introduce TileMap type

frontend/src/Main.elm

@@ -515,9 +515,10 @@ ifTrack model content =
         Loading -> div [] [Html.text "loading"]
         Empty -> div [] [Html.text "no points"]
 
-
+canvas : Coord -> ZoomLevel -> Int -> Int -> Model -> Html Msg
 canvas centre zoom width height model =
-    let (mintile, maxtile) = boundingTiles centre zoom width height
+    let tm = TileMap centre zoom width height
+        (mintile, maxtile) = boundingTiles tm
         -- offset is pixel difference between centre (which *should*
         -- be the middle of the image) and actual middle of the canvas
         (pixelCentreX,pixelCentreY) = pixelFromCoord centre zoom
@@ -538,7 +539,7 @@ canvas centre zoom width height model =
             ,Pointer.onUp (\e -> DragFinish (epos e))
             ,Pointer.onMove (\e -> Drag (epos e))
             ,Pointer.onDown (\e -> DragStart Map (epos e)) ]
-        (tv :: tiles centre zoom width height)
+        (tv :: tiles tm)
 
 
 portalWidth = 600

frontend/src/TileMap.elm

@@ -2,6 +2,7 @@ module TileMap exposing (tiles
                         , FineZoomLevel(..)
                         , ZoomLevel
                         , Coord
+                        , TileMap(..)
                         , toCoord
                         , toZoom
                         , translate
@@ -26,6 +27,9 @@ type alias Coord = { x: Float, y: Float }
 type alias ZoomLevel = Int
 type FineZoomLevel = FineZoomLevel Int
 
+
+type TileMap = TileMap Coord ZoomLevel Int Int
+
 zoomStep = 8
 
 toZoom : FineZoomLevel -> ZoomLevel
@@ -75,8 +79,8 @@ pixelFromCoord c z =
     let {x,y} = tileCovering c (z + 8)
     in (x,y)
 
-boundingTiles : Coord -> ZoomLevel -> Int -> Int -> (TileNumber, TileNumber)
-boundingTiles centre z width height =
+boundingTiles : TileMap -> (TileNumber, TileNumber)
+boundingTiles (TileMap centre z width height) =
     -- find the tiles needed to cover the area (`width` x `height`)
     -- about the point at `centre`
     let delta = pixelsToCoord z ((width // 2), (height // 2))
@@ -97,8 +101,9 @@ tileImg zoom tilenumber = img [ width 256,
                                 height 256,
                                 src (tileUrl tilenumber zoom) ] []
 
-tiles centre zoom width height =
-    let (mintile, maxtile) = boundingTiles centre zoom width height
+tiles tmap =
+    let (TileMap centre zoom width height) = tmap
+        (mintile, maxtile) = boundingTiles tmap
         xs = List.range mintile.x maxtile.x
         ys = List.range mintile.y maxtile.y
     in