Re: [Public WebGL] Weird alpha issue.

[Steve Baker <steve@sjbaker.org>]

I have Minefield set up to auto-update and it actually updated just as I
started typing this email - so I guess I have the latest! ...and the
color is still much darker than in Chrome.

I took a pair of side-by-side screenshots with the latest versions of
both browsers:

  http://www.sjbaker.org/tmp/smoke_differences.png

(It's kinda hard to see the smoke on the Minefield side - but it's much
more obvious in motion).

If it helps, the texture map is in:

  http://www.sjbaker.org/tmp/Smoke.png

 -- Steve



On 10/30/2010 11:08 AM, Benoit Jacob wrote:
> What's your Minefield build? Two weeks ago, I landed important texture fixes that could be related to that. Please try with the latest nightly:
>
> http://nightly.mozilla.org/
>
> Benoit
>
> ----- Original Message -----
>   
>> I'm running some particle system tests - using an RGBA .png image with
>> fuzzy mid-grey translucent smoke puffs. There are lots of particles
>> layered on top of each other.
>>
>> What's odd is that the smoke puff is much lighter in color on Chrome
>> than it is on Minefield - even with both browsers running side-by-side
>> on the exact same Win7/32bit/nVidia machine displaying the exact same
>> scene. Everything else in the scene looks utterly identical in the two
>> windows.
>>
>> I'm kinda suspecting some funky thing going on with pre-multiplied
>> alpha. Is someone messing with my texture?
>>
>> DETAILS:
>>
>> The setup for drawing is:
>>
>> gl.enable ( gl.DEPTH_TEST ) ;
>> gl.depthMask ( false ) ;
>> gl.enable ( gl.BLEND ) ;
>> gl.blendFunc ( gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA ) ;
>>
>> ...with everything else left at default values.
>>
>> The frag shader says:
>>
>> float4 color = texture2D ( fire, UV ).rgba * (1.0-smokeAmount) +
>> texture2D ( smoke, UV ).rgba * smokeAmount ;
>> color.a *= timeVaryingAlpha ;
>> gl_FragColor = color ;
>> }
>>
>> ...and in this case, smokeAmount is 1.0 (so we should see only the
>> smoke
>> map...and that works) and timeVaryingAlpha varies between 0.0 and 1.0
>> as
>> you'd expect.
>>
>> My image 'onload' function says:
>>
>> gl.bindTexture ( gl.TEXTURE_2D, texture ) ;
>> gl.pixelStorei ( gl.UNPACK_FLIP_Y_WEBGL, true);
>> gl.texImage2D ( gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA,
>> gl.UNSIGNED_BYTE, image ) ;
>> gl.generateMipmap ( gl.TEXTURE_2D ) ;
>> gl.bindTexture ( gl.TEXTURE_2D, null ) ;
>>
>> Help!
>>
>> -- Steve
>>
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