[Webkit-unassigned] [Bug 55257] Support creating compositing layers for scrollable frames and iframes

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=55257





--- Comment #56 from Adrienne Walker <enne at google.com>  2011-08-03 10:13:22 PST ---
(In reply to comment #55)

> Chromium overrides this method but I don't believe other ports (including Safari) do.

Hmm.  Thanks for pointing that out.

I'm not sure that I agree with the idea that a iframe with overflow on an otherwise non-composited page should *trigger* compositing.  If the page is already composited, then it makes sense to require compositing for the iframe.  If this were how it behaved, I'd have no problem turning this on by default for other ports.

Given that, what we'd really want is to be able to conditionally require compositing on these iframes.  (Please correct me if I'm wrong here, but) in my understanding of how layout and computing compositing requirements works, we may not know when we're looking at an subframe whether or not the main frame is going to be composited or not, because some later part of the page might be the compositing trigger.  I'm not sure that there's a good way to solve this.  Needing to do layout again to get to a stable result seems like a bad approach.

jamesr suggested the other day that maybe instead of a setting we should just tie this to the force compositing flag.  I'm coming back around to that idea.  This would sidestep the problem of other ports and would provide a much more definitive trigger for when to composite these subframes.

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