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Write font descriptions in the stable Qt 5 10/11-field format

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QFont::toString() is not stable across Qt versions: Qt 6.11 switched to
a 19-field format carrying OpenType weights, which QFont::fromString()
of Qt 5.x and Qt <= 6.10 rejects, leaving a broken font. Projects saved
by a Qt 6.11+ build were therefore unreadable by older builds.

Add QETUtils::fontToString() composing the legacy 10/11-field
description (weight mapped back to the legacy scale with the same
closest-match table Qt uses when parsing) and use it at every site that
stores a font description in a project, element, table config or
settings file. Every Qt version from 5.15 through 6.12-beta parses this
form correctly, so files stay readable by every QET build in
circulation.

See issue #553.
This commit is contained in:
Dieter Mayer
2026-07-30 21:45:23 +02:00
parent 120ca08209
commit 5da1fe5fc8
11 changed files with 77 additions and 11 deletions
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sources/utils/qetutils.cpp
+56
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@@ -150,3 +150,59 @@ void QETUtils::pixelSizedFont(QFont &font)
auto px = font.pointSizeF()/72 * QFontMetrics{font}.fontDpi();
font.setPixelSize(qRound(px));
}
/**
* @brief QETUtils::fontToString
* Serialize a font to the 10/11 field description format written by Qt 5,
* to be used instead of QFont::toString() everywhere a font description is
* stored in a project, element or settings file.
* The format of QFont::toString() is not stable across Qt versions : Qt 6.11
* switched to a 19 field format carrying OpenType weights, which
* QFont::fromString() of Qt 5.x and Qt <= 6.10 rejects, leaving a broken font.
* The 10/11 field form is parsed correctly by every Qt version (they convert
* the legacy weight scale as needed), so composing it ourselves keeps files
* readable by every QET build in circulation.
* See @link https://github.com/qelectrotech/qelectrotech-source-mirror/issues/553 @endlink
* @param font
* @return the font description string
*/
QString QETUtils::fontToString(const QFont &font)
{
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
return font.toString();
#else
//Legacy (Qt 5) weight <- OpenType weight, closest match,
//same table Qt uses when parsing a 10/11 field string.
static const int weight_map[9][2] = {
{0, 100}, {12, 200}, {25, 300}, {50, 400}, {57, 500},
{63, 600}, {75, 700}, {81, 800}, {87, 900}
};
const int weight = font.weight();
int legacy_weight = weight_map[0][0];
int closest_diff = qAbs(weight - weight_map[0][1]);
for (int i = 1 ; i < 9 ; ++i)
{
const int diff = qAbs(weight - weight_map[i][1]);
if (diff < closest_diff) {
closest_diff = diff;
legacy_weight = weight_map[i][0];
}
}
const QChar comma(QLatin1Char(','));
QString description = font.family() + comma +
QString::number(font.pointSizeF()) + comma +
QString::number(font.pixelSize()) + comma +
QString::number(int(font.styleHint())) + comma +
QString::number(legacy_weight) + comma +
QString::number(int(font.style())) + comma +
QString::number(int(font.underline())) + comma +
QString::number(int(font.strikeOut())) + comma +
QString::number(int(font.fixedPitch())) + comma +
QString::number(0);
if (!font.styleName().isEmpty()) {
description += QChar(',') + font.styleName();
}
return description;
#endif
}