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

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.

sources/editor/graphicspart/partdynamictextfield.cpp

@@ -20,6 +20,7 @@
 #include "../../QPropertyUndoCommand/qpropertyundocommand.h"
 #include "../../qetapp.h"
 #include "../elementscene.h"
+#include "../../utils/qetutils.h"
 #include <QApplication>
 
 #include <QColor>
@@ -142,7 +143,7 @@ const QDomElement PartDynamicTextField::toXml(QDomDocument &dom_doc) const
 	root_element.setAttribute("y", QString::number(y));
 	root_element.setAttribute("z", QString::number(zValue()));
 	root_element.setAttribute("rotation", QString::number(QET::correctAngle(rot)));
-	root_element.setAttribute("font", font().toString());
+	root_element.setAttribute("font", QETUtils::fontToString(font()));
 	root_element.setAttribute("uuid", m_uuid.toString());
 	root_element.setAttribute("frame", m_frame? "true" : "false");
 	root_element.setAttribute("text_width", QString::number(m_text_width));

sources/editor/graphicspart/parttext.cpp

@@ -23,6 +23,7 @@
 #include "../elementprimitivedecorator.h"
 #include "../elementscene.h"
 #include "../ui/texteditor.h"
+#include "../../utils/qetutils.h"
 
 /**
 	Constructeur
@@ -165,7 +166,7 @@ const QDomElement PartText::toXml(QDomDocument &xml_document) const
 	xml_element.setAttribute("x", QString::number(x));
 	xml_element.setAttribute("y", QString::number(y));
 	xml_element.setAttribute("text", toPlainText());
-	xml_element.setAttribute("font", font().toString());
+	xml_element.setAttribute("font", QETUtils::fontToString(font()));
 	xml_element.setAttribute("rotation", QString::number(rot));
 	xml_element.setAttribute("color", defaultTextColor().name());
 

sources/factory/ui/addtabledialog.cpp

@@ -221,12 +221,12 @@ void AddTableDialog::saveConfig()
 		header_object.insert("margins", QETUtils::marginsToString(this->headerMargins()));
 		auto me = QMetaEnum::fromType<Qt::Alignment>();
 		header_object.insert("alignment", me.valueToKey(int(this->headerAlignment())));
-		header_object.insert("font", this->headerFont().toString());
+		header_object.insert("font", QETUtils::fontToString(this->headerFont()));
 
 		QJsonObject table_object;
 		table_object.insert("margins", QETUtils::marginsToString(this->tableMargins()));
 		table_object.insert("alignment", me.valueToKey(int(this->tableAlignment())));
-		table_object.insert("font", this->tableFont().toString());
+		table_object.insert("font", QETUtils::fontToString(this->tableFont()));
 
 		QJsonObject config_object;
 		config_object.insert("header", header_object);

sources/properties/terminaldata.cpp

@@ -17,6 +17,8 @@
 */
 #include "terminaldata.h"
 
+#include "../utils/qetutils.h"
+
 #include <QGraphicsObject>
 
 #include <QDebug>
@@ -115,7 +117,7 @@ QDomElement TerminalData::toXml(QDomDocument &xml_document) const
 		xml_element.setAttribute("show_name", "true");
 		xml_element.setAttribute("label_x", QString::number(m_label_pos.x()));
 		xml_element.setAttribute("label_y", QString::number(m_label_pos.y()));
-		xml_element.setAttribute("label_font", m_label_font.toString());
+		xml_element.setAttribute("label_font", QETUtils::fontToString(m_label_font));
 		xml_element.setAttribute("label_rotation", QString::number(m_label_rotation));
 		xml_element.setAttribute("label_halign", static_cast<int>(m_label_halignment));
 		xml_element.setAttribute("label_valign", static_cast<int>(m_label_valignment));

sources/qetgraphicsitem/ViewItem/projectdbmodel.cpp

@@ -22,6 +22,7 @@
 #include "../../qetinformation.h"
 #include "../../qetproject.h"
 #include "../../qetxml.h"
+#include "../../utils/qetutils.h"
 
 #include <QSqlError>
 #include <QSqlRecord>
@@ -252,7 +253,7 @@ QDomElement ProjectDBModel::toXml(QDomDocument &document) const
 	
