different options. - The developer version of a distribution's FreeType package, which is - needed to compile your program against FreeType, includes the file - <tt>ftoption.h</tt>. Compare each platform's copy of - <tt>ftoption.h</tt> to find the differences.</p> - - <p><a href="#top" - class="index"> - <img src="../../image/top.gif" - width="35" - height="19" - align="right" - border="0" - hspace="0" - vspace="0" - alt="Top"></a></p> - - <hr> - - <h1 class="section"> - <a name="autohint"> - The FreeType 2 auto-hinter - </a> - </h1> - - <a name="autohint-work"></a> - <h3> - How does the auto-hinter work? - </h3> - - <p><em>Please note that the name of auto-hinter module is - <b>autofit</b>, which is a reimplementation of the old autohint - module.</em></p> - - <p>A rather complete description of the hinting algorithm (which is - slightly out of date regarding the internal structures) can be found - in the TUG-boat article <a - href="http://www.tug.org/TUGboat/Articles/tb24-3/lemberg.pdf">Real-Time - Grid Fitting of Typographic Outlines</a>.</p> - - <p>The auto-hinter performs grid-fitting on scalable font formats that - use Bézier outlines as their primary glyph image format (this - means nearly all scalable font 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>Currently, the auto-hinter 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. - - <hr> - - <a name="autohint-other-scripts"></a> - <h3> - Why doesn't the auto-hinter work well with my script? - </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 now - supports Asian fonts, but not other complex scripts like Arabic.</p> - - <p>Hinting various scripts isn't really more difficult than Latin, - just different, with a set of different constraints, which must be - hard-coded into the autofit module. Volunteers welcome!</p> - - <p><a href="#top" - class="index"> - <img src="../../image/top.gif" - width="35" - height="19" - align="right" - border="0" - hspace="0" - vspace="0" - alt="Top"></a></p> - - <hr> - - <h1 class="section"> - <a name="other"> - Other questions - </a> - </h1> - - <a name="other-depth"></a> - <h3> - Can I use FreeType to draw text on a pixmap with arbitrary depth? - </h3> - - <p>Not directly, as FreeType is a font library, not a general-purpose - graphics library or text rendering service. However, note that the - anti-aliased renderer allows you to convert a vectorial glyph outline - into a list of ‘spans’ (i.e., horizontal pixel segments - with the same coverage) that can be rendered through user-provided - callbacks.</p> - - <p>By providing the appropriate span callback, you can render - anti-aliased text to any kind of surface. You can also use any - colour, fill pattern or fill image if you want to. This process is - called <em>direct rendering</em>.</p> - - <p>A complete example is given at the end of the <a - href="tutorial/step3.html">FreeType 2 tutorial</a>. - - <p>Note that direct rendering is <em>not</em> available with - monochrome output, as the current renderer uses a two-pass algorithm - to generate glyphs with correct drop-out control.</p> - - <hr> - - <a name="other-color"></a> - <h3> - How can I set the colour of text rendered by FreeType? - </h3> - - <p>Basically, you can't do that, because FreeType is simply a font - library. In general, you need to use your favorite graphics library - to draw the FreeType glyphs with the appropriate colour.</p> - - <p>Note that for anti-aliased glyphs, you can ‘set the - colour’ by using <em>direct rendering</em> as described in <a - href="#other-depth">this answer</a>.</p> - - <hr> - - <a name="other-size"></a> - <h3> - I set the pixel size to 8×8, but the resulting glyphs are - larger (or smaller) than that. Why? - </h3> - - <p>A lot of people have difficulties to understand this topic, because - they think of glyphs as fixed-width or fixed-height - ‘cells’, like those of fonts used in terminals/consoles. - This assumption is not valid with most ‘modern’ font - formats, even for bitmapped-based ones like <b>PCF</b> or - <b>BDF</b>.</p> - - <p>Be aware that the <em>character size</em> that is set either - through <tt>FT_Set_Char_Size()</tt> or <tt>FT_Set_Pixel_Sizes()</tt> - isn't directly related to the dimension of the generated glyph - bitmaps!</p> - - <p>Rather, the character size is indeed the size of <em>an abstract - square</em>, called the <em>EM</em>, used by typographers to design - fonts. Scaling two distinct fonts to the same character size, be it - expressed in points or pixels, generally results in bitmaps with - <em>distinct dimensions</em>!