[Webkit-unassigned] [Bug 73011] New: WebGL canvas pixel buffer format is not compatible with that used by Canvas2d pixel buffer

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=73011

           Summary: WebGL canvas pixel buffer format is not compatible
                    with that used by Canvas2d pixel buffer
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
               URL: http://ponder.org.uk/chromeTest/client.html
        OS/Version: Windows 7
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: WebGL
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: amb26webkit at ponder.org.uk


I reported this issue originally with Chromium and was told to report it here instead: http://code.google.com/p/chromium/issues/detail?id=101378

I can reproduce the error in all versions of Chrome I have tried since Chrome 14 - unfortunately I can't reproduce the issue in WebKit since nightlies won't start on my machine (Windows 7, AMD x64) for a reason I can't determine. The demonstration page referenced is working in Firefox 7 and 8.

What steps will reproduce the problem?
1. Browse to the above URL
2. Type command "sph" in command interpreter at top left

What is the expected result?

A moving pattern of red, yellow and black bands should appear

What happens instead?

Receive a "TypeError" from Chrome - nothing is rendered

Please provide any additional information below. Attach a screenshot if
possible.

The line responsible for the failure is this one (complex.js line 29)
gl.readPixels(0, 0, config.width, config.height, gl.RGBA, gl.UNSIGNED_BYTE, imageData.data);

According to the HTML5 spec, the "data" element of the ImageData structure should be a "Uint8ClampedArray" which one would expect is compatible with the array format read into by gl.readPixels (array of RGBA unsigned bytes). This is the case on recent Firefoxes and the call succeeds. However, on Chrome the type of imageData.data is shown as "CanvasPixelArray" which is not type compatible and the gl.readPixels call fails.

http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-putimagedata

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