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Re: [fxtf-drafts] Clip backdrop root (input) image to border box of element (#342)

From: Mason Freed via GitHub <sysbot+gh@w3.org>
Date: Fri, 21 Jun 2019 20:03:47 +0000
To: public-fxtf-archive@w3.org
Message-ID: <issue_comment.created-504556016-1561147426-sysbot+gh@w3.org>
@mstange, thanks for the comments. I put the language back to just "blur" for the edgemode comment.

I've never quite been able to wrap my head around a drop-shadow backdrop-filter, for a couple reasons. First, it is offset from the original, and the backdrop-filter effect is clipped at the border box. Second, the offset/blurred drop shadow is already specified to be composited *below* the image. So if you're applying a backdrop-filtered drop-shadow, where does the drop shadow composite, exactly? I actually thought about explicitly removing drop-shadow from the spec for backdrop-filter, but I figured someone would come up with a cool use.

Finally, regarding the clipping of the input rect: I did mention this problem on the crbug.com/497522 discussion. As soon as one pixel of the new color passes under the border rect, it can "suddenly" affect a large portion of the filtered output. There's no perfect answer to this problem - there are weird behaviors either way. It seems like the developer feedback is that they would prefer the new behavior - clipping the input. It also has the added benefit of being more performant and being closer to Webkit. I'm not sure how their implementation (which does appear to clip the input to the border box, or something close) works better in this regard - let me know if you know!

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Received on Friday, 21 June 2019 20:04:26 UTC

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