</p> - - <p>Note that historically, the EM corresponded to the width of a - capital ‘M’ in Latin typefaces. However, later - improvements in typography led to designs that greatly deviate from - this rule. Today, it is not possible to connect the EM size to a - specific font ‘feature’ in a reliable way.</p> - - <hr> - - <a name="other-bbox"></a> - <h3> - How can I compute the bounding box of a text string without loading - its glyphs before? - </h3> - - <p>This is not possible in general. Reason is that hinting distorts - the glyph shape for optimal rasterization, and this process sometimes - creates outlines which have considerably different metrics. The - TrueType format provides the (optional) ‘hdmx’ table which - contains device horizontal metrics for selected pixel sizes, but even - here the vertical metrics are missing.</p> - - <p>It is probably best to use both a glyph and a metrics cache to - avoid recomputation.</p> - - <hr> - - <a name="other-antialias"></a> - <h3> - 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 no - sub-sampling and 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. On the other hand, libArt has - been designed for general shape and 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.</p> - - <hr> - - <a name="other-opentype"></a> - <h3> - When will FreeType 2 support OpenType? - </h3> - - <p>Well, the engine already reads OpenType/CFF files perfectly. What - it doesn't do is handling ‘OpenType Layout’ tables.</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. However, - this code is no longer maintained, and we strongly advise to not use - it.</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 like <a href="http://www.pango.org">Pango</a>.</p> - - <p><a href="#top" - class="index"> - <img src="../../image/top.gif" - width="35" - height="19" - align="right" - border="0" - hspace="0" - vspace="0" - alt="Top"></a></p> - </td> - </tr> - </table> - -<font size=-3>Last update: 25-Feb-2011</font> - -<table width="100%" - border="0" - cellspacing="0" - cellpadding="5"> - <tr> - <td bgcolor="#669999"> - <a href="#general" - class="index">General</a> - <a href="#builds" - class="index">Compilation & - Configuration</a> - <a href="#autohint" - class="index">The FreeType 2 - auto-hinter</a> - <a href="#other" - class="index">Other</a> - <font color="#FFFFFF">|</font> - <a href="documentation.html" - class="index">FreeType - documentation</a> - </td> - </tr> - - <tr> - <td bgcolor="#06425F"> - <a href="../../index.html"> - <img src="../../image/fond3.jpg" - align="right" - border="0" - hspace="0" - vspace="0" - alt="FreeType Homepage"> - </a> - </td> - </tr> -</table> + + <p>We have made great efforts to ensure that the library is + efficient, compact, and customizable.</p> + + <a name="general-edit"></a> + <h3>Can I use FreeType to edit fonts or create new + ones?</h3> + + <p>No. The library is specifically designed + to <em>read</em> font files with small code size and very + low memory usage.</p> + + <p>A good, freely available font editor + is <a href="https://fontforge.github.io">FontForge</a>.</p> + + + <a name="builds"></a> + <h1>Compilation & configuration</h1> + + <a name="builds-compile"></a> + <h3>How do I compile the FreeType library?</h3> + + <p>The library can be compiled in various ways, and detailed + documentation is available in documentation directory of + FreeType's source tree.</p> + + <p>For compilation on the command + line, <a href="https://www.gnu.org/software/make">GNU + make</a> is the standard tool. The source bundle also + comes with support files + for <a href="https://cmake.org">CMake</a> and + <a href="https://mesonbuild.org">meson</a> builds, + together with project files + for <a href="https://docs.microsoft.com/visualstudio/windows/">Visual + C++</a> and some other, older graphical IDEs. Note, + however, that those files are sometimes not up to date + since it is contributed code not used by the core + developers.</p> + + <a name="builds-config"></a> + <h3>How do I configure my build of the library?</h3> + + <p>This is fully described in the + file <a href="https://gitlab.freedesktop.org/freetype/freetype/-/blob/master/docs/CUSTOMIZE"><code>CUSTOMIZE</code></a> + in FreeType's documentation directory. Basically, you + have to edit the header + file <a href="https://gitlab.freedesktop.org/freetype/freetype/-/blob/master/include/freetype/config/ftoption.h"><code>ftoption.h</code></a> + for compile-time options and to select the modules with + the + file <a href="https://gitlab.freedesktop.org/freetype/freetype/-/blob/master/modules.cfg"><code>modules.cfg</code></a>. + Finally, it is possible to replace the standard system + interface (dealing with memory allocation and stream I/O) + with a custom one.