Screen Coordinate Systems and Scaling

[hpfx]

(09-24-2015 01:14 PM)Tim Wessman Wrote:  Number two is the first "user" program. The top item is the application program for the currently active application.

By the way, do you know what is this "top item application program" ? and when does this program is run ?
I put a simple MSGBOX in this program and I use the application, but nothing appeared to me.