On Thursday, September 29, 2022 at 12:17:10 PM UTC-7 Chris Harrelson wrote:
> On Thu, Sep 29, 2022 at 12:15 PM Mike Taylor <mike...@chromium.org> wrote: > >> On 9/28/22 3:01 PM, Traian Captan wrote: >> >> Contact emails >> >> tca...@chromium.org >> >> 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). >> >> Is there any current blocker to specifying this (besides someone doing >> the work)? >> > > Currently, the specs intentionally avoid specifying pixel-snapping > behavior, and instead leave it up to engines to decide how they want to do > it. Changing that would be a significant effort. > Once this change lands, won't it be straightforward to specify this specific aspect of snapping? This change is visible in the computed style. > >> 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 >> >> Risks Interoperability 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 name Requires 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+...@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 >> >> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAFxahvsyqk3h2TZwDVJzb1KVgLjqmWDWMs3V9-1sZRA7pXkyOQ%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> >> >> -- >> 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+...@chromium.org. >> > To view this discussion on the web visit >> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/addc5bee-3957-b9f7-9f41-a0a2a7802618%40chromium.org >> >> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/addc5bee-3957-b9f7-9f41-a0a2a7802618%40chromium.org?utm_medium=email&utm_source=footer> >> . >> > -- 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/40644a65-1656-497d-a19d-caad46855c64n%40chromium.org.
