Connected fontSize to UI.

Amended the font size setter, added fontSize as a Q_PROPERTY and added a dummy UI display to ensure that the connection works.

src/contents/ui/MainPage.qml

 /**
  * SPDX-FileCopyrightText: (C) 2020 Carl Schwan <carl@carlschwan.eu>
  *
- * SPDX-License-Identifier: GPL-3.0-or-later
+ * SPDX-LicenseRef: GPL-3.0-or-later
  */
 
 import QtQuick 2.1
@@ -44,6 +44,15 @@ Kirigami.ScrollablePage {
             wrapMode: Text.WordWrap
             Layout.fillWidth: true
         }
+        Kirigami.Heading {
+            level: 1
+            font.bold: true
+            text: i18n("Font size: %1", Kontrast.fontSize)
+
+            color: Kontrast.textColor
+            wrapMode: Text.WordWrap
+            Layout.fillWidth: true
+        }
         Kirigami.Heading {
             level: 3
             font.bold: true

src/kontrast.cpp

@@ -120,7 +120,11 @@ int Kontrast::fontSize() const
 
 void Kontrast::setFontSize(int fontSize)
 {
+    if (m_fontSize == fontSize) {
+        return;
+    }
     m_fontSize = fontSize;
+    Q_EMIT fontSizeChanged();
 }
 
 QColor Kontrast::backgroundColor() const

src/kontrast.h

@@ -26,6 +26,8 @@ class Kontrast : public QObject
 
     Q_PROPERTY(int textLightness READ textLightness WRITE setTextLightness NOTIFY textColorChanged)
 
+    Q_PROPERTY(int fontSize READ fontSize WRITE setFontSize NOTIFY fontSizeChanged)
+
     Q_PROPERTY(QColor backgroundColor READ backgroundColor WRITE setBackgroundColor NOTIFY backgroundColorChanged)
 
     Q_PROPERTY(int backgroundHue READ backgroundHue WRITE setBackgroundHue NOTIFY backgroundColorChanged)
@@ -100,12 +102,13 @@ Q_SIGNALS:
     void backgroundColorChanged();
     void contrastChanged();
     void grabbedColorChanged();
+    void fontSizeChanged();
 
 private:
     QColor m_textColor;
     QColor m_backgroundColor;
     QColor m_grabbedColor;
-    int m_fontSize;
+    int m_fontSize = 24;
     KAboutData m_about;
 };