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Re: [fxtf-drafts] [filter-effects-2] Backdrop filters should not use BackgroundImage

From: Markus Stange via GitHub <sysbot+gh@w3.org>
Date: Tue, 13 Nov 2018 20:49:42 +0000
To: public-fxtf-archive@w3.org
Message-ID: <issue_comment.created-438431485-1542142181-sysbot+gh@w3.org>
In response to @mfreed7:

> The isolation question merely affects which elements get included in the background image that forms the starting point for the backdrop filter. Orthogonal to that, there is the question of how to process that background image, including your question about opacity.

That's true. I was conflating the questions "where does the input come from" and "where does the output go", because I was thinking about this in terms of an implementation that would render based on an intermediate representation (some kind of effect graph) that has lost information about this distinction.

> Without a definition such as the above, it is our belief that many interactions (such as your opacity example) will be difficult for developers to reason about, and will also lead to implementation issues and performance problems.

I fully agree. We need a definition with this level of precision in the spec.

> opacity applied to B will **not** be applied to the backdrop-filtered backdrop. To achieve that, however, you could just change your filter spec to `backdrop-filter: blur(10px) opacity(0.1);`. That would apply the opacity to the filtered content, and should do exactly what you expect.

Well, mostly. It would not do group opacity the way I expect: `<div style="opacity: 0.8;backdrop-filter: blur(10px) opacity(0.8);"><div style="width:100px;height:100px;background:white"></div></div>` - in this example, you'd still be able to see remains of the blurred backdrop behind the white square, whereas the effect I'd like to achieve would have the white square block out the blur entirely. Moreover, having to repeat the opacity value in two different properties makes opacity animations a bit more cumbersome.

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Received on Tuesday, 13 November 2018 20:49:43 UTC

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