2035734 - Box shadow renders incorrectly

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect)

Description

[HaitraMysh]

Attachment: Correct and incorrect box shadow

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:151.0) Gecko/20100101 Firefox/151.0

Steps to reproduce:

When using a display scaling of 125%, the box shadow may render incorrectly. A thin border appears on the right and bottom edges of the box, as shown in the attached image. The issue disappears at some zoom levels when zooming a page in or out.

A reproduction can be seen here: https://jsfiddle.net/HaitraMysh/any0hpf5/

This behavior started occurring in Firefox 151 beta. Using the mozregression tool, I traced the issue to this changeset: https://phabricator.services.mozilla.com/D289944

The problem does not occur in other browsers.

Actual results:

Box shadow rendered incorrectly.

Expected results:

Box shadow should render correctly.

Comment 1

[BugBot [:suhaib / :marco]]

The Bugbug bot thinks this bug should belong to the 'Core::Graphics: WebRender' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[BugBot [:suhaib / :marco]]

:gw, since you are the author of the regressor, bug 2026399, could you take a look? Also, could you set the severity field?

For more information, please visit BugBot documentation.

Comment 3

[Glenn Watson [:gw]]

Attachment: Bug 2035734 - Align box-shadow analytical clip with rounded prim_rect

create_quad_primitive rounds prim_rect in device space, but
element_offset_rel_prim and dest_rect_offset were computed against the
un-rounded prim_rect.min. The shader reconstructs absolute positions
from the rounded local_prim_rect.p0, shifting the analytical element
clip by up to half a device pixel and producing a one-pixel seam on
trailing edges at fractional device coordinates.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/d3e663928dc9
https://hg.mozilla.org/mozilla-central/rev/e2122ca36f94
Align box-shadow analytical clip with rounded prim_rect r=gfx-reviewers,nical

Comment 5

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/e2122ca36f94

Comment 6

[BugBot [:suhaib / :marco]]

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

• If yes, please nominate the patch for beta approval.
  • See https://wiki.mozilla.org/Release_Management/Requesting_an_Uplift for documentation on how to request an uplift.
• If no, please set status-firefox151 to wontfix.

For more information, please visit BugBot documentation.

Comment 7

[Phabricator Automation]

firefox-beta Uplift Approval Request

• User impact if declined/Reason for urgency: Visual artifacts on box-shadows at some zoom levels
• Code covered by automated testing?: yes
• Fix verified in Nightly?: yes
• Needs manual QE testing?: no
• Steps to reproduce for manual QE testing:
• Risk associated with taking this patch: low
• Explanation of risk level: Small patch
• String changes made/needed?: No
• Is Android affected?: yes

Comment 8

[Glenn Watson [:gw]]

Attachment: Bug 2035734 - Align box-shadow analytical clip with rounded prim_rect

create_quad_primitive rounds prim_rect in device space, but
element_offset_rel_prim and dest_rect_offset were computed against the
un-rounded prim_rect.min. The shader reconstructs absolute positions
from the rounded local_prim_rect.p0, shifting the analytical element
clip by up to half a device pixel and producing a one-pixel seam on
trailing edges at fractional device coordinates.

Original Revision: https://phabricator.services.mozilla.com/D297513

Comment 9

[Pulsebot]

https://github.com/mozilla-firefox/firefox/commit/9b6d61a89ef6
https://hg.mozilla.org/releases/mozilla-beta/rev/5ca58f1d17fb