1664906 - APZ display port expiry causes incorrect clip

Status: NEW

(Core :: Panning and Zooming, defect, P3)

Description

[Jim Blandy :jimb]

If a position:absolute element whose parent has a clip-path is scrolled off the top of an ancestor's scrollport, the element is correctly clipped to both the given clip-path region and the scrollport until the APZ display port expires, at which point it pops up outside the scrollport, with only the clip-path region applied. The whole shebang needs to be enclosed in an iframe.

edit: steps to reproduce in comment 5.

Comment 1

[Jim Blandy :jimb]

Attachment: Style sheet for example.

Comment 2

[Jim Blandy :jimb]

Attachment: HTML page for example.

Comment 3

[Jim Blandy :jimb]

Attachment: Inner HTML page for example.

Comment 4

[Jim Blandy :jimb]

Attachment: Outer HTML page for example.

Comment 5

[Jim Blandy :jimb]

To see the bug, visit the outer HTML document attachment (just follow the link from bugzilla), and scroll the inner scrollport to the point that the blue fragment is as wide as possible.

Then wait 15 seconds. A larger portion of a blue circle should appear, partially outside the scrollport. It should be clipped to within the scrollport.

I think the 15 seconds are apz.displayport_expiry_ms, which would suggest that the bug occurs when the displayport expires.

Comment 6

[Botond Ballo [:botond]]

Similar to bug 1607096 comment 2, this bug only affects non-Fission mode.

Jim, out of curiosity, do you recall how you arrived at this testcase? Was it reduced from a website using this pattern in the wild, or just sort of constructed while exploring edge cases?

Comment 7

[Jim Blandy :jimb]

The latter: constructed while exploring edge cases.