OK then. First, thanks Quadraxas for your help. I'll try it. Actually the problem is my buttons should be flaged as OVERLAY. And I'm not sure if I can use something like that : "my_bitmap.flags = OVERLAY;". Hope I can. Thanks for example code again..

@EvilSOB: Hey, now I understand why engine said "undefined" when I used it outside a panel. Thanks for your help, too.

I m going to try it now, hope it works as I wanted...

EDIT: It works! Thank you all for helps...