use register-widget more, fewer arrow widget repaints

pkgs/maps/main.fnl

@@ -126,12 +126,11 @@ label.readout {
                      })))
 
 (fn readout [name text]
-  (let [w
+  (register-widget
+   name
    (doto (Gtk.Label {:label text : name})
      (-> (: :get_style_context)
-              (: :add_class :readout)))]
-    (tset state-widgets name w)
-    w))
+         (: :add_class :readout)))))
 
 (local knot-in-m-s
        (/ 1852 ; metres in nautical mile
@@ -157,6 +156,7 @@ label.readout {
       :speed (widget:set_label
               (string.format "%.1f km/h" (* app-state.speed 3.6)))
       :osm (: (widget:get_window) :invalidate_rect nil)
+      :arrow (: (widget:get_window) :invalidate_rect nil)
       :time (widget:set_label
              (hhmmss (+ utc-offset app-state.time-of-day)))
       )))
@@ -174,8 +174,10 @@ label.readout {
     (: :add (readout :speed "0"))))
 
 (fn arrow []
-  (let [height 40
-        w (Gtk.Label {
+  (let [height 40]
+    (register-widget
+     :arrow
+     (Gtk.Label {
                  :halign Gtk.Align.CENTER
                  :valign Gtk.Align.CENTER
                  :width height :height height
@@ -191,8 +193,7 @@ label.readout {
                    (g:line_to (- height 10) height)
                    (g:fill)
                    true)
-                       })]
-    w))
+                 }))))
 
 
 (local socket-path (or (. arg 1) "/var/run/gnss-share.sock"))