 	//Add index 0,0 data
 	auto index_00 = document.createElement("index00");
-	index_00.setAttribute("font", m_index_0_0_data.value(Qt::FontRole).toString());
+	index_00.setAttribute("font", QETUtils::fontToString(m_index_0_0_data.value(Qt::FontRole).value<QFont>()));
 	auto me = QMetaEnum::fromType<Qt::Alignment>();
 	index_00.setAttribute("alignment", me.valueToKey(m_index_0_0_data.value(Qt::TextAlignmentRole).toInt()));
 	dom_element.appendChild(index_00);

sources/qetgraphicsitem/dynamicelementtextitem.cpp

@@ -23,6 +23,7 @@
 #include "../qetgraphicsitem/conductor.h"
 #include "../qetgraphicsitem/terminal.h"
 #include "../qetinformation.h"
+#include "../utils/qetutils.h"
 #include "crossrefitem.h"
 #include "element.h"
 #include "elementtextitemgroup.h"
@@ -96,7 +97,7 @@ QDomElement DynamicElementTextItem::toXml(QDomDocument &dom_doc) const
 	root_element.setAttribute("uuid", m_uuid.toString());
 	root_element.setAttribute("frame", m_frame? "true" : "false");
 	root_element.setAttribute("text_width", QString::number(m_text_width));
-	root_element.setAttribute("font", font().toString());
+	root_element.setAttribute("font", QETUtils::fontToString(font()));
 	root_element.setAttribute("keep_visual_rotation", m_keep_visual_rotation ? "true" : "false");
 	
 	QMetaEnum me = textFromMetaEnum();

sources/qetgraphicsitem/independenttextitem.cpp

@@ -21,6 +21,7 @@
 #include "../diagramcommands.h"
 #include "../qet.h"
 #include "../qetapp.h"
+#include "../utils/qetutils.h"
 
 #include <QDomElement>
 #include <QSettings>
@@ -80,7 +81,7 @@ QDomElement IndependentTextItem::toXml(QDomDocument &document) const
 	result.setAttribute("y", QString("%1").arg(pos().y()));
 	result.setAttribute("text", toHtml());
 	result.setAttribute("rotation", QString::number(QET::correctAngle(rotation())));
-	result.setAttribute("font", font().toString());
+	result.setAttribute("font", QETUtils::fontToString(font()));
 	
 	return(result);
 }

sources/qetxml.cpp

@@ -18,6 +18,7 @@
 #include "qetxml.h"
 
 #include "NameList/nameslist.h"
+#include "utils/qetutils.h"
 
 #include <QDir>
 #include <QFont>
@@ -477,7 +478,7 @@ QDomElement QETXML::modelHeaderDataToXml(
 					else if (role == Qt::FontRole)
 					{
 						auto font = variant.value<QFont>();
-						text_node.setData(font.toString());
+						text_node.setData(QETUtils::fontToString(font));
 					}
 					else if (role == Qt::TextAlignmentRole)
 					{

sources/ui/configpage/generalconfigurationpage.cpp

@@ -21,6 +21,7 @@
 #include "../../qeticons.h"
 #include "ui_generalconfigurationpage.h"
 #include "../../utils/qetsettings.h"
+#include "../../utils/qetutils.h"
 #include "../../qetmessagebox.h"
 #include <QFileDialog>
 #include <QFontDialog>
@@ -459,7 +460,7 @@ void GeneralConfigurationPage::on_m_dyn_text_font_pb_clicked()
 	QFont font = QFontDialog::getFont(&ok, curFont, this);
 	if (ok)
 	{
-		settings.setValue("diagrameditor/dynamic_text_font", font.toString());
+		settings.setValue("diagrameditor/dynamic_text_font", QETUtils::fontToString(font));
 		QString fontInfos = font.family() + " " +
 							QString::number(font.pointSize()) + " (" +
 							font.styleName() + ")";
@@ -563,7 +564,7 @@ void GeneralConfigurationPage::on_m_indi_text_font_pb_clicked()
 	QFont font = QFontDialog::getFont(&ok, curFont, this);
 	if (ok)
 	{
-		settings.setValue("diagrameditor/independent_text_font", font.toString());
+		settings.setValue("diagrameditor/independent_text_font", QETUtils::fontToString(font));
 		QString fontInfos = font.family() + " " +
 							QString::number(font.pointSize()) + " (" +
 							font.styleName() + ")";

sources/utils/qetutils.cpp

@@ -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
+}

sources/utils/qetutils.h

@@ -32,6 +32,7 @@ namespace QETUtils
 	QMargins marginsFromString(const QString &string);
 	qreal graphicsHandlerSize(QGraphicsItem *item);
     void pixelSizedFont (QFont &font);
+    QString fontToString (const QFont &font);
 
 	bool sortBeginIntString(const QString &str_a, const QString &str_b);