Add necessary resources tooltip to build menu

horizons/gui/tabs/buildtabs.py

@@ -139,6 +139,14 @@ def _set_entry(button, icon, building_id):
 			building = Entities.buildings[building_id]
 			button.helptext = self.session.db.get_building_tooltip(building_id)
 
+			# Add necessary resources to tooltip
+			# [br] means newline
+			button.helptext += '[br]Resources needed:[br]'
+			for resource_id, amount_needed in sorted(building.costs.items()):
+				resource_name = self.session.db.get_res_name(resource_id)
+				button.helptext += u'[br]'
+				button.helptext += _('{resource}: {amount}').format(resource=resource_name, amount = amount_needed)
+
 			enough_res = False # don't show building by default
 			if settlement is not None: # settlement is None when the mouse has left the settlement
 				res_overview = self.session.ingame_gui.resource_overview