[Webkit-unassigned] [Bug 55257] Support creating compositing layers for scrollable and overflowing objects

Mon Mar 7 16:02:23 PST 2011

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

--- Comment #27 from Simon Fraser (smfr) <simon.fraser at apple.com>  2011-03-07 16:02:23 PST ---
(In reply to comment #26)
> Simon,
> 
> without touching canBeComposited() and isSelfPaintingLayer() my proposed change allows for compositing (i)frames that overflow.

Please use separate patches for (i)frames and overflow: scroll divs. I think they share little code.

> Assuming we would want to allow overflowing divs to be composited into their own layers also, what would be the right way to implement it?

I'm not sure. One approach is break the web, and cause overflow to create stacking context. This was suggested to the CSS-WG a couple of years ago, and rejected.

Otherwise, we have to be very careful to allow compositing for overflow without breaking things. I'd have to probably just try it to figure out if it's possible. One approach is to make a series of testcases similar to mine, where it matters that overflow does not create a SC.

> Also, about the testcase: Were you worried that with my change we would create an unwanted stacking context at the 'container' node?

I was worried that your changes would alter the rendering of the test.

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