</p> + + <a name="builds-differences"></a> + <h3>Why does FreeType render differently on different + platforms?</h3> + + <p>Different distributions compile FreeType with different + options. The developer version of a distribution's + FreeType package, which is needed to compile your program + against FreeType, includes the file + <a href="https://gitlab.freedesktop.org/freetype/freetype/-/blob/master/include/freetype/config/ftoption.h"><code>ftoption.h</code></a>. + Compare each platform's copy of + <code>ftoption.h</code> to find the differences.</p> + + + <a name="autohint"></a> + <h1>The FreeType auto-hinter</h1> + + <a name="autohint-work"></a> + <h3>How does the auto-hinter work?</h3> + + <p><em>Please note that the name of auto-hinter module is + <b>autofit</b>, which is a reimplementation of the old + ‘autohint’ module.</em></p> + + <p>A rather complete description of the hinting algorithm + (which is slightly out of date regarding the internal + structures) can be found in the TUGboat + article <a href="http://www.tug.org/TUGboat/Articles/tb24-3/lemberg.pdf">Real-Time + Grid Fitting of Typographic Outlines</a>.</p> + + <p>The auto-hinter performs grid-fitting on scalable font + formats that use Bézier outlines as their primary + glyph image format (this means nearly all scalable font + 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 <a href="https://www.freetype.org/freetype2/docs/reference/ft2-base_interface.html#ft_load_xxx"><code>FT_LOAD_FORCE_AUTOHINT</code></a> + bit flag when calling + function <a href="https://www.freetype.org/freetype2/docs/reference/ft2-base_interface.html#ft_load_glyph"><code>FT_Load_Glyph</code></a>.</p> + + <p>Currently, the auto-hinter 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.</p> + + <a name="autohint-other-scripts"></a> + <h3>Why doesn't the auto-hinter work well with my + script?</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 now supports almost all scripts + available in Unicode.</p> + + <p>Hinting various scripts isn't really more difficult than + Latin, just different, with a set of different + constraints, which must be hard-coded into the autofit + module. If your particular script is still missing and + you are an expert for this script, we would be very glad + to add the necessary code with your help!</p> + + + <a name="other"></a> + <h1>Other questions</h1> + + <a name="other-depth"></a> + <h3>Can I use FreeType to draw text on a pixmap with + arbitrary depth?</h3> + + <p>Not directly, as FreeType is a font library, not a + general-purpose graphics library or text rendering + service. However, the anti-aliased renderer allows you to + convert a vectorial glyph outline into a list of + ‘spans’ (i.e., horizontal pixel segments with + the same coverage) that can be rendered through + user-provided callbacks.</p> + + <p>By providing an appropriate span callback, you can render + anti-aliased text to any kind of surface. You can also + use any colour, fill pattern or fill image if you want to. + This process is called <em>direct rendering</em>.</p> + + <p>A complete example is given in + the <a href="tutorial/step3.html">FreeType tutorial</a>. + + <p>Note that direct rendering is <em>not</em> available with + monochrome output, as the current renderer uses a two-pass + algorithm to generate glyphs with correct drop-out + control.</p> + + <a name="other-color"></a> + <h3>How can I set the colour of text rendered by + FreeType?</h3> + + <p>Basically, you can't do that, because FreeType is simply + a font library. In general, you need to use your favorite + graphics library to draw the FreeType glyphs with the + appropriate colour.</p> + + <p>Note that for anti-aliased glyphs, you can ‘set the + colour’ by using <em>direct rendering</em> as + described in <a href="#other-depth">this answer</a>.</p> + + <a name="other-size"></a> + <h3>I set the pixel size to 8×8, but the resulting + glyphs are larger (or smaller) than that. Why?</h3> + + <p>A lot of people have difficulties to understand this + topic, because they think of glyphs as fixed-width or + fixed-height ‘cells’, like those of fonts used + in terminals or consoles. This assumption is not valid + with most ‘modern’ font formats, it even fails + for bitmapped-based ones like <b>PCF</b> or + <b>BDF</b>.