Intent to implement: support CSS paint-order for HTML text

[Jonathan Kew]

Summary: For text that is stroked as well as filled (using
-webkit-text-stroke), this allows the author to control whether the
stroke is painted before or after the fill. The current behavior is to
always paint the stroke on top, which is often visually poor, and leads
authors to use cumbersome workarounds involving multiple copies of the
text in order to render a stroke behind the fill.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1426146

Link to standard: Currently an open issue in the CSS Fill & Stroke spec:
https://www.w3.org/TR/fill-stroke-3/#issue-57580890

Platform coverage: All

Estimated or target release: Firefox 59 (behind a default-off pref,
pending CSS WG consideration)

Preference behind which this will be implemented:
layout.css.paint-order.enabled

Is this feature enabled by default in sandboxed iframes? Yes

DevTools bug: No special DevTools requirements

Do other browser engines implement this? AFAIK, this property is
currently implemented in other engines only for SVG content (like in
Firefox), not for HTML text

Tests - Is this feature fully tested by web-platform-tests? No, as it is
not yet spec'd (see above). I propose to land a basic mozilla reftest
along with the patches in bug 1426146 (behind a pref); if/when the CSS
WG agrees to accept this issue in the spec, we can migrate the reftest
to WPT

[Emilio Cobos Álvarez]

On 12/24/2017 02:01 PM, Jonathan Kew wrote:
> Tests - Is this feature fully tested by web-platform-tests? No, as it is
> not yet spec'd (see above). I propose to land a basic mozilla reftest
> along with the patches in bug 1426146 (behind a pref); if/when the CSS
> WG agrees to accept this issue in the spec, we can migrate the reftest
> to WPT

Just FYI, other people land tests into WPT with .tentative.html in the
name, like:

https://github.com/w3c/web-platform-tests/pull/8602

Not sure what's preferred, I believe that if the chances of this getting
spec'd are high it may be better, but...

James, do you know whether there's any official guideline for these kind
of situations?

-- Emilio

[James Graham]

The .tentative.html thing is an accepted convention for stuff that tests
the presumed behaviour of a future spec, although it's possible that
there aren't any CSS tests using the pattern yet.

I would certainly encourage using it here rather than having to remember
to upstream a test at some later date.

[fantasai]

As the editor of the spec in question, I can say that the only reason the
issue was open was because we were looking for some combination of implementer
interest and/or confirmation that this is a sane thing to do. jfkthame's intent
to implement is even more formal of a confirmation than we were looking for. :)

I should be able to run it officially past the CSSWG in a few hours, also, and
will prioritize the edit to remove the issue for like tomorrow or something if
that makes things easier. :)

~fantasai