Why EDID is not trustworthy for DPI

Simo Sorce simo at redhat.com
Thu Oct 6 12:21:52 UTC 2011

On Thu, 2011-10-06 at 13:06 +0200, Nicolas Mailhot wrote:
> Le Mer 5 octobre 2011 21:44, Simo Sorce a écrit :
> > Are you saying fonts should change on the fly when I move an app between
> > 2 monitors that have different DPIs ?
> Unfortunately, when you get into situations with more than 150% difference in
> pixel densities between displays (as we've been creeping towards in the last
> decade) that's the only way to display text the user will be able to read.
> You can check it now easily, just get a run-of-the-mill full-hd 15" laptop
> (not even a tiny netbook), a run-of-the-mill 22" or more screen (nothing
> especially uncommon either), create an extended desktop with both screens and
> try to set a satisfying font size. I defy you to find a setting that won't
> look way too small or way too big on one of the screens. And it won't matter
> if the user likes small or big fonts.

Nicolas I am aware of the issue, but I am also aware of the technical
difficulties in doing something like that.
It's not possible today and I am not sure it will be in the near future.

So currently the only option is to tell the user that we do not support
multiple displays where pixel density varies by moire than 10% between

I would even go as far as saying that by default gnome should refuse to
let you join together screens of so high difference in density except we
cannot trust the HW info apparently, so all we are left with is a bad
user experience.


Simo Sorce * Red Hat, Inc * New York

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