1520344 - Store last scroll anchor position in writing-mode relative coordinates

Status: RESOLVED FIXED

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

Description

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

We currently store the last anchor position in absolute (top-left corner) coordinates. This isn't correct based on the spec.

Comment 1

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

Attachment: Bug 1520344 - Store last scroll anchor position in writing-mode relative coordinates. r?dholbert

This commits changes ScrollAnchorContainer to store the offset of the block-start-edge
of the anchor node to the block-start-edge of the scroll frame, instead of the offsets
of physical top-left corners.

The logic to clamp the negative portions of scroll anchor bounding rects is also amended
to only clamp the portion that is beyond the border-start-edge in the block axis.

The 'start-edge-in-block-layout-direction.html' test now passes with these changes. It
was thought that this change was failing due to differences in 'scrollLeft/scrollTop'
but it seems that was a misdiagnosis.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/57aacc322be1
Store last scroll anchor position in writing-mode relative coordinates. r=dholbert

Comment 3

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/57aacc322be1