[Webkit-unassigned] [Bug 159608] New: preserveDrawingBuffer=true wrongly double-buffers on current iOS h/w

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=159608

            Bug ID: 159608
           Summary: preserveDrawingBuffer=true wrongly double-buffers on
                    current iOS h/w
    Classification: Unclassified
           Product: WebKit
           Version: Other
          Hardware: iOS
                OS: iOS 9.2
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebGL
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: reuben.scratton at gmail.com
                CC: dino at apple.com

[F.A.O. Dean Jackson]

Using preserveDrawingBuffer=true on iOS wrongly expects that rendering is done to two alternating backbuffers, i.e. normal double-buffering. As far as I can tell other WebGL implementations treat preserveDrawingBuffer=true as rendering to a single backbuffer which is then copied to the front buffer rather than swapped. 

Here is a simple demo of preserveDrawingBuffer=true written by Gregg Tavares:

http://greggman.com/downloads/examples/webgl/lessons/resources/webgl-preservedrawingbuffer-true.html

This demo looks fine on all desktop browsers and Android but flickers dreadfully on mobile Safari on iOS 9.x and 8.x because of the unexpected double-buffering.

I reported the issue to Gregg and he advised me to report it here, marked for the attention of Dean.

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