LGTM2
On Wed, Oct 5, 2022 at 5:48 PM Philip Jägenstedt <foo...@chromium.org>
wrote:
LGTM1 with some strings attached.
We discussed this in the API owners meeting (present: Chris, Yoav,
Mike, Daniel, me)
Since this matches other implementations and is somewhat
deliberate unspec'd, shipping this sounds good. Very nice to see
highly starred interop issues being fixed :)
Great that tests will be added, presumably those will be tentative
<https://web-platform-tests.org/writing-tests/file-names.html?highlight=tentative>
due to a lack of a spec.
Traian, Philip, since this will be interoperable, can you propose
a spec change that would define it? Or if that runs into some
roadblock, can you loop back to this thread? (This does not block
shipping.)
On Thu, Sep 29, 2022 at 11:55 PM 'Philip Rogers' via blink-dev
<blink-dev@chromium.org> wrote:
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
<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
<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/2114>
https://github.com/w3c/csswg-drafts/issues/5210
<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 <https://crbug.com/1201762>
Launch bug
https://crbug.com/1120347 <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
<https://github.com/w3c/csswg-drafts/issues/5210>
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/4651561863610368
<https://chromestatus.com/feature/4651561863610368>
This intent message was generated by Chrome Platform
Status <https://chromestatus.com/>.
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