xwayland: add wlr_xwayland_set_workareas()

This function allows compositors to set the _NET_WORKAREA property on
the root window. XWayland clients use _NET_WORKAREA to determine how
much of the screen is not covered by panels/docks. The property is used
for example by Qt to determine areas of the screen that popup menus
should not overlap (see QScreen::availableVirtualGeometry).

include/wlr/xwayland/xwayland.h

@@ -16,6 +16,7 @@
 #include <xcb/xcb_icccm.h>
 #include <wlr/util/addon.h>
 
+struct wlr_box;
 struct wlr_xwm;
 struct wlr_data_source;
 struct wlr_drag;
@@ -285,4 +286,14 @@ bool wlr_xwayland_or_surface_wants_focus(
 enum wlr_xwayland_icccm_input_model wlr_xwayland_icccm_input_model(
 	const struct wlr_xwayland_surface *xsurface);
 
+/**
+ * Sets the _NET_WORKAREA root window property. The compositor should set
+ * one workarea per virtual desktop. This indicates the usable geometry
+ * (relative to the virtual desktop viewport) that is not covered by
+ * panels, docks, etc. Unfortunately, it is not possible to specify
+ * per-output workareas.
+ */
+void wlr_xwayland_set_workareas(struct wlr_xwayland *wlr_xwayland,
+	const struct wlr_box *workareas, size_t num_workareas);
+
 #endif

include/xwayland/xwm.h

@@ -88,6 +88,7 @@ enum atom_name {
 	DND_ACTION_PRIVATE,
 	NET_CLIENT_LIST,
 	NET_CLIENT_LIST_STACKING,
+	NET_WORKAREA,
 	ATOM_LAST // keep last
 };