Resolution indpendence

Nicolas Mailhot nicolas.mailhot at
Fri Jun 27 11:31:08 PDT 2008

Le vendredi 27 juin 2008 à 13:32 -0400, Behdad Esfahbod a écrit :
> On Fri, 2008-06-27 at 18:06 +0100, Steven J Newbury wrote:
> > 
> > > HAL sees that it's a TV, assumes a viewing distance of 4m, computes a
> > > dpi-at-arms-distance value of 30 * 4/.7 = 171dpi.  Very decent.
> >
> > This may well be sufficient, but it is a hack.  Ideally it would be better
> > to have a specific "typical viewing distance" value for the hardware device
> > that the toolkits/font renderer/compositor could pick up and utilize in
> > relevant contexts.  It's probably too late for the first two however.
> There are two points of physical information:
>   A) Dots per inch on the display surface (LCD panel, TV screen,
> projector screen, The Wall, ...)
>   B) Viewing distance
> Those two are very real and can be measured.  If we have both, we can
> compute a third value:
>   C) Normalized dpi / angular resolution / whatever you call it.
> Physical dpi times viewing distance does the job.
> At the end, C is all the application developers care about.  That's why
> I suggest we redefine application DPIs to be that.

Actually they also need to care about

D. Preferred user font size in pt (which is then converted in pixels
using C)

Without D people fake C to change what D should be like

> Next question is where to get A and B from.  A is already coming from X
> and EDID info and many devices have buggy values. 

Buggy values = quirks db + (last ressort) config app to set it manually.

> B is nonexistent.
> The solution to both is already there: HAL device info files.  These are
> small XML files setting A and a default value for B depending on the
> manufacturer and model of the display device.  The user can set both.

Actually B should be :
1. typical value for this class of device
2. overriden by typicall value for this model (if known)
3. overriden by a sysadmin (not user-specific, system-specific) setting
in case the device is used outside its usual scope

With maybe 4. automagic distance sensors if we get them someday.


Nicolas Mailhot
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 197 bytes
Desc: Ceci est une partie de message num?riquement sign?e
URL: <>

More information about the xorg mailing list