Settng DPI on gdm and Sessions

Adam Williamson awilliam at redhat.com
Wed May 20 00:48:14 UTC 2009


On Tue, 2009-05-19 at 20:36 -0400, Tom Horsley wrote:
> On Tue, 19 May 2009 17:06:49 -0700
> Adam Williamson wrote:
> 
> > 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.
> 
> It is utter and complete nonsense like this which leads to so many
> idiotic decisions in linux. Caring about DPI having a formally correct
> definition is for those afflicted with OCD. 

...and anyone who ever, say, prints anything.

> Being able
> to read the damn characters most apps put on the screen is what
> virtually everyone in the real world would prefer.

Ironically, that's exactly what resolution independence is intended to
achieve.

> There are two ways to make the characters readable:
> 
> 1. Rewrite every app in creation to conform to yet another new complicated
> Xorg visibility layer for applying magnification factors computed
> from visual acuity of the user, and distance from display, combined
> with several years worth of human factors AI algorithms.
> 
> 2. Lie about the DPI and achieve the mathematically identical effect
> without modifying a single app.

Er, how does this 'achieve the mathematically identical effect'?

I bought a new laptop a few months back. It has an 8", 1600x768
resolution screen. That's a DPI up around 180. If I set it to a DPI of
96, then it's almost impossible to read anything at default font sizes.
Setting the wrong DPI and then doubling all my font sizes to compensate
would be absurd. The correct solution is to set the correct DPI - 180 -
so that characters get rendered at a sensible physical size without me
having to go around changing font sizes to something ridiculous (like a
default of 20 points) all over the place.

(If I were to set the default font size to 20 points in OpenOffice, so I
could actually read a document I was typing, then when I printed it out,
it'd be ridiculously large...)

If you go out and read the reviews for the Vaio P, lots of reviewers
(running Windows, remember, which doesn't allow you to set an arbitrary
DPI, and can't get above 120dpi with any hack) panned it because 'the
fonts are too small'. Which is an absurd complaint caused by the
limitations of using an arbitrary default DPI setting. As more and more
very high resolution displays are released - which they will be - this
will become an issue for more and more people. Proper resolution
independence is the only sane solution. There's no other way you can
properly work when a display's actual physical resolution may be 80dpi
(some old 19" 1024x768 monitor) or 250dpi (a high-end monitor in a
year's time, or an e-ink display...)

> In fact, quite a lot of monitors don't report the correct physical
> dimensions, so unless you can lie about the DPI, you can't even correct
> these display devices to show the absolute anally correct DPI, much
> less the DPI that makes characters visible on your 52DPI HD monitor you
> are sitting 3 feet away from.

So? It's quite easy to exclude obviously wrong dimensions and just go
with a default, or if they're only slightly wrong, the result won't be
terrible (and likely no worse than the entirely arbitrary 96dpi).
-- 
Adam Williamson
Fedora QA Community Monkey
IRC: adamw | Fedora Talk: adamwill AT fedoraproject DOT org
http://www.happyassassin.net




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