Resolution indpendence

Steven J Newbury steve at
Fri Jun 27 10:37:50 PDT 2008

On Fri, 2008-06-27 at 13:32 -0400, Behdad Esfahbod wrote:
> 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.
> 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.  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.
> This is just about defaults.
You won't get an argument from me, I agree this is the way forward.

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