RE: 48px vs 44px target sizing

[Patrick wrote] >  Are we seriously retreading this conversation? There is no reliable way for a developer to determine this. A developer cannot check the actual physical screen size of a device, or the actual precise metrics like screen DPI, therefore a developer cannot determine with any accuracy what actual physical size something is rendered at on an arbitrary target device's screen.

Yes, I agree, that's what I was trying to say.  That is why I was saying we can't assume that the 20mm referred to in the report was actually 50 CSS pixels on the device used.

> Do you have an actual test page where you verified this? And does the page set the ideal viewport of width=device-width?

There are slight variations as you have noted but generally they are close.  I guess this makes the assumption that larger devices will have high device width and smaller devices will have lower device widths in scale that is acceptable.  Currently a iPhone reports the width as 320 with a device pixel ratio of 2.  What if they decided to change the width to 640 and have a device pixel ratio of 1.  I admit I do not understand nearly as much of this as you -- but I do have a concern that things could change in the future - it just seems like a holdover to have an iPhone 6 report it's width as 320.

> How would a developer/auditor test this with any reliability to ensure it's true across devices?

Sorry, I was just thinking through an idea. My mistake.

Jonathan 


-----Original Message-----
From: Patrick H. Lauke [mailto:redux@splintered.co.uk] 
Sent: Tuesday, September 06, 2016 12:34 PM
To: public-mobile-a11y-tf@w3.org
Subject: Re: 48px vs 44px target sizing

On 06/09/2016 17:24, Jonathan Avila wrote:
>> As 1 inch=25.4mm, so 6px per mm on the tablet, although that is 2D 
>> which I think means 2.5px per non-square mm. Therefore 20mm wide = 
>> 50px on that device.
>
> I think this statement is looking the wrong way.  It may be that on 
> that device 20mm = 50px -- but that doesn't mean 50px is going to be
> sufficient on other devices because it won't be 20mm.   If they say
> 20mm is what was needed then we'd need to figure out how many CSS 
> pixels would 20mm be on a target device.

Are we seriously retreading this conversation? There is no reliable way for a developer to determine this. A developer cannot check the actual physical screen size of a device, or the actual precise metrics like screen DPI, therefore a developer cannot determine with any accuracy what actual physical size something is rendered at on an arbitrary target device's screen.

> Just looking at an iPad, a 50px button may be sufficient -- but on an 
> iPhone 6s the same button is considerably smaller -- likely too small 
> for many.

Do you have an actual test page where you verified this? And does the page set the ideal viewport of width=device-width?

> I wonder if we could somehow create a relative size requirement with 
> some minimum.  Like the size of a control in device independent pixels 
> must be no smaller than 1/15 of the smallest viewport dimension with a 
> minimum of 50 device independent pixels.

How would a developer/auditor test this with any reliability to ensure it's true across devices? The reason for choosing CSS pixels when viewport is set to width=device-width is that it's reliably testable, AND shifts the onus of having a sensible ideal viewport on devices/user agents. Adding a relationship to whatever the device's viewport is actually set means that pass/fail will depend on the exact device the developer/auditor is using? Assume that an auditor is using a device/user agent which, for whatever reason, decided - against what most other mainstream devices/browsers do - to adopt a strangely high viewport dimension ... this would result in a fail on that particular device for a control, while the same control would pass if the auditor used another device.

P
--
Patrick H. Lauke

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Received on Tuesday, 6 September 2016 17:08:46 UTC