Bug 226321 – Animation FPS drops if SVG changes from becomes visible from opacity 0

• Component: Animations
• Status: NEW

[Roland Soos]

Created attachment 429862 [details]
Screen recording

Steps to reproduce:
1. Open https://smartslider3.com/bugs/webkit/opacity0dropfps/

Expected result: FPS should be consistent during the animation

Actual result: When the SVG becomes visible from opacity(opacity:0 and then in the next frame gets bigger than 0) cause the animation to feel sluggish as probably rendering of the resource allocate the main thread.


Workaround: use non-zero small opacity like 0.1 for starting point.

Able to reproduce:
iPad 14.5.1
iPhone 14.6

[Roland Soos]

It's possible that not opacity:0 itself cause this issue as we add visiblity:hidden to the elements which has opacity:0. So the cause could be that visibility:hidden changes to visibility:visible.

[data-force-hidden], [data-force-hidden] * {
    visibility: hidden!important;
}

[Alexey Proskuryakov]

I can reproduce on iPhone 12 Pro; animates smoothly on a Mac.

[Simon Fraser (smfr)]

The SVG takes over 500ms to render on iPhone 7 Plus because of the filters (largely the gaussian blur). There's a layering change when opacity and/or transform transitions finish, which triggers a second paint of the SVG which is the visible stall.

Some `will-change:` should fix this. Or you could remove the filters, since (in this example at least) they don't do anything visible.

[Radar WebKit Bug Importer]

<rdar://problem/78601603>

[Roland Soos]

Thank you Simon, you are right. We dropped those filters and used filter="drop-shadow(...)" on the path and everything is the same.

What is the tool what you used to find that it takes 500ms to render that SVG? Is it a tool in Safari(Mac) what I could use during remote debug of the real device?

[Simon Fraser (smfr)]

I used some internal instrumentation, but I think attaching with Web Inspector and collecting a timeline recording would show you some long paints.

[Simon Fraser (smfr)]

Created attachment 430045 [details]
Long paints in timeline