- From: Kenneth Rohde Christiansen <kenneth.christiansen@gmail.com>
- Date: Sun, 21 Oct 2012 16:44:33 +0200
- To: Simon Sapin <simon.sapin@kozea.fr>
- Cc: "www-style@w3.org list" <www-style@w3.org>
Another interesting comment explaining why 160 dpi per css unit makes sense for phones. https://bugs.webkit.org/show_bug.cgi?id=88114#c0 : "This works on phones, but is incorrect on laptops/desktops. The definition of a CSS pixel (http://www.w3.org/TR/css3-values/#reference-pixel) requires a pixel density of 96dpi on devices used at arms length (the reason that 160 works well on phones is because they're held at about 60% of an arm length). It's also common to discretize deviceScaleFactor to the nearest 0.25 or so." Kenneth On Sun, Oct 21, 2012 at 4:36 PM, Kenneth Rohde Christiansen <kenneth.christiansen@gmail.com> wrote: > The first iPhone (and many later phones) shipped with a DPI of 160, > which is what most mobile web apps have been optimized for. > > The iPhone 4, shipped with a DPI of 320 (retina display) and a > device-pixel-ratio == 2.0, meaning that one CSS unit is defined at 160 > DPI still. > > A bit of background: > > http://www.quirksmode.org/blog/archives/2012/06/devicepixelrati.html > http://www.quirksmode.org/blog/archives/2012/07/more_about_devi.html > http://www.rictus.com/muchado/wp-content/uploads/2011/04/multiscreen-dev-with-flex-360flex-2011.pptx.pdf > http://web.archiveorange.com/archive/v/OOYmTvfzzo75fCpH6kHs > > Cheers > Kenneth > > On Sun, Oct 21, 2012 at 2:25 PM, Simon Sapin <simon.sapin@kozea.fr> wrote: >> Le 21/10/2012 14:06, Kenneth Rohde Christiansen a écrit : >> >>> Then that is very different from the device-pixel-ratio it is supposed >>> to replace, as device-pixel-ratio: 1 on iOS etc corresponds to a DPI >>> of 160, and 2 to a DPI of the double. >> >> >> Where is this 160 number coming from? By "a DPI of 160", do you mean device >> pixels per physical inch on a particular device? >> >> The CSS dpi unit is not the same, it is in device pixels per CSS inch. A CSS >> inch is always 96 CSS pixels. >> >> >> About device-pixel-ratio, what is it’s exact definition? I couldn’t find it. >> Apparently it ways supposed to be documented in [1] but according to >> archive.org is never was. >> >> The best hint I found is in a Mozilla bug[2]: >> >>> It looks like Webkit's 'ratio' is the number of device pixels per CSS >>> pixel. >> >> >> >> There is also a CSSWG blog post[3] suggesting that eg. >> (-webkit-device-pixel-ratio: 2) is exactly the same as >> (resolution: 192dpi) >> >> >> [1] http://webkit.org/specs/MediaQueriesExtensions.html >> [2] https://bugzilla.mozilla.org/show_bug.cgi?id=474356#c6 >> [3] >> http://www.w3.org/blog/CSS/2012/06/14/unprefix-webkit-device-pixel-ratio/ >> >> >> -- >> Simon Sapin >> > > > > -- > Kenneth Rohde Christiansen > Senior Engineer, WebKit, Qt, EFL > Phone +45 4093 0598 / E-mail kenneth at webkit.org > > ﹆﹆﹆ -- Kenneth Rohde Christiansen Senior Engineer, WebKit, Qt, EFL Phone +45 4093 0598 / E-mail kenneth at webkit.org ﹆﹆﹆
Received on Sunday, 21 October 2012 14:45:20 UTC