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Re: [css3-values] Editoria,, resolution units: physical inch vs. CSS inch.

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Mon, 22 Oct 2012 16:44:35 -0700
Message-ID: <CAAWBYDAA9tA8q0UKzKXAV_v-+E7QN=VjK-5ihWY-o++NvQw+Lg@mail.gmail.com>
To: Simon Sapin <simon.sapin@kozea.fr>
Cc: "www-style@w3.org list" <www-style@w3.org>
On Sun, Oct 21, 2012 at 5:41 AM, Simon Sapin <simon.sapin@kozea.fr> wrote:
> Hi,
>
> css3-values defines the dpi unit as "dots per inch". (And similarly for
> dpcm.) I think this is too little for two reasons.
>
> First, there is no definition of a "dot". css3-mediaqueries at least imply
> that it is a device pixel.
>
> More importantly, "inch" is ambiguous: it could be a physical inch or a CSS
> inch. I think it should explicitly say "per CSS inch" or "per `in` unit"
> (like it does for dppx), perhaps with a link to section 5.2 where absolute
> length units are defined.

I'm fine with making it clearer in the <resolution> definition that
the lengths mentioned are CSS units, not real lengths.  All existing
uses of <resolution> agree with that.

The definition of "dot" is purposely ambiguous, because it has at
least two definitions, depending on usage.  For MQ, it's a device
pixel.  For Images, its an image pixel.  Each use of <resolution>
needs to define what it means by "dot".  I'm also fine with adding a
requirement to this effect into the spec.

~TJ
Received on Monday, 22 October 2012 23:45:36 GMT

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