Intent to Ship: Support currentcolor in Relative Color Syntax
Kevin Babbitt
Contact emails
Explainer
None
Specification
https://www.w3.org/TR/css-color-5/#resolving-rcs
Design docs
https://docs.google.com/document/d/1568wVjrIRbrU9_O37gPu10cj0CDWRiAc6ZMk9t0JpXs/edit
Summary
Allow relative colors in CSS (using the 'from' keyword) to use 'currentcolor' as a base. This will make it easy for web developers to set complementary colors, based on an element's text color, for that element's borders, shadows, backgrounds, etc.
This feature also includes use cases where color functions are nested with a dependency on 'currentcolor', for example `color-mix(in srgb, rgb(from currentcolor r g b), white))` or `rgb(from rgb(from currentcolor
1 g b) b g r)`.
Blink component
TAG review
https://github.com/w3ctag/design-reviews/issues/894
TAG review status
Issues addressed
The link above is for Relative Color Syntax in general. Tests for 'currentcolor' cases were added as part of the discussion before the TAG signed off on the review. I discussed with Alex Russell, and he supports my interpretation that the TAG is satisfied with
this use case.
Risks
Interoperability and Compatibility
Interoperability: Relative Color Syntax is a focus area for Interop 2024, and inclusion of 'currentcolor' is well covered by existing WPTs, so the risk of other engines not converging on an interoperable implementation is low.
Compatibility: The only risk here is that enabling 'currentcolor' support will "light up" color declarations that are being rejected at present. Total usage of Relative Color Syntax on the Web (including 'currentcolor' or otherwise) is ~0.15% of page loads as of September 1, 2024[1]. I haven't done an analysis of 'currentcolor' in RCS, but given that no major engine supported it until May of this year, I would expect it to be a tiny fraction of those.
[1] https://chromestatus.com/metrics/feature/timeline/popularity/4632
Gecko: Positive (https://github.com/mozilla/standards-positions/issues/841) Implementation bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1893966
WebKit: Shipped/Shipping (https://bugs.webkit.org/show_bug.cgi?id=245970) Changes landed May 13.
Web developers: Positive (https://github.com/web-platform-tests/interop/issues/426) This feature is part of Interop 2024.
Other signals:
WebView application risks
Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?
Low risk. This feature is additive in nature and potential for app impact is cosmetic only.
Debuggability
Covered by existing DevTools support for debugging CSS properties. Property text displays correctly in the Styles and Computed panes. I did identify one minor issue with color swatches in the Styles pane, but that's now fixed:
https://issues.chromium.org/issues/367154236
Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?
Yes
Is this feature fully tested by web-platform-tests?
Yes
There are a few subtest failures that remain with this feature in status=experimental, but those are cases for relative colors *not* based on 'currentcolor' and are being tracked separately.
Flag name on chrome://flags
None
Finch feature name
CSSRelativeColorSupportsCurrentcolor
Requires code in //chrome?
False
Tracking bug
https://issues.chromium.org/issues/325309578
Estimated milestones
|
Shipping on desktop |
131 |
|
Shipping on Android |
131 |
|
Shipping on WebView |
131 |
Anticipated spec changes
Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way).
There are several ongoing discussions in the CSSWG related to colors, mostly around serialization of values. However, I did not find any open issues that were specific to 'currentcolor' support in relative
colors - what I found were instead questions that apply more broadly and thus would need to be considered independently from this feature.
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/4755025804132352?gate=6199731202818048
Links to previous Intent discussions
Intent to Prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/PH0PR00MB11527917FE827C65D0277F0EC0A52%40PH0PR00MB1152.namprd00.prod.outlook.com
This intent message was generated by Chrome Platform Status.
Alex Russell
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Mike Taylor
LGTM2 - thanks for working on this!
To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAA44PQh7cUKOk2x-u6i9Z2AorwOHpzWEBDOGh4agWdKAEGN6LA%40mail.gmail.com.
Chris Harrelson
To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/31887b55-bae4-4d2b-8484-d237ceb09b24%40chromium.org.