Make Utils::realDpi work on QWindow not on QWidget

Small step towards the goal of okularcore not linking to QWidgets

core/document.cpp

@@ -880,7 +880,8 @@ Document::OpenResult DocumentPrivate::openDocumentInternal(const KPluginMetaData
 
     QApplication::setOverrideCursor(Qt::WaitCursor);
 
-    const QSizeF dpi = Utils::realDpi(m_widget);
+    const QWindow *window = m_widget && m_widget->window() ? m_widget->window()->windowHandle() : nullptr;
+    const QSizeF dpi = Utils::realDpi(window);
     qCDebug(OkularCoreDebug) << "Output DPI:" << dpi;
     m_generator->setDPI(dpi);
 

core/utils.cpp

@@ -44,9 +44,9 @@ QRect Utils::rotateRect(const QRect source, int width, int height, int orientati
     return ret;
 }
 
-QSizeF Utils::realDpi(QWidget *widgetOnScreen)
+QSizeF Utils::realDpi(const QWindow *windowOnScreen)
 {
-    const QScreen *screen = widgetOnScreen && widgetOnScreen->window() && widgetOnScreen->window()->windowHandle() ? widgetOnScreen->window()->windowHandle()->screen() : qGuiApp->primaryScreen();
+    const QScreen *screen = windowOnScreen ? windowOnScreen->screen() : qGuiApp->primaryScreen();
 
     if (screen) {
         const QSizeF res(screen->physicalDotsPerInchX(), screen->physicalDotsPerInchY());

core/utils.h

@@ -12,7 +12,6 @@
 
 class QRect;
 class QImage;
-class QWidget;
 
 namespace Okular
 {
@@ -31,14 +30,14 @@ public:
     static QRect rotateRect(const QRect source, int width, int height, int orientation);
 
     /**
-     * Return the real DPI of the display containing given widget
+     * Return the real DPI of the display containing given window
      *
      * On X11, it can indicate the real horizontal DPI value without any Xrdb
      * setting. Otherwise, returns the same as realDpiX/Y(),
      *
-     * @since 0.19 (KDE 4.13)
+     * @since 22.04
      */
-    static QSizeF realDpi(QWidget *widgetOnScreen);
+    static QSizeF realDpi(const QWindow *windowOnScreen);
 
     /**
      * Compute the smallest rectangle that contains all non-white pixels in image),