[maps] add support for multiple resolution tiles

If available in cache, the highest resolution is displayed.
Lower resolution are displayed behind higher resolution.
TODO: change the max resolution for download at runtime in gcs (startup
parameter for now)

This should fix #277 and close #364

sw/lib/ocaml/gm.ml

@@ -29,6 +29,7 @@ open Printf
 
 let tile_size = 256, 256
 let zoom_max = 22
+let zoom_min = 18
 
 let cache_path = ref "/var/tmp"
 
@@ -150,6 +151,8 @@ let is_prefix = fun a b ->
 (** Get the tile or one which contains it from the cache *)
 let get_from_cache = fun dir f ->
   let files = Sys.readdir dir in
+  (* sort files to have the longest names first *)
+  Array.sort (fun a b -> String.length b - String.length a) files;
   let rec loop = fun i ->
     if i < Array.length files then
       let fi = files.(i) in

sw/lib/ocaml/gm.mli

@@ -23,6 +23,8 @@
  *)
 
 val tile_size : int * int
+val zoom_max : int
+val zoom_min : int
 val tile_coverage : float -> int -> float * float
 (** [tile_coverage wgs84_lat zoom] Returns (width,height) *)
 

sw/lib/ocaml/mapCanvas.ml

@@ -152,6 +152,8 @@ class basic_widget = fun ?(height=800) ?width ?(projection = Mercator) ?georef (
   let canvas = GnoCanvas.canvas ~packing:(frame#pack ~expand:true) () in
   let background = GnoCanvas.group canvas#root
   and still = GnoCanvas.group canvas#root in
+  (* create several layers of canvas group to display the map in correct order *)
+  let maps = Array.init (Gm.zoom_max - Gm.zoom_min + 1) (fun _ -> GnoCanvas.group background) in
   let view_cbs = Hashtbl.create 3 in (* Store for view event callback *)
   let region_rectangle = GnoCanvas.rect canvas#root ~props:[`WIDTH_PIXELS 2; `OUTLINE_COLOR "red"] in
 
@@ -184,6 +186,7 @@ class basic_widget = fun ?(height=800) ?width ?(projection = Mercator) ?georef (
     method toolbar = toolbar
     method background = background
     method still = still
+    method maps = maps
     method top_still = 3.5*.s
     method utc_time = utc_time
     method set_utc_time = fun h m s ->
@@ -373,14 +376,23 @@ class basic_widget = fun ?(height=800) ?width ?(projection = Mercator) ?georef (
       self#of_world (xw, yw)
 
 
-    method display_pixbuf = fun ?opacity ((x1,y1), geo1) ((x2,y2), geo2) image ->
+    method display_pixbuf = fun ?opacity ?level ((x1,y1), geo1) ((x2,y2), geo2) image ->
       let x1 = float x1 and x2 = float x2
       and y1 = float y1 and y2 = float y2 in
       let image =
 	match opacity with
 	  None -> image
 	| Some o -> set_opacity image o in
-      let pix = GnoCanvas.pixbuf ~x:(-.x1) ~y:(-.y1)~pixbuf:image ~props:[`ANCHOR `NW] background in
+      let map_layer = match level with
+        | None -> 0
+        | Some l ->
+            if l > Gm.zoom_max then
+              Array.length maps - 1
+            else if l < Gm.zoom_min then
+              0
+            else l - Gm.zoom_min
+      in
+      let pix = GnoCanvas.pixbuf ~x:(-.x1) ~y:(-.y1) ~pixbuf:image ~props:[`ANCHOR `NW] maps.(map_layer) in
       let xw1, yw1 = self#world_of geo1
       and xw2, yw2 = self#world_of geo2 in
 

sw/lib/ocaml/mapCanvas.mli

@@ -43,6 +43,7 @@ class widget :
       float * float -> float -> float -> float -> GnoCanvas.line
     method background : GnoCanvas.group
     method background_event : GnoCanvas.item_event -> bool
+    method maps : GnoCanvas.group array
     method canvas : GnoCanvas.canvas
     method center : Latlong.geographic -> unit
     method circle :
@@ -57,6 +58,7 @@ class widget :
     method display_group : string -> unit
     method display_pixbuf :
       ?opacity:int ->
+      ?level:int ->
       (int * int) * Latlong.geographic ->
       (int * int) * Latlong.geographic -> GdkPixbuf.pixbuf -> GnoCanvas.pixbuf
     method display_xy : string -> unit

sw/lib/ocaml/mapGoogle.ml

@@ -72,7 +72,7 @@ let add_tile = fun tile_key ->
   loop 0 [|gm_tiles|] 0
 
 
-let display_the_tile = fun (geomap:MapCanvas.widget) tile jpg_file ->
+let display_the_tile = fun (geomap:MapCanvas.widget) tile jpg_file level ->
   let south_lat = tile.Gm.sw_corner.LL.posn_lat
   and west_long = tile.Gm.sw_corner.LL.posn_long in
   let north_lat = south_lat +. tile.Gm.height
@@ -83,7 +83,7 @@ let display_the_tile = fun (geomap:MapCanvas.widget) tile jpg_file ->
   try
     let pixbuf = GdkPixbuf.from_file jpg_file in
     ignore (GMain.Idle.add (fun () ->
-      let map = geomap#display_pixbuf ((0,tx), tile.Gm.sw_corner) ((ty,0),ne) pixbuf in
+      let map = geomap#display_pixbuf ((0,tx), tile.Gm.sw_corner) ((ty,0),ne) pixbuf ~level in
       map#raise 1;
       false));
     add_tile tile.Gm.key
@@ -103,7 +103,8 @@ let display_tile = fun (geomap:MapCanvas.widget) wgs84 ->
   let key = desired_tile.Gm.key in
   if not (mem_tile key) then
     let (tile, jpg_file) = Gm.get_tile wgs84 1 in
-    display_the_tile geomap tile jpg_file
+    let level = String.length tile.Gm.key in
+    display_the_tile geomap tile jpg_file level
 
 
 exception New_displayed of int
@@ -135,7 +136,8 @@ let fill_window = fun (geomap:MapCanvas.widget) zoomlevel ->
 	| Empty ->
 	    if zoom = 1 then
 	      let tile, image = Gm.get_image key in
-	      display_the_tile geomap tile image;
+              let level = String.length tile.Gm.key in
+	      display_the_tile geomap tile image level;
 	      raise (New_displayed (zoomlevel+1-String.length tile.Gm.key))
 	    else begin
 	      trees.(i) <- Node (Array.create 4 Empty);