1212020 - [e10s] window.scrollX / scrollY values are "lagging" with APZ enabled

Status: RESOLVED DUPLICATE of bug 1209970

(Core :: Panning and Zooming, defect)

Description

[Matteo Ferretti [:zer0] [:matteo]]

Not sure a better way to formulate that; you can try this test page I made:

https://dl.dropboxusercontent.com/u/5374957/highlighters/apz-test.html

Basically, scripts that rely on `scrollX` / `pageXOffset` and/or `scrollY` / `pageYOffset` to move / draw stuff, are terrible lagging behind the actual scroll. You can see the difference with APZ disabled.

This also affect our devtools – you can try to inspect an element and then scroll, you'll see the inspector's box lag behind with APZ enabled; or you can enable the rulers and scroll the page.

Comment 1

[Markus Stange [:mstange]]

Eliminating the lag completely is a non-goal. We want the compositor to be able to respond to scrolls immediately, and content will always be one frame behind, or more if it blows its budget.

I agree that the current lag is terrible. I filed bug 1209970 about reducing it and making it uniform.

I don't have a good solution for the inspector highlighter. I hope getting the lag down to one frame will make it bearable.

Comment 2

[Kartikaya Gupta (email:[e-mail])]

I'm going to dupe this to bug 1209970 since we don't have any plans on doing anything else with this.