WebGL posted Upside Down from OffscreenCanvas

[Bob Blaine]

Hi,

I don't know if this is a bug or there's something I'm not doing correctly and am hoping for some insight.

I am part of a team developing an application using Chromium Embedded Framework, though I've been able to reproduce this in Chrome 106.0.5249.62.

I've attached a web page that demonstrates the issue. It draws a wireframe box whose vertices are red if Y is positive and Green if Negative. The code uses an OffscreenCanvas for generation of an image from WebGL and moves the image to an ImageBitmapRenderingContext in a canvas in the DOM using the standard transferImageto/from... protocol.

If you start Chrome regularly, the box is red on the top and green on the bottom, however, if you start Chrome with --disable-gpu-compositing, the box is green on top and red on the bottom. Basically the image is Y-flipped in the software compositing process. 

Is there something I should be doing that I'm not? If this is a bug, I'd be glad to file it.

Thanks in advance,
Bob Blaine

[Ken Russell]

Hi Bob,

It looks like this bug's already been filed as https://bugs.chromium.org/p/chromium/issues/detail?id=1342153 . Sorry for the delay in addressing it; I've asked a couple of colleagues if they can look into it sooner. Feel free to add your test case to that bug.

Thanks,

-Ken

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[Bob Blaine]

Thanks, Ken!

(Unfortunately I don't have access to that group.:-))

[Ken Russell]

Hi Bob,

Ah, sorry about that. The bug was filed by a Google-internal team and it looks like it might contain some product-specific details so shouldn't be made publicly visible. Could you please file your bug with your test case and I'll link them together?

Thanks,

-Ken

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[Bob Blaine]

I've submitted this as bug 1380473. 

Thanks for your help!

[Ken Russell]

Thanks for filing it Bob. Have triaged it, have a CL up for review fixing assertion failures with your test case, and am asking a colleague to fix the underlying vertical-flip bug.

-Ken

To view this discussion on the web visit https://groups.google.com/d/msgid/webgl-dev-list/72b36756-5940-4f3e-87e1-078f78e601f9n%40googlegroups.com.