</p> + + <p>Be aware that the <em>character size</em> that is set + either through + function <a href="https://www.freetype.org/freetype2/docs/reference/ft2-base_interface.html#ft_set_char_size"><code>FT_Set_Char_Size</code></a> + or <a href="https://www.freetype.org/freetype2/docs/reference/ft2-base_interface.html#ft_set_pixel_sizes"><code>FT_Set_Pixel_Sizes()</code></a> + isn't directly related to the dimension of the generated + glyph bitmaps!</p> + + <p>Rather, the character size is indeed the size of <em>an + abstract square</em>, called the <em>EM Square</em>, + used by typographers to design fonts. Scaling two + distinct fonts to the same character size, be it + expressed in points or pixels, generally results in + bitmaps with <em>distinct dimensions</em>!</p> + + <p>Note that historically, the EM Square corresponded to the + width of a capital ‘M’ in Latin typefaces + (thus the name). However, later improvements in + typography led to designs that greatly deviate from this + rule. Today, it is not possible to connect the EM size to + a specific font ‘feature’ in a reliable + way.</p> + + <a name="other-bbox"></a> + <h3>How can I compute the bounding box of a text string + without loading its glyphs before?</h3> + + <p>This is not possible in general. Reason is that hinting + distorts the glyph shape for optimal rasterization, and + this process sometimes creates outlines that have + considerably different metrics. The TrueType format + provides the (optional) ‘hdmx’ table that + contains device horizontal metrics for selected pixel + sizes, but even here the vertical metrics are missing.</p> + + <p>It is probably best to use both a glyph and a metrics + cache to avoid recomputation.</p> + + <a name="other-antialias"></a> + <h3>Which anti-aliasing algorithm is used by FreeType?</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 no sub-sampling and + filtering.</p> + + <p>However, these two implementations are radically distinct + and use vastly different models. The FreeType renderer is + optimized specifically for rendering small complex shapes, + like glyphs, at very high speed while using very few + memory. On the other hand, libArt has been designed for + general shape and polygon processing, especially large + ones.</p> + + <p>The FreeType 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.</p> + + <a name="other-opentype"></a> + <h3>When will FreeType support OpenType?</h3> + + <p>Well, the engine already reads OpenType/CFF files + perfectly. What it doesn't do is handling ‘OpenType + Layout’ tables.</p> + + <p>The predecessor of the FreeType, the now defunct + FreeType 1 series, came with a set of extensions that + were used to load and manage OpenType Layout tables. It + even had a demonstration program + named <code>ftstrtto</code> to show its capabilities. + However, this code is no longer maintained, and we + strongly advise to not use it.</p> + </div> + + <!-- ************************************************** --> + + <div class="updated"> + <p>Last update: 16-May-2021</p> + </div> + </div> + </div> + + + <!-- ************************************************** --> + + <div class="col2"> + </div> + </div> +</div> + + +<!-- ************************************************** --> + +<div id="TOC"> + <ul> + <li class="funding"> + <form action="https://www.paypal.com/cgi-bin/webscr" + method="post" + target="_top"> + <input type="hidden" + name="cmd" + value="_s-xclick"> + <input type="hidden" + name="hosted_button_id" + value="SK827YKEALMT4"> + <input type="image" + src="https://www.paypalobjects.com/en_US/i/btn/btn_donateCC_LG.gif" + name="submit" + alt="PayPal - The safer, easier way to pay online!"> + </form> + </li> + <li class="primary"> + <a href="../../index.html">Home</a> + </li> + <li class="primary"> + <a href="../../index.html#news">News</a> + </li> + <li class="primary"> + <a href="index.html">Overview</a> + </li> + <li class="primary"> + <a href="documentation.html">Documentation</a> + </li> + <li class="primary"> + <a href="../../developer.html">Development</a> + </li> + <li class="primary"> + <a href="../../contact.html" + class="emphasis">Contact</a> + </li> + + <li> + <!-- separate primary from secondary entries --> + </li> + + <li class="secondary"> + <a href="ft2faq.html" class="current">FreeType FAQ</a> + </li> + <li class="tertiary"> + <a href="#general">General questions</a> + </li> + <li class="tertiary"> + <a href="#builds">Compilation & configuration</a> + </li> + <li class="tertiary"> + <a href="#autohint">The FreeType auto-hinter</a> + </li> + <li class="tertiary"> + <a href="#other">Other questions</a> + </li> + </ul> +</div> + +</div> <!-- id="wrapper" --> + +<div id="TOC-bottom"> +</div> </body> </html> |