desktop-shell: properly set background widget as opaque

Toytoolkit resets the opaque region which was set manually using the
wayland protocol directly, so use the widget API instead.

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

clients/desktop-shell.c

@@ -695,8 +695,6 @@ background_draw(struct widget *widget, void *data)
 	double sx, sy, s;
 	double tx, ty;
 	struct rectangle allocation;
-	struct display *display;
-	struct wl_region *opaque;
 
 	surface = window_get_surface(background->window);
 
@@ -752,13 +750,6 @@ background_draw(struct widget *widget, void *data)
 	cairo_destroy(cr);
 	cairo_surface_destroy(surface);
 
-	display = window_get_display(background->window);
-	opaque = wl_compositor_create_region(display_get_compositor(display));
-	wl_region_add(opaque, allocation.x, allocation.y,
-		      allocation.width, allocation.height);
-	wl_surface_set_opaque_region(window_get_wl_surface(background->window), opaque);
-	wl_region_destroy(opaque);
-
 	background->painted = 1;
 	check_desktop_ready(background->window);
 }
@@ -1056,6 +1047,7 @@ background_create(struct desktop *desktop)
 	background->widget = window_add_widget(background->window, background);
 	window_set_user_data(background->window, background);
 	widget_set_redraw_handler(background->widget, background_draw);
+	widget_set_transparent(background->widget, 0);
 	window_set_preferred_format(background->window,
 				    WINDOW_PREFERRED_FORMAT_RGB565);