961171 - APZ should pick up dynamic changes made to 'scrollgrab' property

Status: RESOLVED FIXED

(Core :: Panning and Zooming, defect)

Description

[Botond Ballo [:botond]]

Bug 912666 introduced the 'scrollgrab' property. This property is set on a layer's FrameMetrics by RecordFrameMetrics, and APZ gives special scrolling behaviour to layers with this property.

FrameMetrics are transferred from a layer to an APZC in AsyncPanZoomController::NotifyLayersUpdated(). There are two code paths there: on the first paint of a given layer, we copy all FrameMetrics fields, while on subsequent paints we only copy select fields.

The mScrollGrab field is currently not included in the fields copied over on subsequent paints. This means that if JS code dynamically adds or removes the 'scrollgrab' property from an element, APZ may not become aware of this change.

To avoid this, we should copy over the mScrollGrab field on the subsequent-paint code path as well.

Comment 1

[Botond Ballo [:botond]]

Attachment: bug961171.patch

Comment 2

[Botond Ballo [:botond]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/d70ddcedc57d

Comment 3

[Phil Ringnalda (:philor)]

https://hg.mozilla.org/mozilla-central/rev/d70ddcedc57d