* issues
* todo
-** buttons
-** mouse cursor
+** update the to-be-instantiated's pos if the windows is updated
+** manage the physics of the to-be-instantiated with a ghost
+** instructions
** main menu
+** implement the operations of the buttons
+** create one level per item, then levels with more items
+*** e.g. item1, item2, item1+2, item3, item1+2+3, ...
+** build pipeline
** magnet
* waiting
** version 0.0.yymmdd