qt-everywhere-src-5.15.1/qtdoc/doc/src/platforms/emb-fonts.qdoc

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/*!
    \page qt-embedded-fonts.html

    \title Qt for Embedded Linux Fonts
    \ingroup qt-embedded-linux

    Qt normally uses \tt{fontconfig} to provide access to system fonts. If
    \tt{fontconfig} is not available, e.g. in dedicated embedded systems where
    space is at a premium, Qt will fall back to using \c QBasicFontDatabase. In
    this case, Qt applications will look for fonts in Qt's \c lib/fonts/
    directory. Qt will automatically detect prerendered fonts and TrueType fonts.

    Qt uses the
    \l{http://freetype.sourceforge.net/freetype2/index.html}{FreeType 2}
    font engine to produce font output. The formats supported depends on
    the locally installed version of the FreeType library. When using QBasicFontDatabase,
    Qt also supports the Qt Prerendered Font format (\l QPF2),
    a light-weight non-scalable font formats.
    QPF2 is the native format of Qt for Embedded Linux 4.x.

    \image qt-embedded-fontfeatures.png

    All supported fonts use the Unicode character encoding. Most fonts
    available today do, but they usually don't contain \e all the
    Unicode characters. A complete 16-point Unicode font uses over 1
    MB of memory.

    \target FreeType
    \section1 FreeType Formats

    The \l {http://freetype.sourceforge.net/freetype2/index.html}{FreeType 2}
    library can support the following font formats:

    \list
        \li TrueType (TTF)
        \li PostScript Type1 (PFA/PFB)
        \li Bitmap Distribution Format (BDF)
        \li CID-keyed Type1
        \li Compact Font Format (CFF)
        \li OpenType fonts
        \li SFNT-based bitmap fonts
        \li Portable Compiled Format (PCF)
        \li Microsoft Windows Font File Format (Windows FNT)
        \li Portable Font Resource (PFR)
        \li Type 42 (limited support)
    \endlist

    It is possible to add modules to the \l
    {http://freetype.sourceforge.net/freetype2/index.html}{FreeType 2}
    font engine to support other types of font files. For more
    information, see the font engine's own website: \l
    http://freetype.sourceforge.net/freetype2/index.html.

    Glyphs rendered using FreeType are shared efficiently between applications,
    reducing memory requirements and speeding up text rendering.

    \omit
    Qt  will by default use the system FreeType library if it exists.
    Otherwise it will use a copy of the FreeType library in Qt, which by default only
    supports TrueType fonts to reduce footprint.
    \endomit

    \target QPF2
    \section1 Qt Prerendered Font (QPF2)

    The Qt Prerendered Font (QPF2) is an architecture-independent,
    light-weight and non-scalable font format.

    Qt comes with the cross-platform \l makeqpf tool, included in the
    \c tools directory, which allows
    generation of QPF2 files from system fonts.

    QPF2 supports anti-aliasing and complex writing systems, using information
    from the corresponding TrueType font, if present on the system. The format
    is designed to be mapped directly to memory. The same format is used to
    share glyphs from non-prerendered fonts between applications.

    \omit
    \section1 Memory Requirements

    Taking advantage of the way the QPF format is structured, Qt for
    Embedded Linux memory-maps the data rather than reading and parsing it.
    This reduces RAM consumption even further.

    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.
    \endomit

*/