Carbon app does not receive kEventWindowDrawContent on unhiding -

i noticed old carbon application not receive keventwindowdrawcontent when unhiding application. can solve problem redrawing once keventwindowexpanded event i'm still confused why app doesn't keventwindowdrawcontent event when app brought hidden state.

i checked old apple docs , there's no explicit mentioning keventwindowdrawcontent sent when app unhidden, common sense implies should sent because app needs redrawn.

i initial keventwindowdrawcontent message when opening window, though, event handler must have been installed correctly.

does remember old carbon stuff? keventwindowdrawcontent supposed sent on unhiding or not?

this answer received apple engineer:

keventwindowdrawcontent sent when window content has been invalidated. don’t invalidate window content default when window expanded minimized state; window buffer kept valid while window minimized (so drawing window reflected in window’s dock tile), it’s assumed unless app explicitly invalidates, there not reason redraw window because it’s been expanded.

in other words: applications can still draw window while minimized. buffered , automatically drawn when window expanded again. no keventwindowdrawcontent sent in case because window buffer hasn't been invalidated.