Created attachment 415150 [details] The issue Hello, When you have an element that, when hovered, has a "filter: drop-shadow" inside a div, that has also a filter with drop-shadow, everything flickers on hover. This also happens with elements that have a transform on hover. Here is a repro https://codepen.io/RemiVillien/pen/vYXOoEw Everything is very slow and buggy. There isn't any issue with chrome or firefox.
Created attachment 415308 [details] Test reduction
Reduction shows that the blur radius of drop-shadow on composited layers is wrong.
<rdar://problem/71941564>
Note to self: https://dbaron.org/log/20110225-blur-radius
There are various things here. There's a box-shadow rendering bug in Core Graphics (you can work around this by setting a small border-radius). There's a difference between drop-shadow() rendering when software-rendered, and when accelerated (i.e. during the transitions); this is because of clamping of the blur radius, which is pretty high.