how to make lines or points flicker?

hi
in my program,I want to make seme lines or points flicker,how can I do that?

What do u mean by flicker ?
if u want show/hide, use QTimer

I mean that In the program,the lines or the points especially marked flicker in some frequency.if I use the QTime,what is the minimun unit ?Can somebody get some examples?
Thanks in advance!