Add dimensions property to overmap special

Minimum size of the box that can contain whole overmap special

src/omdata.h

@@ -453,6 +453,8 @@ class overmap_special
         void load( const JsonObject &jo, const std::string &src );
         void finalize();
         void check() const;
+        // Minimum size of the box that can contain whole overmap special
+        box dimensions;
     private:
         // These locations are the default values if ones are not specified for the individual OMTs.
         std::set<string_id<overmap_location>> default_locations;

src/overmap.cpp

@@ -911,6 +911,19 @@ void overmap_special::finalize()
         }
     }
 
+    // Calculate dimensions
+    tripoint dimension_min;
+    tripoint dimension_max;
+    for( auto &t : terrains ) {
+        dimension_min = tripoint( std::min( dimension_min.x, t.p.x ),
+                                  std::min( dimension_min.y, t.p.y ),
+                                  std::min( dimension_min.z, t.p.z ) );
+        dimension_max = tripoint( std::max( dimension_max.x, t.p.x ),
+                                  std::max( dimension_max.y, t.p.y ),
+                                  std::max( dimension_max.z, t.p.z ) );
+    }
+    dimensions = box( dimension_min, dimension_max );
+
     for( auto &elem : connections ) {
         const auto &oter = get_terrain_at( elem.p );
         if( !elem.terrain && oter.terrain ) {