Why EDID is not trustworthy for DPI

Simo Sorce simo at redhat.com
Thu Oct 6 15:52:58 UTC 2011

On Thu, 2011-10-06 at 16:44 +0100, Matthew Garrett wrote:
> On Thu, Oct 06, 2011 at 11:35:08AM -0400, Simo Sorce wrote:
> > I am sure display manager can easily grow a button to say something
> > along the lines of: change font resolution to better fit multiple
> > monitors. so that when someone that has widely varying DPIs between
> > monitors plugs a second monitor in they can press that button and get
> > whatever default you like best for that use case.
> We could do that, but you'd still need toolkit support for triggering a 
> re-render of everything. And it'd be pretty dreadful UI ("why doesn't 
> this just happen automatically?"). And suddenly everything on your 
> internal display would be a different size and possibly even in a 
> different place.
The consequences are exactly the reason why I think it should not happen
automatically and a button would be the right compromise.

Avoids WTF surprises if you just plug a monitor in and suddenly all your
stuff changes, and still allows you to fix the size if the other monitor
is too screwed up with the settings you have due to your main monitor.

In all cases where you have widely different DPIs I am sure you will
find 50% of the people wanting the exact opposite oft he other 50% to
happen so not doing anything and letting the user "adjust" the situation
only if he wants to seem the better way.

Plus IIRC display manger tries to remember settings, so this is
something that could be remembered as well so users do not get annoyed
with "but I already told it to do that yesterday when I plugged in the
video projector the firs time".

That said, I am not responsible for any of these changes, so I will
leave it in the hands of the maintainers hoping this discussion have
improved everyone understanding of the issues involved.


Simo Sorce * Red Hat, Inc * New York

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