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Old 10-06-2011, 03:20 PM
Matthew Garrett
 
Default Why EDID is not trustworthy for DPI

On Thu, Oct 06, 2011 at 11:14:56AM -0400, Jon Masters wrote:

> 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?

The specification provides everything needed to express this data
accurately, and proves the worth of specifications by virtue of
approximately nobody actually implementing it correctly.

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Old 10-06-2011, 03:27 PM
"Nicolas Mailhot"
 
Default Why EDID is not trustworthy for DPI

Le Jeu 6 octobre 2011 15:37, Matthew Garrett a écrit :
> On Thu, Oct 06, 2011 at 01:13:21PM +0200, Nicolas Mailhot wrote:
>>
>> Le Mer 5 octobre 2011 23:35, Matthew Garrett a écrit :
>>
>> > This... works badly. Really. Open gimp and add some text. Now double the
>> > size of the font. Save the image and open it in image viewer, and zoom
>> > out so the text is half the size. It doesn't look the same as your
>> > original text.
>> >
>> > Rendering fonts (and even SVGs) well requires you to know the scale that
>> > you're rendering to. More pixels mean you can add more detail. If you
>> > shrink that then the additional detail is still there, getting in the
>> > way of the actually important information. Doing this properly requires
>> > that the original object renderer be part of the scaling process, and
>> > doing that on the fly with reasonable performance just isn't part of our
>> > rendering stack at the moment.
>>
>> Which is exactly why forcing 96dpi on displays which have very different
>> pixel
>> densities *today* is not a good idea at all.
>
> Knowing the number of pixels available means that the output will be
> legible, even if you'd prefer it to be a different size.

I don't call text which is significantly too big or too small legible.

When apps that use different toolkits perform different font size adjustments,
the resulting UIs are inconsistent and generally tiring (uniformity is a huge
factor in text readability)

When basic font sizes are out of whack because the desktop pretends the pixel
density is way different than it is really users try to compensate using all
the available size settings in their apps. The result is a huge heterogeneous
mess. Settings and documents can not be moved from one computer to another
without strange font size changes. Different fonts are not adjusted the same
way by users, because of size rounding in UIs, breaking font set harmony.
Sometimes you get apps that adjust via zooming without re-rendering

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Old 10-06-2011, 03:33 PM
"Nicolas Mailhot"
 
Default Why EDID is not trustworthy for DPI

Le Jeu 6 octobre 2011 17:18, Matthew Garrett a écrit :
> The heuristic isn't the problem. The problem is that we have no
> technology that allows us to handle the complicated case of multiple
> displays, and solving it purely for the simple case makes the
> complicated case *worse*.

How does it make it worse? The heuristic does not solve the complicated case
*at all*. How does removing it could possibly make it worse?

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Old 10-06-2011, 03:35 PM
Simo Sorce
 
Default Why EDID is not trustworthy for DPI

On Thu, 2011-10-06 at 16:18 +0100, Matthew Garrett wrote:
> The heuristic isn't the problem. The problem is that we have no
> technology that allows us to handle the complicated case of multiple
> displays, and solving it purely for the simple case makes the
> complicated case *worse*. Adding additional complexity for what would
> be, at best, a different set of problems doesn't seem like a worthwhile
> way to spend time. The only people who are actively upset by the status
> quo are the ones who have the ability to fix it for their case, anyway.

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.

Simo.


<flamebait>I am not asking for a slider because I guess the options
police would shot it down :-P </flamebait>

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Old 10-06-2011, 03:39 PM
Jon Masters
 
Default Why EDID is not trustworthy for DPI

On Thu, 2011-10-06 at 16:20 +0100, Matthew Garrett wrote:
> On Thu, Oct 06, 2011 at 11:14:56AM -0400, Jon Masters wrote:
>
> > 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?
>
> The specification provides everything needed to express this data
> accurately, and proves the worth of specifications by virtue of
> approximately nobody actually implementing it correctly.

How about an actual DPI value?

Jon.


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Old 10-06-2011, 03:41 PM
Matthew Garrett
 
Default Why EDID is not trustworthy for DPI

On Thu, Oct 06, 2011 at 05:33:48PM +0200, Nicolas Mailhot wrote:
>
> Le Jeu 6 octobre 2011 17:18, Matthew Garrett a écrit :
> > The heuristic isn't the problem. The problem is that we have no
> > technology that allows us to handle the complicated case of multiple
> > displays, and solving it purely for the simple case makes the
> > complicated case *worse*.
>
> How does it make it worse? The heuristic does not solve the complicated case
> *at all*. How does removing it could possibly make it worse?

What heuristic?

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Old 10-06-2011, 03:44 PM
Matthew Garrett
 
Default Why EDID is not trustworthy for DPI

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.

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Old 10-06-2011, 03:46 PM
Matthew Garrett
 
Default Why EDID is not trustworthy for DPI

On Thu, Oct 06, 2011 at 11:39:16AM -0400, Jon Masters wrote:
> On Thu, 2011-10-06 at 16:20 +0100, Matthew Garrett wrote:
> > On Thu, Oct 06, 2011 at 11:14:56AM -0400, Jon Masters wrote:
> >
> > > 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?
> >
> > The specification provides everything needed to express this data
> > accurately, and proves the worth of specifications by virtue of
> > approximately nobody actually implementing it correctly.
>
> How about an actual DPI value?

The DPI depends on the mode. Not all the world is an LCD, and even there
it depends on whether you're native, scaling or scaling with constrained
aspect ratio.

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Old 10-06-2011, 03:52 PM
Simo Sorce
 
Default Why EDID is not trustworthy for DPI

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.

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Old 10-06-2011, 04:00 PM
Simo Sorce
 
Default Why EDID is not trustworthy for DPI

On Thu, 2011-10-06 at 16:46 +0100, Matthew Garrett wrote:
> On Thu, Oct 06, 2011 at 11:39:16AM -0400, Jon Masters wrote:
> > On Thu, 2011-10-06 at 16:20 +0100, Matthew Garrett wrote:
> > > On Thu, Oct 06, 2011 at 11:14:56AM -0400, Jon Masters wrote:
> > >
> > > > 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?
> > >
> > > The specification provides everything needed to express this data
> > > accurately, and proves the worth of specifications by virtue of
> > > approximately nobody actually implementing it correctly.
> >
> > How about an actual DPI value?
>
> The DPI depends on the mode. Not all the world is an LCD, and even there
> it depends on whether you're native, scaling or scaling with constrained
> aspect ratio.

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.

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

Then there will be guy X that hates the big fonts or has a ridiculously
low DPI primary screen and he'll not be happy. You cannot please
everyone with a default, but you can with an easy to discover option.

So whatever is the situation the slider should be right there in the
tool you use to manage the additional monitors or people will be forced
to search and find the menu where he can change "something" to try to
get a better font size and all resulting in poor experience as that menu
is normally well hidden as it is a rarely used option normally.

Simo.

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