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[csswg-drafts] [css-values] clarify that most (all?) high-dpi devices anchor on pixel, rather than physical, unit

From: Patrick H. Lauke via GitHub <sysbot+gh@w3.org>
Date: Mon, 14 Nov 2016 16:33:05 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-189159410-1479141184-sysbot+gh@w3.org>
patrickhlauke has just created a new issue for 

== [css-values] clarify that most (all?) high-dpi devices anchor on 
pixel, rather than physical, unit ==
The section on absolute lengths 
https://drafts.csswg.org/css-values/#absolute-lengths currently 
contains the following:

> For print media and similar high-resolution devices, the anchor unit
 should be one of the standard physical units (inches, centimeters, 
etc). For lower-resolution devices, and devices with unusual viewing 
distances, it is recommended instead that the anchor unit be the pixel
 unit. For such devices it is recommended that the pixel unit refer to
 the whole number of device pixels that best approximates the 
reference pixel.

In essence, this splits devices into "print and high resolution" on 
one side, and "lower-resolution and unusual viewing distances". 
However, most (all?) high-dpi devices (including recent desktop 
monitors, laptops, mobile/tablet devices) currently also anchor on the
 pixel unit. It seems that it's really only print media that (try to) 
anchor on physical units (unless I'm missing some non-print device 
that does this?).

I think it would be important to either rewrite this section to change
 the distinction, or to leave the above as is but then include a note 
straight after clarifying that currently even high-resolution 
desktops/laptops/mobiles/tablets are anchored on the pixel unit.

The reason for bringing this up is that this issue seems to constantly
 rear its head in discussions around being able to use absolute 
measures like "mm" to actually map to physical size of elements *as 
rendered on a device* (most recently I had this discussion in the 
mobile accessibility task force 
 which led to having to demonstrate this practically using 
http://codepen.io/patrickhlauke/full/zqabMR/ ... and I'm aware of 
similar discussions under WICG in relation to large screen / TV 

Happy to draft a PR if this sounds like a reasonable request.

Please view or discuss this issue at 
https://github.com/w3c/csswg-drafts/issues/708 using your GitHub 
Received on Monday, 14 November 2016 16:33:11 UTC

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