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170 lines
8.6 KiB
170 lines
8.6 KiB
14 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/qws.doc:185 -->
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>Fonts in Qt/Embedded</title>
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<font color="#004faf">Home</font></a>
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<font color="#004faf">All Classes</font></a>
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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>Fonts in Qt/Embedded</h1>
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<p> <h2> Supported Formats
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</h2>
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<a name="1"></a><p> Qt/Embedded supports four font formats:
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<p> <center><table cellpadding="4" cellspacing="2" border="0">
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<tr bgcolor="#f0f0f0">
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<td valign="top"><b>TrueType (TTF)</b>
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<td valign="top">The scalable font technology now standard on MS-Windows and Apple
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Macintosh, and becoming popular on X11.
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<tr bgcolor="#d0d0d0">
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<td valign="top"><b>Postscript Type1 (PFA/PFB)</b>
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<td valign="top">Scalable fonts often used by printers, also popular on X11. These
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are similar in functionality to TTF fonts and are not discussed
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further in this document.
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<tr bgcolor="#f0f0f0">
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<td valign="top"><b>Bitmap Distribution Format<br>fonts (BDF)</b>
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<td valign="top">A standard format for non-scalable fonts. A large number of BDF
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fonts are supplied as part of standard X11 distributions - most of
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these can be used with Qt/Embedded. You should <em>not</em> use these in a
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production system: they are very slow to load and take up a <em>lot</em> of
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storage space. Instead, render the BDF to a QPF.
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<tr bgcolor="#d0d0d0">
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<td valign="top"><b>Qt Prerendered Font (QPF)</b>
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<td valign="top">A light-weight non-scalable font format specific to Qt/Embedded.
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</table></center>
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<p> Support for each of these font formats (except QPF which is always
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enabled) can be enabled or disabled independently by using the <a href="emb-features.html">Qt/Embedded Features Definition</a>. There is
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support in Qt/Embedded for writing a QPF font file from any font, so
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you can initially enable TTF and BDF formats, save QPF files for the
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fonts and sizes you need, then remove TTF and BDF support.
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<p> See <a href="makeqpf.html">tools/makeqpf</a> for a tool that helps
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produce QPF files from the TTF and BDF, or just run your application
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with the <tt>-savefonts</tt> option.
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<p> <h2> Memory Requirements
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</h2>
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<a name="2"></a><p> With TTF fonts, each character in the font at a given point size is
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only rendered when first used in a drawing or metrics operation. With
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BDF fonts all characters are rendered when the font is used.
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With QPF fonts, the characters are stored in the same format that Qt
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uses for drawing.
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<p> For example, a 10-point Times font containing the ASCII characters uses
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around 1300 bytes when stored in QPF format.
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<p> Taking advantage of the way the QPF format is structured, Qt/Embedded
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memory-maps the data rather than reading and parsing it.
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This reduces RAM consumption even further.
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<p> Scalable fonts use a larger amount of memory per font, but
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these fonts provide a memory saving if many different sizes of each
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font are needed.
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<p> <h2> Smooth Fonts
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</h2>
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<a name="3"></a><p> TTF, PFA, and QPF fonts can be rendered as <em>smooth</em> anti-aliased
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fonts to give superior readability, especially on low-resolution
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devices. The difference between smooth and non-smooth fonts is
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illustrated below (you may need to change your display to low
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resolution to see the difference):
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<p> <center><img src="unsmooth.png" alt="unsmooth"></center>
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<p> <center><img src="smooth.png" alt="smooth"></center>
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<p> <h2> Unicode
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</h2>
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<a name="4"></a><p> All fonts used by Qt/Embedded use the Unicode character encoding.
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Most fonts available today use this encoding, but they usually don't
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contain all the Unicode characters. A <em>complete</em> 16-point Unicode
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font uses over 1 MB of memory.
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<p> <h2> The font definition file
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</h2>
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<a name="5"></a><p> When Qt/Embedded applications run, they look for a file called
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<tt>$QTDIR/lib/fonts/fontdir</tt> or
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<tt>/usr/local/qt-embedded/lib/fonts/fontdir</tt>. This file defines the
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fonts available to the application. It has the following format:
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<blockquote>
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<em>name</em> <em>file</em> <em>renderer</em> <em>italic</em> <em>weight</em> <em>size</em> <em>flags</em>
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</blockquote>
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where
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<p> <center><table cellpadding="4" cellspacing="2" border="0">
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<tr bgcolor="#a2c511"> <th valign="top">Field <th valign="top">Value
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<tr bgcolor="#f0f0f0"> <td valign="top"><em>name</em> <td valign="top"><tt>Helvetica</tt>, <tt>Times</tt>, etc.
