1624998 - Backplate background color does not transition properly

Status: NEW

(Core :: Layout, defect, P3)

Description

[Tim Nguyen :ntim]

Attachment: backplate-transition-testcase.html

STR:

1. Enable High contrast mode (the testcase does nothing without it, since initial = transparent, as opposed to ButtonFace on HCM)
2. Open testcase (you'll need to make sure the ButtonFace color differs from your chosen background-color, though this should be default on macOS)
3. Hover over the button

AR:
the backplate background transitions abruptly at the end, while the button background transitions properly according to the easing function

ER:
Both should transition the same way

morgan pointed out this bit of code probably needs changing:
https://searchfox.org/mozilla-central/source/layout/generic/nsBlockFrame.cpp#223

Comment 1

[Tim Nguyen :ntim]

Hmm, bug 1624655 will probably break the current testcase...
EDIT: or maybe not, since the widget doesn't use native theming.

Comment 2

[Emilio Cobos Álvarez (:emilio)]

Posted this on Matrix, but just for reference: I think the issue is that the background-color animation runs on the compositor these days, so we don't even hit that code easiest fix would be to block background-color animations to run on the compositor if in hcm or something, I suspect.

Comment 3

[Firefox Bug Husbandry Bot]

Because this bug's Severity has not been changed from the default since it was filed, and it's Priority is P3 (Backlog,) indicating it has been triaged, the bug's Severity is being updated to S3 (normal.)