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Explainer Though not a formal explainer, Emilio has an excellent writeup of this issue at https://crisal.io/words/2020/06/13/rounding-borders.html. Spec With this change to blink, all implementations will agree, and this can be specified (see: https://github.com/w3c/csswg-drafts/issues/5210). Summary Snap border, outline and column-rule widths before layout to avoid gaps between backgrounds and borders caused by paint-time snapping. With this change, Blink will match Gecko and WebKit. Blink component Blink <https://bugs.chromium.org/p/chromium/issues/list?q=component:Blink> Motivation Currently Blink snaps the border widths at paint time. This can cause a visible 1px gap between a parent element's border and a child's background when the border is rounded down during paint since the snapping floors the value but the layout rounded it up to calculate the child’s s position (eg border-width is set to 10.75 pixels, rounded to 10px at paint time, but 11 at layout time). By making this change Blink will also behave like Gecko and WebKit and increase interoperability. Search tags border-width <https://chromestatus.com/features#tags:border-width>, outline-width <https://chromestatus.com/features#tags:outline-width>, column-rule-width <https://chromestatus.com/features#tags:column-rule-width> TAG review Skipping because this is a straightforward interop fix. TAG review status N/A RisksInteroperability and Compatibility Gecko and WebKit already snap borders before layout. This change would make Blink behave the same and increase interoperability and compatibility. The explainer section has a link to a blog post describing the differences in more detail. This issue and the proposed fix have been discussed in: Issue 1201762: [Task] Investigate border snapping before layout <https://crbug.com/1201762>, which is currently blocking 10 issues. This issue was also discussed on: https://github.com/w3c/csswg-drafts/issues/2114 https://github.com/w3c/csswg-drafts/issues/5210 Gecko: Shipped/Shipping WebKit: Shipped/Shipping Web developers: Strongly positive - This has been reported in at least 10 separate bugs with a cumulative star count of 75. 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? No Debuggability N/A Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)? Yes Is this feature fully tested by web-platform-tests <https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md> ? New test will be added with the patch. Flag nameRequires code in //chrome? False Tracking bug https://crbug.com/1201762 Launch bug https://crbug.com/1120347 Estimated milestones M108 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). https://github.com/w3c/csswg-drafts/issues/5210 Link to entry on the Chrome Platform Status https://chromestatus.com/feature/4651561863610368 This intent message was generated by Chrome Platform Status <https://chromestatus.com/>. -- You received this message because you are subscribed to the Google Groups "blink-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+unsubscr...@chromium.org. To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAFxahvsyqk3h2TZwDVJzb1KVgLjqmWDWMs3V9-1sZRA7pXkyOQ%40mail.gmail.com.
