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[csswg-drafts] paint containment vs filter effects (#6325)

From: Florian Rivoal via GitHub <sysbot+gh@w3.org>
Date: Mon, 31 May 2021 05:34:41 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-907074493-1622439279-sysbot+gh@w3.org>
frivoal has just created a new issue for https://github.com/w3c/csswg-drafts:

== paint containment vs filter effects ==
The intent of paint containment is (among other things) that:
> If the containment box is off-screen or obscured, the UA can directly skip trying to paint its contents, as they’re guaranteed to be off-screen/obscured as well.

That doesn't seem to account for [filter effects](https://drafts.fxtf.org/filter-effects/). If you put a blur filter (for example) on an ancestor of an element of paint containment, it can spread the pixels of the contained element beyond the geometry of that element, with no particular boundary. So the contained element may be off-screen, but you still need to repaint it so that the on-screen pixels of the parent with a filter an be rendered correctly.

Is this OK because filters are a composite-time operation rather than paint-time operation, or something like that?

Is this bad and we somehow forgot to take it into account?

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/6325 using your GitHub account


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