Re: minimum target size for mouse

On 21/04/2016 17:57, Gregg Vanderheiden wrote:
> but I don’t understand how an author has any idea what physical size a
> button is on a screen without knowing the size of the screen and the
> current pixel density setting at that moment.
>
> pixels are of no real value.   if we say this is required — it MUST be
> important that it be true for the user.   But if 44 px is different on
> each device and the persons pointing is not….. then….   ????

this is going around the same whirlpool as 
https://github.com/w3c/wcag/issues/181 but in short: there is no way for 
an author to define a physical size as rendered on screen. there are far 
too many variables outside of the author's control.

> are we just assuming that px is some physical size and that a user with
> a physical problem won’t use a screen where 44 px is too small?   (this
> is a potentially valid approach by the way)

yes, the underlying assumption (which will be in the SC and/or the 
understanding etc) is that devices will have a reasonably sane 
implementation of the "reference pixel" 
https://drafts.csswg.org/css-values/#reference-pixel (for mobile web 
content, for instance, this also requires that a site specify that the 
browser use the "ideal viewport" - see 
http://www.quirksmode.org/mobile/metaviewport/ and 
http://patrickhlauke.github.io/web-tv/ideal-viewport/). this can't 
guarantee that 44px will render to the same physical size "as measured 
on screen" on all devices, but that it will in most cases, on most 
common devices with a sane viewport, roughly fall into the correct 
physical size. And yes, the onus will also partially be on users NOT to 
use a device which, by default, renders content far too small for their 
needs.

(most of the points discussed on this list that finally lead to this I 
actually reiterated just yesterday/today on that 
https://github.com/w3c/wcag/issues/181 issue - see also the notes from 
past calls of this group where I cheekily joined in to raise the 
original concern about NOT requiring a physical "as measured on screen" 
size since that's a magic unicorn that authors can't actually 
fulfill/guarantee, since browsers don't have any way of actually setting 
real physical sizes (since even using units like pt, mm, cm etc will 
result in measurements anchored on the pixel, distinct from actual 
physical size).

P
-- 
Patrick H. Lauke

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Received on Thursday, 21 April 2016 19:41:34 UTC