W3C home > Mailing lists > Public > www-style@w3.org > January 2010

Re: Making pt a non-physical unit

From: Robert O'Callahan <robert@ocallahan.org>
Date: Sat, 16 Jan 2010 22:02:11 +1300
Message-ID: <11e306601001160102i4f6c184pc08a1142de36a9f2@mail.gmail.com>
To: David Singer <singer@apple.com>
Cc: www-style Group <www-style@w3.org>
On Sat, Jan 16, 2010 at 3:01 PM, David Singer <singer@apple.com> wrote:

> It is recommended (required?) that a CSS pixel be an integer number of
> device pixels, particularly if the ratio of CSS pixel to device pixel size
> is small.
>

I don't think this recommendation should be part of the spec. It's a
UA-specific, media-specific issue. As it turns out, in Gecko for screens you
get maximum performance and quality with 1 device pixel per CSS pixel, and
if the ratio is not 1, it doesn't really matter whether it's an integer or
not.

In screen media, a CSS pixel is often (recommended to be?) one or more
> device pixels, subtending the angle given above at the eye when viewed from
> the expected viewing distance.  For 96 dpi computer displays read at a
> normal viewing distance, both CSS pixel and CSS inch may map to their true
> counterparts.  For small high-resolution displays intended for 'close up'
> viewing, this means that a CSS pixel may map to a device pixel and that a
> CSS inch may be smaller than a physical inch on the screen, and for large
> displays intended for distant viewing, a CSS inch may be larger than a CSS
> inch.
>

... may be larger than a physical inch.

The rest sounds OK.

Rob
-- 
"He was pierced for our transgressions, he was crushed for our iniquities;
the punishment that brought us peace was upon him, and by his wounds we are
healed. We all, like sheep, have gone astray, each of us has turned to his
own way; and the LORD has laid on him the iniquity of us all." [Isaiah
53:5-6]
Received on Saturday, 16 January 2010 09:02:44 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 17:20:23 GMT