add compass rose

this is still not correct, but it's closer

pkgs/maps/main.fnl

@@ -66,7 +66,7 @@ label.readout {
             :lon 0
             :zoom 17
             :course 0 ; direction of travel
-            :orientation 0 ; map rotation angle from north
+            :orientation {:target 0 :actual 0} ; map rotation angle from north
             :tiles {}
             }
  )
@@ -186,8 +186,10 @@ label.readout {
         (set biggest-n (- i 1)))))
   (let [[x y] (. points biggest-n)
         [nx ny] (. points (+ 1 biggest-n))
-        angle (math.atan (- ny y) (- nx x))]
-    (if (> nx x)
+        angle (math.atan (- ny y) (- nx x))
+        screen-angle (- angle
+                        (/ (* app-state.orientation.target math.pi) 180))]
+    (if (< (math.abs screen-angle) (/ math.pi 2))
         (values
          (* tile-size (- x bounds.min.x))
          (* tile-size (- y bounds.min.y))
@@ -271,7 +273,7 @@ label.readout {
                (draw-onto-map-surface bounds app-state.zoom)))))
 
     (g:translate (+ (/ viewport-width 2))  (+ (/ viewport-height 2)))
-    (g:rotate (* (/ (- 360 app-state.orientation) 180) math.pi))
+    (g:rotate (* (/ (- 360 app-state.orientation.actual) 180) math.pi))
     (g:translate (- (/ viewport-width 2))  (- (/ viewport-height 2)))
 
     (g:set_source_surface map-surface (- offset-x) (- offset-y))
@@ -322,15 +324,22 @@ label.readout {
       (when (not (bounds= old-bounds bounds))
         (fetch-tiles bounds app-state.tiles app-state.zoom)
         (set map-surface nil)))
-    (set app-state.orientation
-         (+ app-state.orientation
-            (* 0.05 (- app-state.course app-state.orientation))))
+    (when (> (math.abs (- app-state.orientation.target app-state.course)) 20)
+      (set app-state.orientation.target app-state.course)
+      (set map-surface nil))
+
+    (when (not (= app-state.orientation.target app-state.orientation.actual))
+      (set app-state.orientation.actual 
+           (+ app-state.orientation.actual
+              (* 0.05 (- app-state.orientation.target app-state.orientation.actual)))))
+    
     (each [name widget (pairs state-widgets)]
       (case name
         :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)
+        :rose (: (widget:get_window) :invalidate_rect nil)
         :time (widget:set_label
                (hhmmss (+ utc-offset app-state.time-of-day)))
         ))))
@@ -359,7 +368,7 @@ label.readout {
                  (fn [self g]
                    (g:set_source_rgb 0.4 0.0 0.1)
                    (g:translate (// height 2) (// height 2))
-                   (g:rotate (* (/ (- app-state.course app-state.orientation)
+                   (g:rotate (* (/ (- app-state.course app-state.orientation.actual)
                                    180) math.pi))
                    (g:translate (// height -2) (// height -2))
                    (g:set_line_width 4)
@@ -370,6 +379,48 @@ label.readout {
                    true)
                  }))))
 
+(fn deg->rad [degrees]
+  (* math.pi (/ degrees 180)))
+
+(fn rose []
+  (let [height 60]
+    (register-widget
+     :rose
+     (Gtk.Label {
+                 :halign Gtk.Align.START
+                 :valign Gtk.Align.START
+                 :width height :height height
+                 :on_draw
+                 (fn [self g]
+                   (g:save)
+                   (g:set_line_width 1)
+                   (g:set_source_rgb 0.4 0.0 0.1)
+                   (g:arc (// height 2) (// height 2)  15
+                          0 (* 2 math.pi))
+                   (g:stroke)
+                   
+                   (g:translate (// height 2) (// height 2))
+                   (g:rotate (- (deg->rad app-state.orientation.actual)))
+                   (g:translate (// height -2) (// height -2))
+                   
+                   (g:set_line_width 2)
+                   (g:move_to (// height 2) height)
+                   (g:line_to (// height 2) 0)
+
+                   (g:move_to 10 20)
+                   (g:line_to (// height 2) 0)
+                   (g:line_to (- height 10) 20)
+                   (g:stroke)
+                   
+                   (g:set_source_rgb 1 1 0)
+                   (g:move_to  (// height -2) (// height -2))
+                   (g:text_path "N")
+                   (g:fill)
+
+                   (g:restore)
+                   true)
+                 }))))
+
 
 (local socket-path (or (. arg 1) "/var/run/gnss-share.sock"))
 
@@ -426,6 +477,7 @@ label.readout {
    (: :add (osm-widget))
    (: :add_overlay (readouts))
    (: :add_overlay (arrow))
+   (: :add_overlay (rose))
    ))
 
 (window:show_all)