[Webkit-unassigned] [Bug 188839] New: [CoordGraphics] Revalidate need for 'coordinated update completion' in ThreadedCompositor

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=188839

            Bug ID: 188839
           Summary: [CoordGraphics] Revalidate need for 'coordinated
                    update completion' in ThreadedCompositor
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: New Bugs
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: zan at falconsigh.net
                CC: magomez at igalia.com

In ThreadedCompositor, we enforce what we call a "coordinated update completion with the client" when any platform layer has been updated (WebGL or GStreamer media). This means that the following frame is not "complete" until a main-thread callback is dispatched in which the client (i.e. CompositingCoordinator and the LayerTreeHost that owns it) is notified of the completion of that frame. Any further flushes and updates are blocked until that callback is dispatched.

As far as I remember this solved various rendering glitches in WebGL content that was re-rendered as the previous rendering results were still in the process of being composited. This is not an ideal solution, but it works -- at the expense of the callback scheduling on the main thread, which can be a problem.

Ideally we'd find and use a different solution that allows correct WebGL content presentation without this additional coordination step.

This report originates from bug #188693.

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