[fxtf-drafts] Nested backdrop-filters: might not correctly define whether outer filtered backdrop affects backdrop image for inner backdrop-filter (#500)

dbaron has just created a new issue for https://github.com/w3c/fxtf-drafts:

== Nested backdrop-filters: might not correctly define whether outer filtered backdrop affects backdrop image for inner backdrop-filter ==
@estelle [raised](https://front-end.social/@estelle/109951180084138057) an issue about the correct rendering of a [testcase](https://codepen.io/estelle/pen/LYJWOrW) with nested `backdrop-filter`.

In this testcase Gecko renders differently from Chromium/WebKit.

I replied ([part 1](https://w3c.social/@dbaron/109954446511970727), [part 2](https://w3c.social/@dbaron/109954453693534311)) that:
 > I think WebKit/Chromium is probably correct based on the intent of the spec (as described in a "NOTE" in [§ 3. Backdrop Root](https://drafts.fxtf.org/filter-effects-2/#BackdropRoot)) but I think Gecko is probably correct based on following actual normative steps in the spec (in [§ 2.1. Filtering and Clipping](https://drafts.fxtf.org/filter-effects-2/#backdrop-filter-operation) and in the section above).
>
> In particular, the definition of backdrop root says that the *intent* of the definition is that ancestors of the backdrop root not contribute to the backdrop root image.  However,  I think in the actual normative text in the spec, I don't see anything that excludes (from the backdrop image used for the inner backdrop-filter) the filtered backdrop that is painted as part of painting a backdrop root that is a backdrop root because it has the outer `backdrop-filter`.

In other words, I think the mechanism for backdrop-filter describes painting the filtered backdrop as part of painting the element with the `backdrop-filter`, which contradicts the note that says that painting the backdrop root and its descendants isn't affected by the backdrop root's ancestors (since, read literally, I think it is, since as far as I can tell that definition includes painting the filtered backdrop of the ancestor).

Please view or discuss this issue at https://github.com/w3c/fxtf-drafts/issues/500 using your GitHub account


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Received on Thursday, 2 March 2023 15:51:30 UTC