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#249 Stabilize and enable intersectionObservers

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opened 2 years ago by wolfbeast · 14 comments

Painted into a corner, but this should work.

Intersections have been moved to be handled with display lists in FF 18. Mostly because a per-update check of visibility is disastrous for some corner cases (it seems to be the more logical approach to me, but hey...).

As a result off-screen animations will be updated and painted. This can take 100% CPU in some cases (e.g. Facebook loading throbber). So, the display lists need an intersection check anyway in the form of an intersectionObserver.

We have the base code for it, but it’s crashy. (damn hash tables again).
So... Fix https://bugzilla.mozilla.org/show_bug.cgi?id=1322717 and we can then likely enable this for UXP.

Looks like there’s a bit more crashiness to be solved.

This is still disabled after issues with the unstable spec and Chromium-based implementation preferences at the time with breaking changes. We should revisit this, see what the spec has settled on now, and implement that, then flip it back on. If big sites still have issues with it we’ll have to either point them to the spec or adjust where needed if we’re still non-compliant.

I would say this one still leads to crashes. Before i have updated to the unstable with this enabled, i never experienced a crash here:

https://www.robtex.com/ip-lookup/5.79.119.119

Getting random crashes when opening/closing such robtex pages with the 64 Bit unstable. Deactivated now

dom.IntersectionObserver.enabled

and the crashes are gone again.

Yup, it does, and the cause is Mozilla’s fucking hashtables again. I’m getting really tired of the crashiness of those things.
At least the crash is easy to track. I’d honestly rather deal with crashes than things “not working as they are supposed to”.

Latest unstable should have this fixed with commit 3cf7e874f

Is isIntersecing implemented in UXP?

It seem this still breaks sites in the wild, see https://forum.palemoon.org/viewtopic.php?p=159684#p159684.

The issue there is a spec change that added isIntersecting as a property, because apparently it’s too difficult to understand for webmasters that 0% intersection equals not intersecting. 😝

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Is isIntersecing implemented in UXP?

I completely didn’t see this. Sorry.

I guess the answer is: “it is now!” 😀

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As far as I can see f6ef8d8ca7 resolved the https://forum.palemoon.org/viewtopic.php?p=159684 issue 👍

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I’m going to disable IntersectionObservers in 28.3.1 because it’s causing too many crashes and crash-evaluation is currently difficult.
Potentially, if the crashes (seems like a CC problem) can be resolved, they can be re-enabled in 28.4, but it’ll need some time to be properly checked on various sites. Keeping it enabled on master so the unstable channel can be a testbed.

Clearing milestone for this and putting it on hold -- I’ve been unable to find a solution for #934 and #935 so far and have run out of avenues to explore. I’m probably missing something blatantly simple but can’t see it.

Considering this feature is WD status, experimental, and so far only being used for less than user-interest focused purposes (tracking, ad-visibility flags, potential profiling by observing scroll position, etc.), it’s not a great loss.

This will be disabled by default on master, also.