the desktop view exposes a way to be desktop win

the desktop shell will set the window as a "desktop" window, always
behind. some other shells will have the desktop as a normal window
the api can still expand

src/shell/desktopview.cpp

@@ -19,11 +19,20 @@
 #include "desktopview.h"
 #include "shellcorona.h"
 
+#include <QQmlEngine>
+#include <QQmlContext>
+#include <QScreen>
+
+#include <KWindowSystem>
+
 #include <Plasma/Package>
 
 DesktopView::DesktopView(ShellCorona *corona, QWindow *parent)
-    : PlasmaQuickView(corona, parent)
+    : PlasmaQuickView(corona, parent),
+      m_stayBehind(false),
+      m_fillScreen(false)
 {
+    engine()->rootContext()->setContextProperty("desktop", this);
     setSource(QUrl::fromLocalFile(corona->package().filePath("views", "Desktop.qml")));
 }
 
@@ -31,6 +40,46 @@ DesktopView::~DesktopView()
 {
     
 }
+
+bool DesktopView::stayBehind() const
+{
+    return m_stayBehind;
+}
+
+void DesktopView::setStayBehind(bool stayBehind)
+{
+    if (stayBehind == m_stayBehind) {
+        return;
+    }
+
+    if (stayBehind) {
+        KWindowSystem::setType(winId(), NET::Desktop);
+    } else {
+        KWindowSystem::setType(winId(), NET::Normal);
+    }
+
+    m_stayBehind = stayBehind;
+    emit stayBehindChanged();
+}
+
+bool DesktopView::fillScreen() const
+{
+    return m_fillScreen;
+}
+
+void DesktopView::setFillScreen(bool fillScreen)
+{
+    if (fillScreen == m_fillScreen) {
+        return;
+    }
+
+    resize(screen()->geometry().width(), screen()->geometry().height());
+    connect(screen(), &QScreen::geometryChanged, [=]{resize(screen()->geometry().width(), screen()->geometry().height());});
+
+    fillScreen = fillScreen;
+    emit fillScreenChanged();
+}
+
 /*
 void DesktopView::showConfigurationInterface(Plasma::Applet *applet)
 {

src/shell/desktopview.h

@@ -29,19 +29,34 @@ class ShellCorona;
 class DesktopView : public PlasmaQuickView
 {
     Q_OBJECT
+    Q_PROPERTY(bool stayBehind READ stayBehind WRITE setStayBehind NOTIFY stayBehindChanged)
+    Q_PROPERTY(bool fillScreen READ fillScreen WRITE setFillScreen NOTIFY fillScreenChanged)
 
 public:
     explicit DesktopView(ShellCorona *corona, QWindow *parent = 0);
     virtual ~DesktopView();
 
+    bool stayBehind() const;
+    void setStayBehind(bool stayBehind);
+
+    bool fillScreen() const;
+    void setFillScreen(bool fillScreen);
+
 protected Q_SLOTS:
     /**
      * It will be called when the configuration is requested
+     * FIXME: this should be moved here
      */
     //virtual void showConfigurationInterface(Plasma::Applet *applet);
 
+Q_SIGNALS:
+    void stayBehindChanged();
+    void fillScreenChanged();
+
 private:
     QPointer<ConfigView> m_configView;
+    bool m_stayBehind : 1;
+    bool m_fillScreen : 1;
 };
 
 #endif // DESKTOVIEW_H

src/shell/qmlpackages/desktop/contents/views/Desktop.qml

@@ -38,6 +38,8 @@ Rectangle {
     }
 
     Component.onCompleted: {
+        desktop.stayBehind = true;
+        desktop.fillScreen = true;
         print("View QML loaded")
     }
 }