1518636 - Precisely calculate anchor suppression triggers for absolute position changes

Status: NEW

(Core :: Layout: Scrolling and Overflow, enhancement, P3)

Description

[Ryan Hunt [:rhunt] (on leave until early May)]

The scroll anchoring specification lists changes to 'position: absolute' as triggering a scroll adjustment suppression [1].

Currently Gecko handles changes to 'position: absolute' by reframing. The current scroll anchoring implementation handles this by detecting when the topmost frame to be reframed changes being absolutely positioned.

This is not correct, as it's possible that an absolute position change could be swallowed by an ancestor frame being reframed.

It's not clear whether this will be an issue, as suppression triggers are heuristics to mitigate some potential feedback loops that could happen, and this solution might be good enough. It currently passes the WPT suite.

[1] https://drafts.csswg.org/css-scroll-anchoring-1/#suppression-triggers

Comment 1

[Ryan Hunt [:rhunt] (on leave until early May)]

This shouldn't block release of scroll anchoring.