[Webkit-unassigned] [Bug 203681] New: Canvas layer not correct when -webkit-overflow-scrolling is set to touch on iOS 13

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=203681

            Bug ID: 203681
           Summary: Canvas layer not correct when
                    -webkit-overflow-scrolling is set to touch on iOS 13
           Product: WebKit
           Version: Safari 13
          Hardware: iPhone / iPad
                OS: iOS 13
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: New Bugs
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: shenyi.914 at gmail.com

Created attachment 382463

  --> https://bugs.webkit.org/attachment.cgi?id=382463&action=review

Demo to reproduce

Hi, I'm one of the maintainer of Apache ECharts(incubating). It uses Canvas to draw charts.

Recently a lot of our developers report to us, when running ECharts on iOS 13, Canvas in the container will cover the tooltip, which is a DIV and has larger z-index compared to canvas.
Apparently they are having wrong layers.

We found it only happens when -webkit-overflow-scrolling of top container is set to touch
It seems this property has been eliminated since iOS 13 https://developer.apple.com/documentation/safari_release_notes/safari_13_release_notes 



index.html in the attachment is a minimal reproducible page. 

Step to reproduce:
Open the index.html in attachment on iOS 13.

Expected result:
Black DIV should be on top of the red triangle, which is drawn by Canvas.

Actual result:
Red triangle is on top of the black DIV.

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