This function must be called by the same thread that created the cursor that is affected.

A cursor show-level count is maintained. It is incremented by a hide operation and decremented by a show operation. The cursor is actually visible if the cursor show-level count is zero, otherwise it is invisible. When decrementing, the cursor show-level count is fixed at zero so as not to show the cursor too many times, but it is possible to hide the cursor a number of times in succession.