Re: [css-fonts] Test for rem/em dimensions based on :root font-size

We actually know why Chromium is behaving how it is.
https://bugs.chromium.org/p/chromium/issues/detail?id=308862#c25 and the
fix is https://bugs.chromium.org/p/chromium/issues/detail?id=308862#c32 (
https://chromium-review.googlesource.com/c/chromium/src/+/1584288).

On Tue, Sep 10, 2019 at 11:43 AM Jon Ronnenberg <jon.ronnenberg@gmail.com>
wrote:

> Thank you for you nice welcome.
>
> It is really daunting to create the first PR, since the project is huge in
> scope, has a lot bots from various issue trackers. I was afraid do ruin
> someones build system or something dramatic. But it turns out that, even
> though https://web-platform-tests.org/ is also huge in scope, the parts I
> needed was actually written very concise. And  I created
> https://github.com/web-platform-tests/wpt/pull/18941 which I eager to get
> feedback on.
>
> > I tried rem-height.html from the bug, but it actually seems to give the
> same result in Chrome and Firefox on Linux.
> > I've also tested percentage.html and still get the same behavior in
> Chrome and Firefox.
>
> Odd. rem-height.html only show difference in rem unit length when the
> viewport is small enough - below 600px width. But percentage.html should
> always show a larger square in Chrome than in Firefox, when click the
> second button (30% root font-size). I just tested in Chrome Canary on
> Windows.
>
> https://github.com/web-platform-tests/wpt/pull/18941 has the test in
> percentage-rem-low.html and a mismatch in percentage-rem-low-ref.html -
> this is as good as a screen shot.
> Is it possible that you can trigger CI screenshot of PR 1894?
>
> Thank you for taking your time
>
> On Tue, Sep 10, 2019 at 11:27 AM Philip Jägenstedt <foolip@google.com>
> wrote:
>
>> I added your test to https://github.com/web-platform-tests/wpt/pull/18957
>> just to see what the screenshots would be, and I've linked them there.
>> Looks like the test would have to be made smaller to fit into 800x600. Not
>> sure what the key difference you'd like to isolate is, but iterating on a
>> PR like this in web-platform-tests should allow you to arrive at a useful
>> test.
>>
>> On Tue, Sep 10, 2019 at 11:08 AM Philip Jägenstedt <foolip@google.com>
>> wrote:
>>
>>> I've also tested percentage.html and still get the same behavior in
>>> Chrome and Firefox.
>>>
>>> On Tue, Sep 10, 2019 at 11:05 AM Philip Jägenstedt <foolip@google.com>
>>> wrote:
>>>
>>>> Hi Jon,
>>>>
>>>> I see that https://crbug.com/308862 has a lot of stars, so this is
>>>> probably an important issue to resolve. Thanks for pushing it!
>>>>
>>>> Tests for parts of the web platform not yet tested are always
>>>> appreciated! You've already found our main documentation site
>>>> https://web-platform-tests.org/ and the ambition is that this should
>>>> be enough to get you through the process. However, the repo is a little
>>>> daunting with a lot of open issues and PRs, so having someone who you can
>>>> poke for reviews and help, well, helps.
>>>>
>>>> A reftest is probably the right tool for this if it depends on a fixed
>>>> viewport width, as reftests are always run at 800x600. Given a page that
>>>> results in different rendering in different browsers it should be fairly
>>>> straightforward to turn it into a reftest.
>>>>
>>>> I tried rem-height.html from the bug, but it actually seems to give the
>>>> same result in Chrome and Firefox on Linux. Can you provide screenshots of
>>>> that or another test case showing the differences between browsers?
>>>>
>>>> On Sun, Sep 8, 2019 at 11:17 PM Jon Ronnenberg <
>>>> jon.ronnenberg@gmail.com> wrote:
>>>>
>>>>> 6 years ago I filed a bug in
>>>>> https://bugs.chromium.org/p/chromium/issues/detail?id=308862 and
>>>>> lately it has been picked up by both Chromium developers and web developers.
>>>>>
>>>>> The short description is that, using percentage value in :root{
>>>>> font-size }  below a certain threshold does not translate to correct rem/em
>>>>> values in blink and webkit. It does work as advertised on w3, in Edge and
>>>>> Firefox. <https://www.w3.org/TR/css-values-3/#rem
>>>>> <https://www.w3..org/TR/css-values-3/#rem>>
>>>>>
>>>>> I have look at the test cases in <
>>>>> https://github.com/web-platform-tests/wpt/tree/master/css/css-values>
>>>>> and searched in issues <
>>>>> https://github.com/web-platform-tests/wpt/issues?utf8=%E2%9C%93&q=is%3Aissue+REM+font-size>
>>>>> but have not found anything that suggest that there exist a test for this
>>>>> issue.
>>>>>
>>>>> Myself and others have provided several test cases in the chromium
>>>>> issue < https://bugs.chromium.org/p/chromium/issues/detail?id=308862>
>>>>> and I am wondering if it is feasible to translate a simple one of them into
>>>>> a test in the web-platform-tests Project.
>>>>>
>>>>> I don't have any experience writing these kind of tests and would need
>>>>> help to get started. I imagine that it could be a reftest <
>>>>> https://web-platform-tests.org/writing-tests/reftests.html> which
>>>>> could be run automatically.
>>>>>
>>>>> Is there interest in this kind of test, is it the right place for such
>>>>> a test and how do I get started?
>>>>>
>>>>