Hi,
in case this is still of some concern to you, I have now had the
opportunity to try this with Qt 5.2.0:
Janusz S. Bien wrote:
Quote/Cytat - "Janusz S. Bien" <jsbien@xxxxxxxxxxxx> (Mon 06 Jan 2014
04:58:44 PM CET):
Gucharmap has an option to turn off fallback, and so does Pango, but for
a Qt application you will need a Qt solution.
For archive, I've found
http://harmattan-dev.nokia.com/docs/platform-api-reference/xml/daily-docs/libqt4/qfont.html
"QFont::NoFontMerging 0x8000 If the font selected for a certain
writing system does not contain a character requested to draw, then Qt
automatically chooses a similar looking font that contains the
character. The NoFontMerging flag disables this feature. Please note
that enabling this flag will not prevent Qt from automatically picking a
suitable font when the selected font does not support the writing system
of the text."
and
https://bugreports.qt-project.org/browse/QTBUG-9816
"Add style strategy to QFont to turn off automatic font resolution
completely
The QFont::NoFontMerging flag turns off font merging within a single
script item, but still allows automatically picking different fonts for
each script item if the currently selected font does not support the
script in question."
I would appreciate very much your comments to the quoted passages: what
is the meaning of "script" or "writing system" in this context? How the
If I understand [1] correctly, Qt splits every piece of text according
to its QFontDatabase::WritingSystem [2] value. This behavior cannot be
changed with QFont::NoFontMerging. Only the behavior later in the
rendering chain (if the selected font misses a glyph despite it being in
the correct "writing system") can be changed.
However, what I've found is that I cannot even reproduce the example in
[1], i. e. QTBUG-1732, although its follow-up bug (QTBUG-9816) is still
marked as "unresolved".
When I try this code:
QFont fn("DejaVu Sans");
fn.setStyleStrategy(QFont::NoFontMerging);
QChar testChar(0x3042);
QString str;
str += testChar;
ui.label->setFont(fn);
ui.label->setText(str);
...Qt shows an empty box instead of \u3042 despite the character very
likely not being in any writing system supported by DejaVu Sans.
Only if I remove the call to setStyleStrategy from the code above, Qt
performs glyph fallback and renders the character with a fallback font.
Maybe something got changed in the implementation inbetween -- after all
there's this other bug that Akira dug up a couple of weeks ago which
suggested that the merging behavior was broken for some time in Qt 4.8
[3]? Or it's a platform issue, and Qt behaves differently for
fontconfig-based platforms...
Anyway. Qt's "charactermap" example (in
qtbase/examples/widgets/widgets/charactermap/) seems to use
QFont::NoFontMerging too.
So I suppose that could work in the end.
-Raimund
[1]
https://bugreports.qt-project.org/browse/QTBUG-1732?focusedCommentId=113192&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-113192
[2] http://qt-project.org/doc/qt-5/qfontdatabase.html#WritingSystem-enum
[3] https://bugreports.qt-project.org/browse/QTBUG-32470
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