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Doc: explain how to check for the existence of a font family

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bb6d68703b67e042e2a7254c2ca6a004a1441cc5 fixed warnings in the
Universal style by using a faster alternative. It's possible that users
will run into these warnings too, and they should be provided with
information to make a more informed choice about which approach they
can use.

Fixes: QTBUG-123360
Pick-to: 6.6 6.5
Change-Id: I4170e9ade40c4b54dbc2bd73d124b2ade4d8c939
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>
(cherry picked from commit ce9f06c1579efda7ae0d259bfaa565f99d89e4f7)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Mitch Curtis 2024-03-15 16:37:06 +08:00 committed by Qt Cherry-pick Bot
parent 56247e4a32
commit 78b7b0472c
1 changed files with 32 additions and 1 deletions
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33
src/gui/text/qfont.cpp
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@ -2993,6 +2993,35 @@ QDataStream &operator>>(QDataStream &stream, QFont::Tag &tag)
info object is \e not updated.
\endlist
\section1 Checking for the existence of a font
Sometimes it can be useful to check if a font exists before attempting
to use it. The most thorough way of doing so is by using \l {exactMatch()}:
\code
const QFont segoeFont(QLatin1String("Segoe UI"));
if (QFontInfo(segoeFont).exactMatch()) {
// Use the font...
}
\endcode
However, this deep search of families can be expensive on some platforms.
\c QFontDatabase::families().contains() is a faster, but less thorough
alternative:
\code
const QLatin1String segoeUiFamilyName("Segoe UI");
if (QFontDatabase::families().contains(segoeUiFamilyName)) {
const QFont segoeFont(segoeUiFamilyName);
// Use the font...
}
\endcode
It's less thorough because it's not a complete search: some font family
aliases may be missing from the list. However, this approach results in
faster application startup times, and so should always be preferred if
possible.
\sa QFont, QFontMetrics, QFontDatabase
*/
@ -3009,6 +3038,8 @@ QDataStream &operator>>(QDataStream &stream, QFont::Tag &tag)
Use QPainter::fontInfo() to get the font info when painting.
This will give correct results also when painting on paint device
that is not screen-compatible.
\sa {Checking for the existence of a font}
*/
QFontInfo::QFontInfo(const QFont &font)
: d(font.d)
@ -3050,7 +3081,7 @@ QFontInfo &QFontInfo::operator=(const QFontInfo &fi)
/*!
Returns the family name of the matched window system font.
\sa QFont::family()
\sa QFont::family(), {Checking for the existence of a font}
*/
QString QFontInfo::family() const
{