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Re: Sub-pixel coordinate granularity

From: Rick Byers <rbyers@google.com>
Date: Tue, 18 Mar 2014 15:29:05 +0000
Message-ID: <CAFUtAY9qUzuR5KxShzixR+FTFMafwatTDG9AgYe0ub+DF7sdCw@mail.gmail.com>
To: "public-pointer-events@w3.org" <public-pointer-events@w3.org>, Jacob Rossi <Jacob.Rossi@microsoft.com>
Cc: Simon Pieters <simonp@opera.com>
Apparently IE returns sub-pixel co-ordinates for pointer events by default
[1].  That blog post says that this only happens at browser zoom >100%, but
shouldn't it also happen on high-DPI devices where 1 CSS pixel is larger
than a screen pixel?  I don't have a high-DPI windows device to test
currently.  Jacob/Asir, can you clarify IE's behavior here?

Also (tangentially related), that blog post indicates that there's web
compat issues with having APIs like Element.scrollTop return fractional
values (and so IE has a proprietary switch "msCSSOMElementFloatMetrics" for
enabling it).  Simon Pieters (CSS OM Spec editor) asked for details on the
web compat impact here [2] but never got any response.  Jacob, can you help
get us some details from the IE team?

This is starting to become very important to us as in blink as we work to
enable scroll-linked touch effects like pull-to-refresh on high-dpi devices.



[2] http://lists.w3.org/Archives/Public/www-style/2012Feb/1331.html

On Wed, Dec 18, 2013 at 12:13 AM, Rick Byers <rbyers@google.com> wrote:

> Hi,
> The latest CSSOM view editors draft extends a number of APIs (including
> MouseEvent) to use 'double' for co-ordinates instead of 'int' (
> http://dev.w3.org/csswg/cssom-view/#extensions-to-the-mouseevent-interface).
>  Since PointerEvent extends MouseEvent, we'd get this improved definition
> "for free".  I think this is valuable, for example, when implementing
> javscript-driven touch dragging or scrolling which should be just as smooth
> as native browser scrolling.
> Thoughts?
>    Rick
Received on Tuesday, 18 March 2014 15:29:57 UTC

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