[css-masking] Add mask-position-{x,y}

[upsuper]

The spec should probably add these two properties and make mask-position a shorthand of those two.

WebKit and Blink have implemented -webkit-mask-position-{x,y}, and Gecko is going to ship the unprefixed form mask-position-{x,y} in Firefox 53.

The syntax should be similiar to background-position-{x,y}, so I suppose this isn't something very controversial.

[upsuper]

Seems to be a duplicate of #99. Not sure why I didn't see that.

[kuoe0]

@upsuper I think it is similar to #99 not duplicate. #99 is for mask-repeat-{x,y} not for mask-position-{x,y}.

[upsuper]

Oh, okay. Thanks.

[dirkschulze]

It seems like *-position-x/*position-y were added to the CSS Background spec. Needs a CSS WG resolution.

[css-meeting-bot]

The Working Group just discussed [css-masking] Add mask-position-{x,y}, and agreed to the following resolutions:

• RESOLVED: create an ED for Masking L2?
• RESOLVED: put mask-position-x/y into that draft

The full IRC log of that discussion

<dael> topic: [css-masking] Add mask-position-{x,y}
<dael> github: https://github.com//issues/103
<dael> krit: One prop atm. There was a proposal to add -x and -y. It's in webkit, I believe. Request was to spec. We agreed to algn as much as possible to background spec. If background won't do position-x and -y then mask won't. Same for mask-repeat.
<dael> fantasai: Background-position-x and -y is in L4 which isn't fpwd but it was resolved to add.
<dael> krit: and repeat?
<dael> fantasai: I don't think so.
<dael> krit: Then since this is CR it's prob. best not to add yet.
<Chris> agree, better not to add them *yet*
<dael> fantasai: I think we had a discussion about repeat and we weren't going to add unless required for compat since there wasn't a use case.
<Chris> yeah it is more alignment between masking and backgrounds
<dael> krit: My concern isn't them having it, but how we handle for masking spec. Since the spec is in CR I don't want to add features that aren't in L4.
<dael> fantasai: I would agree. Adding mask-position-x and -y to L2 might make sense. L1 should stay.
<dael> krit: We don't have a L2 yet. Should we wait or create the L2 already and put the properties in there?
<dael> astearns: I have a question about background-position-x/y. Have blink and webkit already impl it?
<dael> krit: as far as I know yes. For mask it was a webkit prefix.
<dael> astearns: Right.
<dael> astearns: For myself I would like to have a next level of masking with these features since mask-position-x/y is in a couple engines and maybe a third.
<dael> krit: THen we need to resolve to have level 2 and then move it.
<dael> astearns: I think first step is have a resolution to put it into the next level. Once an ED has these features we can have another call.
<Chris> +1 to ED
<dael> krit: I wasn't asking for fpwd, just an ED for L2.
<AmeliaBR> +1 to having a level 2 of Masking
<dael> astearns: Fair.
<dael> astearns: Any objections to creating an ED for Masking L2?
<dael> RESOLVED: create an ED for Masking L2?
<dael> astearns: Obj to putting mask-position-x/y into that draft?
<dael> RESOLVED: put mask-position-x/y into that draft

[gsnedders]

fantasai: Background-position-x and -y is in L4 which isn't fpwd but it was resolved to add.
[…]
krit: My concern isn't them having it, but how we handle for masking spec. Since the spec is in CR I don't want to add features that aren't in L4.
fantasai: I would agree. Adding mask-position-x and -y to L2 might make sense. L1 should stay.

I'm slightly confused by this. background-position-x and background-position-y are in Backgrounds & Borders L4, and we don't want to add mask-position-x and mask-position-x to Masking L1 because they aren't in Backgrounds & Borders L4? It seems silly to have something with at least two independent implementations delayed for years because of process concerns.

It looks like it might be a bit confused with #99 (about adding mask-repeat-*), which appear to only be supported in Blink nowadays?