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<tr bgcolor="#d0d0d0"> <td valign="top"><em>file</em> <td valign="top"><tt>helvR0810.bdf</tt>, <tt>verdana.ttf</tt>, etc.
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<tr bgcolor="#f0f0f0"> <td valign="top"><em>renderer</em> <td valign="top"><tt>BDF</tt> or <tt>FT</tt>
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<tr bgcolor="#d0d0d0"> <td valign="top"><em>italic</em> <td valign="top"><tt>y</tt> or <tt>n</tt>
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<tr bgcolor="#f0f0f0"> <td valign="top"><em>weight</em> <td valign="top"><tt>50</tt> is normal, <tt>75</tt> is bold, etc.
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<tr bgcolor="#d0d0d0"> <td valign="top"><em>size</em> <td valign="top"><tt>0</tt> for scalable or point size * 10 (i.e. <tt>120</tt>
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for 12pt)
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<tr bgcolor="#f0f0f0"> <td valign="top"><em>flags</em> <td valign="top"><ul>
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<li> <tt>s</tt>: smooth (anti-aliased)
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<li> <tt>u</tt>: Unicode range when saving (default is Latin-1)
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<li> <tt>a</tt>: ASCII range when saving (default is Latin-1)
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</ul>
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</table></center>
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<p> The font definition file does not specify QPF fonts; these are loaded
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directly from the directory containing the <tt>fontdir</tt> file, and must
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be named <em>name</em>_<em>size</em>_<em>weight</em><em>italicflag</em>.qpf, where
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<p> <center><table cellpadding="4" cellspacing="2" border="0">
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<tr bgcolor="#a2c511"> <th valign="top">Field <th valign="top">Value
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<tr bgcolor="#d0d0d0"> <td valign="top"><em>name</em> <td valign="top"><tt>helvetica</tt>, <tt>times</tt>, etc. (in lowercase)
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<tr bgcolor="#f0f0f0"> <td valign="top"><em>size</em> <td valign="top">point size * 10 (i.e. <tt>120</tt> for 12pt)
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<tr bgcolor="#d0d0d0"> <td valign="top"><em>italicflag</em> <td valign="top"><tt>i</tt> for italic, otherwise nothing.
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<tr bgcolor="#f0f0f0"> <td valign="top"><em>weight</em> <td valign="top"><tt>50</tt> is normal, <tt>75</tt> is bold, etc.
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</table></center>
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<p> If an application is run with the <tt>-savefonts</tt> command-line option,
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then whenever a font other than a QPF font is used, a corresponding QPF file
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is saved. This allows you to easily find the font usage of your applications
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and to generate QPF files so that you can eventually reduce the memory
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usage of your applications by disabling TTF and BDF support from Qt/Embedded,
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or by modifying the initialization of <tt>qws_savefonts</tt> in
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<tt>kernel/qapplication_qws.cpp</tt> of the Qt/Embedded library source code.
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In extreme cases of memory-saving, it is possible to save partially-rendered
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fonts (i.e. only the characters in "Product Name<sup>TM</sup>") if you are
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certain that these are the only characters you will need from the font.
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See QMemoryManager::savePrerenderedFont() for this functionality.
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<p> <h2> Notes
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</h2>
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<a name="6"></a><p> The font definition file, naming conventions for font files, and the format
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of QPF files may change in versions of Qt/Embedded after 3.
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<p>
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To generate QPF files of different rotations, the program must be re-run with
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an orientation that matches the desired rotation of the QPF output. An example to
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generate all 4 rotations of fonts would be to run the following at a real framebuffer:
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<pre>
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for dpy in LinuxFb Transformed:Rot90 Transformed:Rot180 Transformed:Rot270
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do
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QWS_DISPLAY=$dpy ./makeqpf "$@"
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done
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</pre><p> If programs are only ever run in one orientation on a device, only the one
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appropriate set of fonts is needed.
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<p>
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When enabled, Qt/Embedded uses the powerful FreeType2 library to implement
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TrueType and Type1 support.
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<p>
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<!-- eof -->
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<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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</table></div></address></body>
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</html>
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