Why EDID is not trustworthy for DPI

Adam Williamson awilliam at redhat.com
Wed Oct 5 19:31:50 UTC 2011

On Wed, 2011-10-05 at 18:49 +0100, Matthew Garrett wrote:

> So, ok, now you have some belief about the DPI. But which DPI? If you're 
> dual head, you've got two. Unless they match you're screwed - there's no 
> magic way to get applications to reflow text just because you've moved 
> the window between screens, and what would you do with a window that's 
> halfway between? You can argue that this is a corner case and obviously 
> yes it's a corner case but if you can't even pretend to fix the corner 
> case then your solution isn't a solution any more than 96dpi is.

There's no _magic_ way to fix anything, no. Things get fixed by code
writers writing code. That would seem to be the obvious thing to do...

Like I replied to ajax, I suspect when the problem of assuming
everything's 96dpi becomes simply too acute, instead of fixing
everything really properly so that all displays correct report their
size and all desktops actually do resolution independence perfectly so
it doesn't _matter_ if one of your displays is 98dpi and the other is
215dpi, everything still looks perfect, the industry will just wind up
with a slightly more sophisticated bodge where we have a few 'standard'
resolutions and just figure out which one your displays are closest to.
But that's still going to require some kind of sensible handling of the
case where one monitor is roughly 100dpi and the other is roughly
200dpi, unless we simply say 'you can't do that, all your displays have
to be in the same DPI Category'.
Adam Williamson
Fedora QA Community Monkey
IRC: adamw | Twitter: AdamW_Fedora | identi.ca: adamwfedora

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