bug#50424: 27.2; Tab bar button mouse face not clearing entirely

[Juri Linkov]

> I think all it's doing is ensuring the total area the image takes up
> is the same whether there's a relief or not.
>
> The total width = image + relief width + margin width, so if you
> reduce the size of the relief you have to increase the size of the
> margin by the same amount to make sure it takes up the same amount of
> space and doesn't move.
>
> As far as I can see, what's happening here is that the margin is
> pushing the relief one pixel into the separator to the left, so I
> suspect that's why it's not being cleared.
>
> I'm somewhat surprised that it's not pushing the right hand side one
> pixel too far in the other direction and causing it to not be cleared
> either, but maybe that's just chance.
>
> The change below fixes it here, but I've not made sure it does the
> right thing with different sized margins and so on.

Thanks, I really appreciate your help.  After seeing the result
of your patch, one question that came up is whether it's possible
not to change the previously used dimensions?  With enlarged height
and width, now the buttons are not vertically aligned: