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Old 10-06-2011, 04:12 PM
Matthew Garrett
 
Default Why EDID is not trustworthy for DPI

On Thu, Oct 06, 2011 at 12:00:36PM -0400, Simo Sorce wrote:

> So in that case you really should just give an option to the user to
> easily change DPI (no need to call the option 'DPIs', it can be a slider
> with no mention of DPI if you prefer) *if* it is needed.
> Chances are that a much wider font resulting from high density primary
> display derived DPI number combined with low resolution video projector
> screen will show big fonts and that will happen to be *exactly* what you
> want so the guy back there at the end of the room has a chance to
> actually read something

I absolutely agree that there should be an easy mechanism to globally
change font size. But I don't think tying it to DPI is helpful.

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Old 10-06-2011, 04:12 PM
Adam Jackson
 
Default Why EDID is not trustworthy for DPI

On Thu, 2011-10-06 at 11:14 -0400, Jon Masters wrote:
> On Tue, 2011-10-04 at 13:54 -0400, Adam Jackson wrote:
> > EDID does not reliably give you the size of the display.
>
> How about "EDID as it exists today". Since you're able to so beautifully
> explain what the pitfalls are, I'd assume you've raised this with the
> VESA and asked that they revisit this in the future to accurately
> provide DPI information that Operating Systems can rely on?

Given that successive revisions of the spec have gone out of their way
to make it acceptable for displays to provide _less_ useful information,
on the grounds of manufacturing cost reduction, I think the momentum is
quite in the other direction.

More pragmatically, VESA are not the people with any influence here.
The only thing that matters to a monitor vendor is what Windows does
when you plug it in. Linux can stamp its little foot all it wants. No
one will care. If you want to be a big enough player in that market to
have some influence, you have to start by playing in the sandbox that's
already built, and in that sandbox physical dimensions are just not
reliable and never will be.

Cope.

- ajax
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Old 10-06-2011, 04:41 PM
Bruno Wolff III
 
Default Why EDID is not trustworthy for DPI

On Thu, Oct 06, 2011 at 12:00:36 -0400,
Simo Sorce <simo@redhat.com> wrote:
>
> My main use case here is video projectors, and in that case there is no
> way on earth you'll ever know the DPI as it depends on the distance from
> the wall, and again even if you knew the distance from the wall you'd
> know nothing because the optimal DPI will also depend on the distance of
> the crowd from the wall.

What you really want to know is the resolution per angle or arc. And that
would be relatively constant for a project regardless of distance from
the surface it is projecting on.
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Old 10-06-2011, 04:46 PM
Jon Masters
 
Default Why EDID is not trustworthy for DPI

On Thu, 2011-10-06 at 12:12 -0400, Adam Jackson wrote:
> On Thu, 2011-10-06 at 11:14 -0400, Jon Masters wrote:
> > On Tue, 2011-10-04 at 13:54 -0400, Adam Jackson wrote:
> > > EDID does not reliably give you the size of the display.
> >
> > How about "EDID as it exists today". Since you're able to so beautifully
> > explain what the pitfalls are, I'd assume you've raised this with the
> > VESA and asked that they revisit this in the future to accurately
> > provide DPI information that Operating Systems can rely on?
>
> Given that successive revisions of the spec have gone out of their way
> to make it acceptable for displays to provide _less_ useful information,
> on the grounds of manufacturing cost reduction, I think the momentum is
> quite in the other direction.
>
> More pragmatically, VESA are not the people with any influence here.
> The only thing that matters to a monitor vendor is what Windows does
> when you plug it in. Linux can stamp its little foot all it wants. No
> one will care. If you want to be a big enough player in that market to
> have some influence, you have to start by playing in the sandbox that's
> already built, and in that sandbox physical dimensions are just not
> reliable and never will be.
>
> Cope.

Ok. I can cope, and not to flog a dead horse here...but has any effort
been made anywhere on the Open Source side of things to influence future
EDID specs? I'm sure Linux can stamp all it wants and nobody will care,
but it probably doesn't hurt to raise this for discussion next time
there's an update to the standard - or, shock, reach out to MSFT and see
if they have any interest in working together on fixing this experience
which perhaps also causes problems they care about on Windows.

Just a suggestion.

Jon.


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Old 10-06-2011, 05:14 PM
Simo Sorce
 
Default Why EDID is not trustworthy for DPI

On Thu, 2011-10-06 at 17:12 +0100, Matthew Garrett wrote:
> On Thu, Oct 06, 2011 at 12:00:36PM -0400, Simo Sorce wrote:
>
> > So in that case you really should just give an option to the user to
> > easily change DPI (no need to call the option 'DPIs', it can be a slider
> > with no mention of DPI if you prefer) *if* it is needed.
> > Chances are that a much wider font resulting from high density primary
> > display derived DPI number combined with low resolution video projector
> > screen will show big fonts and that will happen to be *exactly* what you
> > want so the guy back there at the end of the room has a chance to
> > actually read something
>
> I absolutely agree that there should be an easy mechanism to globally
> change font size. But I don't think tying it to DPI is helpful.

