draw road labels always left->right

pkgs/maps/main.fnl

@@ -211,6 +211,24 @@ label.readout {
         (when (not (. tbl k))
           (tiles.fetch cq x y zoom #(tset tbl k $1)))))))
 
+;; iso 9899:1999 says
+;; "The atan2 functions return arctan y/x in the interval [−π , +π ] radians"
+
+(fn clamp-angle [rad]
+  (let [circle (* 2 math.pi)]
+    (if
+     (< rad (- math.pi)) (clamp-angle (+ rad circle))
+     (> rad  math.pi) (clamp-angle (- rad circle))
+     rad)))
+
+(define-tests :clamp-angle
+  (expect= (clamp-angle 2) 2)
+  (expect= (clamp-angle (+ (* 4 math.pi) 2)) 2)
+  (expect= (clamp-angle (- 2 (* 4 math.pi))) 2))
+
+(fn deg->rad [deg]
+  (* math.pi (/ deg 180)))
+
 (fn draw-onto-map-surface [surface bounds zoom]
   (let [{ : num-tiles-x : num-tiles-y } bounds
         road-width 14
@@ -228,7 +246,7 @@ label.readout {
       (g:fill)
 
       (g:translate (+ (// bounds.pixels.x 2))  (+ (// bounds.pixels.y 2)))
-      (g:rotate (* (/ (- app-state.orientation-target) 180) math.pi))
+      (g:rotate (deg->rad (- app-state.orientation-target)))
       (g:translate (- (// bounds.pixels.x 2))  (- (// bounds.pixels.y 2)))
 
       (cairo-roads g lines bounds)
@@ -248,7 +266,13 @@ label.readout {
 
                   (g:save)
                   (g:move_to x y)
-                  (g:rotate angle)
+
+                  (let [theta (clamp-angle
+                               (- angle (deg->rad app-state.orientation-target)))]
+                    (if (and (> theta 0) (< theta math.pi))
+                        (g:rotate (- angle (/ math.pi 2)))
+                        (g:rotate (- angle (* math.pi 1.5)))))
+
                   (g:rel_move_to (- (// w 2)) 3)
                   (g:text_path n)
                   (g:fill)

pkgs/maps/tiles.fnl

@@ -77,7 +77,7 @@
         (set biggest-n (- i 1)))))
   (let [[x y] (. points biggest-n)
         [nx ny] (. points (+ 1 biggest-n))
-        angle (math.atan (- ny y) (- nx x))]
+        angle (math.atan (- nx x) (- y ny))]
     [(/ (+ nx x) 2) (/ (+ ny y) 2) angle]))
 
 
@@ -92,7 +92,6 @@
               (icollect [_ nd (ipairs e.nodes)]
                 (let [node (. nodes nd)
                       (tx ty) (latlon->tile node.lat node.lon zoom)]
-                  ;;(print e.tags.name e.id e.name node.lat node.lon)
                   [ tx ty ]))]
           (tset
            lines