[fxtf-drafts] [filter-effects] Suggestion: add offset attribute(s) to feTurbulence

BigBadaboom has just created a new issue for https://github.com/w3c/fxtf-drafts:

== [filter-effects] Suggestion: add offset attribute(s) to feTurbulence ==
https://www.w3.org/TR/filter-effects/#feTurbulenceElement

Idea for future enhancement:

Is it feasible to add an `offset` (`offsetX`/`offsetY`) attribute(s) to the `<feTurbulence>` filter primitive?

This would enable a great number of effects that rely on a continuously varying noise function.  At the moment it is possible in a rather messy way using `<feTurbulence stitchTiles>` and  `<feOffset>`. But it must repeat at some point, and the filter has to be as large as the turbulence repeat size, to avoid clipping.

See demo of a simple fire filter here:
https://codepen.io/PaulLeBeau/pen/EQoraz

 *(This works well in Chrome, but there is a discontinuity in Firefox, which I haven't investigated yet. It may be due to FF either not implementing `stitchTiles` yet, or possibly a bug in `feOffset`.)*

In any case, being able to move the noise anywhere in "noise space" would be very useful.

How this would work in conjunction with `stitchTiles` TBD.  Either have the offset ignored when stitchTiles is on, or preferably, have it be modulo the width and height.  Ie. `(offsetX + x) mod width` etc.


Please view or discuss this issue at https://github.com/w3c/fxtf-drafts/issues/257 using your GitHub account