Sure call it the way you prefer, does need to be DPI necessarily, but
the concept of DPI would give a clue to all apps about what they are
asked to do, whether it is font or some other rendering.

Simo.

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Old 10-06-2011, 05:49 PM
Adam Williamson
 
Default Why EDID is not trustworthy for DPI

On Thu, 2011-10-06 at 12:00 -0400, Simo Sorce wrote:

> So in that case you really should just give an option to the user to
> easily change DPI (no need to call the option 'DPIs', it can be a slider
> with no mention of DPI if you prefer) *if* it is needed.

There actually is one, only it's called the Text Scaling Factor, and
it's hidden in the Accessibility panel. It effectively sets the DPI to
96*TSF, so you have to do desired dpi / 96 to figure out what you want
to set it to.

(That's a much better UI! Now, both people who know what DPI is and how
to calculate it and people who don't are lost and confused. equality ho!
)
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Old 10-06-2011, 05:58 PM
Felix Miata
 
Default Why EDID is not trustworthy for DPI

On 2011/10/06 15:33 (GMT+0100) Matthew Garrett composed:

> On Thu, Oct 06, 2011 at 09:30:50AM -0500, Chris Adams wrote:

>> I would wager that the majority of Fedora systems are single monitor
>> (or, in the case of notebooks, single monitor much of the time); can't
>> we at least try to correct for that case first, and _then_ try to deal
>> with multi-monitor setups?

> Changing the current behaviour doesn't make the most common case
> significantly better, but potentially makes a less common (but still
> common) case significantly worse. What's the benefit?

Nearly always the permanent display will have the higher actual DPI. This means:

1-96 makes everything undersize too often on internal displays
2-the external display has bigger text than the internal
3-accurate on the internal rarely means no text anywhere is illegible
4-it's invariably easier to make too big Xorg text smaller than the converse
5-what Nicolas Mailhot wrote

What happens to/for multiple display users should only be fussed over after
an appropriate strategy is developed for the vast majority that use a single
display at a time.
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words are persuasive." Proverbs 16:21 (New Living Translation)

Team OS/2 ** Reg. Linux User #211409 ** a11y rocks!

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Old 10-06-2011, 05:59 PM
Simo Sorce
 
Default Why EDID is not trustworthy for DPI

On Thu, 2011-10-06 at 11:41 -0500, Bruno Wolff III wrote:
> On Thu, Oct 06, 2011 at 12:00:36 -0400,
> Simo Sorce <simo@redhat.com> wrote:
> >
> > My main use case here is video projectors, and in that case there is no
> > way on earth you'll ever know the DPI as it depends on the distance from
> > the wall, and again even if you knew the distance from the wall you'd
> > know nothing because the optimal DPI will also depend on the distance of
> > the crowd from the wall.
>
> What you really want to know is the resolution per angle or arc. And that
> would be relatively constant for a project regardless of distance from
> the surface it is projecting on.

No, I do not really care because the apparent size of stuff depends on
the distance of the viewer from the projected surface too, so having
that value doesn't really tell you how big you should display stuff.

Also I do not need to know the resolution per arc to know that 10 pixels
are always 10 pixel just bigger because the wall is farther, except they
are still too little for the job because the crowd is even farther from
the wall than the projector is

Simo.

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Old 10-06-2011, 06:01 PM
Bill Nottingham
 
Default Why EDID is not trustworthy for DPI

Simo Sorce (simo@redhat.com) said:
> My main use case here is video projectors, and in that case there is no
> way on earth you'll ever know the DPI as it depends on the distance from
> the wall, and again even if you knew the distance from the wall you'd
> know nothing because the optimal DPI will also depend on the distance of
> the crowd from the wall.

Obviously you embed radar in every projector.

Bill
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Old 10-06-2011, 06:13 PM
Jef Spaleta
 
Default Why EDID is not trustworthy for DPI

On Thu, Oct 6, 2011 at 10:01 AM, Bill Nottingham <notting@redhat.com> wrote:
> Obviously you embed radar in every projector.

Quite possible to do with existing off the shelf ultrasonic or diode
laser telemetry being used for DYI robotic range finding. In fact you
can get ones that use i2c for data acquisition.I could probably mock
something up with an arduino unit to do the measurement. Though I'd
need some help getting a projector to use the calculation and hand it
back over the wire to the computer.


-jef"sort of kidding...sort of"spaleta
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