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Re: [css3-mediaqueries] DPI in resolution media queries

From: Lea Verou <leaverou@gmail.com>
Date: Wed, 15 Feb 2012 21:34:32 +0200
Message-ID: <4F3C08C8.3090601@gmail.com>
To: Sylvain Galineau <sylvaing@microsoft.com>
CC: Boris Zbarsky <bzbarsky@MIT.EDU>, "www-style@w3.org" <www-style@w3.org>
On 15/2/12 21:17, Sylvain Galineau wrote:
> [Boris Zbarsky:]
>> On 2/15/12 12:00 PM, Sylvain Galineau wrote:
>>> OK, sorry for being slow. If the DPI causes the UA to get its inches
>>> completely wrong, how does it get it right with MQs?
>> CSS.1 requires that UAs ignore the real DPI to some extent and set inches
>> to exactly 96 CSS px.
>>
> Yes, I recall that fun discussion. A CSS pixel is 1/96 of an inch. But if
> the UA can't get its CSS pixels right, how can you assume dpi/dpcm works?
If I recall the css3-values prose correctly, a pixel is 1/96 of a CSS 
inch, but a CSS inch is based on the assumption of a 96dpi resolution. 
So, it's the inches/cm that CSS gets wrong, not the pixels.
If some devices use pixel ratios like 4 physical pixels for each CSS 
pixel, it's exactly because CSS never provided a mechanism to define 
something with physical dimensions. As a result, authors make designs 
that are based on pixel lengths, and thus, would be way too small on 
high-dpi devices such as iPhone 4.
Received on Wednesday, 15 February 2012 19:35:06 GMT

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