1980357 - drop-shadow() with 0 offset + spread + radius don't render correctly

Status: NEW

(Core :: Graphics: WebRender, defect)

Description

[psychpsyo]

Attachment: filterTransition.html

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:141.0) Gecko/20100101 Firefox/141.0

Steps to reproduce:

I put a filter with multiple drop-shadows on an element and tried to transition them.
See attached example file for specifics. The bug happens after un-hovering the element. The transition to the hovered state is fine.

Actual results:

The transition is smooth in one direction, but not in the other. At the very end, it snaps to the final position.
Note that Chrome has the same problem, except that it does not jump to the correct final position, but lingers on the incorrect last frame of the transition. So this might be something with the spec.

Expected results:

The transition should have smoothly arrived at the final position.

Comment 1

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

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

Comment 2

[psychpsyo]

Update:
I messed something up when testing Chromium yesterday, it does not have the bug. Firefox just doesn't show stacked drop-shadow()s like these right. That jump at the end of the animation is from the correct position to the incorrect rendering.

Comment 3

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

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

For more information, please visit BugBot documentation.

Comment 4

[Emilio Cobos Álvarez [:emilio]]

Yeah I agree the issue is with the initial rendering. Even changing it to drop-shadow(0 0 .25em black) drop-shadow(0.01px 0 0 red) "fixes" this.

So this is not about the CSS transitions or the interpolation, but about the graphics rendering...

Comment 5

[Emilio Cobos Álvarez [:emilio]]

Attachment: Test-case, both squares should render ~identically.

Comment 6

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

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

For more information, please visit BugBot documentation.