[Webkit-unassigned] [Bug 203187] New: CSS Animation, Canvas 2D and WebGL: Layout reported incorrectly

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=203187

            Bug ID: 203187
           Summary: CSS Animation, Canvas 2D and WebGL: Layout reported
                    incorrectly
           Product: WebKit
           Version: Safari 13
          Hardware: Macintosh
                OS: macOS 10.14
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: cdata at google.com
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Created attachment 381398

  --> https://bugs.webkit.org/attachment.cgi?id=381398&action=review

Screen recording of bug in Safari 13.0.2 on MacOS 10.14

When using a combination of CSS Animations, CanvasRenderingContext2D and WebGLRenderingContext, it is possible to cause DOM layout to be misreported by both `window.getComputedStyle` and `element.getBoundingClientRect` (and possibly other methods).

Here is a minimal test case demonstrating the issue: http://lopsided-motion.glitch.me/safari-13-measure-position-bug.html

The test case shows an animating black square. We attempt to read the computed CSS transform property (as well as the bounding rect) in a requestAnimationFrame callback. The layout value that we read is not correct.

I have also added a screen recording of Safari 13.0.2 demonstrating the behavior.

The following browsers were tested and DO NOT exhibit the problem (they work as intended):

 - Chrome 77
 - Firefox 69
 - Safari 12.1

The computer used to reproduce the bug and test other browsers is a 15" 2017 MacBook Pro with Radeon 560 / Intel HD Graphics 630 running macOS 10.14.6

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