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[fxtf-drafts] [filter-effects] What is the null output for the alpha channel of feTurbulence?

From: Amelia Bellamy-Royds via GitHub <sysbot+gh@w3.org>
Date: Fri, 24 Feb 2017 22:31:27 +0000
To: public-fxtf-archive@w3.org
Message-ID: <issues.opened-210175881-1487975486-sysbot+gh@w3.org>
AmeliaBR has just created a new issue for 
https://github.com/w3c/fxtf-drafts:

== [filter-effects] What is the null output for the alpha channel of 
feTurbulence? ==
Browsers are currently inconsistent about what they return for a 
`<feTurbulence>` filter with no turbulence (i.e., with the default 
`baseFrequency="0").

- Chrome and MS Edge return a fully transparent layer when 
`type="turbulence"` but a half-transparent gray layer when 
`type="fractalNoise"`.
- Firefox returns a fully transparent layer in both cases.

[See CodePen test case](http://codepen.io/AmeliaBR/pen/zZxozG/)

I assume this is related to the fact that the `turbulence` algorithm 
returns values from 0 to 1, but the `fractalNoise` algorithm returns 
values from -1 to +1. In both cases, the results are then supposed to 
be scaled to the range of the color channel.  But [the spec 
text](https://drafts.fxtf.org/filters/#feTurbulenceElement) doesn't 
specifically say anything about the alpha channel. 

I'm leaning towards just calling this a Firefox bug, but I haven't 
actually deconstructed the algorithms to confirm that this is so. And 
either way, the spec text about scaling by 255 to get a color value 
should be clarified to encompass the alpha channel.



Please view or discuss this issue at 
https://github.com/w3c/fxtf-drafts/issues/112 using your GitHub 
account
Received on Friday, 24 February 2017 22:31:36 UTC

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