7/* Global variables should be avoided for they increase program’s complexity immensely and because their values can be changed by any function that is called. But it is a necessity in this case.
8 * CylinderGeometry and SphereGeometry implement a caching scheme which is effective iff there is one instance of these objects. Hence they are defined as global variables.
9 * Another approach would be to define these as singleton classes but that is mostly frowned upon and does not provide us any benefit in comparison to declaring global variables.