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Re: [Public WebGL] Weird alpha issue.



I tried your test case with top-of-tree Chrome on Mac and Windows.
Both do not have the background leaking issue you saw here.  Can you
try the same build and confirm?

For the Windows build, you need to pass in --use-gl=desktop flag.
Apparently there is a bug in ANGLE, so without the flag you won't see
the WebGL canvas at all - at least that's the case on my machine.

Mo

On Sun, Oct 31, 2010 at 2:02 PM, Steve Baker <steve@sjbaker.org> wrote:
> 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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