[css-color] Is relative color syntax ready to ship?

[nt1m]

https://www.w3.org/TR/css-color-5/#relative-colors

https://www.w3.org/TR/css-color-5/#serial-relative-color

This came up as an Interop 2023 proposal, and there is an implementation in WebKit, and we were wondering if this is ready to ship?

cc @svgeesus @emilio @lilles

[emilio]

@nt1m how does the WebKit implementation (and what does the spec say) about currentColor and similar usual-suspects?

[gsnedders]

See also #7310 (comment)

Re-opening since we dropped the ball on Relative Color Syntax. Jen asked about RCS in the initial post in this issue; there was a brief discussion on May 25 but nothing was decided as none of the editors were on the call.

Interop2022 is considering dropping it because of lack of signals from CSSWG.

And the following comment:

There wasn't a resolution that it was not ready. Nor was there a resolution that it was ready. I re-opened the issue because the question you asked didn't really get much discussion nor a clear resolution. There was a passing mention by @emilio that there was only one implementation (in WebKit) and they "would like more feedback on relative color syntax".

(Both @svgeesus)

[nt1m]

@nt1m how does the WebKit implementation (and what does the spec say) about currentColor and similar usual-suspects?

I think we'll end up matching what color-mix() will be doing (cc @mdubet who will be working on fixing that)

[svgeesus]

Yes, matching color-mix() seems the way forward.

[yairEO]

And for the sake of the record, for me who has no idea what color-mix() has implemented, what exactly should happen with currentColor & relative-color?

(I came here investigating especially this use-case)

[svgeesus]

@yairEO from Serializing Relative Color Functions :

The serialization of the result of a relative color function is a , as defined in CSS Color 4 § 15 Serializing Values. The form used is the same as that used to specify the relative color, but using the absolute form.

So the result of a color-mix() between currentColor and RCS is the same exactly as a mix between currentColor and any other absolute color.

Or did you mean an RCS where the origin color is currentColor?

[yairEO]

My question is this use-case:

div{ color:red; background:rgb(from currentColor r g b / 50%); }

[svgeesus]

Yeah that would serialize as specified; it can't fully resolve because the value of the color property could be different on child elements or child pseudo-elements.

[svgeesus]

This needs explicit spec text for resolving the RCS value when currentColor is the origin , saying that the RCS serializes as specified so that child elements are handled correctly. There is already similar text in Resolving color-mix() Valuesfor resolving color-mix() so as noted by @nt1m we should re-use that:

If all parameters resolve to the corresponding colors in their respective color spaces, the computed value is the mixed color, in the specified mixing color space, resolved according to CSS Color 4 § 14 Resolving Values. Otherwise (if currentColor was used in the function), the computed value is the color-mix() function with each parameter resolved according to CSS Color 4 § 14 Resolving Values, thus preserving inheritance into child elements.