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