Comment # 11 on bug 973590 from Stefan Hundhammer

(In reply to Ladislav Slez���k from comment #8)
> Yes, that makes sense, but in this case the placement is NOT identical.
> 
> Here with some options the bootloader type is on the left:
> https://bugzilla.suse.com/attachment.cgi?id=672621
> 
> Without any option on aarch64 the bootloader type is centered:
> https://bugzilla.suse.com/attachment.cgi?id=671276


I assume this is in a VBox, and this is one row of that VBox. Probably that row
is also a separate HBox.

If there is only one widget in a VBox row, it will be horizontally centered if
the widget is not stretchable, and if it is, it will be stretched to take up
the complete width.

So if it's a HBox, the HBox is stretchable if any of its children is
stretchable. If none of them is stretchable, the HBox is also not stretchable;
so its parent VBox will horizontally center it.

I guess that is what happened here: By default (unless given the hstretchable
option), it is not stretchable. If there is still another widget in that HBox
that is stretchable, that one will make the whole row stretch, and the
stretchable widget(s) will get the excess space in the horizontal dimension,
i.e. those stretchable widgets will become wider.

But if there is none that could take up the excess width, rather than
artificially blowing up the combo box (which would also look bad), it remains
as wide as it is, so its HBox parent remains as wide as it is, so that whole
HBox is centered.


That is a general principle of how our layout widgets (VBox and HBox) work.