1786632 - AboutWelcome progress bar test fails for noninteger display scaling factors

Status: RESOLVED FIXED

(Firefox :: Messaging System, defect, P2)

Description

[Shane Hughes [:aminomancer]]

It's possible for the test test_aboutwelcome_with_progress_bar to fail if display scaling factor is not an integer. I assume there aren't already any try configurations to test for different scaling factors, or else there would be intermittent failure reports.

Basically it's testing the computed style for height: 6px, but it's possible that the computed style is actually height: 5.33px or something like that. The progress indicator has no inner height, but rather a 3px border. So, its height varies because the computed border width varies depending on the device pixels to CSS pixels ratio. (border is the only property with subpixel scaling)

That is Firefox's border subpixel rounding working as intended for 150% display scaling, but the tests don't account for it, so I had to delete them while I was debugging with that test file.

The trouble is it's impossible to know exactly how it's going to round, because it depends on the layout. You could check that it's within a range — for border-width: 3px on 2 sides, we should always get 7 > n > 5. But test_element_styles doesn't have a comparison option and that would be a bit complicated.

This isn't super important, but the only workarounds I know of are changing scaling factor or temporarily modifying/deleting the test. Changing the scaling factor on Windows 8 and 10 has some discouraging side effects that stick around until reboot (at least for me), so I tend to assiduously avoid it.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The severity field is not set for this bug.
:tspurway, could you have a look please?

For more information, please visit auto_nag documentation.

Comment 2

[hanna A]

Attachment: Bug 1786632 - AboutWelcome progress bar test fails for noninteger display scaling factors r=mviar

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5d545a5e72d6
AboutWelcome progress bar test fails for noninteger display scaling factors r=mviar

Comment 4

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/5d545a5e72d6

Comment 5

[BugBot [:suhaib / :marco/ :calixte]]

The patch landed in nightly and beta is affected.
:halemu, is this bug important enough to require an uplift?

• If yes, please nominate the patch for beta approval.
• If no, please set status-firefox106 to wontfix.

For more information, please visit auto_nag documentation.

Comment 6

[hanna A]

No, an uplift is not needed for this. I've updated the flag. Thanks!