W3C home > Mailing lists > Public > www-style@w3.org > October 2013

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

From: Bruno Racineux <bruno@hexanet.net>
Date: Thu, 17 Oct 2013 14:23:47 -0700
To: "Tab Atkins Jr." <jackalmage@gmail.com>, www-style list <www-style@w3.org>
Message-ID: <CE859F89.7684D%bruno@hexanet.net>
On 9/20/13 12:03 PM, "Tab Atkins Jr." <jackalmage@gmail.com> wrote:

>I've been talking with out layout/compositor people here on Blink for
>a while now, and one of the things that has shaken out as a big helper
>in getting things to work *fast* is having strong, guaranteed methods
>to isolate parts of the page.
>In particular, isolating the painting of an element seems like a big
>win - having some way to guarantee that the element can be
>hard-clipped to its boundary without losing anything important.
>overflow:hidden doesn't *quite* do this - abspos and fixpos elements
>can escape the bounds of the element.
>As well, overflow:hidden still allows scrolling into the hidden area,
>through JS.  This isn't an edge-case - this technique is used by a lot
>of JS libraries.  This means that we can't depend on the element only
>painting its visible area - we have to speculatively paint further, so
>we can scroll smoothly at a moment's notice.
>To get around both of these issues and provide stronger optimization
>guarantees to the browser, I suggest we add a "clip" or "contained"
>value to overflow.  This does a strong clipping - nothing inside the
>element can paint outside the element's rect.
>It also acts as a positioning root for abspos inside the element, and
>kills fixpos, reverting it to abspos with the element as its
>positioning root.
>The value also completely prevents scrolling - the scrollWidth/Height
>of the element is its visible width/height.

Does this proposal address "clearing the float" at all?

I would be ideal is there was a native solution for this by now, rather
than the 'clearfix' hacks.

And while 'overflow:hidden' helps, it's not a comprehensive solution to
Received on Thursday, 17 October 2013 21:24:18 UTC

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