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Re: Technolog Agnostic / Independent

From: Patrick H. Lauke <redux@splintered.co.uk>
Date: Mon, 10 Apr 2017 18:50:20 +0100
To: w3c-wai-gl@w3.org
Message-ID: <a6d0bcef-740e-498a-5a09-4356a9e216c8@splintered.co.uk>
On 10/04/2017 18:40, Wayne Dick wrote:
> This 2.1 project has reached a breaking point for the old notion of one
> SC for all technologies. The idea is not to drop technology
> independence, but to expand it to fit things like geometric reality.
>
> Screen size is so significant that SCs relating visual interface really
> need a concept like "break point". Developers certainly do not treat
> mobile phones like desktops. There are things you do not do on a small
> screen. Few people write code on a mobile phone. People with low visual
> acuity will probably read very little on a mobile phone.
>
> It does not make sense to treat tiny screens like big screens when we
> are discussing visual accessibility. We need a concept like "technology
> agnostic where appropriate". Or a concept like break points for size.
>
> Consider font size. There are two factors to consider. Screen size S and
> viewing distance D. If font size of s at distance d that is sufficient
> then 3/4(s) at 3/4(d) will also be sufficient.  So we need a break down
> for testable prescriptions:
>
> Screen Size    Viewing Distance    Font-Size % of Height/Width
> s0 to s1          d0 to d1                f1
> s[n-1] to s[n] d[n-1] to d[n]         fn
>
> Note that the Font-Size percent can be computed using pixels using
> breaks points.

The problem here being that web content authors have no way to determine:

a) physical dimensions of a screen
b) viewing distance that the user may be at

Which is why the only good approximation we can rely on are CSS pixel 
dimensions (of the viewport) when the device is rendering content in 
whatever the device's "ideal viewport" is (in HTML terms, the size that 
things are rendered at in the browser when the meta viewport is set to 
width=device-width).

This ideal viewport is what the device manufacturer and user agent have 
determined would be the "best" resolution for their particular 
device/environment and general use. (since device manufacturers and 
native user agents *can* either know the actual physical dimensions of 
the device and the average viewing distance of the user a priori, or can 
query certain device metrics not exposed to web content/JavaScript).

P
-- 
Patrick H. Lauke

www.splintered.co.uk | https://github.com/patrickhlauke
http://flickr.com/photos/redux/ | http://redux.deviantart.com
twitter: @patrick_h_lauke | skype: patrick_h_lauke
Received on Monday, 10 April 2017 17:50:52 UTC

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