Re: [csswg-drafts] [css-transforms] Zero value in perspective() function (#413)

The CSS Working Group just discussed `Zero value in perspective() function`, and agreed to the following:

* `RESOLVED: 0 is allowed with 1px being the render time clamp`

<details><summary>The full IRC log of that discussion</summary>
&lt;dael> Topic: Zero value in perspective() function<br>
&lt;dael> github:<br>
&lt;dael> AmeliaBR: The issue is that now spec says perspective param needs to be a positive non-0 which goes against general rule that we don't have indeterminate ranges that include everything except exact value. need firm closed range<br>
&lt;dael> AmeliaBR: Eric put together a PR for exact wording. Prop: it's a closed range that's UA determined for the end of the range<br>
&lt;dael> AmeliaBR: No, his is specifically 0 is valid but when you give 0 then your matrix eq is the identity matrix. 0 is valid parsing value with clearly defined behavior<br>
&lt;AmeliaBR> Eric's PR text:<br>
&lt;dael> smfr: Problem with 0 as identity you get discontinuity of animating from 0. 0 is no perspective and then you animate to non-0 and it's super close. It's like scale 0 which is non-invertable. perspective(0) should be like perspective(infinity)<br>
&lt;dael> AmeliaBR: Expecting perspective(0) to be same as infinitly large which is no transformation. Does cause discontinuity when moving from that to a very small value<br>
&lt;dael> dino: I don't htink matters what we do. If you animate to 0 it's a horrible result. Rather it disappears or infinity it looks bad<br>
&lt;dael> AmeliaBR: Just important to have a clear rule<br>
&lt;dael> dino: 0 = infinity is best user result even though it doesn't quite make sense<br>
&lt;dael> Rossen_: Where do we take this?<br>
&lt;dael> AmeliaBR: Do we accept Eric W. proposed edits?<br>
&lt;dael> dbaron: The discussion you were having made me feel like we'd be better saying it's UA defined close range at some amount slightly above 0 rather than say 0 is valid<br>
&lt;dael> dino: Should be clampped a fair way above 0. I fyou want to do something good for user don't let them get close<br>
&lt;dael> TabAtkins: 0 not valid or valid and clampped upward<br>
&lt;dael> dbaron: I was saying not valid, but okay with clamp upward<br>
&lt;dael> TabAtkins: IN general that's an open range and I don't like that. Much prefer 0 is valid with a UA clamp to reasonable minimum.<br>
&lt;dael> AmeliaBR: Agree we don't want UA dependent limits for parsing validity. Actual rendering clampping upwards seems reasonable<br>
&lt;dael> TabAtkins: Letting 0 be eq to a minimum value UA clamps to, that's the best situation. That's our normal principle for these ranges<br>
&lt;dael> AmeliaBR: TabAtkins will you make edits for this interpretation?<br>
&lt;dael> TabAtkins: Yeah<br>
&lt;dael> AmeliaBR: Other question is on impl and what do they do and who will change<br>
&lt;dael> dino: webkit is willing to change. It's rendering time. CSS goes to 0, but won't paint as 0<br>
&lt;dael> TabAtkins: Agreed<br>
&lt;dael> mwoodrow: I think gecko would be willing to change but I'd like to define it in the spec<br>
&lt;dael> TabAtkins: 1px?<br>
&lt;dael> mwoodrow: Fine<br>
&lt;dael> myles: Need to say if 0 returned by gCS?<br>
&lt;dael> TabAtkins: If it's a render time clamp gCS will be 0<br>
&lt;dael> AmeliaBR: As far as limit 1px should be valid and used on exact math. 0px not exact math and somewhere in there browsers are allowed to clamp rendering code<br>
&lt;dael> TabAtkins: Right now I don't think...I think every browser does 1px and down below. Render depends on precision or when the rendering library barfs. I'm fine with UA defined limit with a suggest of 1px. I fwe want defined 1px is a nice thing to hit<br>
&lt;dael> florian: If we have a specific value it's not an open range anymore<br>
&lt;dael> Rossen_: Proposal is<br>
&lt;dael> TabAtkins: 0 is allowed with 1px being the render time clamp<br>
&lt;dael> Rossen_: Objections?<br>
&lt;dael> RESOLVED: 0 is allowed with 1px being the render time clamp<br>

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Received on Wednesday, 2 October 2019 23:59:32 UTC