Re: let's bump to 10mm from 9mm

On 17/12/2015 22:32, Patrick H. Lauke wrote:
> On 17/12/2015 22:06, Richards, Jan wrote:
[...]
>> So 44px was 11 mm on my desktop monitor but 8.5mm on my Samsung Note
>> phone.
>>
>> Maybe the SC wording needs to be more vague and then CSS px and mm
>> measurements can be offered as sufficient techniques?
>
> I'd be in favor of having the *normative* text be more vague.
>
> I fear though that even if it was softened to something like "must be at
> least as large as an average person's fingertip" (see for instance the
> note on "Size and positioning of UI" in
> https://msdn.microsoft.com/en-us/library/windows/apps/hh465370.aspx),
> the end result is still that there's now a hard requirement to achieve a
> minimum physical size, but that there's no way for a developer to
> actually *guarantee* this as they can't check for physical device size,
> whether or not that device has implemented a sensible device pixel
> ratio, and they can't test on every possible device out in the wild and
> coming out in the future. Unless a strong note/exemption can be added
> somehow to the normative text which puts the onus on device/OS/UA having
> implemented a sensible mapping?
>
> In a further *informative* note we could then provide commonly
> used/suggested sizes such as 44x44px, and clarify that it may not always
> be possible for a developer to explicitly know the exact physical size
> that this will map to, as it depends on multiple factors outside of
> their control.


Having slept on this, I *think* it may be appropriate to to have the 
actual wording of the SC provide a hard value in CSS pixels, e.g. "Touch 
Target Size: One dimension of any touch target measures at least 44px ...".

In the explanatory text, it would then ideally mention that we're 
talking CSS pixels, rather than hardware pixels (with a reference back 
to CSS 2 http://www.w3.org/TR/CSS2/syndata.html#length-units); 
additionally, in that text it should clearly state that authors cannot 
directly control the actual physical size that 44px are rendered at on a 
screen, as this depends on hardware/OS/UA, but that 44px was chosen 
because "generally" it renders at an approximate size of 9mm.

This way, the SC is consistently testable (by checking the dimensions in 
CSS pixels), and it clarifies at which point authors are not in control 
anymore of how things are *actually* rendered.

P
-- 
Patrick H. Lauke

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Received on Friday, 18 December 2015 10:21:23 UTC