Update 2D canvas color serialization

[annevk]

Although fillStyle, strokeStyle, and shadowColor setters accepted all kinds of CSS color values, those could not be serialized. Update that by relying on CSS Color for serialization instead, which now has a HTMLCompatible named parameter to preserve compatibility with 2D canvas and for certain colors.

While here, also link the algorithm to be used for color space conversion and correct the reference for 'relative-colorimetric'.

Fixes #8917.

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@Kaiido do you happen to know if we already have test coverage for this?

@weinig this might be of interest to you.

• At least two implementers are interested (and none opposed):
  • WebKit
  • Chromium (per August 15 WHATNOT)
  • Gecko (per August 15 WHATNOT)
• Tests are written and can be reviewed and commented upon at:
  • 2D canvas color parsing and serialization web-platform-tests/wpt#47148
• Implementation bugs are filed:
  • Chromium: N/A
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=1919710
  • WebKit: https://bugs.webkit.org/show_bug.cgi?id=278392
• MDN issue is filed: N/A, bug fix
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

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/canvas.html ( diff )
/infrastructure.html ( diff )

[annevk]

@whatwg/canvas @whatwg/css please review.

[Kaiido]

@Kaiido do you happen to know if we already have test coverage for this?

I think @mysteryDate did add tests for the serialization of color-mix() recently, but other serialization tests all seem to be about "HTMLCompatible" cases, so I guess new tests are needed, but Aaron will know better than me.

[domenic]

Let's get w3c/csswg-drafts#10550 (comment) resolved.

[domenic]

Preexisting issue, not necessary to fix: it'd be nice if "CSS color" linked to some definition, in all its usage sites.

[svgeesus]

it'd be nice if "CSS color" linked to some definition, in all its usage sites.

Agreed, I suggest https://drafts.csswg.org/css-color-4/#typedef-color

which says

Colors in CSS are represented by the <color> type:

[svgeesus]

@annevk what do you think, does that link work for you?

[annevk]

I've decided to not address this for now. I think what we want in HTML is mostly some kind of abstract concept and not a syntax construct. We want to reference what that gets parsed into in a number of places.

[mysteryDate]

@Kaiido do you happen to know if we already have test coverage for this?

I think @mysteryDate did add tests for the serialization of color-mix() recently, but other serialization tests all seem to be about "HTMLCompatible" cases, so I guess new tests are needed, but Aaron will know better than me.

I don't believe we have any tests for this for canvas specifically, those would go in the .yaml files in /html/canvas/. Quick search turns up nothing:

https://source.chromium.org/search?q=f:wpt%20f:canvas%20oklab&sq=package:chromium

I think that I didn't add any because I was waiting for the spec to update.

[mysteryDate]

This all looks good to me! Thanks for doing this @annevk !

[svgeesus]

@annevk does my suggested link to resolve @domenic comment work here?

[annevk]

@svgeesus I was out sick, hence the delay here. I think that works, but I see that @domenic hasn't replied yet to the recent updates to CSS Color which were primarily blocking this PR. I'll see about reviewing those now and supplying you with better examples.

[annevk]

@domenic it now uses the "with HTML-compatible serialization requested" wording. Good enough? I'll file implementation bugs too.