1849323 - [HiDPI] box-shadow rendered unevenly at uneven scaling factors, e.g. 150%, 250%

Status: NEW

(Core :: Graphics: WebRender, defect)

Description

[David Warner]

+++ This bug was initially created as a clone of Bug #1181554 +++

This is happening for me at 150% zoom in Windows 11 and Linux (X.Org). The original test case illustrates the problem: https://bugzilla.mozilla.org/attachment.cgi?id=8630995

STR:

• change your OS scaling factor to 150%
• log out or restart if your OS suggests doing so (logging out should be sufficient on Windows)
• log in again, start Firefox, load the reduced testcase that phlsa is going to attach

Actual result: the box-shadow is one device pixel thick on some sides, two devices pixels on others

Expected result: As with e.g. CSS borders, the box-shadow should have the same thickness on all four sides

Comment 1

[David Warner]

Attachment: Uneven border example

Strangely enough, if I use Firefox's built-in 'Take Screenshot' feature, the border is rendered correctly in the result (1px on all edges).

Comment 2

[Mayank Bansal]

can repro on a Win11x64 machine.

Comment 3

[David Warner]

Tailwind UI uses box-shadow extensively for input field borders - this page has some good examples of uneven borders at 150%: https://tailwindui.com/components/application-ui/forms/form-layouts

Comment 4

[David Warner]

Attachment: Screenshot_20230823_204515.png

Comment 5

[David Warner]

The Cloudflare login page has another nice example: https://dash.cloudflare.com/login

Comment 6

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

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

For more information, please visit BugBot documentation.

Comment 7

[Jim Mathies [:jimm]]

Can reproduce, windows 11, 150%. One extra pixel on the left and top of the square.

Comment 8

[Jim Mathies [:jimm]]

Dropping into gfx triage so the team knows about it. Also an ni for Markus since he did the parent work.

Comment 9

[Markus Stange [:mstange]]

Glenn may have a better idea where the right place to snap the box shadow spread radius in WebRender is.

Comment 10

[Kelsey Gilbert [:jgilbert]]

Windows at 150% is "pretty much a default configuration" in ahale's words, so this should probably be S2 as a rendering defect in common CSS at for those users.

Comment 12

[Jim Mathies [:jimm]]

This doesn't qualify as S2.