remove MapZoom{In,Out} messages

they can both be replaced with MapScale

frontend/src/Main.elm

@@ -177,9 +177,7 @@ fetchTrack start duration = Http.get
 -- UPDATE
 
 type Msg
-  = MapZoomIn
-  | MapZoomOut
-  | MapScale Float
+  = MapScale Int
   | PointerDown (Int, Int)
   | PointerMove (Int, Int)
   | PointerUp (Int, Int)
@@ -195,15 +193,8 @@ update msg model = (newModel msg model, Cmd.none)
 
 newModel msg model =
     case msg of
-        MapZoomIn ->
-            { model | zoom = incZoom model.zoom zoomStep }
-
-        MapZoomOut ->
-            { model | zoom = incZoom model.zoom -zoomStep }
-
         MapScale y ->
-            let dir = floor(abs(y)/y)
-            in { model | zoom = incZoom model.zoom dir }
+            { model | zoom = incZoom model.zoom y }
 
         PointerDown (x,y) ->
             { model | drag = Dragging (x,y) (x,y) }
@@ -420,7 +411,8 @@ withSwallowing m =
 
 -- FIXME should do something useful with deltaMode as well as deltaY
 mapWheelDecoder =
-    D.map (withSwallowing << MapScale) (D.field "deltaY" D.float)
+    let sgn x = floor((abs x)/x)
+    in D.map (withSwallowing << MapScale << sgn) (D.field "deltaY" D.float)
 
 timeWheelDecoder =
     D.map (withSwallowing << TimeScale) (D.field "deltaY" D.float)
@@ -443,8 +435,8 @@ viewDiv model =
                     [canvasV]
               , text ("Zoom level " ++ (String.fromInt (toZoom model.zoom)))
               , span []
-                  [ button [ onClick MapZoomOut ] [ text "-" ]
-                  , button [ onClick MapZoomIn ] [ text "+" ]
+                  [ button [ onClick (MapScale -zoomStep) ] [ text "-" ]
+                  , button [ onClick (MapScale zoomStep) ] [ text "+" ]
                   ]
               ]
         , div [ style "display" "flex"