nicolas.mailhot at laposte.net
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
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.
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