Implement plasma-surface open-under-cursor

The surface is positioned at the current cursor location but kept in
bounds to keep it fully visible when the cursor is near the screen border.

src/wayland/plasmashell_interface.cpp

@@ -46,6 +46,7 @@ public:
     bool m_skipTaskbar = false;
     bool m_skipSwitcher = false;
     bool m_panelTakesFocus = false;
+    bool m_openUnderCursorRequested = false;
 
 private:
     void org_kde_plasma_surface_destroy_resource(Resource *resource) override;
@@ -59,6 +60,7 @@ private:
     void org_kde_plasma_surface_panel_auto_hide_show(Resource *resource) override;
     void org_kde_plasma_surface_set_panel_takes_focus(Resource *resource, uint32_t takes_focus) override;
     void org_kde_plasma_surface_set_skip_switcher(Resource *resource, uint32_t skip) override;
+    void org_kde_plasma_surface_open_under_cursor(Resource *resource) override;
 };
 
 PlasmaShellInterface::PlasmaShellInterface(Display *display, QObject *parent)
@@ -148,6 +150,15 @@ void PlasmaShellSurfaceInterfacePrivate::org_kde_plasma_surface_set_position(Res
     Q_EMIT q->positionChanged();
 }
 
+void PlasmaShellSurfaceInterfacePrivate::org_kde_plasma_surface_open_under_cursor(Resource *resource)
+{
+    if (surface && surface->buffer()) {
+        wl_resource_post_error(resource->handle, -1, "open_under_cursor: surface has a buffer");
+    }
+    m_openUnderCursorRequested = true;
+    Q_EMIT q->openUnderCursorRequested();
+}
+
 void PlasmaShellSurfaceInterfacePrivate::org_kde_plasma_surface_set_role(Resource *resource, uint32_t role)
 {
     Q_UNUSED(resource)
@@ -272,6 +283,11 @@ bool PlasmaShellSurfaceInterface::isPositionSet() const
     return d->m_positionSet;
 }
 
+bool PlasmaShellSurfaceInterface::wantsOpenUnderCursor() const
+{
+    return d->m_openUnderCursorRequested;
+}
+
 PlasmaShellSurfaceInterface::PanelBehavior PlasmaShellSurfaceInterface::panelBehavior() const
 {
     return d->m_panelBehavior;

src/wayland/plasmashell_interface.h

@@ -74,6 +74,11 @@ public:
      */
     bool isPositionSet() const;
 
+    /**
+     * @returns Whether the surface has requested to be opened under the cursor.
+     */
+    bool wantsOpenUnderCursor() const;
+
     /**
      * Describes possible roles this PlasmaShellSurfaceInterface can have.
      * The role can be used by the server to e.g. change the stacking order accordingly.
@@ -159,6 +164,12 @@ Q_SIGNALS:
      * A change of global position has been requested.
      */
     void positionChanged();
+
+    /**
+     * The surface has requested to be initially shown under the cursor. Can only occur
+     * before any buffer has been attached.
+     */
+    void openUnderCursorRequested();
     /**
      * A change of the role has been requested.
      */

src/xdgshellwindow.cpp

@@ -438,6 +438,17 @@ void XdgSurfaceWindow::installPlasmaShellSurface(PlasmaShellSurfaceInterface *sh
     auto updatePosition = [this, shellSurface] {
         move(shellSurface->position());
     };
+    auto moveUnderCursor = [this, shellSurface] {
+        // Wait for the first commit
+        auto connection = new QMetaObject::Connection;
+        *connection = connect(this, &Window::windowShown,  [this, connection] () {
+            disconnect(*connection);
+            if (input()->hasPointer()) {
+                move(input()->globalPointer().toPoint());
+                keepInArea(workspace()->clientArea(PlacementArea, this));
+            }
+        });
+    };
     auto updateRole = [this, shellSurface] {
         NET::WindowType type = NET::Unknown;
         switch (shellSurface->role()) {
@@ -486,6 +497,7 @@ void XdgSurfaceWindow::installPlasmaShellSurface(PlasmaShellSurfaceInterface *sh
         workspace()->updateClientArea();
     };
     connect(shellSurface, &PlasmaShellSurfaceInterface::positionChanged, this, updatePosition);
+    connect(shellSurface, &PlasmaShellSurfaceInterface::openUnderCursorRequested, this, moveUnderCursor);
     connect(shellSurface, &PlasmaShellSurfaceInterface::roleChanged, this, updateRole);
     connect(shellSurface, &PlasmaShellSurfaceInterface::panelBehaviorChanged, this, [this] {
         updateShowOnScreenEdge();
@@ -511,6 +523,9 @@ void XdgSurfaceWindow::installPlasmaShellSurface(PlasmaShellSurfaceInterface *sh
     if (shellSurface->isPositionSet()) {
         updatePosition();
     }
+    if (shellSurface->wantsOpenUnderCursor()) {
+        moveUnderCursor();
+    }
     updateRole();
     updateShowOnScreenEdge();
     connect(this, &XdgSurfaceWindow::frameGeometryChanged,
@@ -707,7 +722,10 @@ bool XdgToplevelWindow::isMinimizable() const
 
 bool XdgToplevelWindow::isPlaceable() const
 {
-    return !m_plasmaShellSurface || !m_plasmaShellSurface->isPositionSet();
+    if (m_plasmaShellSurface) {
+        return !m_plasmaShellSurface->isPositionSet() && !m_plasmaShellSurface->wantsOpenUnderCursor();
+    }
+    return true;
 }
 
 bool XdgToplevelWindow::isTransient() const