Physical ouptut sizes

[Nicolas Mailhot]

Le vendredi 06 octobre 2006 à 16:31 +0200, Matthias Hopf a écrit :
> On Oct 06, 06 13:31:21 +0200, Xavier Bestel wrote:
> > On Thu, 2006-10-05 at 22:54 -0700, Keith Packard wrote:

> > How about being able to specify a "pseudo" physical size, for
> > videoprojectors ? I mean, when on such a display, I'd like e.g. Impress
> > to believe it's on a 14" monitor, to have big readable fonts.
> > Whatever the mean, it would be a good thing.
> 
> But that is actually a deficiency in the font scaling system, which
> tries to get the same font size in meter (well, mm in fact), independent
> of the screen resolution.

Actually the problem is it *doesn't* try to get the same font size in
meter (well, mm in fact), independent of the screen resolution, so
people got used to lying about the screen resolution instead of changing
the font size.

GNOME for example uses a fake DPI for font sizing (gconf key). And the
OLPC people workaround this by dynamically changing this key when
switching modes, instead of trusting the value the X server provides
(yay for workarounding the workaround)

> The IMHO cleaner solution would be to either
> have a desired standard font size, or some sort of a general font
> scaling factor.

People faking the absolute DPI used by the font system at the user level
breaks badly for systems where the user is roaming from one hardware
setup to another (nfs homes, OLPC). It means the user has to re-tune
manually his font settings every time the hardware changes.

People setting their preferred font ratio by setting a font size in pt
does not work either - you will receive documents in sizes other people
specified, so even if you choose 24pt as preferred size you'll have to
handle 12pt documents (the w3c tried very hard to avoid this problem by
inciting site authors not to specify an absolute font size, but we all
know it mostly failed. and this would have only worked for web pages
anyway)

Unfortunately that's the two tunings current FLOSS desktops expose.
They're both wrong and the result is a mess (changing manually the
font/zoom tunings every time the hardware changes or you receive an
external document)

Like you wrote an ideal system would have :

1. the X server reporting the exact hardware DPI (in the case of
projectors: perceived DPI) to provide an hardware-independant and
user-independant baseline.

2. Desktop projects agreeing on the default UI font size in pt (probably
10 or 12 pt)

3. each user selecting *once* the zoom factor to apply over the raw
X-server provided DPI so the default font size in pt looks good. This
would be the only user-level tuneable

Unfortunately a lot of people are still in deep denial the problem even
exists. Since it seems MS did its homework with Vista and actually
separated font sizing from resolution (removing the requirement for
screens to have about 96dpi as main resolution), we may see hardware we
can't handle gracefully soonish.

Regards,

-- 
Nicolas Mailhot