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Re: Utility of background-composite and background-blend-mode?

From: Simon Fraser <smfr@me.com>
Date: Thu, 14 Mar 2013 10:57:42 -0700
Cc: robert@ocallahan.org, public-fx@w3.org
Message-id: <6C591B07-65AF-4467-BC1B-8A2B8E44A173@me.com>
To: Rik Cabanier <cabanier@gmail.com>
On Mar 14, 2013, at 10:08 AM, Rik Cabanier <cabanier@gmail.com> wrote:

> On Thu, Mar 14, 2013 at 3:53 AM, Robert O'Callahan <robert@ocallahan.org> wrote:
> On Thu, Mar 14, 2013 at 5:00 PM, Rik Cabanier <cabanier@gmail.com> wrote:
> I create a jsfiddle testcase: http://jsfiddle.net/vSjXM/5/
> and attached the rendering of WebKit and Firefox that has the blending patch. (https://bugzilla.mozilla.org/show_bug.cgi?id=841601)
> The behavior you described indeed happens. As soon as an element is scrolled, it goes to an offscreen bitmap (ffox_scrolling vs ffox_no_scrolling).
> Webkit does not seems to suffer from this.
> You mean "Webkit doesn't do this optimization" :-).
> yeah :-)
> FF doesn't seem to do the 'position: fixed' optimization. There was a report on the chromium graphics mailing list that seemed to indicate that it improves performance.
> This is actually a sign that browsers should standardize this. Pages might have different performance characteristics because they don't specify what operations are expense. This makes it harder for authors.

I disagree. Performance characteristics can change as browsers evolve, and they are very much an implementation detail of the engine. I would hate to be locked into a situation where every UA has to have the same performance characteristics.

> Is this something we can detect and disable if we detect blending in the element?
> Another difference is that 'position: fixed' didn't create a buffer in Firefox, but it did in WebKit.
> It does create a buffer is the scrollable div goes under it; just like you said :-)
> These differences should all be fixed so blending and filter chains that access the background can work.
> I'm not sure what you're suggesting. Are you suggesting we write Webkit's buffer-creation rules into a spec and modify other browsers to follow those rules if blending is detected in the page?
> As Dirk said, we need to come up with a set of rules that specify when these special stacking contexts are created. This will most likely need changes on all browsers.

By "special stacking contexts" you mean ones that create groups (in the http://dbaron.org/log/20130306-compositing-blending sense)?

> Current browser behavior and optimization should not change (that code is there for a good reason); only in the new context of blending and filtering should there be new behavior.



Received on Thursday, 14 March 2013 18:00:21 UTC

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