Expose Qt.application.font

This is useful in order to specify font sizes that are some multiple of
the default size (which is almost always guaranteed to be a sensible,
legible size). For example:

Text {
    text: "Large text"
    font.pixelSize: Qt.application.font.pixelSize * 2
}

Other options are:

- "<h3>Large text</h3>" - adds extra space below the text since it's a
HTML element, so not really useful if you want a decent layout.

- Hard-coding a pixel size. Works OK when used in combination with
Qt::AA_EnableHighDpiScaling, and so long as you guess the correct size
that works for each device/display you're targeting. Doesn't work
without setting Qt::AA_EnableHighDpiScaling.

- Using FontMetrics/TextMetrics. Works fine, but is a bit verbose.

- Use an empty Text element. Creates an unnecessary item. Was
superseded by FontMetrics/TextMetrics.

- defaultPixelSize/implicitPixelSize and
defaultPointSize/implicitPointSize. There are already font-related
properties outside of the font grouped property, so this wouldn't be
out of place, but the API is already quite large.

[ChangeLog][QtQuick] Added Qt.application.font property.

Change-Id: I2d0899f2a6b717aab9afcea59f42fbf3715d8406
Task-number: QTBUG-50298
Reviewed-by: Liang Qi <liang.qi@theqtcompany.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/tests/auto/quick/qquickapplication/tst_qquickapplication.cpp b/tests/auto/quick/qquickapplication/tst_qquickapplication.cpp
index 1bd163fc4a..114f906736 100644
--- a/tests/auto/quick/qquickapplication/tst_qquickapplication.cpp
+++ b/tests/auto/quick/qquickapplication/tst_qquickapplication.cpp
@@ -47,6 +47,7 @@ private slots:
     void active();
     void state();
     void layoutDirection();
+    void font();
     void inputMethod();
     void styleHints();
     void cleanup();
@@ -196,6 +197,21 @@ void tst_qquickapplication::layoutDirection()
     QCOMPARE(Qt::LayoutDirection(item->property("layoutDirection").toInt()), Qt::LeftToRight);
 }
 
+void tst_qquickapplication::font()
+{
+    QQmlComponent component(&engine);
+    component.setData("import QtQuick 2.0; Item { property font defaultFont: Qt.application.font }", QUrl::fromLocalFile(""));
+    QQuickItem *item = qobject_cast<QQuickItem *>(component.create());
+    QVERIFY(item);
+    QQuickView view;
+    item->setParentItem(view.rootObject());
+
+    QVariant defaultFontProperty = item->property("defaultFont");
+    QVERIFY(defaultFontProperty.isValid());
+    QCOMPARE(defaultFontProperty.type(), QVariant::Font);
+    QCOMPARE(defaultFontProperty.value<QFont>(), qApp->font());
+}
+
 void tst_qquickapplication::inputMethod()
 {
     // technically not in QQuickApplication, but testing anyway here