Add function to iterate (curved) circular tile area

src/map_func.h

@@ -440,6 +440,16 @@ bool CircularTileSearch(TileIndex *tile, uint radius, uint w, uint h, TestTileOn
 
 bool EnoughContiguousTilesMatchingCondition(TileIndex tile, uint threshold, TestTileOnSearchProc proc, void *user_data);
 
+/**
+ * A callback function type for iterating tiles.
+ *
+ * @param tile The tile to test
+ * @param user_data additional data for the callback function to use
+ */
+typedef void TileIteratorProc(TileIndex tile, void *user_data);
+
+void IterateCurvedCircularTileArea(TileIndex centre_tile, uint diameter, TileIteratorProc proc, void *user_data);
+
 /**
  * Get a random tile out of a given seed.
  * @param r the random 'seed'