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Re: Proposal for "overflow:clip" for stronger painting isolation

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Fri, 20 Sep 2013 13:36:55 -0700
Message-ID: <CAAWBYDApjjLKNjhM8Gvsta_LnnM_EfWpMEdedtypDHep4=tVng@mail.gmail.com>
To: Nick Cameron <nick@ncameron.org>
Cc: www-style list <www-style@w3.org>
On Fri, Sep 20, 2013 at 12:54 PM, Nick Cameron <nick@ncameron.org> wrote:
> I think this is a good idea. I would like to be able to isolate for layout
> as well as painting. Perhaps overflow: clip and known (fixed?) width and
> height are enough. "nothing inside the element can paint outside the
> element's rect" seems necessary, but possibly not sufficient - do we need to
> also guarantee that nothing outside the element can paint inside the
> element's rect? Possibly only in the same stacking context? Perhaps having
> overflow: clip start a new stacking context is enough.

No, you can't guarantee the opposite, as you'd need to somehow prevent
things from overlapping, and ensure that the element itself was
opaque.  Stacking context (which, if not implied by what I already
described, should be added to the effects) lets you render the element
as an independent layer, which is enough.

Basically, it's unnecessary to guarantee the opposite.  It doesn't
help us in any important way, and it would be a massive and
impossible-to-enforce restriction.

> Is 'hard' clipping plus a fixed size element enough to guarantee that we can
> use the element as a layout boundary? That is, changing the size of
> something inside the element cannot affect anything outside the element and
> vice-versa (other than position of the element, which does not require
> reflow). I can't think of a counterexample, but I am no css expert.

Yes, it is, I think.

~TJ
Received on Friday, 20 September 2013 20:37:42 UTC

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