Add methods to convert QgsTextFormat to and from QFonts

python/core/qgstextrenderer.sip.in

@@ -1235,6 +1235,8 @@ of rendered text.
 .. seealso:: :py:func:`setFont`
 
 .. seealso:: :py:func:`namedStyle`
+
+.. seealso:: :py:func:`toQFont`
 %End
 
     QFont scaledFont( const QgsRenderContext &context ) const;
@@ -1262,6 +1264,8 @@ of rendered text.
 .. seealso:: :py:func:`font`
 
 .. seealso:: :py:func:`setNamedStyle`
+
+.. seealso:: :py:func:`fromQFont`
 %End
 
     QString namedStyle() const;
@@ -1445,6 +1449,28 @@ Returns new mime data representing the text format settings.
 Caller takes responsibility for deleting the returned object.
 
 .. seealso:: :py:func:`fromMimeData`
+%End
+
+    static QgsTextFormat fromQFont( const QFont &font );
+%Docstring
+Returns a text format matching the settings from an input ``font``.
+Unlike setFont(), this method also handles the size and size units
+from ``font``.
+
+.. versionadded:: 3.2
+
+.. seealso:: :py:func:`toQFont`
+%End
+
+    QFont toQFont() const;
+%Docstring
+Returns a QFont matching the relevant settings from this text format.
+Unlike font(), this method also handles the size and size units
+from the text format.
+
+.. versionadded:: 3.2
+
+.. seealso:: :py:func:`fromQFont`
 %End
 
     static QgsTextFormat fromMimeData( const QMimeData *data, bool *ok /Out/ = 0 );

src/core/qgstextrenderer.cpp

@@ -1608,6 +1608,55 @@ QMimeData *QgsTextFormat::toMimeData() const
   return mimeData;
 }
 
+QgsTextFormat QgsTextFormat::fromQFont( const QFont &font )
+{
+  QgsTextFormat format;
+  format.setFont( font );
+  if ( font.pointSizeF() > 0 )
+  {
+    format.setSize( font.pointSizeF() );
+    format.setSizeUnit( QgsUnitTypes::RenderPoints );
+  }
+  else if ( font.pixelSize() > 0 )
+  {
+    format.setSize( font.pixelSize() );
+    format.setSizeUnit( QgsUnitTypes::RenderPixels );
+  }
+
+  return format;
+}
+
+QFont QgsTextFormat::toQFont() const
+{
+  QFont f = font();
+  switch ( sizeUnit() )
+  {
+    case QgsUnitTypes::RenderPoints:
+      f.setPointSizeF( size() );
+      break;
+
+    case QgsUnitTypes::RenderMillimeters:
+      f.setPointSizeF( size() * 2.83464567 );
+      break;
+
+    case QgsUnitTypes::RenderInches:
+      f.setPointSizeF( size() * 72 );
+      break;
+
+    case QgsUnitTypes::RenderPixels:
+      f.setPixelSize( static_cast< int >( std::round( size() ) ) );
+      break;
+
+    case QgsUnitTypes::RenderMapUnits:
+    case QgsUnitTypes::RenderMetersInMapUnits:
+    case QgsUnitTypes::RenderUnknownUnit:
+    case QgsUnitTypes::RenderPercentage:
+      // no meaning here
+      break;
+  }
+  return f;
+}
+
 QgsTextFormat QgsTextFormat::fromMimeData( const QMimeData *data, bool *ok )
 {
   if ( ok )

src/core/qgstextrenderer.h

@@ -1055,6 +1055,7 @@ class CORE_EXPORT QgsTextFormat
      * \see scaledFont()
      * \see setFont()
      * \see namedStyle()
+     * \see toQFont()
      */
     QFont font() const;
 
@@ -1075,6 +1076,7 @@ class CORE_EXPORT QgsTextFormat
      * \param font desired font
      * \see font()
      * \see setNamedStyle()
+     * \see fromQFont()
      */
     void setFont( const QFont &font );
 
@@ -1224,6 +1226,24 @@ class CORE_EXPORT QgsTextFormat
      */
     QMimeData *toMimeData() const SIP_FACTORY;
 
+    /**
+     * Returns a text format matching the settings from an input \a font.
+     * Unlike setFont(), this method also handles the size and size units
+     * from \a font.
+     * \since QGIS 3.2
+     * \see toQFont()
+     */
+    static QgsTextFormat fromQFont( const QFont &font );
+
+    /**
+     * Returns a QFont matching the relevant settings from this text format.
+     * Unlike font(), this method also handles the size and size units
+     * from the text format.
+     * \since QGIS 3.2
+     * \see fromQFont()
+     */
+    QFont toQFont() const;
+
     /**
      * Attempts to parse the provided mime \a data as a QgsTextFormat.
      * If data can be parsed as a text format, \a ok will be set to true.

tests/src/python/test_qgstextrenderer.py

@@ -392,6 +392,50 @@ def testFontFoundFromXml(self):
         f.readXml(parent, QgsReadWriteContext())
         self.assertTrue(f.fontFound())
 
+    def testFromQFont(self):
+        qfont = getTestFont()
+        qfont.setPointSizeF(16.5)
+        qfont.setLetterSpacing(QFont.AbsoluteSpacing, 3)
+
+        format = QgsTextFormat.fromQFont(qfont)
+        self.assertEqual(format.font().family(), qfont.family())
+        self.assertEqual(format.font().letterSpacing(), 3.0)
+        self.assertEqual(format.size(), 16.5)
+        self.assertEqual(format.sizeUnit(), QgsUnitTypes.RenderPoints)
+
+        qfont.setPixelSize(12)
+        format = QgsTextFormat.fromQFont(qfont)
+        self.assertEqual(format.size(), 12.0)
+        self.assertEqual(format.sizeUnit(), QgsUnitTypes.RenderPixels)
+
+    def testToQFont(self):
+        s = QgsTextFormat()
+        f = getTestFont()
+        f.setLetterSpacing(QFont.AbsoluteSpacing, 3)
+        s.setFont(f)
+        s.setNamedStyle('Italic')
+        s.setSize(5.5)
+        s.setSizeUnit(QgsUnitTypes.RenderPoints)
+
+        qfont = s.toQFont()
+        self.assertEqual(qfont.family(), f.family())
+        self.assertEqual(qfont.pointSizeF(), 5.5)
+        self.assertEqual(qfont.letterSpacing(), 3.0)
+
+        s.setSize(5)
+        s.setSizeUnit(QgsUnitTypes.RenderPixels)
+        qfont = s.toQFont()
+        self.assertEqual(qfont.pixelSize(), 5)
+
+        s.setSize(5)
+        s.setSizeUnit(QgsUnitTypes.RenderMillimeters)
+        qfont = s.toQFont()
+        self.assertAlmostEqual(qfont.pointSizeF(), 14.17, 2)
+
+        s.setSizeUnit(QgsUnitTypes.RenderInches)
+        qfont = s.toQFont()
+        self.assertAlmostEqual(qfont.pointSizeF(), 360.0, 2)
+
     def imageCheck(self, name, reference_image, image):
         self.report += "<h2>Render {}</h2>\n".format(name)
         temp_dir = QDir.tempPath() + '/'