libweston: Post damage intentionally when remapping a subsurface view

We used to do this through a byzantine path involving the view's plane
transitioning from NULL to primary - but that doesn't work very well
when we want to track the plane in the paint node, because the paint
node will never have a NULL plane state.

This can be removed later when we track damage on paint nodes.

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>

libweston/compositor.c

@@ -3109,6 +3109,15 @@ view_list_add_subsurface_view(struct weston_compositor *compositor,
 
 	assert(view);
 
+	/* We used to mysteriously depend on the view->plane transition
+	 * from NULL to primary to generate damage when a view that was
+	 * unmapped became remapped. Forcing damage here is a little
+	 * more obvious.
+	 *
+	 * We can't use weston_view_damage_below() because the clip region
+	 * isn't correct until after we render, and by then it's too late.
+	 */
+	weston_surface_damage(view->surface);
 	weston_view_update_transform(view);
 	view->is_mapped = true;