Settng DPI on gdm and Sessions

[Adam Williamson]

On Tue, 2009-05-19 at 19:26 -0600, Christopher A. Williams wrote:

> > It sounds like you're not really following the concept of DPI. I'm not
> > sure how you could possibly see different DPI settings as "sharp" or
> > "not sharp", that just isn't the effect of changing DPI at all. All it
> > does is cause characters to be rendered larger (high DPI) or smaller
> > (low DPI).
> 
> Actually I do understand this quite well.
> 
> > > Regardless of all of that, there should always be a way to tell X what
> > > DPI you want anyway. Who said the manufacturer's "correct" setting is
> > > the best for you, and that's assuming they use a standard way of
> > > specifying that? 
> > 
> > OK, clearly you don't understand the concept.
> > 
> > There's no such thing as a DPI that's 'best for you'. DPI means dots per
> > inch. The correct DPI is a pure mathematical calculation based on the
> > size of the display and the resolution in use. There is no room for
> > subjectivity.
> 
> I could go on for a while here. I understand the concept of DPI a lot
> better than you attribute to me.

Fair enough. If you do, that's fine I have nothing to add. However, the
way your message was written didn't seem to imply a good understanding
of the issue.

There are clearly problems with the current practical implementation of
resolution independence, and the cited use cases (long viewing distances
etc) are some of them. That's (partly) why we don't have it already thus
making everyone super happy.

To answer the practical issues raised -as Felix said, it's certainly
possible to configure the DPI at the X server level, but (again as he
said) the way to do this varies depending on the driver in use,
unfortunately. You used to be able to do it fairly definitively for any
driver using /etc/X11/Xresources (there's an Xft.dpi setting in that
file which is supposed to override the X server's DPI value), but this
doesn't appear to work consistently any more, unfortunately. I think a
bug report requesting a consistent place to override the automatically
calculated (or just arbitrarily chosen) DPI setting for X would
certainly be valid.

When GNOME's not defaulting to 96 dpi, it automatically inherits X's
setting, but if you override it via GNOME's font configuration dialog,
it sets it in a private way and the changed setting applies only to GTK+
apps. I think KDE is the same way. It might be nice if this were all
co-ordinated between X, GNOME and KDE so that you can choose a manual
setting either directly in some config file, or the GNOME / KDE apps
would just poke that config file. Then it'd be nice and consistent.

But in the long run the issue isn't just going to go away, and
arbitrarily defaulting to 96dpi on all displays isn't the answer. It's
horrible for very high-resolution displays, which are already fairly
easily available and will only become more so.
-- 
Adam Williamson
Fedora QA Community Monkey
IRC: adamw | Fedora Talk: adamwill AT fedoraproject DOT org
http://www.happyassassin.net