[Webkit-unassigned] [Bug 219445] New: Changing transforms on layer-backed elements with large subtrees can be incredibly slow, could be O(1)

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=219445

            Bug ID: 219445
           Summary: Changing transforms on layer-backed elements with
                    large subtrees can be incredibly slow, could be O(1)
           Product: WebKit
           Version: Safari 13
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Compositing
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: jan at framer.com

Created attachment 415238

  --> https://bugs.webkit.org/attachment.cgi?id=415238&action=review

Reproduction and details

Open the attached reproduction file and note the instructions. When profiling, you'll note heavy activity in "Styles Recalculated".

Expected:
Changing a transform on a layer-backed element after it has laid out and painted is independent of the complexity of the subtree.

Actual:
There's a huge performance difference, implying the subtree is getting dirtied for no reason.

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