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Re: [Public WebGL] Weird alpha issue.



OK - I finally have a reasonably simple test case at:

    http://www.sjbaker.org/test/index.php

...I apologize if some of the code doesn't look exactly pretty - it's
been brutally ripped out of a 5000 line application.  The checkerboard
background helps you see the blending issues clearly - but it's a bit
hard on the eyes!

We should see a dark brown canvas on a checkerboard background - with a
chair and a grey translucent 'smoke puff' slicing through it.

* The only setup that I've found seems to display it "correctly" (ie
without dest-alpha) is Chrome under Linux/64bit...but I don't have a Mac
to test on so we'll give Safari the benefit of the doubt right now.

* Minefield lets the background 'leak' through the image (presumably
because we can't shut off destination-alpha because of bug 539771. 
(That's a **REALLY** serious bug!)

* Chrome under Windows7/32bit also lets the background leak through -
but does a weird compositing job.

* None of the browsers are getting the alpha=0 thing right.

* If you remove the "alpha:false" from the getContext call - you can
also see that Chrome and Minefield composite the resulting dest-alpha
canvas differently.

> If you go to about:config and set
>    layers.accelerate-all=false
>    layers.accelerate-none=true
> Does that make a difference?

No...no difference at all.

> If yes, you have found a bug in our accelerated compositing code.
> If no, we can't conclude anything.

Oh.   :-(

  -- Steve

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