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

The CSS Working Group just discussed `backdrop-filter`.

<details><summary>The full IRC log of that discussion</summary>
&lt;gregwhitworth> Topic: backdrop-filter<br>
&lt;Rossen> github:<br>
&lt;gregwhitworth> chrishtr: for reasons of implementation complexity, number 1 and avoiding situations developers would find confusing<br>
&lt;gregwhitworth> chrishtr: I want backdrop-filter to only apply to containing isolated group, which in spec terms is the background image of the group<br>
&lt;gregwhitworth> chrishtr: takes the group - applies filter and then clips and paint behind it and then paint on top<br>
&lt;gregwhitworth> chrishtr: issue 53, was originally filed to change the spec to not image but all the images from the root<br>
&lt;gregwhitworth> chrishtr: the prefixed impl that Safari has that draws everything up to the root - and unprefixed version in Edge also has that<br>
&lt;gregwhitworth> chrishtr: the reason I prefer it to the isolated group is because it's easier to implement and more performant<br>
&lt;gregwhitworth> chrishtr: whereas if you draw all the way up to the root we'll need to implement a new algo<br>
&lt;gregwhitworth> chrishtr: if you go to an isolated group that is above the containing isolated group you may have to take into account other graphical effects into account with filters that move pixels, etc<br>
&lt;gregwhitworth> chrishtr: this inreases complexity a lot<br>
&lt;gregwhitworth> chrishtr: this makes it complicated for developers - there are a few scenarios in the issue<br>
&lt;gregwhitworth> chrishtr: there's an element with backdrop-filter, somewhere in the ancestor an alement has opacity but it isn't in the isolated group but that opacity must be included  - so you're getting doulbe opacity<br>
&lt;gregwhitworth> krit: I have to agree that opacity is indeed strange, did you do testing on Edge/Safari<br>
&lt;gregwhitworth> chrishtr: yes, there are screenshots in the issue and they do double opacity<br>
&lt;gregwhitworth> krit: I think there is developer desire to do it on the entire section, not just the isolated group<br>
&lt;gregwhitworth> mstange: can you mention a case that would be impossible?<br>
&lt;gregwhitworth> krit: when you do an animation that has a filter on it<br>
&lt;gregwhitworth> krit: there wouldn't be any backdrop filter on it since it's animating<br>
&lt;gregwhitworth> mstange: that sounds like an animation issue<br>
&lt;gregwhitworth> mstange: that sounds like an ordering issue<br>
&lt;gregwhitworth> mstange: I agree with chrishtr that it would be easier to implement and be more predictable for authors<br>
&lt;gregwhitworth> krit: how does it work more consisted with mix-blend-modes?<br>
&lt;gregwhitworth> krit: you have two divs on top of each other, the second would be an isolation group - you would blend them together<br>
&lt;gregwhitworth> chrishtr: mix blend mode and isolation groups are not always the same<br>
&lt;gregwhitworth> s/chrishtr/mstange<br>
&lt;gregwhitworth> mstange: I'm interested in seeing scenarios in which I'm wrong<br>
&lt;gregwhitworth> krit: or maybe I'm missing some<br>
&lt;gregwhitworth> ... looking at codepen<br>
&lt;gregwhitworth> Simon: as I understand anything that creates a stacking context creates an isolation group<br>
&lt;gregwhitworth> Simon that is contrary to the point of backdrop-filter which should apply to everything behind you<br>
&lt;gregwhitworth> chrishtr: yeah<br>
&lt;gregwhitworth> chrishtr: I think this needs more discussion offline<br>
&lt;gregwhitworth> Rossen: ok, thank you chrishtr<br>
&lt;krit> mstange:<br>

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Received on Tuesday, 23 October 2018 14:24:33 UTC