W3C home > Mailing lists > Public > www-style@w3.org > December 2014

Re: [selectors] Proposal :enter and :leave

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Mon, 22 Dec 2014 11:21:15 -0800
Message-ID: <CAAWBYDCNo2GZ3gOg02qon2rk5FUwTNN7KXVpBNSfQLBFn46+Cg@mail.gmail.com>
To: John Fischer <jfroffice@gmail.com>
Cc: Benjamin Poulain <benjamin@webkit.org>, www-style list <www-style@w3.org>
On Sun, Dec 21, 2014 at 2:59 PM, John Fischer <jfroffice@gmail.com> wrote:
> Benjamin,
>      Effectively this proposal seems to be a feature expensive as we need to
> have 2 -passes of computation at minimal.
>      :hover seems to be moreless the same problem . So.
>      Maybe we could find a way to limit computation.

:hover does indeed suffer from the "style depends on layout" problem,
but there's an important difference that makes it okay to deal with:
it passes through and depends on hit-detection as well, not just
layout.  This means that a single layout pass is always stable,
because hit-detection information doesn't change during a single
layout pass.  Even if this layout changes which elements match :hover,
it does so for the *next* layout.  This also provides a natural place
to break loops, if you want - just don't update hit-detection
information until the mouse moves, for example.

Anything with a "smaller" loop, particularly one that takes place
solely in layout code, is much more difficult to deal with.  You don't
have a natural place to break loops, and layout doesn't have the
ability to complete a full cycle with stable information, because it
depends on its own computations.

So one can't use :hover as an existence proof to support adding new
"style depends on layout" abilities.

Received on Monday, 22 December 2014 19:22:02 UTC

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