Help: Fix font point sizes with litehtml

Change-Id: Ia2d7434ed965b00075747c0bdd43d90a236b99dd
Reviewed-by: Cristian Adam <cristian.adam@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/help/qlitehtml/container_qpainter.cpp

@@ -505,7 +505,8 @@ void DocumentContainer::draw_text(litehtml::uint_ptr hdc,
 
 int DocumentContainer::pt_to_px(int pt)
 {
-    return pt;
+    // magic factor of 11/12 to account for differences to webengine/webkit
+    return m_paintDevice->physicalDpiY() * pt * 11 / m_paintDevice->logicalDpiY() / 12;
 }
 
 int DocumentContainer::get_default_font_size() const
@@ -847,6 +848,11 @@ void DocumentContainer::get_language(litehtml::tstring &language, litehtml::tstr
     Q_UNUSED(culture)
 }
 
+void DocumentContainer::setPaintDevice(QPaintDevice *paintDevice)
+{
+    m_paintDevice = paintDevice;
+}
+
 void DocumentContainer::setScrollPosition(const QPoint &pos)
 {
     m_scrollPosition = pos;

src/plugins/help/qlitehtml/container_qpainter.h

@@ -29,6 +29,7 @@
 
 #include <QFont>
 #include <QHash>
+#include <QPaintDevice>
 #include <QPixmap>
 #include <QRect>
 #include <QString>
@@ -120,6 +121,7 @@ public:
     void get_media_features(litehtml::media_features &media) const override;
     void get_language(litehtml::tstring &language, litehtml::tstring &culture) const override;
 
+    void setPaintDevice(QPaintDevice *paintDevice);
     void setDocument(const QByteArray &data, litehtml::context *context);
     litehtml::document::ptr document() const;
     void setScrollPosition(const QPoint &pos);
@@ -166,6 +168,7 @@ private:
     QUrl resolveUrl(const QString &url, const QString &baseUrl) const;
     void drawSelection(QPainter *painter, const QRect &clip) const;
 
+    QPaintDevice *m_paintDevice = nullptr;
     litehtml::document::ptr m_document;
     QString m_baseUrl;
     QRect m_clientRect;

src/plugins/help/qlitehtml/qlitehtmlwidget.cpp

@@ -422,6 +422,7 @@ QUrl QLiteHtmlWidget::url() const
 
 void QLiteHtmlWidget::setHtml(const QString &content)
 {
+    d->documentContainer.setPaintDevice(viewport());
     d->documentContainer.setDocument(content.toUtf8(), &d->context);
     verticalScrollBar()->setValue(0);
     horizontalScrollBar()->setValue(0);