With GTK2, the entire form/window appears to be being hidden (I didn't remember that behaviour, but I've upgraded the distro since writing this and there was a point-level libgtk upgrade).
It's the same irrespective of the presence or hide/show (I've stuck the form name in there to be absolutely unambiguous), of the constraint change, or of the APM I added for good measure.
'z': begin
Form1.Hide;
{ with Constraints do begin
MinWidth := 0;
MinHeight := 0
end; }
case BorderStyle of
bsSizeable: BorderStyle := bsNone
otherwise
BorderStyle := bsSizeable
end;
Form1.Show;
Application.ProcessMessages;
testCard(true)
end;
Everything else works fine: testcard() basically paints a bullseye with rings at adjustable positions.
I wonder whether there's any overlap here with people who've used circular output which presumably didn't have a caption?
In any event, Qt5 works and I suspect I might have to live with that.
MarkMLl