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

From: Jon Ronnenberg <jon.ronnenberg@gmail.com>
Date: Tue, 10 Sep 2019 11:43:07 +0200
Message-ID: <CAPEZGVt70HK3XCVrw4JvT9=eNb+k8m87=c=-38fRGPwnvA=1fQ@mail.gmail.com>
To: Philip Jägenstedt <foolip@google.com>
Cc: public-test-infra <public-test-infra@w3.org>
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?
>>>>
>>>
Received on Tuesday, 10 September 2019 09:43:44 UTC

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