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Re: [media-queries] chicken-egg problem with font-based lengths

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Mon, 20 Aug 2012 10:21:34 -0700
Message-ID: <CAAWBYDBwsRHpK2MA8SpEsGGmTRAMBw82++eVi=gGm_2JxNKkBw@mail.gmail.com>
To: Felix Miata <mrmazda@earthlink.net>
Cc: www-style@w3.org
On Mon, Aug 20, 2012 at 10:10 AM, Felix Miata <mrmazda@earthlink.net> wrote:
> On 2012/08/20 08:11 (GMT-0700) Tab Atkins Jr. composed:
>> It appears that you are, in general, confused about what the px unit
>> represents - it is *not* the same size as a device pixel, in general.
> Yes it is the same, due to this gem from
> http://dev.w3.org/csswg/css3-values/#lengths
> "...pixel unit refer to the whole number of device pixels that best
> approximates the reference pixel."

Given that I was one of the editors of that spec, and I've explained
this exact issue several times, I'm pretty sure I know what I'm
talking about.

>> Instead, it's defined in terms of visual angles, so that 1px will look
> Technical definition doesn't matter. Reality does.

If you think we would have defined the length units in such a stupid
way if reality didn't force our hand, then I'm sorry you have such a
poor conception of our abilities.

>> like approximately the same length on any device.  Desktop browsers
>> generally size the px unit to be an integer multiple of device pixels,
> Precisely why I wrote what I wrote. Until device density reaches 192 DPI, a
> CSS pixel equals a device pixel, because browsers only use integer
> multiples.

There are desktop browsers today that are in the "2 device pixels per
CSS px" realm.  (Well, laptop, but that's the same class.)

There are lots of browsers on mobile devices that have ratios other
than 1:1.  Some are 2:1, but there are tons that have non-integer

Received on Monday, 20 August 2012 17:22:22 UTC

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