[Webkit-unassigned] [Bug 209802] New: Performance issue with the canvas "globalCompositeOperation" when set to "destination-in"

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=209802

            Bug ID: 209802
           Summary: Performance issue with the canvas
                    "globalCompositeOperation" when set to
                    "destination-in"
           Product: WebKit
           Version: Safari 13
          Hardware: Macintosh
                OS: macOS 10.14
            Status: NEW
          Severity: Major
          Priority: P2
         Component: Canvas
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: register at edouardmercier.fr
                CC: dino at apple.com

Created attachment 395026

  --> https://bugs.webkit.org/attachment.cgi?id=395026&action=review

A stand-alone sample file which demonstrates the issue

On a canvas "CanvasRenderingContext2D" 2D context, when using the "globalCompositeOperation" with the value "destination-in", but also the "source-in", "source-out" and "source-atop" values (all possible values referred at https://developer.apple.com/documentation/webkitjs/canvasrenderingcontext2d/global_compositing_operation_constants have been assessed), we notice a performance penalty with a magnitude of 10 compared to other values (in particular with the "destination-out".

This occurs at least on macOS 10.3, 10.4, in Safari 12, 13 and "Technology Preview".

This performance issue causes a severe harm to fluid animations. 

We have designed and attached a stand-alone HTML page which demonstrates the issued (we are aware that the "performance.now()" function does not have a precision below the millisecond, but since the "globalCompositeOperation" parameter set to one of the value which causes performance issue causes a response type over 10 ms, this lack of accuracy does not prevent from revealing the issue).

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