Properly update scale when upgrading a map

items.lua

@@ -422,7 +422,7 @@ local function copy_map_item(stack)
         copy_meta:set_int("cartographer:map_id", new_id);
         copy_meta:set_string("description", map_description(new_id,
                                                             dest.x, dest.z,
-                                                            dest.w, dest.h));
+                                                            dest.w * dest.scale, dest.h * dest.scale));
     end
 
     return copy;
@@ -446,9 +446,28 @@ local function resize_map_item(meta, size)
         local map = maps.get(id);
         map:resize(size, size);
 
-        meta:set_string("description", map_description(id,
-                                                       chunk.from(map.x), chunk.from(map.z),
-                                                       chunk.from(map.w), chunk.from(map.h)));
+        meta:set_string("description", map_description(id, map.x, map.z, map.w * map.scale, map.h * map.scale));
+    end
+end
+
+-- Change the scale of the given map item
+--
+-- meta: A metadata object containing the map data
+-- scale: The new scale
+local function rescale_map_item(meta, scale)
+    local old_scale = meta:get_int("cartographer:scale");
+
+    if old_scale >= scale then
+        return;
+    end
+
+    meta:set_int("cartographer:scale", scale);
+
+    local id = meta:get_int("cartographer:map_id");
+    if id > 0 then
+        local map = maps.get(id);
+        map:rescale(scale);
+        meta:set_string("description", map_description(id, map.x, map.z, map.w * map.scale, map.h * map.scale));
     end
 end
 
@@ -456,4 +475,5 @@ return {
     create = create_map_item,
     copy = copy_map_item,
     resize = resize_map_item,
+    rescale = rescale_map_item,
 };

map_api.lua

@@ -11,6 +11,19 @@ for _,loaded_map in ipairs(map_data.maps) do
     setmetatable(loaded_map, Map);
 end
 
+-- Rescale this map
+--
+-- scale: The new scale
+function Map.rescale(self, scale)
+    if scale >= self.scale then
+        local difference = math.floor(scale / self.scale);
+
+        self.fill = {};
+        self.markers = {};
+        self.scale = scale;
+    end
+end
+
 -- Resize this map
 --
 -- w: The new width

table.lua

@@ -716,6 +716,7 @@ minetest.register_on_player_receive_fields(function(player, name, fields)
                     local smeta = stack:get_meta();
                     smeta:set_int("cartographer:detail", 1 + detail);
                     map_item.resize(smeta, size);
+                    map_item.rescale(smeta, scale);
 
                     local map = maps.get(smeta:get_int("cartographer:map_id"));
                     if map then